U.S. patent application number 14/382403 was filed with the patent office on 2015-04-09 for lithium ion batteries comprising nanofibers.
This patent application is currently assigned to CORNELL UNIVERSITY. The applicant listed for this patent is CORNELL UNIVERSITY. Invention is credited to Daehwan Cho, Nathaniel S. Hansen, Yong Lak Joo, Kyoung Woo Kim.
Application Number | 20150099185 14/382403 |
Document ID | / |
Family ID | 54478370 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150099185 |
Kind Code |
A1 |
Joo; Yong Lak ; et
al. |
April 9, 2015 |
LITHIUM ION BATTERIES COMPRISING NANOFIBERS
Abstract
Lithium ion batteries, electrodes, nanofibers, and methods for
producing same are disclosed herein. Provided herein are batteries
having (a) increased energy density; (b) decreased pulverization
(structural disruption due to volume expansion during
lithiation/de-lithiation processes); and/or (c) increased lifetime.
In some embodiments described herein, using high throughput,
water-based electrospinning process produces nanofibers of high
energy capacity materials (e.g., ceramic) with nanostructures such
as discrete crystal domains, mesopores, hollow cores, and the like;
and such nanofibers providing reduced pulverization and increased
charging rates when they are used in anodic or cathodic
materials.
Inventors: |
Joo; Yong Lak; (Ithaca,
NY) ; Hansen; Nathaniel S.; (Portland, OR) ;
Cho; Daehwan; (Ithaca, NY) ; Kim; Kyoung Woo;
(Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNELL UNIVERSITY |
ITHACA |
NY |
US |
|
|
Assignee: |
CORNELL UNIVERSITY
ITHACA
NY
|
Family ID: |
54478370 |
Appl. No.: |
14/382403 |
Filed: |
February 28, 2013 |
PCT Filed: |
February 28, 2013 |
PCT NO: |
PCT/US13/28132 |
371 Date: |
September 2, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61605937 |
Mar 2, 2012 |
|
|
|
61701854 |
Sep 17, 2012 |
|
|
|
61717222 |
Oct 23, 2012 |
|
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Current U.S.
Class: |
429/231.8 ;
264/465; 429/218.1; 429/231.95; 429/246 |
Current CPC
Class: |
D01D 5/0069 20130101;
D01D 5/003 20130101; H01M 2/145 20130101; H01M 4/0471 20130101;
H01M 4/133 20130101; H01M 4/134 20130101; H01M 4/136 20130101; H01M
10/0525 20130101; H01M 4/1395 20130101; H01M 2004/021 20130101;
H01M 4/13 20130101; H01M 4/131 20130101; D01F 1/09 20130101; Y02E
60/10 20130101; D01F 1/10 20130101; H01M 2/162 20130101; H01M
4/1393 20130101; H01M 2/1633 20130101; D01F 9/20 20130101; H01M
4/0469 20130101 |
Class at
Publication: |
429/231.8 ;
429/246; 429/231.95; 429/218.1; 264/465 |
International
Class: |
H01M 2/16 20060101
H01M002/16; H01M 2/14 20060101 H01M002/14; H01M 10/0525 20060101
H01M010/0525 |
Claims
1-91. (canceled)
92. A lithium-ion battery comprising an anode in a first chamber, a
cathode in a second chamber, and a separator between the first
chamber and the second chamber, and the separator comprising one or
more polymer nanocomposite nanofiber(s) comprising a polymer matrix
with ceramic and/or clay nanostructures embedded therein.
93. The battery of claim 92, wherein the polymer is PE, UHMWPE, PP,
PVA, PAN, PEO, PVP, PVDF, Nylon, aramid, PET, Polyimide, PMMA, or a
combination thereof.
94. The battery of claim 92, wherein the polymer nanocomposite
comprises a ceramic, and the ceramic is silica, zirconia, or
alumina.
95. The battery of claim 92, wherein the polymer nanocomposite
nanofiber comprises a clay, and the clay is bentonite, aluminum
phyllosilicate, montmorillonite, kaolinite, illite, vermiculite,
smectite, chlorite, silicate clay, sesquioxide clays, allophane,
imogolite, fluorohectorate, laponite, bentonite, beidellite,
hectorite, saponite, nontronite, sauconite, ledikite, magadiite,
kenyaite, stevensite, or a combination thereof.
96. The battery of claim 92, wherein the one or more polymer
nanocomposite nanofiber(s) comprises on average 1-15 wt. % ceramic
and clay.
97. The battery of claim 92, wherein the separator has an average
pore diameter of less than 1 micron.
98. The battery of claim 92, wherein the separator has a peak pore
diameter distribution of less than 1 micron.
99. The battery of claim 92, wherein the separator has a thickness
of 15-100 micron.
100. The battery of claim 92, wherein the battery retains at least
70% of its discharge capacity (mAh/g) after 100 cycles at a charge
rate of at least 250 mA per gram of separator.
101. The battery of claim 92, wherein the one or more polymer
nanocomposite nanofiber(s) has an average diameter of less than 1
micron, an average aspect ratio of at least 100, and an average
specific surface area of at least 100 m.sup.2/g.
102. The battery of claim 92, wherein the one or more polymer
nanocomposite nanofiber(s) has an average length of at least 1000
microns.
103. The battery of claim 92, wherein the cathode comprises one or
more lithium-containing nanofiber comprising a matrix of a lithium
material.
104. The battery of claim 103, wherein the one or more
lithium-containing nanofiber has an average diameter of less than 1
micron and an aspect ratio of at least 100.
105. The battery of claim 92, wherein the anode comprises one or
more anodic nanofiber, the anodic nanofiber comprising Si, Sn, Ge,
or an oxide of Si, Sn, or Ge.
106. The battery of claim 105, wherein the anodic nanofiber(s)
comprises discrete domains comprising the Si, Sn, or Ge, or oxide
Si, Sn, or Ge, the discrete domains being embedded in a carbon
backbone.
107. The battery of claim 105, wherein the one or more anodic
nanofiber(s) comprise, on average, at least 50 wt % of Si, Sn, Ge,
or an oxide of Si, Sn, or Ge.
108. A lithium-ion battery comprising an anode in a first chamber,
a cathode in a second chamber, and a separator between the first
chamber and the second chamber, and the separator allowing ion
transfer between the first chamber and second chamber in a
temperature dependent manner, the separator comprising one or more
polymer nanocomposite nanofiber comprising a polymer matrix with
ceramic nanostructures embedded therein, the polymer being PE,
UHMWPE, PP, PVA, PAN, PEO, PVP, PVDF, Nylon, aramid, PET,
Polyimide, PMMA, or a combination thereof, and the ceramic being
silica, zirconia, alumina, or a combination thereof; the anode
comprises one or more anodic nanofiber, the anodic nanofiber
comprising Si, Sn, Ge, or an oxide of Si, Sn, or Ge; and the
cathode comprises one or more lithium-containing nanofiber
comprising a matrix of a lithium material.
109. A process for producing a battery separator, the process
comprising gas assisted electrospinning a fluid stock to form a
nanofiber mat, the fluid stock comprising (i) a plurality of
nanoparticles, and (ii) a polymer, the separator comprising one or
more nanofiber(s) comprising a continuous polymer matrix with
non-aggregated nanoparticles embedded therein.
110. The process of claim 109, further comprising annealing the
nanofiber mat.
111. The process of claim 109, further comprising compressing the
nanofiber mat.
Description
CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional
Application Nos. 61/605,937, filed Mar. 2, 2012, 61/701,854, filed
Sep. 17, 2012, and 61/717,222, filed Oct. 23, 2012, all of which
are incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] Generally, a battery is a device that converts chemical
energy directly to electrical energy, consisting of a number of
voltaic cells; each voltaic cell comprises two half-cells connected
in series by a conductive electrolyte containing anions and
cations. Typically, one half-cell includes electrolyte and the
electrode to which anions (negatively charged ions) migrate (i.e.,
the anode or negative electrode); the other half-cell includes
electrolyte and the electrode to which cations (positively charged
ions) migrate (i.e., the cathode or positive electrode). In the
redox reaction that powers the battery, cations are reduced
(electrons are added) at the cathode, while anions are oxidized
(electrons are removed) at the anode. In general, the electrodes do
not touch each other but are electrically connected by the
electrolyte. Some cells use two half-cells with different
electrolytes. In some instances, a separator between half-cells
allows ions to flow, but prevents mixing of the electrolytes.
SUMMARY OF THE INVENTION
[0003] Provided herein are batteries (e.g., lithium ion batteries),
battery components, nanofibers useful in batteries, and processes,
apparatuses and systems for preparing such batteries, battery
components, and nanofibers. In some embodiments, provided herein
are lithium-containing nanofibers, electrodes and batteries
comprising such nanofibers, as well as processes and systems for
preparing the same. In certain embodiments, provided herein are
high (e.g., anodic) energy capacity nanofibers, electrodes and
batteries comprising such nanofibers, as well as processes and
systems for preparing the same. In some embodiments, provided
herein are polymer, polymer-clay composite, and polymer-ceramic
nanocomposite nanofibers, separators and batteries comprising such
nanofibers, as well as processes and systems for preparing the
same.
[0004] In some embodiments, provided herein is a lithium-ion
battery comprising:
[0005] a positive electrode, the positive electrode comprising one
or more lithium-containing nanofiber;
[0006] a negative electrode, the negative electrode comprising one
or more anodic nanofiber, the nanofiber comprising a high energy
capacity material;
[0007] a separator, the separator comprising one or more polymer
nanocomposite nanofiber; or a combination thereof.
[0008] In some embodiments, a battery comprises (a) and (b). In
other embodiments, a battery comprises (a) and (c). In certain
embodiments, a battery comprises (b) and (c). In some embodiments,
a battery comprises (a), (b) and (c). In certain embodiments, a
battery comprises (a). In some embodiments, a battery comprises
(b). In certain embodiments, a battery comprises (c).
[0009] In specific embodiments, the lithium ion battery comprises
an anode in a first chamber, a cathode in a second chamber, and a
separator between the first chamber and the second chamber, and the
separator allowing ion transfer (e.g., Li+ ion transfer) between
the first chamber and second chamber, e.g., in a temperature
dependent manner.
[0010] In some embodiments, a battery provided herein comprises a
separator comprising a polymer nanocomposite nanofiber. In certain
embodiments, the polymer nanocomposite nanofiber comprises a
continuous polymer matrix with ceramic and/or clay nanostructures
embedded therein. In some embodiments, the polymer comprises PE,
UHMWPE, PP, PVA, PAN, PEO, PVP, PVDF, Nylon, aramid, PET,
Polyimide, PMMA, or a combination thereof. In specific embodiments,
the polymer comprises PAN. In other specific embodiments, the
polymer comprises PE or PP. In some embodiments, the polymer
nanocomposite comprises a ceramic. In specific embodiments, the
ceramic is silica, zirconia, or alumina. In some embodiments, the
nanocomposite nanofiber comprises a clay. In specific embodiments,
the clay is bentonite, aluminum phyllosilicate, montmorillonite,
kaolinite, illite, vermiculite, smectite, chlorite, silicate clay,
sesquioxide clays, allophane, imogolite, fluorohectorate, laponite,
bentonite, beidellite, hectorite, saponite, nontronite, sauconite,
ledikite, magadiite, kenyaite, stevensite, or a combination
thereof. In some embodiments, the polymer nanocomposite nanofiber
comprises 1-15 wt. % clay (e.g., 3-12 wt. %). In certain
embodiments, the polymer nanocomposite nanofiber comprises 1-15 wt.
% ceramic (e.g., 3-12 wt. %). In some embodiments, the polymer
nanocomposite nanofiber comprises 1-15 wt. % of ceramic and clay
combined (e.g., 3-12 wt. %). In some embodiments, the separator
does not shrink or melt at elevated temperatures (e.g., at or above
150 V). In further or alternative embodiments, the battery
comprises an electrolyte and the separator is wettable by the
electrolyte. In further or alternative embodiments, the separator
has an average pore diameter of less than 1 micron (e.g., less than
0.5 micron). In further or alternative embodiments, the separator
has a peak pore diameter distribution of less than 1 micron (e.g.,
less than 0.5 micron). In further or alternative embodiments, the
polymer nanocomposite nanofibers are annealed. In further or
alternative embodiments, the polymer nanocomposite nanofibers are
compressed. In further or alternative embodiments, the separator
has a thickness of 10-200 micron. In specific embodiments, the
separator has a thickness of 15-100 micron. In more specific
embodiments, the separator has a thickness of 30-100 micron. In
still more specific embodiments, the separator has a thickness of
30-70 micron. In further or alternative embodiments, the separator
has less than a 0.1% weight loss between 20.degree. C. and
200.degree. C. In further or alternative embodiments, the battery
retains at least 50% of its discharge capacity (mAh/g) after 100
cycles at a charge rate of at least 250 mA per gram of separator.
In specific embodiments, the battery retains at least 70% of its
discharge capacity (mAh/g) after 100 cycles at a charge rate of at
least 250 mA per gram of separator. In further or alternative
embodiments, the battery comprising a separator that has an Rct
that is less than 150 ohms (e.g., less than 120, or less than 100
ohms) in a half cell comprising 32 mg of LiCoO.sub.2 powder as
cathode and having a constant voltage=VOC (1.7-2.0V) (e.g., in a
system illustrated in FIG. 48). In further or alternative
embodiments, the battery comprising a separator that has an Rs that
is less than 40 ohms in a half cell comprising 32 mg of LiCoO.sub.2
powder as cathode and having a constant voltage=VOC (1.7-2.0V)
(e.g., in a system illustrated in FIG. 48). In further or
alternative embodiments, the polymer nanocomposite nanofiber has a
diameter of less than 2 micron, or less than 1 micron (e.g., less
than 500 nm). In further or alternative embodiments, the polymer
nanocomposite nanofiber has an aspect ratio of at least 10 (e.g.,
at least 100, at least 1000, at least 10,000). In further or
alternative embodiments, the polymer nanocomposite nanofiber has a
specific surface area of at least 10 m.sup.2/g (e.g., at least 30
m.sup.2/g, at least 100 m.sup.2/g, at least 300 m.sup.2/g, at least
500 m.sup.2/g, or at least 1000 m.sup.2/g, e.g., as measured by
BET). In further or alternative embodiments, the polymer
nanocomposite nanofiber has a length of at least 1 micron (e.g., at
least 10 microns, at least 100 micron, at least 1,000 micron).
[0011] In some embodiments, the positive electrode comprises one or
more lithium-containing nanofiber. In certain embodiments, the one
or more lithium-containing nanofiber comprises a continuous matrix
of a lithium material. In specific embodiments, the continuous
matrix of a lithium material is a continuous core matrix or a
continuous tubular matrix surrounding a hollow core. In some
embodiments, the one or more lithium containing nanofiber comprises
a continuous matrix of a first material (e.g., carbon, metal or
ceramic), and discrete domains of lithium material embedded in the
first material.
[0012] In some embodiments, the lithium material has the following
formula (I): Li.sub.aM.sub.bX.sub.c (I). In some embodiments, M is
one or more metal element (e.g., Fe, Ni, Co, Mn, V, Ti, Zr, Ru, Re,
Pt, Bi, Pb, Cu, Al, Li, or a combination thereof). In certain
embodiments, X is one or more non-metal (e.g., X represents C, N,
O, P, S, SO.sub.4, PO.sub.4, Se, halide, F, CF, SO.sub.2,
SO.sub.2Cl.sub.2, I, Br, SiO.sub.4, BO.sub.3, or a combination
thereof) (e.g., a non-metal anion). In some embodiments, a is 1-5
(e.g., 1-2), b is 0-2, and c is 0-10 (e.g., 1-4, or 1-3). In
specific embodiments, X is selected from the group consisting of O,
SO.sub.4, PO.sub.4, SiO.sub.4, and BO.sub.3. In more specific
embodiments, X is selected from the group consisting of O,
PO.sub.4, and SiO.sub.4. In further or alternative embodiments, M
is Mn, Ni, Co, Fe, V, Al, or a combination thereof. In specific
embodiments, the lithium material is LiMn.sub.2O.sub.4,
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, LiCoO.sub.2, LiNiO.sub.2,
LiFePO.sub.4, or Li.sub.2FePO.sub.4F. In other specific
embodiments, the lithium material is
LiNi.sub.b1Co.sub.b2Mn.sub.b3O.sub.2, wherein b1+b2+b3=1, and
wherein 0.ltoreq.b1, b2, b3<1. In yet other specific
embodiments, the lithium material is LiMn.sub.2O.sub.4,
LiMnPO.sub.4, LiNiPO.sub.4, LiCoPO.sub.4,
Li.sub.3V.sub.2(PO.sub.4).sub.3, Li.sub.2FeSiO.sub.4,
Li.sub.2MnSiO.sub.4, LiFeBO.sub.3, or LiMnBO.sub.3. In still other
embodiments, the lithium material of formula (I) is
Li.sub.2SO.sub.y', wherein y' is 0-4, (e.g., Li.sub.2S or
Li.sub.2SO.sub.4).
[0013] In some embodiments, the lithium material comprises at least
50 wt. % (e.g., at least 80 wt. %) of the lithium-containing
nanofiber. In further or alternative embodiments, the
lithium-containing nanofiber comprises at least 2.5 wt. % lithium.
In further or alternative embodiments, at least 10% (e.g., about
25%) of the atoms present in the lithium-containing nanofiber are
lithium atoms. In further or alternative embodiments, the
lithium-containing nanofiber has a diameter of less than 1 micron
(e.g., less than 500 nm). In further or alternative embodiments,
the lithium-containing nanofiber has an aspect ratio of at least 10
(e.g., at least 100, at least 1,000, at least 10,000). In further
or alternative embodiments, the lithium-containing nanofiber has a
specific surface area of at least 10 m.sup.2/g (e.g., at least 30
m.sup.2/g, at least 100 m.sup.2/g, at least 300 m.sup.2/g, at least
500 m.sup.2/g, or at least 1000 m.sup.2/g, e.g., as measured by
BET). In further or alternative embodiments, the lithium-containing
nanofiber has a length of at least 1 micron (e.g., at least 10
microns, at least 100 micron, at least 1,000 micron). In further or
alternative embodiments, the lithium-containing nanofibers having
an initial capacity of at least 100 mAh/g (e.g., at a
charge/discharge rate of 0.1 C).
[0014] In some embodiments, the negative electrode comprises one or
more nanofiber comprising a high energy capacity material. In some
embodiments, the nanofiber comprises a continuous matrix of high
energy capacity material. In specific embodiments, the continuous
matrix of a high energy capacity material is a continuous core
matrix or a continuous tubular matrix surrounding a hollow core. In
some embodiments, the nanofiber comprises a continuous matrix of a
first material (e.g., carbon, metal or ceramic), and discrete
domains of high energy capacity material embedded in the first
material. In specific embodiments, the high energy capacity
material is Si, Sn, Ge, an oxide thereof, a carbide thereof, an
alloy thereof, or a combination thereof. In some embodiments, the
nanofiber comprises a continuous matrix of porous silicon (e.g.,
mesoporous silicon). In certain embodiments, the nanofiber
comprises a continuous matrix of silicon alloy, tin oxide, tin, or
germanium. In some embodiments, the nanofiber comprises a carbon
matrix (e.g., backbone or tube surrounding a hollow core) with
silicon-containing domains (e.g., silicon nanoparticles) embedded
therein. In certain embodiments, the nanofiber comprises a carbon
backbone with tin-containing or germanium-containing domains (e.g.,
silicon nanoparticles) embedded therein. In some embodiments, the
nanofiber comprises a ceramic backbone with tin-containing or
germanium-containing domains (e.g., silicon nanoparticles) embedded
therein. In certain embodiments, domains of the nanofibers have an
average diameter of less than 100 nm (e.g., less than 60 nm, 10-80
nm, or the like). In further or alternative embodiments, the
nanofibers comprise, on average, less than 25 wt. % of carbon. In
further or alternative embodiments, the nanofibers comprise, on
average, at least 50 elemental wt. % of high energy capacity
material. In specific embodiments, the nanofibers comprise, on
average, at least 75 elemental wt. % of high energy capacity
material. In further or alternative embodiments, domains of the
nanofibers are non-aggregated. In further or alternative
embodiments, the nanofibers have a specific energy capacity of at
least 500 mAh/g on a first cycle at 0.1 C (e.g., as measured in a
half-cell). In more specific embodiments, the nanofibers have a
specific energy capacity of at least 1000 mAh/g on a first cycle at
0.1 C. In still more specific embodiments, the nanofibers have a
specific energy capacity of at least 1500 mAh/g on a first cycle at
0.1 C. In yet more specific embodiments, the nanofibers have a
specific energy capacity of at least 2000 mAh/g on a first cycle at
0.1 C. In further or alternative embodiments, the nanofiber has a
diameter of less than 1 micron (e.g., less than 500 nm). In further
or alternative embodiments, the nanofiber has an aspect ratio of at
least 10 (e.g., at least 100, at least 1000, at least 10,000, or
the like). In further or alternative embodiments, the nanofiber has
a specific surface area of at least 10 m.sup.2/g (e.g., at least 30
m.sup.2/g, at least 100 m.sup.2/g, at least 300 m.sup.2/g, at least
500 m.sup.2/g, or at least 1000 m.sup.2/g, e.g., as measured by
BET). In further or alternative embodiments, the nanofiber has a
length of at least 1 micron (e.g., at least 10 microns, at least
100 micron, at least 1,000 micron).
[0015] In further or alternative embodiments, the cathode or anode
has a specific energy capacity retention of at least 25% (e.g., at
least 30%, at least 40%, at least 50%) after 100 cycles at 0.1 C.
In further or alternative embodiments, the cathode or anode has a
specific energy capacity retention of at least 25% (e.g., at least
30%, at least 40%, at least 50%, at least 60%, at least 70%) after
50 cycles at 0.1 C.
[0016] In some embodiments, provided herein is a battery comprising
any separator described herein, any positive electrode (cathode)
described herein, and any negative electrode (anode) described
herein.
[0017] In some embodiments, provided herein is a process for
preparing a nanofiber for use in a lithium ion battery, the process
comprising
[0018] electrospinning a fluid stock to form nanofibers, the fluid
stock comprising or prepared by combining:
[0019] a metal precursor (e.g., lithium precursor, silicon
precursor, tin precursor, germanium precursor, or the like) or a
plurality of metal nanostructures (e.g., nanoparticles) (e.g.,
comprising lithium metal oxide--for cathode nanofibers,
silicon--for anode nanofibers, clay--for separator nanofibers,
ceramic--for separator nanofibers, or the like) and
[0020] a polymer; and
[0021] optionally thermally treating the nanofibers.
[0022] Provided in some embodiments is a process for producing
lithium-containing nanofibers (e.g., for a lithium ion battery
positive electrode), the process comprising:
[0023] electrospinning a fluid stock to form as-spun nanofibers,
the fluid stock comprising lithium precursor, an optional second
metal precursor, and a polymer; and
[0024] optionally thermally treating the as-spun nanofibers to
produce the lithium containing nanofibers.
[0025] In some embodiments, the process further comprises
chemically treating (e.g., oxidizing, such as with air) the as-spun
nanofibers. In certain embodiments, the process further comprises
chemically treating (e.g., oxidizing, such as with air) the lithium
containing nanofibers (e.g., to oxidize the lithium material and
remove carbon).
[0026] Provided in certain embodiments herein is a process for
producing lithium containing nanofibers, the process comprising
[0027] electrospinning a fluid stock to form as-spun nanofibers,
the fluid stock comprising a plurality of nanoparticles and a
polymer, the plurality of nanoparticles comprising a lithium
material; and
[0028] optionally thermally treating the as-spun nanofibers to
produce the lithium containing nanofibers.
[0029] In some embodiments, provided herein is a process for
producing nanofibers (e.g., for use in a lithium ion battery
negative electrode), the process comprising:
[0030] electrospinning a fluid stock to form as-spun nanofibers,
the fluid stock comprising or prepared by combining high energy
capacity precursor and polymer; and
[0031] optionally thermally treating the as-spun nanofibers.
[0032] Provided in certain embodiments herein, is a process for
producing nanofibers (e.g., for use in a lithium ion battery
negative electrode), the process comprising:
[0033] electrospinning a fluid stock to form as-spun nanofibers,
the fluid stock comprising a plurality of nanoparticles and a
polymer, the plurality of nanoparticles comprising a high energy
capacity anodic material; and
[0034] optionally thermally treating the as-spun nanofibers.
[0035] In some embodiments, provided herein is a process for
producing a nanofiber, the process comprising gas assisted
electrospinning a fluid stock to form the nanofibers, the fluid
stock comprising (i) a plurality of nanoparticles, and (ii) a
polymer, the nanofibers comprising a continuous polymer matrix with
non-aggregated nanoparticles embedded therein. In specific
embodiments, the gas assistances is provided along or around a
common axis as the electrospun stock/jet.
[0036] In certain embodiments, the polymer of any process described
herein is polyvinyl alcohol (PVA), polyvinyl acetate (PVAc),
polyethylene oxide (PEO), polyvinyl ether, polyvinyl pyrrolidone,
polyglycolic acid, hydroxyethylcellulose (HEC), ethylcellulose,
cellulose ethers, polyacrylic acid, polyisocyanate,
polyacrylonitrile (PAN), or a combination thereof. In specific
embodiments, the polymer is PVA (e.g., wherein the fluid stock
comprises water). In other specific embodiments, the polymer is PAN
(e.g., wherein the fluid stock comprises DMF). In some embodiments,
the electrospinning of the fluid stock according to any process
described herein is gas assisted (e.g., coaxially--along or around
the same axis--gas assisted). In certain embodiments, any precursor
provided herein (e.g., high capacity precursor, lithium precursor,
silicon precursor, metal precursor) is a metal acetate, metal
nitrate, metal acetylacetonate, metal halide, or any combination
thereof.
[0037] As described herein, controlling the crystal size,
concentration, and morphology of high energy capacity materials
within the anode and cathode is useful for (a) increasing the
energy density of the battery while (b) decreasing the
pulverization (structural disruption due to volume expansion during
lithiation/de-lithiation processes) and (c) increasing the lifetime
of the battery. In some embodiments described herein, using high
throughput, water-based spinning process produces nanofibers of
high energy capacity materials (e.g., ceramic) with nanostructures
such as discrete crystal domains, mesopores, hollow cores, and the
like which reduce pulverization and increase charging rates when
they are applied to anodic or cathodic materials.
[0038] Provided in certain embodiments here are batteries (e.g.,
lithium-ion batteries) comprising an electrolyte and, for example:
[0039] a. an electrode, the electrode comprising a plurality of
nanofibers comprising domains of a high energy capacity material
(e.g., in a continuous matrix material); [0040] b. an electrode,
the electrode comprising porous nanofibers, the nanofibers
comprising a high energy capacity material (e.g., "pure" nanofibers
of the high energy capacity material); [0041] c. an anode in a
first chamber, a cathode in a second chamber, and a separator
between the first chamber and the second chamber, the separator
comprising polymer nanofibers, and the separator allowing ion
transfer between the first chamber and second chamber in a
temperature dependent manner; or [0042] d. any combination
thereof.
[0043] Also, provided in certain embodiments herein methods for
producing an electrode, the methods comprising, for example: [0044]
a. electrospinning a fluid stock to form nanofibers, the fluid
stock comprising a high energy capacity material or precursor
thereof and a polymer; [0045] b. heating the nanofibers; and [0046]
c. assembling the nanofibers into an electrode.
[0047] Further embodiments are also contemplated herein, such as
those described in the claims and the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings of which:
[0049] FIG. 1 illustrates (a) an SEM and XRD image of a nanofiber
comprising a continuous matrix of (crystalline) SnO.sub.2 (panel
A), (b) an SEM and XRD image of a nanofiber comprising a continuous
matrix of Ge (panel B), and (c) an SEM and XRD image of a nanofiber
comprising a Si in a continuous matrix of carbon (panel C).
[0050] FIG. 2 illustrates (a) an SEM and XRD image of a nanofiber
comprising (crystalline) Sn in a continuous matrix of (amorphous)
Sn (panel A), (b) an SEM and XRD image of a nanofiber comprising
(crystalline) Sn in a continuous matrix carbon (panel B), (c) an
SEM and XRD image of a nanofiber comprising (crystalline) Sn in a
continuous matrix of alumina (Al.sub.2O.sub.3) (panel C) and (d) an
SEM and XRD image of a nanofiber comprising (crystalline) Sn in a
continuous matrix of zirconia (ZrO.sub.2) (panel D).
[0051] FIG. 3 illustrates (a) an SEM and XRD image of a nanofiber
comprising (crystalline) Ge in a continuous matrix of carbon
(carbonized from PAN) (panel A), (b) an SEM and XRD image of a
nanofiber comprising (crystalline) Ge in a continuous matrix
alumina (Al.sub.2O.sub.3) (panel B) and (c) an SEM and XRD image of
a nanofiber comprising (crystalline) Ge in a continuous matrix of
zirconia (ZrO.sub.2) (panel C).
[0052] FIG. 4 illustrates silicon/polymer and silicon/carbon
nanocomposite nanofibers. Panel A illustrates an SEM image of
polymer/Si nanoparticle nanocomposite nanofibers. Panel B
illustrates an SEM image of carbon/Si nanoparticle nanocomposite
nanofibers. Panel C illustrates a TEM image of carbon/Si
nanoparticle nanocomposite nanofibers.
[0053] FIG. 5 illustrates a TEM image for silicon/carbon
nanocomposite nanofibers.
[0054] FIG. 6 illustrates charge/discharge curves of 1.sup.st cycle
and 25.sup.th cycle (panel A) and plotted curves of Coulombic
efficiencies (panel B) for Si/C nanofibers provided herein compared
against Si nanoparticles alone.
[0055] FIG. 7 illustrates plotted graphs of discharge capacities of
silicon nanoparticles in carbon nanofibers provided herein compared
to silicon nanoparticles alone at various discharge rates.
[0056] FIG. 8 illustrates cyclic voltammograms (panel A) and
Nyquist plots (panel B) of silicon nanoparticles and certain Si/C
nanofibers provided herein.
[0057] FIG. 9 illustrates an X-Ray diffraction (XRD) pattern for
certain Si/C nanofibers provided herein.
[0058] FIG. 10 illustrates an (a) SEM image of as-spun silicon
precursor/polymer nanofibers, (b) SEM image of silica nanofibers
(heated from (a)), (c) TEM image of silica nanofibers, (d) TEM
image of Si/MgO nanofibers (silica nanofibers heated under vacuum
with Mg), and (e) TEM image of mesporous silicon nanofibers (HCl
treated from (d)).
[0059] FIG. 11 illustrates a schematic of a synthetic process for
preparing mesoporous silicon nanofibers.
[0060] FIG. 12 illustrates X-Ray Diffraction of as-spun silicon
precursor/polymer nanofibers (bottom), silica nanofibers (second
from bottom), Si/MgO nanofibers (second from top), and mesporous
silicon nanofibers (top).
[0061] FIG. 13 illustrates the capacity of certain Sn/alumina,
Ge/carbon, and Ge/alumina nanofibers provided herein.
[0062] FIG. 14 illustrates co-axial electrospinning needle
apparatus.
[0063] FIG. 15 illustrates a schematic of an exemplary process or
system for preparing nanofibers provided herein.
[0064] FIG. 16 illustrates an SEM image for a polymer-Si
(nanoparticle) nanocomposite nanofiber (Panel A); an SEM image of a
silicon/carbon nanocomposite nanofiber prepared by treatment at
900.degree. C. (Panel B); and an SEM image of a silicon/carbon
nanocomposite nanofiber prepared by treatment at 1200.degree. C.
(Panel C).
[0065] FIG. 17 illustrates normalized XRD peaks for the
silicon/carbon nanofibers prepared at 500, 700, and 900.degree.
C.
[0066] FIG. 18 illustrates SEM images for silicon/carbon
nanocomposite nanofibers prepared by treatment at 500.degree. C.
(panel A), 700.degree. C. (panel B), and 900.degree. C. (panel
C).
[0067] FIG. 19 illustrates TGA curves for Super P (Timcal) carbon
(a) compared to silicon/carbon nanocomposite nanofibers prepared by
treatment at 900.degree. C. (b) and 1200.degree. C. (c).
[0068] FIG. 20 illustrates Raman spectra for Super P (Timcal)
carbon (a) compared to silicon/carbon nanocomposite nanofibers
prepared by treatment at 900.degree. C. (b) and 1200.degree. C.
(c).
[0069] FIG. 21 illustrates SEM images for certain polymer-Si
(nanoparticle) nanocomposite nanofibers (panel A for 20:1; panel B
for 2:1; panel C for 1:1); and SEM images of certain silicon/carbon
nanocomposite after treatment of the polymer-Si nanofibers to 900 C
in argon (panel D for the treated 20:1 polymer:Si as-spun fiber,
panel E for 2:1, panel F for 1:1).
[0070] FIG. 22 illustrates certain nanofibers prepared by
electrospinning a fluid stock comprising polymer and nanoparticles
without a gas-assisted process.
[0071] FIG. 23 illustrates an X-Ray photoelectron spectrograph
(XPS) of certain silicon/carbon nanocomposite nanofibers.
[0072] FIG. 24 illustrates SEM images of certain as spun polymer:Si
(100 nm nanoparticles) (5:1) nanofibers (Panel A) and the calcined
carbon-silicon nanocomposite nanofibers resulting therefrom (Panel
B).
[0073] FIG. 25 illustrates SEM images of certain as spun polymer:Si
(3.2:1) nanofibers (Panel A) and the calcined carbon-silicon
nanocomposite nanofibers resulting therefrom (Panel B).
[0074] FIG. 26 illustrates SEM images of certain as spun polymer:Si
(1.84:1) nanofibers (Panel A) and the calcined carbon-silicon
nanocomposite nanofibers resulting therefrom (Panel B).
[0075] FIG. 27 illustrates a TEM image of microtomed hollow Si/C
nanocomposite nanofibers described herein (from Si nanoparticles
having an average diameter of 100 nm).
[0076] FIG. 28 illustrates SEM images of certain as-spun polymer-Si
(50 nm nanoparticles) nanofibers (Panel A), and the calcined
carbon-silicon nanocomposite nanofibers resulting therefrom (Panel
B).
[0077] FIG. 29 illustrates TEM images of certain microtomed hollow
carbon-Si (50 nm) nanocomposite nanofibers described herein.
[0078] FIG. 30 illustrates an SEM image of lithium cobalt oxide
nanofibers (Panel A); and SEM images of lithium cobalt oxide
nanofibers prepared using 1:1, 1:1.5, and 1:2 molar ratios of
cobalt acetate-to-lithium acetate (Panel B).
[0079] FIG. 31 (panel A) illustrates the XRD pattern for the
lithium cobalt oxide nanofibers and illustrates the XRD pattern
(panel B) for nanofibers prepared using 1:1, 1:1.5, and 1:2 molar
ratios of cobalt acetate-to-lithium acetate.
[0080] FIG. 32 illustrates the charge/discharge capacities for
lithium cobalt oxide nanofiber cathodes in a lithium ion battery
half cell.
[0081] FIG. 33 (panel A) illustrates an SEM image of as-spun
nanofibers comprising polymer and metal (lithium, nickel, cobalt,
manganese) precursor. Panel B illustrates an SEM image of thermally
treated lithium (nickel/cobalt/manganese) oxide nanofibers (treated
at 650 C in air). Panel C illustrates a TEM image of the thermally
treated nanofibers.
[0082] FIG. 34 illustrates the XRD pattern for certain lithium
(nickel/cobalt/manganese) oxide nanofibers.
[0083] FIG. 35 illustrates the charge/discharge capacities for
certain lithium (nickel/cobalt/manganese) oxide nanofibers
prepared.
[0084] FIG. 36 illustrates SEM images for
Li[Li.sub.0.2Mn.sub.0.56Ni.sub.0.16Co.sub.0.08]O.sub.2 nanofibers
(Panel B) and the pre-treatment, as-spun precursor nanofibers
therefor (Panel A).
[0085] FIG. 37 illustrates the charge/discharge capacities for
Li[Li.sub.0.2Mn.sub.0.56Ni.sub.0.16Co.sub.0.08]O.sub.2
nanofibers.
[0086] FIG. 38 illustrates SEM images for
Li.sub.0.8Mn.sub.0.4Ni.sub.0.4Co.sub.0.4O.sub.2nanofibers (Panel B)
and the pre-treatment, as-spun precursor nanofibers therefor (Panel
A).
[0087] FIG. 39 illustrates SEM images of certain as-spun nanofibers
(from a stock prepared by combining polymer, lithium acetate and
manganese acetate) (Panel A), and lithium manganese oxide
nanofibers (Panel B). Panel C illustrates a TEM image of certain
lithium manganese oxide nanofibers.
[0088] FIG. 40 illustrates the XRD pattern for certain lithium
manganese oxide nanofibers.
[0089] FIG. 41 illustrates the charge/discharge capacity of certain
lithium manganese oxide nanofibers for about 40 cycles.
[0090] FIG. 42 illustrates an XRD pattern for certain lithium
(nickel/manganese) oxide nanofibers.
[0091] FIG. 43 illustrates SEM images for certain lithium iron
phosphate nanofibers (Panel B) and the pre-treatment, as-spun
precursor nanofibers therefor (Panel A).
[0092] FIG. 44 illustrates an XRD pattern for certain lithium iron
phosphate nanofibers.
[0093] FIG. 45 illustrates SEM images for certain lithium sulfide
containing (with carbon) nanofibers (Panel B) and the
pre-treatment, as-spun precursor nanofibers therefor (Panel A).
Panel C illustrates a TEM image of the lithium sulfide containing
nanofibers.
[0094] FIG. 46 illustrates the XRD pattern for lithium sulfate
containing (with carbon) nanofibers.
[0095] FIG. 47 illustrates the pore size distribution of various
polymer containing nanofiber mats (e.g., for use in separators)
provided herein.
[0096] FIG. 48 illustrates a Nyquist plot of various separators
provided herein (compared to commercial PE separator).
[0097] FIG. 49 illustrates the cycle test results of commercial PE
(Celgard) and various nanofiber separators provided herein.
[0098] FIG. 50 illustrates a TGA curve of certain nanofiber (e.g.,
for separators) provided herein.
[0099] FIG. 51 illustrates C rate capacity tests for discharge
capacity of half cells (with lithium cobalt oxide) using a
separator provided herein.
[0100] FIG. 52 illustrates C rate capacity tests for discharge
capacity of half cells (with lithium manganese oxide) using a
separator provided herein.
[0101] FIG. 53 illustrates SEM images of certain PAN:nanoclay
nanofibers (91:9) provided herein.
[0102] FIG. 54 illustrates SEM images of certain PAN nanofibers
provided herein.
[0103] FIG. 55 illustrates SEM images of PAN/nanoclay (95.5/4.5)
nanofibers compressed at 1 Mpa for 15 seconds.
[0104] FIG. 56 illustrates SEM images of PAN/nanoclay (95.5/4.5)
nanofibers compressed at 3 Mpa for 15 seconds.
[0105] FIG. 57 illustrates SEM images of PAN/nanoclay (95.5/4.5)
nanofibers compressed at 5 Mpa for 15 seconds. Panel A illustrates
an SEM image of a front view and Panel B illustrates an SEM image
of a back view of the compressed mat.
[0106] FIG. 58 illustrates an exemplary structure of a
nanocomposite nanofiber having a tubular matrix material with
discrete domains (e.g., nanoparticles) embedded therein and a
hollow core (Panel A); and an exemplary nanocomposite having a core
matrix or backbone material with discrete domains (e.g.,
nanoparticles) embedded therein (Panel B).
[0107] FIG. 59 illustrates the full cell performance of Si/C
nanofibers with Li(Ni.sub.1/3Co.sub.1/3Mn.sub.1/3)O.sub.2
nanofibers.
[0108] FIG. 60 illustrates the full cell performance of Si/C
nanofibers with
Li[Li.sub.0.2Mn.sub.0.56Ni.sub.0.16Co.sub.0.08]O.sub.2
nanofibers.
DETAILED DESCRIPTION OF THE INVENTION
[0109] Described in certain embodiments herein are batteries (e.g.,
lithium-ion batteries), nanofiber cathodes, nanofiber anodes, and
nanofiber separators. Also, provided in certain embodiments herein
are lithium containing nanofibers (e.g., for use in a cathode /
positive electrode in a lithium ion battery). Provided in some
embodiments herein are nanofibers comprising a material capable of
lithium uptake--such as lithium alloying or lithium integration
(e.g., when used as an anode material in a lithium ion battery).
Provided in further embodiments herein are polymer and polymer
nanocomposite (e.g., polymer-nanoclay and polymer-nanoceramic)
nanofibers (e.g., and battery separators comprising the same).
[0110] In some embodiments, provided herein are batteries (e.g.,
lithium ion batteries) comprising an electrode (e.g., comprising
nanofibers--such as those described herein) and methods for making
such batteries (e.g., lithium ion battery). In some embodiments,
the electrode comprises a plurality of nanofibers, the nanofibers
comprising domains of a high energy capacity material (e.g., a
material that has a high specific capacity (mAh/g) when used as an
electrode material in a lithium ion battery). In some embodiments,
the electrode comprises nanofibers comprising a continuous matrix
of a high energy capacity material (e.g., a backbone of, a core
continuous matrix, a tubular continuous matrix (with a hollow core)
of a high energy capacity material). In some embodiments, the
electrode comprises porous nanofibers, the nanofibers comprising a
high energy capacity material.
[0111] Described in certain embodiments herein are batteries (e.g.,
lithium-ion batteries) and methods for making a battery (e.g.,
lithium ion battery) comprising a separator. In some embodiments,
the battery comprises an anode in a first chamber, a cathode in a
second chamber, and a separator between the first chamber and the
second chamber. In some embodiments, the separator comprises
polymer nanofibers. In some embodiments, the separator allows ion
transfer between the first chamber and second chamber in a
temperature dependent manner.
[0112] In some embodiments, the lithium-ion battery comprises an
electrolyte.
Batteries
[0113] In certain embodiments, provided herein is a battery (e.g.,
lithium ion battery) comprising any one or more feature selected
from the group consisting of:
[0114] an electrode (e.g., cathode or positive electrode)
comprising a lithium-containing nanofiber (e.g., as described
herein, such as comprising a continuous matrix of a lithium
material--such as lithium metal oxide, a lithium metal phosphate,
or the like--or comprising non-aggregated nano-domains of a lithium
material embedded in a continuous matrix material);
[0115] an electrode (e.g., anode or negative electrode) comprising
a high energy density nanofiber (e.g., comprising a continuous
matrix of a material having a high specific capacity in lithium ion
batteries (e.g., higher than carbon)--such as Si, Sn, SnO.sub.2,
Al, an Sn alloy, an Si alloy, or the like--or comprising
non-aggregated nano-domains of a material having a high specific
capacity embedded in a continuous matrix material);
[0116] a polymer nanofiber separator (e.g., as described
herein--such as comprising PAN nanofibers, polymer-nanoclay
nanocomposite nanofibers, polymer-nanoceramic nanofibers, or the
like); or
[0117] any combination thereof.
[0118] In some aspects, any battery (e.g., lithium-ion battery)
described herein has a high charge capacity. In further or
alternative embodiments, any battery (e.g., lithium ion battery)
described herein has a high energy capacity. In still further or
additional embodiments, a battery (e.g., a lithium ion battery)
provided herein has a high stability at elevated temperatures, is
stable over a high number of charge cycles, has a fast recharging
time, has a high energy density, and/or a high power density, among
other performance features. In some aspects methods are described
for making electrodes suitable for use in batteries (e.g., lithium
ion batteries) having a high charge capacity, having a high energy
capacity, having a high stability at elevated temperatures, are
stable over a high number of charge cycles, having a fast
recharging time, having a high energy density, and/or having a high
power density, among other performance features. Intercalation and
deintercalation of lithium ions to and from the electrodes of
lithium ion batteries causes the volume of the electrodes to expand
and contract in some instances. In some embodiments, the electrodes
comprising the battery are not pulverized, broken, degraded,
reduced to pieces, and/or reduced to particles. In some
embodiments, the electrode (or the high energy capacity material
portions of the electrode, such as Si nanoparticles in embedded
within a carbon matrix of a nanofiber, or a mesoporous Si
nanofiber) is capable of expanding its volume by about 10%, about
20%, about 50%, about 100%, about 150%, about 200%, about 300%,
about 400%, about 500%, and the like. In some embodiments, the
electrode (or the high energy capacity material portions of the
electrode) is capable of expanding its volume by at least 10%, at
least 20%, at least 50%, at least 100%, at least 150%, at least
200%, at least 300%, at least 400%, at least 500%, or more. In some
instances, this expansion is achieved without, with minimal, or
with reduced (e.g., as described herein) pulverization, breaking,
degradation, or reduction to pieces or particles (e.g., of the
electrode, or of the nanofibers, or portions thereof, within the
electrode).
[0119] In some instances, lithium ion batteries lose charge
capacity over time and/or charge cycles (i.e., one cycle of
discharge and recharge of the battery). In some instances,
pulverization of the electrodes or reorganization of crystalline
forms (e.g., into a form that does not allow relithiation) may be a
cause that decreases the charge capacity of the electrodes. In some
embodiments, the batteries described herein have a high charge
capacity after a plurality of charge cycles. In some embodiments,
the charge capacity of the battery is degraded by about 1%, about
2%, about 5%, about 10% or about 20% after 100 charge cycles.
[0120] In some embodiments, the charge capacity of the battery is
degraded by at most 1%, at most 2%, at most 5%, at most 10% or at
most 20% or at most 30% or at most 50% after 100 charge cycles. In
some embodiments, the charge capacity of the battery is degraded by
at most 1%, at most 2%, at most 5%, at most 10% or at most 20% or
at most 30% or at most 50% after 20 charge cycles, 40 charge
cycles, 50 charge cycles, 75 charge cycles, or the like.
[0121] In some instances, lithium ion batteries lose energy
capacity over time and/or charge cycles. Without limitation,
pulverization of the electrodes may be the or one cause that
decreases the energy capacity of the electrodes. In some
embodiments, the batteries described herein have a high energy
capacity after a plurality of charge cycles. In some embodiments,
the energy capacity of the battery is degraded by about 1%, about
2%, about 5%, about 10% or about 20% after 100 charge cycles. In
some embodiments, the energy capacity of the battery is degraded by
at most 1%, at most 2%, at most 5%, at most 10% or at most 20% or
at most 30% or at most 50% after 100 charge cycles. In some
embodiments, the energy capacity of the battery is degraded by at
most 1%, at most 2%, at most 5%, at most 10% or at most 20% or at
most 30% or at most 50% after 20 charge cycles, 40 charge cycles,
50 charge cycles, 75 charge cycles, or the like.
[0122] In one aspect, the lithium ion batteries described herein
are stable. In some embodiments, stable battery has an energy
density of at least 50%, at least 75%, at least 90%, and the like
of its initial value (e.g., after 50 charge cycles, at least 100
charge cycles, at least 300 charge cycles, or more). In some
embodiments, the battery is stable if the power density of the
battery is at least 50%, at least 75%, at least 90%, and the like
of its initial value (e.g., after 50 charge cycles, at least 100
charge cycles, at least 300 charge cycles, or more). In some
embodiments, the battery is stable if the energy capacity of the
battery is at least 50%, at least 75%, at least 90%, and the like
of its initial value (e.g., after 50 charge cycles, at least 100
charge cycles, at least 300 charge cycles, or more). In some
embodiments, the battery is stable if the charge capacity of the
battery is at least 50%, at least 75%, at least 90%, and the like
of its initial value (e.g., after 50 charge cycles, at least 100
charge cycles, at least 300 charge cycles, or more). In some
embodiments, the battery is stable if the recharging time of the
battery is at least 50%, at least 75%, at least 90%, and the like
of its initial value (e.g., after 50 charge cycles, at least 100
charge cycles, at least 300 charge cycles, or more). Further, in
some instances, a battery provided herein has an energy density or
charge capacity at least 300% higher, at least 500% higher, at
least 800% higher, or more than a comparable carbon anode.
[0123] In one aspect, the lithium ion batteries described herein
are stable over a high number of charge cycles. The number of
charge cycles is any suitable number. In some embodiments, the
battery is stable after about 50, about 100, about 500, about
1,000, about 5,000, or about 10,000 charge cycles. In some
embodiments, the battery is stable after at least 50, at least 100,
at least 500, at least 1,000, at least 5,000, or at least 10,000
charge cycles.
[0124] In one aspect, the lithium ion batteries described herein
are stable at high temperatures. In some embodiments, the battery
is stable at 50.degree. C., at 75.degree. C., at 100.degree. C., at
150.degree. C., at 200.degree. C., at 300.degree. C., at
400.degree. C., and the like. In some embodiments, the battery is
stable at a high temperature for any suitable amount of time. In
some embodiments, the battery is stable for 1 hour, 1 day, 1 week,
1 month, or one year. In one embodiment, the battery is stable for
at least 7 days at a temperature of 150.degree. C.
[0125] In one aspect, the lithium ion batteries described herein
are capable of being recharged quickly. In some embodiments, the
battery is capable of being recharged in any suitable amount of
time including about 30 minutes, about 1 hour, about 2 hours, about
3 hours, about 4 hours, about 5 hours, about 7 hours, about 9
hours, and the like. In some embodiments, the battery is capable of
being recharged in less than 30 minutes, less than 1 hour, less
than 2 hours, less than 3 hours, less than 4 hours, less than 5
hours, less than 7 hours, less than 9 hours, and the like. The
notation (C/1) indicates that the battery is capable of being
recharged in 1 hour, (C/5 or 0.2 C) in 5 hours, and the like.
[0126] In one aspect, the lithium ion batteries described herein
have a high energy density. The energy density is any suitably high
value. In some embodiments, the battery has an energy density of
about 100, about 150, about 200, about 250, about 300, about 350,
about 400, or about 500 Wh/kg. In some embodiments, the battery has
an energy density of at least 100, at least 150, at least 200, at
least 250, at least 300, at least 350, at least 400, or at least
500 Wh/kg.
[0127] In one aspect, the lithium ion batteries described herein
have a high power density. The power density is any suitably high
value. In some embodiments, the battery has a power density of
about 300, about 400, about 500, about 750, about 1,000, about
1,200, about 1,400, about 1,600, about 1,800, about 2,000, about
3,000, and the like W/kg. In some embodiments, the battery has a
power density of at least 300, at least 400, at least 500, at least
750, at least 1,000, at least 1,200, at least 1,400, at least
1,600, at least 1,800, at least 2,000, at least 3,000, and the like
W/kg.
Negative Electrode/Anode and Nanofibers Therefor
[0128] In some embodiments, an anode (or negative electrode)
described herein comprises a plurality of nanofibers. In certain
embodiments, an anode provided herein comprises a plurality of
nanofibers comprising a high energy capacity material. In specific
embodiments, the anode comprises a continuous matrix material
(e.g., carbon, ceramic, or the like) and discrete domains of a high
energy capacity material. In other specific embodiments, the anode
comprises a continuous matrix of a high energy capacity material.
In some instances, the anode or high energy capacity material
comprises Si, Ge, Sn, Co, Cu, Fe, any oxidation state thereof, or
any combination thereof. In certain embodiments, the anode or high
energy capacity material comprises Si, Ge, Sn, Al, an oxide
thereof, a carbide thereof, or an alloy thereof. In specific
embodiments, the anode or high energy capacity material comprises
SiO.sub.2, Sn, Si, Al, Ge, or an Si alloy. In certain embodiments,
provided herein are mesoporous nanofibers (e.g., comprising a
continuous silicon matrix).
[0129] FIG. 1 illustrates (a) an SEM image of a nanofiber
comprising a continuous matrix of (crystalline) SnO.sub.2 (panel
A), (b) an SEM image of a nanofiber comprising a continuous matrix
of Ge (panel B), and (c) an SEM image of a nanofiber comprising a
Si in a continuous matrix of carbon (panel C). In some instances,
the nanofibers of FIG. 1 are prepared by electrospinning a fluid
stock comprising a polymer (e.g., PVA) and a metal precursor (e.g.,
tin precursor, germanium precursor, or silicon precursor,
respectively), subsequently followed by thermal treatment (e.g.,
under oxidizing, inert, or reducing conditions--such as using
hydrogen or a sacrificial oxidizing agent). FIG. 2 illustrates (a)
an SEM image of a nanofiber comprising (crystalline) Sn in a
continuous matrix of (amorphous) Sn (panel A), (b) an SEM image of
a nanofiber comprising (crystalline) Sn in a continuous matrix
carbon (panel B), (c) an SEM image of a nanofiber comprising
(crystalline) Sn in a continuous matrix of alumina
(Al.sub.2O.sub.3) (panel C) and (d) an SEM image of a nanofiber
comprising (crystalline) Sn in a continuous matrix of zirconia
(ZrO.sub.2) (panel D). In some instances, the nanofibers of FIG. 2
are optionally prepared by electrospinning a fluid stock comprising
(i) Sn nanoparticles, and (ii) tin precursor and polymer (e.g.,
PVA), polymer (e.g., PAN), aluminum precursor (e.g., aluminum
acetate) and polymer (e.g., PVA), or zirconium precursor (e.g.,
zirconium acetate) and polymer (e.g., PVA), respectively, followed
by thermal treatment (e.g., under inert conditions, such as in (b),
or oxidizing conditions, such as in (a), (c) or (d)). FIG. 3
illustrates (a) an SEM image of a nanofiber comprising
(crystalline) Ge in a continuous matrix of carbon (carbonized from
PAN) (panel A), (b) an SEM image of a nanofiber comprising
(crystalline) Ge in a continuous matrix alumina (Al.sub.2O.sub.3)
(panel B) and (d) an SEM image of a nanofiber comprising
(crystalline) Ge in a continuous matrix of zirconia (ZrO.sub.2)
(panel C). In some instances, the nanofibers of FIG. 3 are
optionally prepared by electrospinning a fluid stock comprising (i)
Ge nanoparticles, and (ii) polymer (e.g., PAN), aluminum precursor
(e.g., aluminum acetate) and polymer (e.g., PVA), or zirconium
precursor (e.g., zirconium acetate) and polymer (e.g., PVA),
respectively, followed by thermal treatment (e.g., under inert
conditions, such as in (a), or oxidizing conditions, such as in (b)
or (c)). In specific embodiments, the electrospinning of such fluid
stocks is gas assisted.
[0130] FIG. 11 illustrates a schematic of a synthetic process for
preparing nanofibers (e.g., mesoporous nanofibers) of a high energy
capacity material described herein. In some embodiments, a fluid
stock is prepared by combining a polymer and a precursor (of a high
energy capacity material). In certain embodiments, the fluid stock
is then electrospun to prepare an as-spun nanofiber. In specific
embodiments, thermal treatment then calcines the precursor to
either a high energy capacity material, or a material that can be
converted to a high energy capacity material (e.g., SiO.sub.2, as
illustrated in FIG. 11). In some embodiments, the calcined material
is then converted to a high energy capacity material--e.g., through
reduction of the calcined material, such as with hydrogen or a
sacrificial oxidizing agent, such as magnesium. In some instances,
the reducing agent is optionally removed following chemical
treatment. In the case of using such a process for preparing
silicon nanofibers, FIG. 10 illustrates SEM (a-b) and TEM (c-e)
images of the nanofibers including images of (a) the as-spun fiber,
(b) fiber heated in air, (c) fiber heated in air, (d) fiber heated
under vacuum with Mg, and (e) HCl treated fiber. FIG. 12
illustrates X-Ray Diffraction of the nanofibers at various stages
of the synthetic process.
[0131] In some embodiments, a nanofiber provided herein comprises
(i) a silicon material (e.g., silicon); and (ii) a continuous
matrix material (e.g., ceramic, metal, or carbon). In certain
embodiments, the continuous matrix is a continuous core matrix
(e.g., not a hollow tube). In some embodiments, the silicon
material forms discrete isolated domains of the nanofibers. In some
specific embodiments, the silicon material domains are
non-aggregated. In some embodiments, the silicon material is a
nanoparticle comprising silicon. In certain embodiments, the
silicon discrete domain material (e.g., silicon nanoparticle) is
embedded within the continuous matrix material (e.g., in a
continuous matrix material/backbone material), such as illustrated
in FIG. 58 or FIG. 4 (which illustrates a nanofiber 400 having a
matrix material 402 with domains (nanoparticles) 401 embedded
therein) or FIG. 5.
[0132] In some embodiments, the silicon material domains are
non-aggregated. In specific embodiments, the nanofibers comprises
less than 50% of domains (e.g., Si nanoparticles) that are
aggregated. In specific embodiments, the nanofibers comprises less
than 40% of domains (e.g., Si nanoparticles) that are aggregated.
In specific embodiments, the nanofibers comprises less than 25% of
domains (e.g., Si nanoparticles) that are aggregated. In specific
embodiments, the nanofibers comprises less than 10% of domains
(e.g., Si nanoparticles) that are aggregated. In specific
embodiments, the nanofibers comprises less than 5% of domains
(e.g., Si nanoparticles) that are aggregated.
[0133] In some embodiments, provided herein is a battery (e.g., a
primary or secondary cell) comprising at least one nanofiber
described herein. In specific instances, the battery comprises
plurality of such nanofibers, e.g., a non-woven mat thereof. In
some embodiments, the battery comprises at least two electrodes
(e.g., an anode and a cathode) and a separator, at least one of the
electrodes comprising at least one nanofiber described herein. In
specific embodiments, the battery is a lithium-ion battery and the
anode comprises at least one nanofiber described herein (e.g., a
nanofiber mat thereof). Likewise, provided herein is an electrode
comprising any nanofiber described herein (e.g., a nanofiber mat
comprising one or more such nanofibers).
[0134] In some embodiments, the batteries comprise a negative
electrode (anode) comprising a plurality of nanofibers described
herein. In specific embodiments, the negative electrode or
plurality of nanofibers have a discharge capacity or specific
energy capacity of at least 1500 mAh/g on a first cycle at 0.1 C
(e.g., as determined by half cell or full cell testing). In further
or alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 2000 mAh/g on a first cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 1400 mAh/g on a 10th cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 1800 mAh/g on a 10th cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 1000 mAh/g on a 50th cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 1600 mAh/g on a 50th cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 250 mAh/g on a 98th cycle at 0.1 C. In further or
alternative embodiments, the negative electrode or plurality of
nanofibers have a discharge capacity or specific energy capacity of
at least 400 mAh/g on a 98th cycle at 0.1 C.
[0135] In certain embodiments, provided herein is a negative
electrode comprising high energy capacity material (e.g., silicon
nanoparticles) or a plurality of nanofibers having an discharge
capacity or specific energy capacity on a 25.sup.th cycle at 0.1 C
that is at least 40% of the discharge capacity or specific energy
capacity on the 1.sup.st cycle at 0.1 C. In further or alternative
embodiments, provided herein is a negative electrode comprising
high energy capacity material (e.g., silicon nanoparticles) or
plurality of nanofibers having an discharge capacity or specific
energy capacity on a 25.sup.th cycle at 0.1 C that is at least 50%
of the discharge capacity or specific energy capacity on the
1.sup.st cycle at 0.1 C. In certain embodiments, provided herein is
a negative electrode comprising high energy capacity material
(e.g., silicon nanoparticles) or plurality of nanofibers having an
discharge capacity or specific energy capacity on a 98.sup.th cycle
at 0.1 C that is at least 10% of the discharge capacity or specific
energy capacity on the 1.sup.st cycle at 0.1 C. In further or
alternative embodiments, provided herein is a negative electrode
comprising high energy capacity material (e.g., silicon
nanoparticles) or plurality of nanofibers having an discharge
capacity or specific energy capacity on a 98.sup.th cycle at 0.1 C
that is at least 20% of the discharge capacity or specific energy
capacity on the 1.sup.st cycle at 0.1 C. In certain embodiments,
provided herein is a negative electrode comprising high energy
capacity material (e.g., silicon nanoparticles) or plurality of
nanofibers having an discharge capacity or specific energy capacity
on a 98.sup.th cycle at 0.1 C that is at least 20% of the discharge
capacity or specific energy capacity on the 10.sup.th cycle at 0.1
C. In further or alternative embodiments, provided herein is a
negative electrode comprising high energy capacity material (e.g.,
silicon nanoparticles) or plurality of nanofibers having an
discharge capacity or specific energy capacity on a 98.sup.th cycle
at 0.1 C that is at least 30% of the discharge capacity or specific
energy capacity on the 10.sup.th cycle at 0.1 C.
[0136] FIG. 6 illustrates charge/discharge curves of 1.sup.st cycle
and 25.sup.th cycle (panel A) and plotted curves of Coulombic
efficiencies (panel B) for Si/C nanofibers provided herein compared
against Si nanoparticles alone. In some embodiments, provided
herein is a plurality of nanofibers or a negative electrode
comprising Si nanoparticles having a capacity at least as great as
set forth in FIG. 6. In some embodiments, provided herein is a Si
containing negative electrode or plurality of nanofibers having a
Coulombic efficiency of at least 80% over 25 cycles. In some
embodiments, provided herein is a Si containing negative electrode
or plurality of nanofibers having a Coulombic efficiency of at
least 90% over 25 cycles.
[0137] FIG. 7 illustrates plotted graphs of discharge capacities of
silicon nanoparticles in carbon nanofibers provided herein compared
to silicon nanoparticles alone at various discharge rates. In
certain embodiments, a nanofiber provided herein has a discharge
capacity at least as great as the values set forth in FIG. 7 at any
given cycle number or discharge rate. FIG. 13 illustrates the
capacity of other nanofibers (Sn/alumina, Ge/carbon, and
Ge/alumina) provided herein. In certain embodiments, provided
herein is a nanofiber having a discharge capacity of at least 750
mAh/g (e.g., after 25 cycles) at 0.1 C. In certain embodiments,
provided herein is a nanofiber having a discharge capacity of at
least 1000 mAh/g (e.g., after 25 cycles) at 0.1 C. In certain
embodiments, provided herein is a nanofiber having a discharge
capacity of at least 1450 mAh/g (e.g., after 25 cycles) at 0.1 C.
In some embodiments provided herein is a nanofiber having a
discharge capacity of at least 1150 mAh/g (e.g., after 25 cycles)
at 0.5 C. In some embodiments, provided herein is a nanofiber
having a discharge capacity of at least 1000 mAh/g (e.g., after 25
cycles) at a discharge rate of 0.8 C. In some embodiments, provided
herein are nanofibers having a energy capacity, discharge capacity,
or charge capacity of at least 30% theoretical capacity for the
material (e.g., after 25 cycles). In some embodiments, provided
herein are nanofibers having a energy capacity, discharge capacity,
or charge capacity of at least 40% theoretical capacity for the
material (e.g., after 25 cycles). In certain embodiments, provided
herein are nanofibers having a energy capacity, discharge capacity,
or charge capacity of at least 50% theoretical capacity for the
material (e.g., after 25 cycles). In some embodiments, provided
herein are nanofibers having a energy capacity, discharge capacity,
or charge capacity of at least 60% theoretical capacity for the
material (e.g., after 25 cycles or initial cycle). n some
embodiments, provided herein are nanofibers having a energy
capacity, discharge capacity, or charge capacity of at least 70%
theoretical capacity for the material (e.g., after 25 cycles or
initial cycle). n some embodiments, provided herein are nanofibers
having a energy capacity, discharge capacity, or charge capacity of
at least 80% theoretical capacity for the material (e.g., after 25
cycles or initial cycle).
[0138] FIG. 8 illustrates cyclic voltammograms (panel A) and
Nyquist plots (panel B) of silicon nanoparticles and certain Si/C
nanofibers described herein. In specific embodiments, the charge
transport resistance (e.g., as determined from AC impedance) of a
described herein is as demonstrated in FIG. 8. In some embodiments,
the charge transport resistance of a nanofiber described herein is
less than 100.OMEGA.. In specific embodiments, the charge transport
resistance of a nanofiber described herein is less than 75.OMEGA..
In more specific embodiments, the charge transport resistance of a
nanofiber described herein is less than 65.OMEGA.. In specific
embodiments, the charge transport resistance of a nanofiber
described herein is less than 60.OMEGA.. In further or alternative
embodiments, the solution (polarization) resistance of a nanofiber
provided herein is less than 5.OMEGA. (e.g., compared to 7.4.OMEGA.
of pure silicon nanoparticles). In specific embodiments, the
solution (polarization) resistance of a nanofiber provided herein
is less than 4.OMEGA.. In more specific embodiments, the solution
(polarization) resistance of a nanofiber provided herein is less
than 3.5.OMEGA..
[0139] In specific embodiments, provided herein is a nanofibers
comprising a backbone (e.g., a continuous matrix material, such as
a continuous core matrix), the backbone comprising nanoparticles
embedded therein, the backbone comprising carbon and the
nanoparticles comprising a high energy capacity material (e.g.,
silicon). In more specific embodiments, the nanofiber has an X-Ray
diffraction (XRD) pattern similar or identical to that forth in
FIG. 9. In some embodiments, the nanofiber has an XRD pattern with
at least 3 of the peaks in the XRD pattern set forth in FIG. 9. In
some embodiments, the nanofiber has an XRD pattern with at least 4
of the peaks in the XRD pattern set forth in FIG. 9. In some
embodiments, the nanofiber has an XRD pattern with at least 5 of
the peaks in the XRD pattern set forth in FIG. 9 In some
embodiments, the nanofiber has an XRD pattern with at least 3 of
the following peaks: 28.37.degree..+-.0.03, 47.20.degree..+-.0.03,
56.09.degree..+-.0.03, 69.02.degree..+-.0.03, and
76.37.degree..+-.0.03. In certain embodiments, the nanofiber has an
XRD pattern with at least 4 of the following peaks:
28.37.degree..+-.0.03, 47.20.degree..+-.0.03,
56.09.degree..+-.0.03, 69.02.degree..+-.0.03, and
76.37.degree..+-.0.03. In some embodiments, the nanofiber has an
XRD pattern with at least 5 of the following peaks:
28.37.degree..+-.0.03, 47.20.degree..+-.0.03,
56.09.degree..+-.0.03, 69.02.degree..+-.0.03, and
76.37.degree..+-.0.03.
[0140] In various embodiments, the high energy capacity material in
a nanocomposite nanofiber provided herein is any suitable high
energy capacity material. In some embodiments, the high energy
capacity material is an elemental metal (e.g., silicon, germanium,
or tin), an oxide thereof (e.g., tin oxide), or an alloy thereof
(e.g., a silicon metal oxide). In certain embodiments, the high
energy capacity material is a material suitable for use in a
lithium ion battery anode or negative electrode. In some
embodiments, a nanofiber herein comprises a material that is a
precursor material capable of being converted into a material
suitable for use in a lithium ion battery anode or negative
electrode. In various embodiments, the high energy capacity
material is in a crystalline state. In various embodiments, the
high energy capacity material is in a zero oxidation state, a
positive oxidation state, or a combination thereof. In specific
embodiments, the high energy capacity material is generally in a
zero oxidation state (e.g., a +0 oxidation state, or having an
average oxidation state of less than +0.05, on average).
[0141] In specific embodiments, a nanocomposite nanofiber provided
herein comprises high energy capacity nanoparticles. In specific
embodiments, the nanoparticles are silicon nanoparticles and
comprise at least 90 wt. % zero oxidation silicon and less than 10
wt % silicon dioxide. In specific embodiments, the nanoparticles
are silicon nanoparticles and comprise at least 60 wt. % zero
oxidation silicon and less than 20 wt % silicon dioxide and less
than 20% silicon carbide. In some embodiments, the nanoparticles
are silicon nanoparticles and comprise at least 50 wt. % zero
oxidation silicon and less than 30 wt % silicon dioxide and less
than 30% silicon carbide. In some specific embodiments, the silicon
nanoparticles comprise at least 95 wt. % zero oxidation silicon and
less than 5 wt % silicon dioxide. In still more specific
embodiments, the silicon nanoparticles comprise 90-99 wt. % zero
oxidation silicon and 0.01 (or 0.1) wt % to 5 wt % silicon
dioxide.
[0142] In certain embodiments, the discrete high energy capacity
material domain (e.g., silicon nanoparticle) has an average
diameter of less than 200 nm. In specific embodiments, the average
diameter is 1 nm to 200 nm. In some embodiments, the average
diameter is less than 100 nm. In specific embodiments, the average
diameter is 10 nm to 100 nm. In more specific embodiments, the
average diameter is 10 nm to 80 nm. In still more specific
embodiments, the average diameter is 20 nm to 70 nm.
[0143] In certain embodiments, provided herein are nanofibers
comprising a high energy capacity material and other optional
components. In specific embodiments, the nanofibers comprise at
least 25% by weight of high energy capacity material (e.g., on
average for a plurality of nanofibers). In more specific
embodiments, the nanofibers comprise at least 50% by weight of the
high energy capacity material (e.g., on average for a plurality of
nanofibers). In still more specific embodiments, the nanofibers
comprise at least 60% by weight of the high energy capacity
material (e.g., on average for a plurality of nanofibers).
[0144] In yet more specific embodiments, the nanofibers comprise at
least 70% by weight of the high energy capacity material (e.g., on
average for a plurality of nanofibers). In specific embodiments,
the nanofibers comprise at least 80% by weight of the high energy
capacity material (e.g., on average for a plurality of
nanofibers).
[0145] In certain embodiments, the nanofibers comprise at least 25%
by weight of silicon (e.g., on an elemental basis) (e.g., on
average for a plurality of nanofibers). In specific embodiments,
the nanocomposite nanofibers comprise at least 50% by weight of the
silicon (e.g., on average for a plurality of nanofibers).
[0146] In more specific embodiments, the nanocomposite nanofibers
comprise at least 75% by weight of silicon (e.g., on average for a
plurality of nanofibers). In yet more specific embodiments, the
nanocomposite nanofibers comprise at least 90% by weight of silicon
(e.g., on average for a plurality of nanofibers). In specific
embodiments, the nanocomposite nanofibers comprise at least 95% by
weight of silicon (e.g., on average for a plurality of
nanofibers).
[0147] FIG. 23 illustrates an X-Ray photoelectron spectrograph
(XPS) of silicon/carbon nanocomposite nanofibers described herein.
In certain embodiments, nanofibers provided herein comprise (e.g.,
on average) at least 10% by weight of a second silicon material
(e.g., silicon oxide and/or silicon carbide). In specific
embodiments, nanofibers provided herein comprise (e.g., on average)
at least 20% by weight of a second silicon material. In more
specific embodiments, nanofibers provided herein comprise (e.g., on
average) at least 30% by weight of a second silicon material. In
some embodiments, nanofibers provided herein comprise (e.g., on
average) less than 30% by weight of a second silicon material. In
specific embodiments, nanofibers provided herein comprise (e.g., on
average) less than 20% by weight of a second silicon material.
[0148] In some embodiments, the silicon material comprises silicon,
silicon oxide, silicon carbide or a combination thereof. In
specific embodiments, the silicon material comprises silicon. In
some embodiments, the silicon of the silicon material is
substantially in a zero oxidation state. In specific embodiments,
at least 50%, at least 60%, at least 70%, at least 80%, at least
90%, at least 95%, or the like of the silicon in the silicon
material is in a neutral (zero) oxidation state.
[0149] In certain embodiments, the silicon material is or comprises
one or more material represented by formula (I):
Si.sub.xSn.sub.qM.sub.yC.sub.z (I)
[0150] In some embodiments, M is one or more metal (e.g., Mn, Mo,
Nb, W, Ta, Fe, Cu, Ti, V, Cr, Ni, Co, Zr, Y, or a combination
thereof). In certain embodiments, (q+x)>2y+z; q>0, and
z.gtoreq.0. In some embodiments, q, x, y, and z represent atomic
percent values. In more specific embodiments, q, x, and y are each
.gtoreq.0.
[0151] Second Material
[0152] In some embodiments, a nanocomposite nanofiber provided
herein comprises a silicon material and a second material. In
certain embodiments, additional materials are optionally present.
In some embodiments, the second materials is a continuous matrix
material, as described herein. In certain embodiments, the second
material is a second silicon material, as described herein, e.g.,
silicon and silica.
[0153] In some embodiments, the second material is a polymer (e.g.,
an organic polymer, such as a water soluble organic polymer). In
other embodiments, the second material is a metal oxide, a ceramic,
a metal (e.g., a single metal material or an alloy), carbon, or the
like. In some embodiments, the second material comprises at least
3%, at least 5%, at least 10%, at least 15%, at least 20%, at least
30% or the like of the second material (e.g., carbon).
[0154] In certain embodiments, provided herein is an electrode
(e.g., negative electrode or anode) comprising a plurality of
nanofibers, the nanofibers comprising a continuous matrix of a high
energy capacity material (e.g., silicon). In other embodiments,
provided herein is an electrode (e.g., negative electrode or anode)
comprising a plurality of nanofibers, the nanofibers comprising (a)
a continuous matrix material; and (b) discrete, isolated (i.e.,
non-aggregated) domains of a high energy capacity material (e.g.,
silicon). In specific embodiments, at least 50% of the high energy
capacity material (e.g., silicon) has an oxidation state of zero.
In more specific embodiments, at least 70% of the high energy
capacity material (e.g., silicon) has an oxidation state of zero.
In still more specific embodiments, at least 80% of the high energy
capacity material (e.g., silicon) has an oxidation state of zero.
In yet more specific embodiments, at least 90% of the high energy
capacity material (e.g., silicon) has an oxidation state of zero.
In more specific embodiments, at least 95% of the high energy
capacity material (e.g., silicon) has an oxidation state of
zero.
[0155] In some embodiments, the electrode comprises a plurality of
nanofibers having a continuous matrix of high energy capacity
material (e.g., silicon). In certain embodiments, the continuous
matrix of high energy capacity material (e.g., silicon) is porous
(e.g., mesoporous). In certain embodiments, the continuous matrix
of high energy capacity material (e.g., silicon) is hollow (e.g.,
hollow silicon nanofibers--or silicon tube nanofibers). In specific
embodiments, the nanofibers comprise (e.g., on average) at least
50% high energy capacity material (e.g., silicon) (e.g., by
elemental analysis). In specific embodiments, the nanofibers
comprise (e.g., on average) at least 70% high energy capacity
material (e.g., silicon). In more specific embodiments, the
nanofibers comprise (e.g., on average) at least 80% high energy
capacity material (e.g., silicon). In still more specific
embodiments, the nanofibers comprise (e.g., on average) at least
90% high energy capacity material (e.g., silicon). In yet more
specific embodiments, the nanofibers comprise (e.g., on average) at
least 95% high energy capacity material (e.g., silicon).
[0156] In some embodiments, the electrode comprises a plurality of
nanofibers comprising (a) a matrix; and (b) a plurality of
isolated, discrete domains comprising high energy capacity material
(e.g., silicon). In specific embodiments, the matrix is a
continuous matrix of carbon (e.g., amorphous carbon). In certain
embodiments, the matrix and/or discrete high energy capacity
material (e.g., silicon) domains are porous (e.g., mesoporous). In
certain embodiments, the continuous matrix is hollow. In specific
embodiments, the nanofibers comprise (e.g., on average) at least
30% high energy capacity material (e.g., silicon) (e.g., by
elemental analysis). In specific embodiments, the nanofibers
comprise (e.g., on average) at least 50% high energy capacity
material (e.g., silicon). In more specific embodiments, the
nanofibers comprise (e.g., on average) at least 60% high energy
capacity material (e.g., silicon). In still more specific
embodiments, the nanofibers comprise (e.g., on average) at least
70% high energy capacity material (e.g., silicon). In yet more
specific embodiments, the nanofibers comprise (e.g., on average) at
least 80% high energy capacity material (e.g., silicon). In
specific embodiments, the discrete domains comprise (e.g., on
average) at least 50% high energy capacity material (e.g., silicon)
(e.g., by elemental analysis). In specific embodiments, the
discrete domains comprise (e.g., on average) at least 70% high
energy capacity material (e.g., silicon).
[0157] In more specific embodiments, the discrete domains comprise
(e.g., on average) at least 80% high energy capacity material
(e.g., silicon). In still more specific embodiments, the discrete
domains comprise (e.g., on average) at least 90% high energy
capacity material (e.g., silicon). In yet more specific
embodiments, the discrete domains comprise (e.g., on average) at
least 95% high energy capacity material (e.g., silicon).
[0158] In some embodiments, provided herein is a battery comprising
such an electrode (e.g., anode). In specific embodiments, the
battery is a secondary cell. Also, provided in certain embodiments
herein are nanofibers or nanofiber mats comprising one or more such
nanofiber as described herein.
[0159] In some embodiments, negative electrodes provided herein are
prepared by depositing high energy (anodic) capacity nanofibers
onto a current collector, thereby creating a negative electrode
comprising the nanofibers in contact with a current collector. In
certain embodiments, as-treated nanofibers are ground in a mortal
and pestle to produce processed nanofibers, which are then
deposited on a current collector. In some embodiments, the
processed nanofibers are dispersed in a solvent to prepare a
composition, the composition is deposited onto a current collector,
and evaporation of the solvent results in formation of an electrode
on the current collector. In specific embodiments, the composition
further comprises a binder.
[0160] In further or alternative specific embodiments, the
composition further comprises a conductive material (e.g., carbon
black)--e.g., to improve electron mobility.
Positive Electrode/Cathode and Nanofibers Therefor
[0161] In some embodiments, the nanofibers provide herein comprise
a backbone material (a core matrix material). In specific
embodiments, the backbone material is a lithium material described
herein. In other specific embodiments, the backbone material is a
continuous matrix material with non-aggregated domains embedded
therein, the non-aggregated domains comprising a lithium material
described herein (e.g., a nanoparticle comprising a lithium
material described herein). In certain embodiments, nanofibers
described herein comprise a hollow core. In specific embodiments,
the nanofibers described herein comprise a continuous matrix
material surrounding the hollow core. In more specific embodiments,
the continuous matrix material comprises a lithium material
described herein. In other specific embodiments, the continuous
matrix material comprises non-aggregated domains embedded therein,
the non-aggregated domains comprising a lithium material described
herein (e.g., a nanoparticle comprising a lithium material
described herein). In various embodiments herein, a continuous
matrix material is comprises a ceramic, a metal, or carbon. In
specific embodiments, the continuous matrix material is a
conductive material.
[0162] In certain embodiments, the lithium material (e.g., core
matrix lithium material) provided herein is crystalline. In some
embodiments, the lithium material comprises a layered crystalline
structure. In certain embodiments, the lithium material comprises a
spinel crystalline structure. In certain embodiments, the lithium
material comprises an olivine crystalline structure.
[0163] In some embodiments, the lithium material is any material
capable of intercalating and deintercalating lithium ions. In some
embodiments, the lithium material is or comprises a lithium metal
oxide, a lithium metal phosphate, a lithium metal silicate, a
lithium metal sulfate, a lithium metal borate, or a combination
thereof. In specific embodiments, the lithium material is a lithium
metal oxide. In other specific embodiments, the lithium material is
a lithium metal phosphate. In other specific embodiments, the
lithium material is a lithium metal silicate. In other specific
embodiments, the lithium material is lithium sulfide.
[0164] In some embodiments, provided herein is a nanofiber
comprising a lithium material (e.g., a continuous core matrix of a
lithium material). In some embodiments, the nanofibers comprise a
continuous matrix of a lithium material. In certain embodiments,
the nanofibers comprises a continuous matrix material (e.g.,
carbon, ceramic, or the like) and discrete domains of a lithium
material (e.g., wherein the discrete domains are non-aggregated).
In specific embodiments, the continuous matrix material is a
conductive material (e.g., carbon). In further embodiments,
provided herein is a cathode (or positive electrode) comprising a
plurality of nanofibers comprising a lithium material. In some
embodiments, less than 40% of the nanoparticles are aggregated
(e.g., as measured in any suitable manner, such as by TEM). In
specific embodiments, less than 30% of the nanoparticles are
aggregated). In more specific embodiments, less than 25% of the
nanoparticles are aggregated). In yet more specific embodiments,
less than 20% of the nanoparticles are aggregated). In still more
specific embodiments, less than 10% of the nanoparticles are
aggregated). In more specific embodiments, less than 5% of the
nanoparticles are aggregated). In some instances, the lithium
material is or comprises LiCoO.sub.2,
LiCo.sub.x1Ni.sub.y1Mn.sub.z1O.sub.2,
LiMn.sub.x1Ni.sub.y1Co.sub.z1V.sub.a1O.sub.4, Li.sub.2S,
LiFe.sub.x1Ni.sub.y1Co.sub.z1V.sub.a1PO.sub.4, any oxidation state
thereof, or any combination thereof. Generally, x1, y1, z1, and a1
are independently selected from suitable numbers, such as a number
from 0 to 5 or from greater than 0 to 5.
[0165] In certain embodiments, provided herein is a plurality of
nanofibers, the nanofibers comprising lithium, such as a continuous
matrix of a lithium containing material (e.g., a lithium salt or
lithium alloy/insertion compound, such as a lithium metal oxide).
In other embodiments, provided herein is an electrode (e.g.,
positive electrode or cathode) comprising a plurality of
nanofibers, the nanofibers comprising (a) a continuous matrix
material; and (b) discrete, isolated domains comprising lithium. In
some embodiments, the continuous matrix or isolated domains
comprise lithium in the form of a lithium containing metal alloy.
In specific embodiments, the lithium containing metal alloy is a
lithium metal oxide. In some embodiments, the nanofiber(s) comprise
a lithium containing material of the following formula (I):
Li.sub.aM.sub.bX.sub.c (I)
[0166] In certain embodiments, M represents one or more metal
element (e.g., M represents Fe, Ni, Co, Mn, V, Ti, Zr, Ru, Re, Pt,
Bi, Pb, Cu, Al, Li, or a combination thereof) and X represents one
or more non-metal (e.g., X represents C, N, O, P, S, SO.sub.4,
PO.sub.4, Se, halide, F, CF, SO.sub.2, SO.sub.2Cl.sub.2, I, Br,
SiO.sub.4, BO.sub.3, or a combination thereof) (e.g., a non-metal
anion). In some embodiments, a is 0.5-5, or 1-5 (e.g., 1-2), b is
0-2, and c is 0-10 (e.g., 1-4, or 1-3).
[0167] In some embodiments, X is selected from the group consisting
of O, SO.sub.4, PO.sub.4, SiO.sub.4, BO.sub.3. In more specific
embodiments, X is selected from the group consisting of O,
PO.sub.4, and SiO.sub.4. In certain embodiments, M is Mn, Ni, Co,
Fe, V, Al, or a combination thereof.
[0168] In certain embodiments, a lithium material of formula (I) is
LiMn.sub.2O.sub.4, LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2,
LiCoO.sub.2, LiNiO.sub.2, LiFePO.sub.4, Li.sub.2FePO.sub.4F, or the
like. In some embodiments, a lithium material of formula (I) is
LiNi.sub.b1Co.sub.b2Mn.sub.b3O.sub.2, wherein b1+b2+b3=1, and
wherein 0<b1, b2, b3<1. In some embodiments, a lithium
material of formula (I) is LiNi.sub.b1Co.sub.b2Al.sub.b3O.sub.2,
wherein b1+b2+b3=1, and wherein 0<b1, b2, b3<1. In certain
embodiments, a lithium material of formula (I) is
LiMn.sub.2O.sub.4, LiMn.sub.b1Fe.sub.b2O.sub.4 (wherein b1+b2=2,
e.g., b1=1.5), LiMnPO.sub.4, LiNiPO.sub.4, LiCoPO.sub.4,
Li.sub.3V.sub.2(PO.sub.4).sub.3, Li.sub.2FeSiO.sub.4,
Li.sub.2MnSiO.sub.4, LiFeBO.sub.3, or LiMnBO.sub.3.
[0169] In some embodiments, the lithium material of formula (I) is
Li.sub.2SO.sub.y', wherein y' is 0-4, such as Li.sub.2S or
Li.sub.2SO.sub.4.
[0170] In more specific embodiments, the lithium metal of formula
(I) is represented by the lithium metal of formula (Ia):
Li.sub.aM.sub.bO.sub.2 (Ia)
[0171] In specific embodiments, M, a, and b are as described above.
In specific embodiments, a lithium metal of formula (Ia) has the
structure LiMO.sub.2 (e.g.,
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2). In some embodiments, a
and b are each 1 and the one or more metal of M have an average
oxidation state of 3.
[0172] In more specific embodiments, the lithium metal of formula
(Ia) is represented by the lithium metal of formula (Ib):
Li(M'.sub.(1-g)O.sub.2 Ib)
[0173] In certain embodiments, M' represents one or more metal
element (e.g., M' represents Fe, Ni, Co, Mn, V, Li, Cu, Zn, or a
combination thereof). In some embodiments, g is 0-1 (e.g.,
0<g<1). In specific embodiments, M' represents one or more
metal having an average oxidation state of 3.
[0174] In more specific embodiments, the lithium metal of formula
(Ia) or (Ib) is represented by the lithium metal of formula
(Ic):
Li.sub.(1-2h)/3)M''.sub.hMn.sub.(2-b)/3)O.sub.2 (Ic)
[0175] In certain embodiments, M'' represents one or more metal
element (e.g., M'' represents Fe, Ni, Co, Zn, V, or a combination
thereof). In some embodiments, h is 0-0.5 (e.g., 0<h<0.5,
such as 0.083<h<0.5). In a specific embodiment, the lithium
metal of formula (Ic) is
Li[Li.sub.(1-2h)/3Ni.sub.h.Co.sub.(h-h')Mn.sub.(2-h)/3)O.sub.2,
wherein h' is 0-0.5 (e.g., 0<h'<0.5).
[0176] In more specific embodiments, the lithium metal of formula
(Ia) is represented by the lithium metal of formula (Id):
LiNi.sub.bCo.sub.b.M'''.sub.b-O.sub.2 (Id)
[0177] In certain embodiments, M''' represents one or more metal
element (e.g., M''' represents Fe, Mn, Zn, V, or a combination
thereof). In some embodiments, each of b', b'', and b''' is
independently 0-2 (e.g., 0-1, such as 0<b', b'', and b'''<1).
In specific embodiments, the sum of b', b'', and b''' is 1. In some
embodiments, the one or more metal of M''' when taken together with
the Ni and Co have an average oxidation state of 3.
[0178] In some embodiments, the lithium metal of formula (I) is
represented by the lithium metal of formula (Ie):
Li.sub.aM.sub.bO.sub.3 (Ie)
[0179] In specific embodiments, M, a, and b are as described above.
In specific embodiments, a lithium metal of formula (Ie) has the
structure Li.sub.2MO.sub.3 (e.g., Li.sub.2MnO.sub.3). In some
embodiments, a is 2, b is 1 and the one or more metal of M have an
average oxidation state of 4.
[0180] In certain embodiments, provided herein is an electrode
(e.g., positive electrode or cathode) comprising a plurality of
nanofibers, the nanofibers comprising a continuous matrix of a
lithium containing metal (e.g., a lithium metal alloy, such as a
lithium metal oxide). In other embodiments, provided herein is an
electrode (e.g., positive electrode or cathode) comprising a
plurality of nanofibers, the nanofibers comprising (a) a continuous
matrix material; and (b) discrete, isolated domains of a lithium
containing metal (e.g., a lithium metal alloy, such as a lithium
metal oxide).
[0181] In some embodiments, the plurality of nanofibers have a
continuous matrix of a lithium containing material. In certain
embodiments, the continuous matrix of lithium containing material
is porous (e.g., mesoporous). In certain embodiments, the
continuous matrix of lithium containing material is hollow (e.g.,
hollow lithium containing metal nanofibers).
[0182] In specific embodiments, the nanofibers comprise (e.g., on
average) at least 50% lithium containing material (e.g., by
elemental analysis). In specific embodiments, the nanofibers
comprise (e.g., on average) at least 70% lithium containing
material. In more specific embodiments, the nanofibers comprise
(e.g., on average) at least 80% lithium containing material. In
still more specific embodiments, the nanofibers comprise (e.g., on
average) at least 90% lithium containing material. In yet more
specific embodiments, the nanofibers comprise (e.g., on average) at
least 95% lithium containing material.
[0183] In certain embodiments, the nanofibers comprise (e.g., on
average) at least 0.5 wt. % lithium (e.g., by elemental analysis).
In specific embodiments, the nanofibers comprise (e.g., on average)
at least 1 wt. % lithium (e.g., by elemental analysis). In more
specific embodiments, the nanofibers comprise (e.g., on average) at
least 2.5 wt. % lithium (e.g., by elemental analysis). In still
more specific embodiments, the nanofibers comprise (e.g., on
average) at least 5 wt. % lithium (e.g., by elemental analysis). In
specific embodiments, the nanofibers comprise (e.g., on average) at
least 7 wt. % lithium (e.g., by elemental analysis). In more
embodiments, the nanofibers comprise (e.g., on average) at least 10
wt. % lithium (e.g., by elemental analysis).
[0184] In some embodiments, lithium atoms constitute (e.g., on
average) at least 10% of the atoms present in the nanofibers. In
specific embodiments, lithium atoms constitute (e.g., on average)
at least 20% of the atoms present in the nanofibers. In more
specific embodiments, lithium atoms constitute (e.g., on average)
at least 30% of the atoms present in the nanofibers. In still more
specific embodiments, lithium atoms constitute (e.g., on average)
at least 40% of the atoms present in the nanofibers. In yet more
specific embodiments, lithium atoms constitute (e.g., on average)
at least 50% of the atoms present in the nanofibers. For example,
in certain embodiments, provided herein are nanofibers comprising
pure LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, which comprises about
7 wt. % lithium (6.94 mol wt. Li/96.46 mol wt.
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2) and about 25% lithium
atoms (1 lithium atom / (1 lithium atom+1/3 nickel atom+1/3
manganese atom+1/3 cobalt atom+2 oxygen atoms)).
[0185] In some embodiments, the electrode comprises a plurality of
nanofibers comprising (a) a matrix; and (b) a plurality of
isolated, discrete domains comprising a lithium containing metal
(e.g., a lithium alloy/intercalculation compound, such as a lithium
metal oxide). In specific embodiments, the matrix is a continuous
matrix of carbon (e.g., amorphous carbon). In certain embodiments,
the matrix and/or discrete lithium containing domains are porous
(e.g., mesoporous). In certain embodiments, the continuous matrix
is hollow. In specific embodiments, the nanofibers comprise (e.g.,
on average) at least 30% lithium material (e.g., by elemental
analysis). In specific embodiments, the nanofibers comprise (e.g.,
on average) at least 40% lithium material. In more specific
embodiments, the nanofibers comprise (e.g., on average) at least
50% lithium material. In still more specific embodiments, the
nanofibers comprise (e.g., on average) at least 70% lithium
material. In yet more specific embodiments, the nanofibers comprise
(e.g., on average) at least 80% lithium material. In some
embodiments, the nanofibers comprise lithium containing domains
that comprise (e.g., on average) at least 70% lithium material. In
more specific embodiments, the domains comprise (e.g., on average)
at least 80% lithium material. In still more specific embodiments,
the domains comprise (e.g., on average) at least 90% lithium
material. In yet more specific embodiments, the domains comprise
(e.g., on average) at least 95% lithium material. In certain
embodiments, the nanofibers comprise (e.g., on average) at least
0.1 wt. % lithium (e.g., by elemental analysis). In specific
embodiments, the nanofibers comprise (e.g., on average) at least
0.5 wt. % lithium (e.g., by elemental analysis). In more specific
embodiments, the nanofibers comprise (e.g., on average) at least 1
wt. % lithium (e.g., by elemental analysis). In still more specific
embodiments, the nanofibers comprise (e.g., on average) at least
2.5 wt. % lithium (e.g., by elemental analysis). In specific
embodiments, the nanofibers comprise (e.g., on average) at least 5
wt. % lithium (e.g., by elemental analysis). In more embodiments,
the nanofibers comprise (e.g., on average) at least 10 wt. %
lithium (e.g., by elemental analysis). In some embodiments, lithium
atoms constitute (e.g., on average) at least 10% of the atoms
present in the nanofibers. In specific embodiments, lithium atoms
constitute (e.g., on average) at least 5% of the atoms present in
the nanofibers or the domains. In more specific embodiments,
lithium atoms constitute (e.g., on average) at least 10% of the
atoms present in the nanofibers or domains. In still more specific
embodiments, lithium atoms constitute (e.g., on average) at least
20% of the atoms present in the nanofibers or domains. In yet more
specific embodiments, lithium atoms constitute (e.g., on average)
at least 30% of the atoms present in the nanofibers or domains. In
further embodiments, lithium atoms constitute (e.g., on average) at
least 40%, at least 50%, or the like of the atoms present in the
domains.
[0186] In certain embodiments, provided herein are
lithium-containing-nanofibers comprising a lithium material
described herein, wherein up to 50% of the lithium is absent. In
some instances, the lithium is absent due to delithiation
(de-intercalculation of lithium) during lithium ion battery
operation. In other instances, the lithium is absent due to
volatility and/or sublimation of the lithium component. In specific
embodiments, up to 40% of the lithium is absent. In more specific
embodiments, up to 30% of the lithium is absent. In still more
specific embodiments, up to 20% of the lithium is absent. In yet
more specific embodiments, up to 10% of the lithium is absent.
[0187] In some embodiments, provided herein is a battery comprising
such an electrode (e.g., cathode). In specific embodiments, the
battery is a secondary cell. Also, provided in certain embodiments
herein are nanofibers or nanofiber mats comprising one or more such
nanofiber as described herein.
[0188] In some embodiments, lithium-containing nanofibers provided
herein have an initial capacity of at least 60 mAh/g as a cathode
in a lithium ion battery (e.g., at a charge/discharge rate of 0.1
C--such as in a half cell with lithium as the counter electrode).
In specific embodiments, lithium-containing nanofibers provided
herein have an initial capacity of at least 80 mAh/g as a cathode
in a lithium ion battery (e.g., at a charge/discharge rate of 0.1
C). In more specific embodiments, lithium-containing nanofibers
provided herein have an initial capacity of at least 100 mAh/g as a
cathode in a lithium ion battery (e.g., at a charge/discharge rate
of 0.1 C). In still more specific embodiments, lithium-containing
nanofibers provided herein have an initial capacity of at least 120
mAh/g as a cathode in a lithium ion battery (e.g., at a
charge/discharge rate of 0.1 C). In yet more specific embodiments,
lithium-containing nanofibers provided herein have an initial
capacity of at least 160 mAh/g as a cathode in a lithium ion
battery (e.g., at a charge/discharge rate of 0.1 C). In more
specific embodiments, lithium-containing nanofibers provided herein
have an initial capacity of at least 180 mAh/g as a cathode in a
lithium ion battery (e.g., at a charge/discharge rate of 0.1
C).
[0189] In certain embodiments, lithium-containing nanofibers have a
capacity (e.g., charge, discharge, and/or specific capacity) at
least 50% initial capacity after 50 cycles. In specific
embodiments, lithium-containing nanofibers have a capacity (e.g.,
charge, discharge, and/or specific capacity) at least 60% initial
capacity after 50 cycles. In more specific embodiments,
lithium-containing nanofibers have a capacity (e.g., charge,
discharge, and/or specific capacity) at least 70% initial capacity
after 50 cycles. In certain embodiments, lithium-containing
nanofibers have a capacity (e.g., charge, discharge, and/or
specific capacity) at least 50% initial capacity after 40 cycles.
In specific embodiments, lithium-containing nanofibers have a
capacity (e.g., charge, discharge, and/or specific capacity) at
least 60% initial capacity after 40 cycles. In more specific
embodiments, lithium-containing nanofibers have a capacity (e.g.,
charge, discharge, and/or specific capacity) at least 70% initial
capacity after 40 cycles. FIG. 32 illustrates the charge/discharge
capacities for lithium cobalt oxide nanofiber cathodes in a lithium
ion battery half cell. FIG. 41 illustrates the charge/discharge
capacity of the lithium manganese oxide nanofiber cathodes in a
lithium ion battery half cell.
[0190] In some embodiments, provided herein is a battery comprising
such an electrode (e.g., cathode). In specific embodiments, the
battery is a secondary cell. Also, provided in certain embodiments
herein are nanofibers or nanofiber mats comprising one or more such
nanofiber as described herein.
[0191] In some embodiments, positive electrodes provided herein are
prepared by depositing lithium-containing nanofibers onto a current
collector, thereby creating a positive electrode comprising the
nanofibers in contact with a current collector. In certain
embodiments, as-treated nanofibers are ground in a mortal and
pestle to produce processed nanofibers, which are then deposited on
a current collector. In some embodiments, the processed nanofibers
are dispersed in a solvent to prepare a composition, the
composition is deposited onto a current collector, and evaporation
of the solvent results in formation of an electrode on the current
collector. In specific embodiments, the composition further
comprises a binder.
[0192] In further or alternative specific embodiments, the
composition further comprises a conductive material (e.g., carbon
black)--e.g., to improve electron mobility.
Separator and Nanofibers Therefor
[0193] Described herein are lithium-ion batteries and methods for
making a lithium ion battery comprising a separator. In some
embodiments, the battery comprises an anode in a first chamber, a
cathode in a second chamber, and a separator between the first
chamber and the second chamber. In some embodiments, the separator
comprises polymer nanofibers. In some embodiments, the separator
allows ion transfer between the first chamber and second chamber in
a temperature dependent manner.
[0194] In certain embodiments, provided herein are nanofibers
comprising a polymer matrix (e.g., continuous matrix, or continuous
core matrix or backbone) and optionally comprising thermally stable
nanostructures embedded therein. In specific embodiments, the
nanostructures are present. In some embodiments, the thermally
stable nanostructures have any suitable shape or configuration. In
specific embodiments, the thermally stable nanostructures comprise
a clay or ceramic. In specific embodiments, such nanofibers are for
use in or as a battery separator (e.g., a lithium ion battery
separator).
[0195] In certain embodiments, provided herein are nanofibers
comprising a polymer matrix (e.g., continuous matrix, or continuous
core matrix or backbone) and comprising nanoclay and/or nanoceramic
structures embedded therein. In some embodiments, the thermally
stable structures have any suitable shape or configuration.
[0196] In some embodiments, non-limiting exemplary clays (e.g., in
nanoclay structures) provided herein are selected from the group
consisting of bentonite, aluminum phyllosilicate, montmorillonite,
kaolinite, illite, vermiculite, smectite, chlorite, silicate clay,
sesquioxide clays, allophane, imogolite, fluorohectorate, laponite,
bentonite, beidellite, hectorite, saponite, nontronite, sauconite,
ledikite, magadiite, kenyaite, stevensite, and combinations
thereof. In specific embodiments, the clay (e.g., nanoclay) is a
hydrophilic clay (e.g., nanoclay), such as bentonite. In some
embodiments, non-limiting exemplary ceramics (e.g., in nanoceramic
structures) provided herein are selected from the group consisting
of silica, alumina, titania, beryllia, silicon carbide, and
combinations thereof. In some embodiments, non-limiting exemplary
ceramics include metal oxide ceramics, metal carbide ceramics,
metal silicate ceramics, metal nitride ceramics, and the like.
[0197] In some embodiments, nanofibers (e.g., for use as
separators) comprise any suitable amount of thermally stable
nanostructured material. In specific embodiments, such nanofibers
comprise (e.g., on average) about 0.1 wt % to about 70 wt %
nanoclay and/or nanoceramic (cumulatively). In more specific
embodiments, nanofibers comprise (e.g., on average) about 0.5 wt %
to about 50 wt % nanoclay and/or nanoceramic (cumulatively). In
still more specific embodiments, nanofibers comprise (e.g., on
average) about 2 wt % to about 25 wt % nanoclay and/or nanoceramic
(cumulatively). In still more specific embodiments, nanofibers
comprise (e.g., on average) about 3 wt % to about 10 wt % nanoclay
and/or nanoceramic (cumulatively).
[0198] Any suitable polymer is used. In some embodiments, the
polymer comprises a water soluble polymer, a thermoplastic, or a
solvent soluble polymer. In certain embodiments, the polymer is a
polyolefin. In some embodiments, the polymer is polyethylene (PE)
(e.g., ultra-high molecular weight polyethylene (UHMWPE)),
polypropylene (PP), polyvinyl alcohol (PVA), polyacrylonitrile
(PAN), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP),
polyvinylidene fluoride (PVDF), nylon, aramid, polyethylene
terephthalate (PET), polyimide (PI), or any combination thereof. In
specific embodiments, the polymer is polyacrylonitrile (PAN). In
other specific embodiments, the polymer is polyethylene (PE) or
polypropylene (PP). Other polymers described herein (e.g.,
electrospinnable polymers described herein) are optionally
utilized.
[0199] In specific embodiments, provided herein is a lithium ion
battery separator comprising nanofiber, the nanofiber comprising
(i) a continuous polymer matrix; and (ii) nanoclay and/or
nanoceramic (e.g., a ceramic nanoparticle) embedded within the
continuous polymer matrix. In specific embodiments, the polymer
matrix is a thermoplastic, a water soluble polymer, or a solvent
soluble polymer. In more specific embodiments, the polymer is PE,
PP, meta-aramid, or PAN. In still more specific embodiments, the
polymer is PAN.
[0200] In some embodiments, a process for producing (e.g.,
polymer-clay or polymer-ceramic) nanocomposite nanofibers (e.g.,
for use as battery separators--such as lithium ion battery
separators) comprises electrospinning a fluid stock to form as-spun
nanofibers, the fluid stock comprising a plurality of
nanostructures and a polymer, the plurality of nanostructures
comprising a clay, a ceramic, or a combination thereof. In some
embodiments, the process further comprises annealing the
nanofibers. In certain embodiments, the thermal treatment occurs
under inert conditions (e.g., in an argon atmosphere).
[0201] In further or alternative embodiments, the process further
comprise compressing the nanofibers (e.g., electrospinning or
assembling a non-woven mat of nanofibers and subsequently
compressing the non-woven mat). In certain embodiments, the
electrospinning is gas assisted. In specific embodiments, the
electrospinning is coaxially gas assisted. In other embodiments,
fluid is a solvent based solution. In some embodiments, the polymer
is a solvent soluble polymer, such as polyacrylonitrile (PAN)
(e.g., soluble in DMF), or a polyolefin (e.g., polyethylene (PE) or
polypropylene (PP)).
[0202] In some embodiments, nanofibers (e.g., for use in a
separator herein) are thermally treated (e.g., annealed)
nanofibers. In specific embodiments, the nanofibers are annealed at
a temperature of less than 300.degree. C., e.g., 100.degree.
C.-200.degree. C. In some embodiments, the nanofibers are annealed
at a temperature below the melt temperature of the polymer
therein.
[0203] In certain embodiments, nanofibers (e.g., for use in a
separator herein) are compressed. In some embodiments, the
nanofibers are formed into a non-woven mat and compressed. Any
suitable pressure is optionally utilized. In some embodiments, the
nanofibers are compressed at a pressure of 0.1 Mpa to 10 Mpa. In
some embodiments, the nanofibers are compressed at a pressure of 1
Mpa to 5 Mpa.
[0204] In some embodiments, a separator (e.g., in a lithium ion
battery) provided herein comprises a nanofiber mat, comprising a
(or a plurality of) nanofiber(s) provided herein, the separator
having a thickness of 10 to 100 microns. In specific embodiments,
the thickness is 20-60 microns. In more specific embodiments, the
thickness is 30-50 microns.
[0205] In some embodiments, a separator provided herein has an
average pore size of less than 1 micron. In specific embodiments, a
separator provided herein has an average pore size of less than 0.5
micron. In some embodiments, a separator provided herein has a peak
pore size distribution at less than 1 micron. In specific
embodiments, a separator provided herein has a peak pore size
distribution at less than 0.5 micron. FIG. 47 illustrates the pore
size distribution of various nanofiber mats (e.g., for use in
separators) provided herein.
[0206] FIG. 48 illustrates a Nyquist plot of different separators
provided herein (compared to commercial PE separator), wherein 32
mg of LiCoO.sub.2 powder is used as a cathode (e.g., in a half
cell) and the constant voltage=VOC (1.7-2.0V)-Cd=double layer
capacitor (charge-transfer process); Rct=polarization (charge
transport) resistor; W=Warburg resistor; Rs=solution resistor. FIG.
48 indicates the decreased cell resistance (Rct and Rs) for the
separators provided herein compared to commercial (Celgard)
polyethylene separators. In some embodiments, provided herein is a
separator having an Rct of less than 200 ohms, less than 150 ohms,
less than 100 ohms, or the like (e.g., wherein 32 mg of LiCoO.sub.2
is used as a cathode and the constant voltage=VOC (1.7-2.0V), such
as with the circuit illustrated in FIG. 48). In some embodiments, a
separator provided herein has an Rs, Cd, and/or Rct less than or
equal to that found for the PAN nanofiber separator, or either of
the PAN/nanoclay nanofiber separators under the conditions set
forth in FIG. 48.
[0207] In some embodiments, provided herein are separators that are
stable for at least 50 cycles at 0.2 C. In some embodiments,
provided herein are separators that are stable for at least 70
cycles at 0.2 C. In some embodiments, provided herein are
separators that are stable for at least 90 cycles at 0.2 C. In some
embodiments, provided herein are separators that are stable for at
least 100 cycles at 0.2 C. In certain embodiments, stability refers
to maintaining at least 60% of initial charge capacity of a battery
(e.g., lithium ion battery cell). In certain embodiments, stability
refers to maintaining at least 70% of initial charge capacity of a
battery (e.g., lithium ion battery cell). In certain embodiments,
stability refers to maintaining at least 80% of initial charge
capacity of a battery (e.g., lithium ion battery cell). FIG. 49
illustrates the cycle test results of commercial PE (Celgard) and
various nanofiber separators provided herein (top PAN/NC in legend
: compressed PAN/nanoclay nanocomposite nanofibers; second PAN/NC
in legend:compressed and annealed PAN/nanoclay nanocomposite
nanofibers; third PAN/NC in legend:not compressed and not annealed
PAN/nanoclay nanocomposite nanofibers).
[0208] In some embodiments, the nanofibers (e.g., for use in
separators herein) have high thermal stability. In specific
instances, such nanofibers have less than a 0.5 wt % loss (e.g., as
measured by TGA) between room temperature and 200.degree. C. In
more specific embodiments, such nanofibers have less than a 0.2 wt
% loss (e.g., as measured by TGA) between room temperature and
200.degree. C. In still more specific embodiments, such nanofibers
have less than a 0.2 wt % loss (e.g., as measured by TGA) between
room temperature and 200.degree. C. FIG. 50 illustrates improved
thermal stability of annealed nanofibers provided herein versus
non-annealed nanofibers. In some instances, improved thermal
stability is evidence of decreased contaminants--e.g., leading to
improved battery cycling, as observed in FIG. 49.
[0209] In some embodiments, batteries provided herein having a
separator as described herein retain discharge capabilities at
about 1.5 C, following 5 cycles at about 0.1 C, 5 cycles at about
0.2 C, and 5 cycles at about 0.5 C. In some embodiments, batteries
provided herein having a separator as described herein retain
discharge capabilities at about 0.5 C, following (sequentially) 5
cycles at about 0.1 C, 5 cycles at about 0.2 C, 5 cycles at about
0.5 C, 5 cycles at about 1.5 C, 5 cycles at about 0.1 C, and 5
cycles at about 0.2 C. In some embodiments, batteries provided
herein having a separator as described herein retain discharge
capabilities at about 1.5 C, following (sequentially) 5 cycles at
about 0.1 C, 5 cycles at about 0.2 C, 5 cycles at about 0.5 C, 5
cycles at about 1.5 C, 5 cycles at about 0.1 C, 5 cycles at about
0.2 C, and 5 cycles at about 0.5 C. In some instances, such
discharge capabilities are at least 50% of the initial discharge
capabilities at the same C (e.g., for the same or identical cell).
In specific instances, such discharge capabilities are at least 60%
of the initial discharge capabilities at the same C (e.g., for the
same or identical cell). In more specific instances, such discharge
capabilities are at least 70% of the initial discharge capabilities
at the same C (e.g., for the same or identical cell). FIG. 51 and
FIG. 52 illustrate plots of a C rate capability test comparing a
polymer-nanoclay nanofiber separator provided herein to a
commercial (Celgard) polyethylene separator, and demonstrates the
superior capabilities of the separators provided herein.
[0210] In some instances, the separators described herein are a
safety feature. For example, stopping the ion transfer between the
first chamber and second chamber above a certain temperature
prevents the battery from exploding and/or catching fire in some
instances.
[0211] In some embodiments, the battery described herein comprises
a separator, wherein the separator allows transfer of ions between
the first chamber and second chamber below a temperature (e.g., the
melting point of the polymer comprising the nanofibers) and
prohibits or allows reduced ion transfer above the temperature. The
temperature is any suitable temperature (e.g., a temperature below
which the battery explodes). In some instances, the temperature is
about 60.degree. C., about 80 V, about 100 V, about 150.degree. C.,
about 200 V, about 300 V, about 400.degree. C., about 500 V, and
the like. In some instances, the temperature is at least 60.degree.
C., at least 80.degree. C., at least 100 V, at least 150 V, at
least 200 V, at least 300.degree. C., at least 400.degree. C., at
least 500.degree. C., and the like. In some instances, the
temperature is at most 60 V, at most 80.degree. C., at most 100 V,
at most 150 V, at most 200.degree. C., at most 300.degree. C., at
most 400 V, at most 500 V, and the like.
[0212] In some embodiments, the separator does not shrink or melt
at elevated temperatures (e.g., above 80 .degree. C., above
100.degree. C., above 150 V, above 200.degree. C., above 300 V,
above 400 V, and the like). In some embodiments, the separator is
wettable by the electrolyte. In some embodiments, the separator is
not soluble in the electrolyte.
[0213] In some embodiments, the separator comprises polymer
nanofibers. Any suitable method for electrospinning is used. For
example, elevated temperature electrospinning is described in U.S.
Pat. No. 7,326,043 filed on Oct. 18, 2004; U.S. patent application
Ser. No. 13/036,441 filed on Feb. 28, 2011; and U.S. Pat. No.
7,901,610 filed on Jan. 10, 2008. In some embodiments, the
electrospinning step comprises co-axially electrospinning the fluid
stock with a second fluid. Co-axial electrospinning is described in
PCT Patent Application PCT/US11/24894 filed on Feb. 15, 2011. In
some embodiments, the second fluid is a gas (i.e., the
electrospinning is gas assisted). Gas-assisted electrospinning is
described in PCT Patent Application PCT/US11/24894 filed on Feb.
15, 2011. Briefly, gas-assisted electrospinning comprises expelling
a stream of gas at high velocity along with the fluid stock (e.g.,
as a stream inside the fluid stock or surrounding the fluid stock),
which can increase the through-put of an electrospinning process.
In some embodiments, the fluid stock surrounds the gas stream. In
some embodiments, the nanofibers comprise a hollow core (e.g., when
electrospun with an inner gas stream).
Electrolytes
[0214] In one aspect, described herein is a lithium-ion battery
comprising an electrolyte and: (a) an electrode, the electrode
comprising a plurality of nanofibers comprising domains of a high
energy capacity material; (b) an electrode, the electrode
comprising porous nanofibers, the nanofibers comprising a high
energy capacity material; (c) an anode in a first chamber, a
cathode in a second chamber, and a separator between the first
chamber and the second chamber, the separator comprising polymer
nanofibers, and the separator allowing ion transfer between the
first chamber and second chamber in a temperature dependent manner;
or (d) any combination thereof.
[0215] In some embodiments, the electrolyte is a lithium salt in an
organic solvent.
[0216] A liquid electrolyte conducts lithium ions, acting as a
carrier between the cathode and the anode when a battery passes an
electric current through an external circuit. In some embodiments,
the conductivity of liquid electrolyte at room temperature
(20.degree. C.) are in the range of 10 mS/cm, increasing by
approximately 30-40% at 40.degree. C. and decreasing by a slightly
smaller amount at 0.degree. C.
[0217] Any suitable material and/or solution is used as the
electrolyte. In some instances, lithium is highly reactive to
water, therefore, nonaqueous or aprotic solutions are used. In some
embodiments, the electrolyte is a mixture of organic carbonates
such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), or
diethyl carbonate comprising complexes of lithium ions. In some
embodiments, these non-aqueous electrolytes use non-coordinating
anion salts such as lithium hexafluorophosphate (LiPF.sub.6),
lithium hexafluoroarsenate monohydrate (LiAsF.sub.6), lithium
perchlorate (LiClO.sub.4), lithium tetrafluoroborate (LiBF.sub.4),
and lithium triflate (LiCF.sub.3SO.sub.3).
[0218] In some embodiments, organic solvents decompose on anodes
during charging. Here, when organic solvents are used as the
electrolyte, the solvent decomposes on initial charging and forms a
solid layer called the solid electrolyte interphase (SEI), which is
electrically insulating yet provides sufficient ionic conductivity
in some embodiments. In some instances, the interphase prevents
decomposition of the electrolyte after the second charge. For
example, ethylene carbonate is decomposed at a relatively high
voltage, 0.7 V vs. lithium, and forms a dense and stable
interface.
[0219] In some embodiments, a suitable solution are composite
electrolytes based on POE (poly(oxyethylene)). In various
embodiments, POE is either solid (high molecular weight) and be
applied in dry Li-polymer cells, or liquid (low molecular weight)
and be applied in regular Li-ion cells.
Nanofibers
[0220] In some embodiments, a battery (e.g., lithium ion battery)
provided herein comprises a plurality of electrodes, one or more of
the electrodes comprising nanofibers (e.g., a nanofiber as
described herein). In certain embodiments, a battery (e.g., lithium
ion battery) provided herein comprises a plurality of electrodes
(e.g., a positive and a negative electrode) and a separator, one or
more of the electrodes and/or the separator comprising nanofibers.
In specific embodiments, provided herein is a battery (e.g.,
lithium ion battery) comprising a positive electrode (cathode), a
negative electrode (anode), and a separator, all of which comprise
nanofibers. Also, provided herein the nanofibers themselves,
regardless of presence in a battery, electrode, or separator
described herein.
[0221] In some embodiments, nanofibers provided herein comprise a
matrix material (e.g., a continuous matrix material, a continuous
core matrix material or backbone, or a continuous tube matrix
material that surrounds a hollow core). In some embodiments (e.g.,
for nanofibers for use in electrodes), the matrix material provides
structural support for domains of high energy capacity material
(e.g., discrete, isolated domains of high energy capacity
material). In certain embodiments (e.g., for nanofibers for use in
separators), the matrix material provides structural support for
domains of (e.g., chemically and/or thermally) inert material
(e.g., discrete, isolated domains of inert material), such as
nanoclay or nanoceramic.
[0222] In some embodiments, a nanofiber matrix material comprises a
high energy capacity material (e.g., the nanofiber is "pure" high
energy material and does not comprise the domains discussed above).
In some embodiments, the nanofibers (e.g., pure high energy
material nanofibers) comprise (e.g., on average) at least 75 wt. %
(e.g., by elemental analysis, TGA analysis, or the like) of the
high energy material, at least 80 wt. %, at least 85%, at least
90%, at least 95%, at least 98%, or the like of the high energy
material.
[0223] In some embodiments, the nanofiber matrix comprises Si, Ge,
Sn, Fe, Co, Cu, Ni, LiCo.sub.xNi.sub.yMn.sub.zO.sub.2,
LiMn.sub.xNi.sub.yCo.sub.zV.sub.aO.sub.4, S, sulfur encapsulated in
carbon, Li.sub.2S, Fe.sub.xNi.sub.yCo.sub.zV.sub.aPO.sub.4,
LiFe.sub.xNi.sub.yCo.sub.zV.sub.aPO.sub.4, any oxidation state
thereof, or any combination thereof.
[0224] In some embodiments, domains of the high energy capacity
material are dispersed in a nanofiber matrix, the matrix comprising
polymer (e.g., PVA, PAN, PEO, PVP, PPO, PS, PMMA, PC, cellulose),
carbon (e.g., graphite, amorphous), ceramic (e.g., Al.sub.2O.sub.3,
ZrO.sub.2, TiO.sub.2), Si (e.g., amorphous silicon), Ge, Sn, metal
(e.g., Fe, Cu, Co, Ag, Ni, Au), any oxidation state thereof, or any
combination thereof. In some embodiments, the nanofiber matrix is
polymer, carbon, metal, or ceramic. In specific embodiments, the
nanofiber matrix is polymer or carbon. In more specific
embodiments, (e.g., wherein the nanofiber is for use in a
separator), the nanofiber matrix is polymer. In other specific
embodiments, (e.g., wherein the nanofiber is for use as an
electrode), the nanofiber matrix is carbon.
[0225] In some embodiments, the domains of high energy capacity
material comprise crystalline high energy capacity material. In
some embodiments, the domains of high energy capacity material
comprise amorphous high energy capacity material. In some
embodiments, the domains of high energy capacity material comprise
nanoparticles comprising the high energy capacity material.
[0226] In some instances, intercalation of lithium ions expands the
volume of the high energy material during operation of the battery.
In one aspect, the domains of high energy capacity material are
spaced sufficiently far apart in the nanofiber to avoid
pulverization of the electrode during operation of the battery. In
some embodiments, the spaces between the domains in the nanofiber
matrix are sufficient to avoid impingement of the domains upon each
other upon expansion of the electrode during operation of the
battery.
[0227] The domains, nanostructures, or nanoparticles provided
herein (e.g., of high energy material) have any suitable size. In
some instances, the domains, nanostructures, or nanoparticles have
an average diameter of about 5 nm, about 10 nm, about 20 nm, about
30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80
nm, about 90 nm, about 100 nm, about 130 nm, about 150 nm, about
200 nm, and the like. In some instances, the domains,
nanostructures, or nanoparticles have an average diameter of at
most 5 nm, at most 10 nm, at most 20 nm, at most 30 nm, at most 40
nm, at most 50 nm, at most 60 nm, at most 70 nm, at most 80 nm, at
most 90 nm, at most 100 nm, at most 130 nm, at most 150 nm, at most
200 nm, and the like. In some instances, e.g., wherein the domain,
nanostructure, or nanoparticle is not spherical, the diameter
refers to the (e.g., average of the plurality of structures)
shortest cross-sectional distance across the structure. For
example, the diameter of a cylinder refers to the diameter of the
circular portion of the cylinder. In some instances, the domains,
nanostructures, or nanoparticles have an average length of about 5
nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50
nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100
nm, about 130 nm, about 150 nm, about 200 nm, and the like. In some
instances, the domains, nanostructures, or nanoparticles have an
average length of at most 5 nm, at most 10 nm, at most 20 nm, at
most 30 nm, at most 40 nm, at most 50 nm, at most 60 nm, at most 70
nm, at most 80 nm, at most 90 nm, at most 100 nm, at most 130 nm,
at most 150 nm, at most 200 nm, at most 400 nm, at most 600 nm, at
most 800 nm, and the like. In some instances, e.g., wherein the
domain, nanostructure, or nanoparticle is not spherical, the length
refers to the (e.g., average of the plurality of structures)
longest cross-sectional distance across the structure (for
spherical structures, the length is the same as the diameter).
[0228] In one aspect, the domains of high energy material have a
uniform size. In some instances, the standard deviation of the size
of the domains is about 50%, about 60%, about 70%, about 80%, about
100%, about 120%, about 140%, about 200%, and the like of the
average size of the domains (i.e., the size is uniform).
[0229] In some instances, the standard deviation of the size of the
domains is at most 50%, at most 60%, at most 70%, at most 80%, at
most 100%, at most 120%, at most 140%, at most 200%, and the like
of the average size of the domains (i.e., the size is uniform).
[0230] The domains of high energy material have any suitable
distance between each other (separation distance).
[0231] In some instances, the domains have an average separation
distance of about 2 nm, about 5 nm, about 10 nm, about 20 nm, about
30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80
nm, about 90 nm, about 100 nm, about 130 nm, about 150 nm, about
200 nm, and the like. In some instances, the domains have an
average diameter of at most 2 nm, at most 5 nm, at most 10 nm, at
most 20 nm, at most 30 nm, at most 40 nm, at most 50 nm, at most 60
nm, at most 70 nm, at most 80 nm, at most 90 nm, at most 100 nm, at
most 130 nm, at most 150 nm, at most 200 nm, and the like.
[0232] FIG. 4 and FIG. 5 illustrate nanofibers prepared by
electrospinning a fluid stock comprising polymer and nanoparticles
with a gas-assisted (e.g., coaxially gas assisted) process
described herein. FIG. 22 illustrates certain nanofibers prepared
by electrospinning a fluid stock comprising polymer and
nanoparticles without a gas-assisted process described herein. FIG.
5 and FIG. 6 illustrate non-aggregation of nanoparticles within the
matrix / backbone material, whereas FIG. 22 illustrates aggregation
of nanoparticles within the matrix material.
[0233] In some embodiments, the domains are uniformly distributed
and/or are non-aggregated within the nanofiber matrix. In some
instances, the standard deviation of the distances between a given
domain and the nearest domain to the given domain is about 50%,
about 60%, about 70%, about 80%, about 100%, about 120%, about
140%, about 200%, and the like of the average of the distances
(i.e., uniform distribution). In some instances, the standard
deviation of the distances between a given domain and the nearest
domain to the given domain is at most 50%, at most 60%, at most
70%, at most 80%, at most 100%, at most 120%, at most 140%, at most
200%, and the like of the average of the distances (i.e., uniform
distribution).
[0234] In some embodiments, the domains (e.g., nanoparticles) are
non-aggregated. In specific embodiments, less than 40% of the
domains (e.g., nanoparticles) are aggregated (e.g., as measured in
any suitable manner, such as by TEM). In specific embodiments, less
than 30% of the domains are aggregated. In more specific
embodiments, less than 25% of the domains are aggregated. In yet
more specific embodiments, less than 20% of the domains are
aggregated. In still more specific embodiments, less than 10% of
the domains are aggregated. In more specific embodiments, less than
5% of the domains are aggregated.
[0235] The domains, nanostructures, or nanoparticles described
herein have any suitable shape. In some embodiments, the domains
comprise spheres, ovoids, ovals, cubes, cylinders, cones, layers,
polyhedrons (e.g., a three dimensional geometry with any number of
flat faces and straight edges), channels, geometric shapes,
non-geometric shapes, or any combination thereof.
[0236] In some embodiments, the domains of high energy material
have a uniform shapes (morphology), e.g., they are mostly all
spheres, mostly all cubes, and the like. In some embodiments,
substantially uniform shapes include at least 50%, at least 60%, at
least 70%, at least 80%, at least 90%, at least 95%, or at least
99% of the pores are a given shape. In some instances, a domain
deviates from an ideal sphere by a certain amount and still be
considered a "sphere", for example. In some instances, the
deviation is by as much as 1%, 5%, 10%, 20%, or 50% for example
(e.g., the diameter of a spherical domain when measured in one
direction may be 20% greater than the diameter of the domain when
measured in a second direction and still be considered a "sphere").
In some embodiments, the domains comprise a plurality of shapes
including without limitation a mixture of 2, 3, 4, or 5 shapes.
[0237] The high energy capacity material (e.g., domains of high
energy capacity material) comprise any suitable volume of the
nanofiber. In some instances, the domains comprise about 10%, about
20%, about 30%, about 40%, about 50%, about 60%, about 70%, about
80%, about 90%, and the like of the volume of the nanofiber. In
some instances, the domains comprise at least 10%, at least 20%, at
least 30%, at least 40%, at least 50%, at least 60%, at least 70%,
at least 80%, at least 90%, and the like of the volume of the
nanofiber. In some instances, the domains comprise at most 10%, at
most 20%, at most 30%, at most 40%, at most 50%, at most 60%, at
most 70%, at most 80%, at most 90%, and the like of the volume of
the nanofiber.
[0238] The high energy capacity material (e.g., domains of high
energy capacity material) comprise any suitable mass of the
nanofiber. In some instances, the high energy capacity material
constitutes about 10%, about 20%, about 30%, about 40%, about 50%,
about 60%, about 70%, about 80%, about 90%, and the like of the
mass of the nanofiber. In some instances, the high energy capacity
material constitutes at least 10%, at least 20%, at least 30%, at
least 40%, at least 50%, at least 60%, at least 70%, at least 80%,
at least 90%, and the like of the mass of the nanofiber. In some
instances, the domains comprise at most 10%, at most 20%, at most
30%, at most 40%, at most 50%, at most 60%, at most 70%, at most
80%, at most 90%, and the like of the mass of the nanofiber. In
specific embodiments, e.g., wherein the nanofiber comprises a
continuous matrix of a high-energy capacity material, the nanofiber
comprises at least 65% by weight of the high-energy capacity
material. In more specific embodiments, e.g., wherein the nanofiber
comprises a continuous matrix of a high-energy capacity material,
the nanofiber comprises at least 75% by weight of the high-energy
capacity material. In still more specific embodiments, e.g.,
wherein the nanofiber comprises a continuous matrix of a
high-energy capacity material, the nanofiber comprises at least 85%
by weight of the high-energy capacity material. In yet specific
embodiments, e.g., wherein the nanofiber comprises a continuous
matrix of a high-energy capacity material, the nanofiber comprises
at least 90% by weight of the high-energy capacity material. In
specific embodiments, e.g., wherein the nanofiber comprises a
continuous matrix of a high-energy capacity material, the nanofiber
comprises at least 95% by weight of the high-energy capacity
material. In specific embodiments, e.g., wherein the nanofiber
comprises a continuous matrix of a high-energy capacity material,
the nanofiber comprises at least 98% by weight of the high-energy
capacity material. In some embodiments, e.g., wherein the nanofiber
comprises a continuous matrix of a first material (e.g., carbon)
and domains (e.g., discrete domain, such as non-aggregated
nanoparticles) of high-energy capacity material, the nanofiber
comprises at least 30% by weight of the high-energy capacity
material. In specific embodiments wherein the nanofiber comprises a
continuous matrix of a first material and domains of high-energy
capacity material, the nanofiber comprises at least 50% by weight
of the high-energy capacity material. In more specific embodiments
wherein the nanofiber comprises a continuous matrix of a first
material and domains of high-energy capacity material, the
nanofiber comprises at least 60% by weight of the high-energy
capacity material. In yet more specific embodiments wherein the
nanofiber comprises a continuous matrix of a first material and
domains of high-energy capacity material, the nanofiber comprises
at least 70% by weight of the high-energy capacity material. In
still more specific embodiments wherein the nanofiber comprises a
continuous matrix of a first material and domains of high-energy
capacity material, the nanofiber comprises at least 75% by weight
of the high-energy capacity material. In more specific embodiments
wherein the nanofiber comprises a continuous matrix of a first
material and domains of high-energy capacity material, the
nanofiber comprises at least 80% by weight of the high-energy
capacity material. In specific embodiments wherein the nanofiber
comprises a continuous matrix of a first material and domains of
high-energy capacity material, the nanofiber comprises 70% to 90%
by weight of the high-energy capacity material.
[0239] In some embodiments, gas assisted electrospinning processes
or apparatus described herein providing or providing a device
configured to provide a flow of gas along the same axis as an
electrospun fluid stock.
[0240] In some instances, that gas (or gas needle) is provided
along the same axis with the fluid stock (or fluid stock needle)
(e.g., and adjacent thereto). In specific instances, the gas (or
gas needle) is provided coaxially with the fluid stock (or fluid
stock needle). FIG. 14 illustrates co-axial electrospinning
apparatus 1400. The coaxial needle apparatus comprises an inner
needle 1401 and an outer needle 1402, both of which needles are
coaxially aligned around a similar axis 1403 (e.g., aligned with 5
degrees, 3 degrees, 1 degree, or the like). In some embodiments,
further coaxial needles may be optionally placed around, inside, or
between the needles 1401 and 1402, which are aligned around the
axis 1403. In some instances, the termination of the needles is
optionally offset 1404.
[0241] In some embodiments provided herein is a process (e.g.,
using a needle as illustrated in FIG. 14) or product prepared by
such a process, the process comprising gas assisted electrospinning
a fluid stock to form nanofibers, the fluid stock comprising (i) a
plurality of nanoparticles, and (ii) a polymer, the nanofibers
comprising a continuous polymer matrix with non-aggregated
nanoparticles embedded therein.
[0242] In certain embodiments provided herein is a process (e.g.,
using a needle as illustrated in FIG. 14) or product prepared by
such a process, the process comprising gas assisted electrospinning
a fluid stock to form as-spun nanofibers, the fluid stock
comprising (i) a plurality of nanoparticles, and (ii) a polymer,
and (b) thermally treating the as-spun nanofibers to produce
thermally treated nanofibers, the thermally treated nanofibers
comprising a continuous matrix (e.g., carbon matrix if thermally
treated in an inert environment with no metal precursor present; or
a metal, metal oxide, or ceramic matrix if a suitable metal
precursor is present in the fluid stock--particularly if this or an
additional thermal treatment with air is utilized) with
non-aggregated nanoparticles embedded therein. In specific
embodiments, the gas assistance is coaxial gas assistance. In some
embodiments, the nanoparticles are non-aggregated in the fluid
stock. In certain instances, gas assistance of the electrospinning
of a nano-particle containing fluid stock increases fluid
throughput and reduces or prevents nanoparticle aggregation in the
needle apparatus, thereby reducing or preventing nanoparticle
aggregation in the as-spun fiber. In specific embodiments, the
nanofibers comprises less than 50% of nanoparticles that are
aggregated. In specific embodiments, the nanofibers comprises less
than 40% of nanoparticles that are aggregated. In specific
embodiments, the nanofibers comprises less than 25% of
nanoparticles that are aggregated. In specific embodiments, the
nanofibers comprises less than 10% of nanoparticles that are
aggregated. In specific embodiments, the nanofibers comprises less
than 5% of nanoparticles that are aggregated.
[0243] FIG. 58 (Panel A) illustrates a nanocomposite nanofiber 5800
comprising (i) a hollow core, (ii) discrete domains of high energy
capacity material (e.g., silicon) 5801 in the sheath layer, and
(ii) a continuous core matrix 5802 in the sheath layer. As
illustrated in the cross-sectional view 5803, the discrete domains
of high energy capacity material 5804 may penetrate into the core
5805 of the nanocomposite nanofiber.
[0244] FIG. 58 (Panel B) illustrates a nanocomposite nanofiber 5806
comprising (i) discrete domains of high energy capacity material
(e.g., silicon) 5807 in/on a (ii) a continuous core matrix 5808
layer. As illustrated in the cross-sectional view 5809, the
discrete domains of high energy capacity material 5810 may
penetrate into the core 5811 of the nanocomposite nanofiber. In
some instances, the nanocomposite nanofibers comprise high energy
capacity material on the surface of the nanofiber. And in some
instances, the nanofibers comprise or further comprise discrete
domains of high energy capacity material completely embedded within
the core matrix material. In certain embodiments, the continuous
matrix also forms a coating layer over the domains.
[0245] In some embodiments, a majority of the nanoparticles or
discrete domains comprise a surface that is at least 50% coated
with the matrix material (e.g., carbon). In specific embodiments, a
majority of the nanoparticles or discrete domains comprise a
surface that is at least 75% coated with the matrix material (e.g.,
carbon). In more specific embodiments, a majority of the
nanoparticles or discrete domains comprise a surface that is at
least 85% coated with the matrix material (e.g., carbon). In still
more specific embodiments, a majority of the nanoparticles or
discrete domains comprise a surface that is at least 90% coated
with the matrix material (e.g., carbon). In yet more specific
embodiments, a majority of the nanoparticles or discrete domains
comprise a surface that is at least 95% coated with the matrix
material (e.g., carbon). In some specific embodiments, at least
50%, at least 60%, at least 70%, at least 80%, at least 90%, or at
least 95% of the nanoparticles or discrete domains comprise a
surface that is at least 50%, at least 75%, at least 85%, at least
90%, or at least 95% coated with the matrix material (e.g.,
carbon).
[0246] In certain embodiments, continuous matrix materials of any
nanocomposite nanofiber described herein is continuous over at
least a portion of the length of the nanocomposite nanofiber. In
some embodiments, the continuous matrix material runs along at
least 10% the length of the nanofiber (e.g., on average for a
plurality of nanofibers). In more specific embodiments, the
continuous matrix material runs along at least 25% the length of
the nanofiber (e.g., on average for a plurality of nanofibers). In
still more specific embodiments, the continuous matrix runs along
at least 50% the length of the nanofiber (e.g., on average for a
plurality of nanofibers). In yet more specific embodiments, the
continuous matrix runs along at least 75% the length of the
nanofiber (e.g., on average for a plurality of nanofibers). In some
embodiments, the continuous matrix is found along at least 50%, at
least 60%, at least 70%, at least 80%, at least 90%, at least 95%,
at least 98%, or at least 99% the length of the nanofiber (e.g., on
average for a plurality of nanofibers). In some embodiments, the
continuous matrix material runs along at least 1 micron of the
length of the nanofiber (e.g., on average for a plurality of
nanofibers). In more specific embodiments, the continuous matrix
material runs along at least 10 microns of the length of the
nanofiber (e.g., on average for a plurality of nanofibers). In
still more specific embodiments, the continuous matrix runs along
at least 100 microns of the length of the nanofiber (e.g., on
average for a plurality of nanofibers). In yet more specific
embodiments, the continuous matrix runs along at least 1 mm of the
length of the nanofiber (e.g., on average for a plurality of
nanofibers).
[0247] In some embodiments, a nanocomposite nanofiber provide
herein comprises discrete domains within the nanocomposite
nanofiber. In specific embodiments, the discrete domains comprise a
silicon material. In other embodiments, the discrete domains
comprise a tin material, or a germanium material. In yet other
embodiments, the discrete domains comprise a lithium material. In
certain embodiments, the discrete domains are non-aggregated. In
some embodiments, the non-aggregated domains are dispersed, e.g.,
in a substantially uniform manner, along the length of the
nanofiber.
[0248] In certain embodiments, the nanocomposite nanofibers
provided herein do not comprise a concentration of domains in one
segment (e.g., a 500 nm, 1 micron, 1.5 micron, 2 micron) that is
over 10 times (e.g., 20 times, 30 times, 50 times, or the like) as
concentrated as an immediately adjacent segment. In some
embodiments, the segment size for such measurements is a defined
length (e.g., 500 nm, 1 micron, 1.5 micron, 2 micron). In other
embodiments, the segment size is a function of the average domain
(e.g., particle) size (e.g., the segment 5 times, 10 times, 20
times, 100 times the average domain size). In some embodiments, the
domains have a (average) size 1 nm to 1000 nm, 1 nm to 500 nm, 1 nm
to 200 nm, 1 nm to 100 nm, 20 nm to 30 nm, 1 nm to 20 nm, 30 nm to
90 nm, 40 nm to 70 nm, 15 nm to 40 nm, or the like.
[0249] In some embodiments, the nanocomposite nanofibers comprise a
plurality of segments (e.g., 0.5 micron, 1 micron, 1.5 micron, 2
micron, or the like) comprising discrete domains (e.g.,
nanoparticles) described herein, the plurality of segments having
an average concentration of discrete domains therein (i.e.,
domains/particles per segment). In specific embodiments, a majority
of the plurality of segments having a concentration of discrete
domains within 80% of the average. In more specific embodiments, a
majority of the plurality of segments having a concentration of
discrete domains within 60% of the average. In yet more specific
embodiments, a majority of the plurality of segments having a
concentration of discrete domains within 50% of the average. In
still more specific embodiments, a majority of the plurality of
segments having a concentration of discrete domains within 40% of
the average. In in more specific embodiments, a majority of the
plurality of segments having a concentration of discrete domains
within 30% of the average. In still more specific embodiments, a
majority of the plurality of segments having a concentration of
discrete domains within 20% of the average. In still more specific
embodiments, at least 30%, at least 50%, at least 60%, at least
70%, at least 80%, or at least 90% of the plurality of segments
having a concentration of discrete domains within 90%, 80%, 60%,
50%, 40%, 30%, or 20% of the average.
[0250] In some embodiments, the nanofibers comprise a hollow core.
In some embodiments, the nanofibers comprise a core comprising a
highly conductive material. In some embodiments, the highly
conductive material is a metal.
Nanofiber Characteristics
[0251] The nanofibers have any suitable diameter. In some
embodiments, a collection of nanofibers comprises nanofibers that
have a distribution of fibers of various diameters. In some
embodiments, a single nanofiber has a diameter that varies along
its length. In some embodiments, fibers of a population of
nanofibers or portions of a fiber accordingly exceed or fall short
of the average diameter. In some embodiments, the nanofiber has on
average a diameter of about 20 nm, about 30 nm, about 40 nm, about
50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about
100 nm, about 130 nm, about 150 nm, about 200 nm, about 250 nm,
about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700
nm, about 800 nm, about 900 nm, about 1,000 nm, about 1,500 nm,
about 2,000 nm and the like. In some embodiments, the nanofiber has
on average a diameter of at most 20 nm, at most 30 nm, at most 40
nm, at most 50 nm, at most 60 nm, at most 70 nm, at most 80 nm, at
most 90 nm, at most 100 nm, at most 130 nm, at most 150 nm, at most
200 nm, at most 250 nm, at most 300 nm, at most 400 nm, at most 500
nm, at most 600 nm, at most 700 nm, at most 800 nm, at most 900 nm,
at most 1,000 nm, at most 1,500 nm, at most 2,000 nm and the like.
In some embodiments, the nanofiber has on average a diameter of at
least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at
least 60 nm, at least 70 nm, at least 80 nm, at least 90 nm, at
least 100 nm, at least 130 nm, at least 150 nm, at least 200 nm, at
least 250 nm, at least 300 nm, at least 400 nm, at least 500 nm, at
least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, at
least 1,000 nm, at least 1,500 nm, at least 2,000 nm and the like.
In yet other embodiments, the nanofiber has on average a diameter
between about 50 nm and about 300 nm, between about 50 nm and about
150 nm, between about 100 nm and about 400 nm, between about 100 nm
and about 200 nm, between about 500 nm and about 800 nm, between
about 60 nm and about 900 nm, and the like.
[0252] Generally, the aspect ratio of a nanofiber is the length of
a nanofiber divided by its diameter. In some embodiments, aspect
ratio refers to a single nanofiber. In some embodiments, aspect
ratio is applied to a plurality of nanofibers and reported as a
single average value, the aspect ratio being the average length of
the nanofibers of a sample divided by their average diameter.
Diameters and/or lengths are measured by microscopy in some
instances. The nanofibers have any suitable aspect ratio. In some
embodiments the nanofiber has an aspect ratio of about 10, about
10.sup.2, about 10.sup.3, about 10.sup.4, about 10.sup.5, about
10.sup.6, about 10.sup.7, about 10.sup.8, about 10.sup.9, about
10.sup.10, about 10.sup.11, about 10.sup.12, and the like. In
certain embodiments the nanofiber has an aspect ratio of at least
10, at least 10.sup.2, at least 10.sup.3, at least 10.sup.4, at
least 10.sup.5, at least 10.sup.6, at least 10.sup.7, at least
10.sup.8, at least 10.sup.9, at least 10.sup.10, at least
10.sup.11, at least 10.sup.12, and the like. In other embodiments,
the nanofiber is of substantially infinite length and has an aspect
ratio of substantially infinity.
[0253] In some embodiments, the nanocomposite nanofiber is
crosslinked In specific instances, the second material (e.g.,
non-silicon containing second material) of the nanocomposite
nanofiber provided herein is crosslinked with the second material
of one or more adjacent nanofiber.
[0254] In some embodiments, nanofibers provided herein comprise
(e.g., on average) at least 99%, at least 98%, at least 97%, at
least 96%, at least 95%, at least 90%, at least 80%, or the like of
metal, oxygen and carbon, when taken together, by mass (e.g.,
elemental mass). In specific embodiments, nanofibers (e.g., on
average) provided herein comprise at least 99%, at least 98%, at
least 97%, at least 96%, at least 95%, at least 90%, at least 80%,
or the like of metal and oxygen, when taken together, by mass
(e.g., elemental mass). In some embodiments, nanofibers provided
herein comprise (e.g., on average) at least 99%, at least
[0255] 98%, at least 97%, at least 96%, at least 95%, at least 90%,
at least 80%, or the like of high energy capacity material, oxygen
and carbon, when taken together, by mass (e.g., elemental mass). In
specific embodiments, nanofibers (e.g., on average) provided herein
comprise at least 99%, at least 98%, at least 97%, at least 96%, at
least 95%, at least 90%, at least 80%, or the like of high energy
capacity material and carbon, when taken together, by mass (e.g.,
elemental mass).
[0256] In some embodiments, nanofibers provided herein are porous.
In some embodiments, the porous nanofibers comprise high energy
capacity material. In some embodiments, the anode comprises porous
nanofibers, the nanofibers comprising Si, Ge, Sn, Co, Cu, Fe, any
oxidation state thereof, or any combination thereof. In some
embodiments, the cathode comprises porous nanofibers, the
nanofibers comprising a lithium-containing material described
herein (e.g., comprising a continuous matrix of LiCoO.sub.2,
LiCO.sub.xNi.sub.yMn.sub.zO.sub.2,
LiMn.sub.xNi.sub.yCo.sub.zV.sub.aO.sub.4,
LiFe.sub.xNi.sub.yCo.sub.zV.sub.aPO.sub.4, any oxidation state
thereof, or any combination thereof).
[0257] In some embodiments, the porous nanofibers comprise any one
or more of: (a) a surface area of at least 10 .pi. r h, wherein r
is the radius of the nanofiber and h is the length of the
nanofiber; (b) a specific surface area of at least 100 m.sup.2/g;
(c) a porosity of at least 20% and a length of at least 50 .mu.m;
(d) a porosity of at least 35%, wherein the nanofiber is
substantially contiguous; (e) a porosity of at least 35%, wherein
the nanofiber is substantially flexible or non-brittle; (f) a
plurality of pores with an average diameter of at least 1 nm; (g) a
plurality of pores, wherein the pores have a substantially uniform
shape; (h) a plurality of pores, wherein the pores have a
substantially uniform size; and (i) a plurality of pores, wherein
the pores are distributed substantially uniformly throughout the
nanofiber. In some embodiments, the nanofibers comprise mesoporous
pores.
[0258] In various embodiments, nanofibers provided herein have a
high surface area and methods are described for making nanofibers
having a high surface area. In some instances, ordering of the
pores results in a high surface area and/or specific surface area
(e.g., surface area per mass of nanofiber and/or surface area per
volume of nanofiber) in some instances. In some embodiments, the
porous nanofibers have a specific surface area of about 50
m.sup.2/g, about 100 m.sup.2/g, about 200 m.sup.2/g, about 500
m.sup.2/g, about 1,000 m.sup.2/g, about 2,000 m.sup.2/g, about
5,000 m.sup.2/g, about 10,000 m.sup.2/g, and the like. In some
embodiments, the porous nanofibers have a specific surface area of
at least 10 m.sup.2/g, at least 50 m.sup.2/g, at least 100
m.sup.2/g, at least 200 m.sup.2/g, at least 500 m.sup.2/g, at least
1,000 m.sup.2/g, at least 2,000 m.sup.2/g, at least 5,000
m.sup.2/g, at least 10,000 m.sup.2/g, and the like. In some
embodiments, nanofibers that have a high surface area. The
"specific surface area" is the surface area of at least one fiber
divided by the mass of the at least one fiber. The specific surface
area is calculated based on a single nanofiber, or based on a
collection of nanofibers and reported as a single average value.
Techniques for measuring mass are known to those skilled in the
art. In some embodiments, the surface area is measured by physical
or chemical methods, for example by the Brunauer-Emmett, and Teller
(BET) method where the difference between physisorption and
desorption of inert gas is utilized to determine the surface area
or by titrating certain chemical groups on the nanofiber to
estimate the number of groups on the surface, which is related to
the surface area by a previously determined titration curve. Those
skilled in the art of chemistry will be familiar with methods of
titration.
[0259] In some embodiments, the porous nanofibers are cylindrical.
Neglecting the area of the two circular ends of a cylinder, the
area of the cylinder is estimated to be two times the mathematical
constant pi (.pi.) times the radius of the cross section of the
cylinder (r) times the length of the nanofiber (h), (i.e., 2 .pi. r
h). In some embodiments, the surface area of the porous nanofiber
is greater than 2 .pi. r h. In some embodiments, the surface area
of the porous nanofiber is about 4 .pi. r h, about 10 .pi. r h,
about 20 .pi. r h, about 50 .pi. r h, about 100 .pi. r h, and the
like. In some embodiments, the surface area of the porous nanofiber
is at least 4 .pi. r h, at least 10 .pi. r h, at least 20 .pi. r h,
at least 50 .pi. r h, at least 100 .pi. r h, and the like.
[0260] In one aspect, described herein are nanofibers having a high
porosity. Also described herein are methods for making nanofibers
with a high porosity. "Porosity" is used interchangeably with "void
fraction" and is a measure of the porous spaces in a material.
Porosity is the fraction of the sum total volume of the pores
divided by the total volume. In some embodiments, the total volume
used in the calculation of porosity is the volume occupied by a
collection of porous nanofibers (e.g., fibers arranged as a filter
mat). In some embodiments, the total volume used in the calculation
of porosity is the volume defined by the outer perimeter of a
porous nanofiber. For example, the total volume of a cylindrical
nanofiber is estimated to be the mathematical constant pi (.pi.)
times the square of the radius of the cross section of the cylinder
(r.sup.2) times the length of the nanofiber (h), (i.e., .pi.
r.sup.2 h). Porosity is represented as a percentage ranging from 0%
to 100%.
[0261] The porosity of the nanofibers described herein is any
suitable value. In some embodiments, the porosity is about 1%,
about 5%, about 10%, about 20%, about 25%, about 30%, about 35%,
about 40%, about 45%, about 50%, about 55%, about 60%, about 70%,
about 80%, and the like. In some embodiments, the porosity is at
least 1%, at least 5%, at least 10%, at least 20%, at least 25%, at
least 30%, at least 35%, at least 40%, at least 45%, at least 50%,
at least 55%, at least 60%, at least 70%, at least 80%, and the
like. Described herein are nanofibers and methods for making
nanofibers that have a plurality of pores. The pores may be of any
suitable size or shape. In some embodiments the pores are
"mesopores", having a diameter of less than 100 nm (e.g., between 2
and 50 nm, on average). In some embodiments, the pores are
"ordered", such as having a substantially uniform shape, a
substantially uniform size and/or are distributed substantially
uniformly through the nanofiber. In some embodiments, nanofibers
described herein have a high surface area and/or specific surface
area (e.g., surface area per mass of nanofiber and/or surface area
per volume of nanofiber). In some embodiments, nanofibers described
herein comprise ordered pores, e.g., providing substantially
flexible and/or non-brittleness.
[0262] In one aspect, described herein is a method for producing an
ordered mesoporous nanofiber, the method comprising: (a) coaxially
electrospinning a first fluid stock with a second fluid stock to
produce a first nanofiber, the first fluid stock comprising at
least one block co-polymer and a silicon component (e.g., silicon
precursor), the second fluid stock comprising a coating agent, and
the first nanofiber comprising a first layer (e.g., core) and a
second layer (e.g., coat) that at least partially coats the first
layer; (b) annealing the first nanofiber; (c) optionally removing
the second layer from the first nanofiber to produce a second
nanofiber comprising the block co-polymer; and (d) selectively
removing at least part of the block co-polymer from the first
nanofiber or the second nanofiber (e.g. thereby producing an
ordered mesoporous nanofiber). Additional coaxial layers are
optional--e.g., comprising a precursor and block copolymer for an
additional mesoporous layer, or a precursor and a polymer as
described herein for a non-mesoporous layer.
[0263] In some embodiments, the block co-polymer comprises a
polyisoprene (PI) block, a polylactic acid (PLA) block, a polyvinyl
alcohol (PVA) block, a polyethylene oxide (PEO) block, a
polyvinylpyrrolidone (PVP) block, polyacrylamide (PAA) block or any
combination thereof (i.e., thermally or chemically degradable
polymers). In some embodiments, the block co-polymer comprises a
polystyrene (PS) block, a poly(methyl methacrylate) (PMMA) block, a
polyacrylonitrile (PAN) block, or any combination thereof.
[0264] In some embodiments, the coating layer and at least part of
the block co-polymer (concurrently or sequentially) is selectively
removed in any suitable manner, such as, by heating, by ozonolysis,
by treating with an acid, by treating with a base, by treating with
water, by combined assembly by soft and hard (CASH) chemistries, or
any combination thereof. Additionally, U.S. Application Ser. No.
61/599,541 and International Application Ser. No. PCT/US13/26060,
filed Feb. 14, 2013, is incorporated herein by reference for
disclosures related to such techniques.
Batteries and Electrodes
[0265] In one aspect, the nanofiber has a high porosity and is
long. Methods for measuring the length of a nanofiber include, but
are not limited to microscopy, optionally transmission electron
microscopy ("TEM") or scanning electron microscopy ("SEM"). The
nanofiber has any suitable length. A given collection of nanofibers
comprises nanofibers that have a distribution of fibers of various
lengths. Therefore, certain fibers of a population accordingly
exceed or fall short of the average length. In some embodiments,
the nanofiber has an average length of about 20 .mu.m, about 50
.mu.m, about 100 .mu.m, about 500 .mu.m, about 1,000 .mu.m, about
5,000 .mu.m, about 10,000 .mu.m, about 50,000 .mu.m, about 100,000
.mu.m, about 500,000 .mu.m, and the like. In some embodiments, the
nanofiber has an average length of at least about 10 .mu.m, at
least about 20 .mu.m, at least about 50 .mu.m, at least about 100
.mu.m, at least about 500 .mu.m, at least about 1,000 .mu.m, at
least about 5,000 .mu.m, at least about 10,000 .mu.m, at least
about 50,000 .mu.m, at least about 100,000 .mu.m, at least about
500,000 .mu.m, and the like. The nanofiber optionally has any of
these (or other suitable) lengths in combination with any of the
porosities described herein (e.g., 20%).
[0266] In one aspect, the nanofiber has a high porosity and is
substantially contiguous. A nanofiber is substantially contiguous
if when following along the length of the nanofiber, fiber material
is in contact with at least some neighboring fiber material over
substantially the entire nanofiber length.
[0267] "Substantially" the entire length means that at least 80%,
at least 90%, at least 95%, or at least 99% of the length of the
nanofiber is contiguous. The nanofiber is optionally substantially
contiguous in combination with any of the porosities described
herein (e.g., 35%).
[0268] In one aspect, the nanofiber has a high porosity and is
substantially flexible or non-brittle. Flexible nanofibers are able
to deform when a stress is applied and optionally return to their
original shape when the applied stress is removed. A substantially
flexible nanofiber is able to deform by at least 5%, at least 10%,
at least 20%, at least 50%, and the like in various embodiments. A
non-brittle nanofiber does not break when a stress is applied. In
some embodiments, the nanofiber bends (e.g., is substantially
flexible) rather than breaks. A substantially non-brittle nanofiber
is able to deform by at least 5%, at least 10%, at least 20%, at
least 50%, and the like without breaking in various embodiments.
The nanofiber is optionally substantially flexible or non-brittle
in combination with any of the porosities described herein (e.g.,
35%).
[0269] In some embodiments, described herein are nanofibers
comprising ordered pores. In certain embodiments, ordered pores
have a substantially uniform shape, a substantially uniform size,
are distributed substantially uniformly in the nanofiber, or any
combination thereof. In one aspect, ordered pores provide a
nanofiber having a higher surface area, a more contiguous
nanofiber, a more flexible nanofiber and/or less brittle nanofiber
when compared with a nanofiber lacking pores, or lacking ordered
pores.
[0270] The pores optionally have any suitable shape. Exemplary
shapes include spheres, ovoids, ovals, cubes, cylinders, cones,
polyhedrons (e.g., a three dimensional geometry with any number of
flat faces and straight edges), layers, channels, geometric shapes,
non-geometric shapes, or any combination thereof. In some
embodiments, the pore(s) form a helical channel in a cylindrical
nanofiber such that the nanofiber is a helical nanofiber.
Additional exemplary shapes include axially aligned concentric
cylinders and radially aligned stacked donuts.
[0271] Various shaped pores can have various "characteristic
dimensions". For example, one characteristic dimension of a sphere
is its diameter (i.e., any straight line segment that passes
through the center of the spherical pore and whose endpoints are on
the edges of the pore). Other characteristic dimensions of a sphere
optionally include its radius, circumference, and the like. Since
nanofibers having pores of any shape and methods for making
nanofibers with pores of any shape are described here, in some
embodiments, the characteristic dimension are other than a
diameter. Exemplary characteristic dimensions include the width,
thickness, or length of the pore. In some embodiments, the
characteristic distance is the longest distance passing through the
center of the pore or the shortest distance passing through the
center of the pore. The characteristic dimension is any suitable
measurement represented in units of length. In some embodiments,
the pores have an average characteristic dimension of about 0.1 nm,
about 0.5 nm, about 1 nm, about 2 nm, about 5 nm, about 10 nm,
about 25 nm, about 50 nm, about 100 nm, about 200 nm, about 500 nm,
and the like. In some embodiments, the pores have an average
characteristic dimension of at least 0.1 nm, at least 0.5 nm, at
least 1 nm, at least 2 nm, at least 5 nm, at least 10 nm, at least
25 nm, at least 50 nm, at least 100 nm, at least 200 nm, at least
500 nm, and the like. In some embodiments, the pores have an
average characteristic dimension of at most 0.1 nm, at most 0.5 nm,
at most 1 nm, at most 2 nm, at most 5 nm, at most 10 nm, at most 25
nm, at most 50 nm, at most 100 nm, at most 200 nm, at most 500 nm,
and the like.
[0272] In some embodiments, the nanofibers have pores with a
substantially uniform shape, e.g., they are mostly all spheres,
mostly all cubes, and the like. In some embodiments, substantially
uniform shapes include at least 50%, at least 60%, at least 70%, at
least 80%, at least 90%, at least 95%, or at least 99% of the pores
are a given shape. In some instances, a pore deviates from an ideal
sphere by a certain amount and still be considered a "sphere", for
example. The deviation may be by as much as 1%, 5%, 10%, 20%, or
50% for example (e.g., the diameter of a spherical pore when
measured in one direction may be 20% greater than the diameter of
the pore when measured in a second direction and still be
considered a "sphere"). In some embodiments, the pores optionally
have a plurality of shapes including without limitation a mixture
of 2, 3, 4, or 5 shapes.
[0273] In some embodiments, the pores have a substantially uniform
size. The plurality of pores have a characteristic dimension as
described herein. In some embodiments, the pores are of a
substantially uniform size when the standard deviation of the
characteristic dimension is about 5%, about 10%, about 15%, about
20%, about 30%, about 50%, about 100%, and the like of the average
value of the characteristic dimension. In some embodiments, the
pores are of a substantially uniform size when the standard
deviation of the characteristic dimension is at most 5%, at most
10%, at most 15%, at most 20%, at most 30%, at most 50%, at most
100%, and the like of the average value of the characteristic
dimension. In some embodiments, the pores do not have a
substantially uniform size.
[0274] In some embodiments, the pores are distributed substantially
uniformly throughout the nanofiber. Each pore of the plurality of
pores will be separated from its nearest neighboring pore by a
certain distance (i.e., "separation distance"). The separation
distance is optionally measured from the center of one pore to the
center of the nearest pore, from the center of one pore to the
nearest boundary edge of the nearest pore, from the edge of one
pore to the nearest boundary edge of the nearest pore, and the
like. A plurality of pores will have a plurality of these
"separation distances". In some embodiments, the pores are
distributed substantially uniformly throughout the nanofiber when
the standard deviation of the separation distances is about 5%,
about 10%, about 15%, about 20%, about 30%, about 50%, about 100%,
and the like of the average separation distance. In some
embodiments, the pores are distributed substantially uniformly
throughout the nanofiber when the standard deviation of the
separation distances is at most 5%, at most 10%, at most 15%, at
most 20%, at most 30%, at most 50%, at most 100%, and the like of
the average separation distance.
Process
[0275] In one aspect, described herein is a process for producing
an electrode or nanofiber that comprises electrospinning a fluid
stock to form nanofibers, the fluid stock comprising a high energy
capacity material or precursor thereof and a polymer.
[0276] In one aspect, a process is described for producing
nanofibers, such as high energy capacity nanofibers,
lithium-containing nanofibers, high anodic energy capacity
nanofibers, nanofibers with high lithium uptake capability, high
performance separator nanofibers, and the like.
[0277] In some embodiments the process comprises: (a)
electrospinning a fluid stock to form nanofibers, the fluid stock
comprising (i) a metal precursor (e.g., lithium precursor, silicon
precursor, tin precursor, germanium precursor, or the like) or
nanostructures (e.g., nanoparticles) (e.g., comprising lithium
metal oxide--for cathode nanofibers, silicon--for anode nanofibers,
clay--for separator nanofibers, ceramic--for separator nanofibers,
or the like) and (ii) a polymer; and (b) thermally treating the
nanofibers. In some embodiments, electrospinning of the fluid stock
is gas assisted (e.g., coaxially gas assisted). In further
embodiments, a lithium ion battery electrode or separator is
optionally formed using such nanofibers (or smaller nanofibers,
such as fragments produced by sonication of the thermally treated
nanofibers--any disclosure of nanofibers herein is intended to
include such nanofibers as well).
[0278] In specific embodiments, a process for producing lithium
containing nanofibers comprises (a) electrospinning a fluid stock
to form as-spun nanofibers, the fluid stock comprising lithium
precursor, a second metal precursor, and a polymer; and (b)
thermally treating the as-spun nanofibers to produce the lithium
containing nanofibers. In more specific embodiments, the process
further comprises chemically treating (e.g., oxidizing, such as
with air) the nanofibers. In certain embodiments, the chemical
treatment occurs simultaneously with step (b). In other
embodiments, the chemical treatment step occurs after step (b)
(e.g., wherein step (b) occurs under inert conditions, such as
under argon atmosphere). In certain embodiments, the
electrospinning is gas assisted. In specific embodiments, the
electrospinning is coaxially gas assisted. In some embodiments, the
fluid stock is aqueous. In specific embodiments, the polymer is a
water soluble polymer, such as polyvinyl alcohol (PVA).
[0279] In specific embodiments, a process for producing lithium
containing nanofibers comprises (a) electrospinning a fluid stock
to form as-spun nanofibers, the fluid stock comprising a plurality
of nanoparticles and a polymer, the plurality of nanoparticles
comprising a lithium material; and (b) thermally treating the
as-spun nanofibers to produce the lithium containing nanofibers. In
certain embodiments, the thermal treatment occurs under inert
conditions (e.g., in an argon atmosphere). In certain embodiments,
the electrospinning is gas assisted. In specific embodiments, the
electrospinning is coaxially gas assisted. In some embodiments, the
fluid stock is aqueous. In specific embodiments, the polymer is a
water soluble polymer, such as polyvinyl alcohol (PVA). In other
embodiments, fluid is a solvent based solution. In some
embodiments, the polymer is a solvent soluble polymer, such as
polyacrylonitrile (PAN).
[0280] In specific embodiments, a process for producing anodic
nanofibers (e.g., lithium ion battery anodic nanofibers) comprises
(a) electrospinning a fluid stock to form as-spun nanofibers, the
fluid stock comprising high energy capacity precursor (e.g., a
metal precursor of a high specific capacity (mAh/g) lithium ion
battery anodic material) and polymer; and (b) thermally treating
the as-spun nanofibers (e.g., to produce the anodic nanofibers or a
precursor thereof--e.g., thermal treatment may produce SiO.sub.2
nanofiber, which is a precursor to Si nanofiber). In more specific
embodiments, the process further comprises chemically treating
(e.g., reducing, such as with a reducing agent (e.g., H.sub.2) or a
sacrificial oxidizing agent) the nanofibers. In certain
embodiments, the chemical treatment occurs simultaneously with step
(b). In other embodiments, the chemical treatment step occurs after
step (b). In certain embodiments, the electrospinning is gas
assisted. In specific embodiments, the electrospinning is coaxially
gas assisted. In some embodiments, the fluid stock is aqueous. In
specific embodiments, the polymer is a water soluble polymer, such
as polyvinyl alcohol (PVA).
[0281] In specific embodiments, a process for producing anodic
nanofibers comprises (a) electrospinning a fluid stock to form
as-spun nanofibers, the fluid stock comprising a plurality of
nanoparticles and a polymer, the plurality of nanoparticles
comprising a high energy capacity anodic material (e.g., a high
specific capacity (mAh/g)--such as higher than carbon or greater
than 500 mAh/g at 0.1 C--for example Si nanoparticles) (or a
precursor thereof--e.g., SiO.sub.2 as a precursor for Si); and (b)
thermally treating the as-spun nanofibers (e.g., to produce the
anodic containing nanofibers, or a precursor thereof). In certain
embodiments, the thermal treatment occurs under inert conditions
(e.g., in an argon atmosphere). In certain embodiments, the
electrospinning is gas assisted. In specific embodiments, the
electrospinning is coaxially gas assisted. In some embodiments, the
fluid stock is aqueous. In specific embodiments, the polymer is a
water soluble polymer, such as polyvinyl alcohol (PVA). In other
embodiments, fluid is a solvent based solution. In some
embodiments, the polymer is a solvent soluble polymer, such as
polyacrylonitrile (PAN) (e.g., soluble in DMF).
[0282] In specific embodiments, a process for producing (e.g.,
polymer-clay or polymer-ceramic) nanocomposite nanofibers (e.g.,
for use as battery separators--such as lithium ion battery
separators) comprises electrospinning a fluid stock to form as-spun
nanofibers, the fluid stock comprising a plurality of
nanostructures and a polymer, the plurality of nanostructures
comprising a clay, a ceramic, or a combination thereof. In some
embodiments, the process further comprises annealing the
nanofibers. In certain embodiments, the thermal treatment occurs
under inert conditions (e.g., in an argon atmosphere).
[0283] In further or alternative embodiments, the process further
comprise compressing the nanofibers (e.g., electrospinning or
assembling a non-woven mat of nanofibers and subsequently
compressing the non-woven mat). In certain embodiments, the
electrospinning is gas assisted. In specific embodiments, the
electrospinning is coaxially gas assisted. In other embodiments,
fluid is a solvent based solution. In some embodiments, the polymer
is a solvent soluble polymer, such as polyacrylonitrile (PAN)
(e.g., soluble in DMF), or a polyolefin (e.g., polyethylene (PE) or
polypropylene (PP)).
[0284] In some embodiments, the treatment process comprises (a)
thermal treatment; (b) chemical treatment (also, if concurrent with
a thermal treatment may be referred to herein as treating with a
calcination reagent); or (c) a combination thereof. In specific
embodiments, treatment of the as-spun nanocomposite nanofiber
comprises thermally treating the as-spun nanocomposite nanofiber
under oxidative conditions (e.g., air). In other specific
embodiments, treatment of the as-spun nanocomposite nanofiber
comprises thermally treating the as-spun nanocomposite nanofiber
under inert conditions (e.g., argon). In still other specific
embodiments, treatment of the as-spun nanocomposite nanofiber
comprises thermally treating the as-spun nanocomposite nanofiber
under reducing conditions (e.g., hydrogen, or a hydrogen/argon
blend).
[0285] In certain embodiments, the as-spun nanofiber is heated to a
temperature of about 100.degree. C. to about 2000.degree. C., about
500 to 2000 C, at least 900.degree. C., at least 1000.degree. C.,
or the like. In specific embodiments, the as-spun nanofiber is
heated to a temperature of about 1000.degree. C. to about
1800.degree. C., or about 1000.degree. C. to about 1700.degree. C.
In specific embodiments, the thermal treatment step is at
600.degree. C. to 1200.degree. C. In more specific embodiments, the
thermal treatment step is at 700.degree. C. to 1100.degree. C. In
still more specific embodiments, the thermal treatment step is at
800.degree. C. to 1000.degree. C. (e.g., in an inert or reducing
atmosphere).
[0286] In one aspect, the process has a high yield (e.g., which is
desirable for embodiments in which the precursor is expensive). In
some embodiments, the metal atoms in the nanofiber are about 3%,
about 10%, about 20%, about 30%, about 33%, about 40%, about 50%,
about 60%, about 70%, about 80%, about 90%, about 95%, about 98%,
or about 100% of the number of (e.g., in moles) metal (i.e.,
silicon and other metal) molecules in the fluid stock.
[0287] In some embodiments, the fluid stock uniform or homogenous.
In specific embodiments, the process described herein comprises
maintaining fluid stock uniformity or homogeneity. In some
embodiments, fluid stock uniformity and/or homogeneity is achieved
or maintained by any suitable mechanism, e.g., by agitating,
heating, or the like. Methods of agitating include, by way of
non-limiting example, mixing, stirring, shaking, sonicating, or
otherwise inputting energy to prevent or delay the formation of
more than one phase in the fluid stock.
[0288] Any suitable method for electrospinning is used. For
example, elevated temperature electrospinning is described in U.S.
Pat. No. 7,326,043 filed on Oct. 18, 2004; U.S. patent application
Ser. No. 13/036,441 filed on Feb. 28, 2011; and U.S. Pat. No.
7,901,610 filed on Jan. 10, 2008.
[0289] In some embodiments, the electrospinning step comprises
co-axially electrospinning the fluid stock with a second fluid.
Co-axial electrospinning is described in PCT Patent Application
PCT/US11/24894 filed on Feb. 15, 2011.
[0290] In some embodiments, the second fluid is a gas (i.e., the
electrospinning is gas assisted). Gas-assisted electrospinning is
described in PCT Patent Application PCT/US11/24894 filed on Feb.
15, 2011, which is incorporated herein for such disclosure.
Briefly, gas-assisted electrospinning comprises expelling a stream
of gas at high velocity along with the fluid stock (e.g., as a
stream inside the fluid stock or surrounding the fluid stock),
which can increase the through-put of an electrospinning process.
In some embodiments, the fluid stock surrounds the gas stream. In
some embodiments, the nanofibers comprise a hollow core (e.g., when
electrospun with an inner gas stream).
[0291] In some embodiments, the nanofibers are porous. Without
limitation, porous nanofibers have a high surface area, which
increases the rate of intercalation and deintercalation of lithium
ions. Methods for producing ordered porous nanofibers are described
in U.S. Provisional Patent Application No. 61/599,541 filed on Feb.
16, 2012. As described therein, co-axially electrospinning a fluid
stock comprising a block co-polymer surrounded by a coating, then
annealing to allow the blocks of the block co-polymer to assembled
ordered phase elements, followed by selective removal of at least
one of the phases produces ordered porous nanofibers. As described
herein, in some embodiments, the second fluid comprises a coating
agent, wherein the second fluid surrounds the fluid stock (i.e.,
forming a coated nanofiber, for example that retains its morphology
when heated to assemble the blocks of a block co-polymer into
ordered phase elements).
[0292] In some embodiments, the nanofibers comprise a core
material. In some embodiments, the core material is highly
conductive. In some embodiments, the highly conductive material is
a metal. In one aspect, described herein are methods for producing
nanofibers, the nanofibers comprising a core material, optionally a
highly conductive core material, optionally a metal core. In some
embodiments, the second fluid comprises a material having a high
electrical conductivity, wherein the polymer solution surrounds the
second fluid (i.e., forming a nanofiber having a highly conductive
core). Any method for producing a nanofiber having a highly
conductive core is suitable.
Fluid Stocks
[0293] In various embodiments described herein nanofibers (e.g.,
for use as various components in batteries) are prepared according
to processes described herein and using fluid stocks provided
herein. In some embodiments, the fluid stock is well mixed. In some
embodiments, nanofiber precursor molecules are distributed evenly
on the polymer in the fluid stock.
[0294] In certain embodiments, fluid stocks provided for various
processes described herein comprise a polymer. In specific
embodiments, the polymer is a polymer that it suitable for
electrospinning (e.g., as a melt, an aqueous solution, or a solvent
solution). In some embodiments, the fluid stock further comprises
an additional component, such as a metal precursor and/or a metal
(including silicon), metal oxide (including lithium metal oxide),
ceramic, or clay (such as a nanoparticle or nanostructure--which
terms are used interchangeably herein--thereof).
[0295] In some embodiments, the fluid stock comprises an aqueous
medium (e.g., water or an aqueous mixture, such as water/alcohol,
water/acetic acid, or the like). In other embodiments, the fluid
stock comprises a solvent (e.g., DMF). In still other embodiments,
the fluid stock comprises melted polymer (without water or
non-aqueous solvent).
[0296] In some embodiments, a polymer in a process, fluid stock or
nanofiber described herein is an organic polymer. In some
embodiments, polymers used in the compositions and processes
described herein are hydrophilic polymers, including water-soluble
and water swellable polymers. In some aspects, the polymer is
soluble in water, meaning that it forms a solution in water. In
other embodiments, the polymer is swellable in water, meaning that
upon addition of water to the polymer the polymer increases its
volume up to a limit. Exemplary polymers suitable for the present
methods include but are not limited to polyvinyl alcohol ("PVA"),
polyvinyl acetate ("PVAc"), polyethylene oxide ("PEO"), polyvinyl
ether, polyvinyl pyrrolidone, polyglycolic acid,
hydroxyethylcellulose ("HEC"), ethylcellulose, cellulose ethers,
polyacrylic acid, polyisocyanate, and the like. In some
embodiments, the polymer is isolated from biological material. In
some embodiments, the polymer is starch, chitosan, xanthan, agar,
guar gum, and the like. In other instances, e.g., wherein silicon
nanoparticles are utilized as the silicon component, other
polymers, such as polyacrylonitrile ("PAN") are optionally utilized
(e.g., with DMF as a solvent). In other instances, a polyacrylate
(e.g., polyalkacrylate, polyacrylic acid, polyalkylalkacrylate,
such as poly(methyl methacrylate) (PMMA),or the like), or
polycarbonate is optionally utilized. In some instances, the
polymer is polyacrylonitrile (PAN), polyvinyl alcohol (PVA), a
polyethylene oxide (PEO), polyvinylpyridine, polyisoprene (PI),
polyimide, polylactic acid (PLA), a polyalkylene oxide,
polypropylene oxide (PPO), polystyrene (PS), a polyarylvinyl, a
polyheteroarylvinyl, a nylon, a polyacrylate (e.g., poly acrylic
acid, polyalkylalkacrylate--such as polymethylmethacrylate (PMMA),
polyalkylacrylate, polyalkacrylate), polyacrylamide,
polyvinylpyrrolidone (PVP) block, polyacrylonitrile (PAN),
polyglycolic acid, hydroxyethylcellulose (HEC), ethylcellulose,
cellulose ethers, polyacrylic acid, polyisocyanate, or a
combination thereof.
[0297] In some embodiments, a polymer described herein (e.g., in a
process, precursor nanofiber, a fluid stock, or the like) is a
polymer (e.g., homopolymer or copolymer) comprising a plurality of
reactive sites. In certain embodiments, the reactive sites are
nucleophilic (i.e., a nucleophilic polymer) or electrophilic (i.e.,
an electrophilic polymer). For example, in some embodiments, a
nucleophilic polymer described herein comprises a plurality of
alcohol groups (such as polyvinyl alcohol--PVA--or a cellulose),
ether groups (such as polyethylene oxide--PEO--or polyvinyl
ether--PVE), and/or amine groups (such as polyvinyl pyridine,
((di/mono)alkylamino)alkyl alkacrylate, or the like).
[0298] In certain embodiments, the polymer is a nucleophilic
polymer (e.g., a polymer comprising alcohol groups, such as PVA).
In some embodiments, the polymer is a nucleophilic polymer and a
silicon and/or optional metal precursor is an electrophilic
precursor (e.g., a metal acetate, metal chloride, or the like). In
specific embodiments, the nucleophilic polymer and the precursor
form a precursor-polymer association in the fluid stock and/or the
as-spun nanocomponsite nanofiber and that association is a reaction
product between a nucleophilic polymer and electrophilic
precursor(s).
[0299] In other embodiments, the polymer is an electrophilic
polymer (e.g., a polymer comprising chloride or bromide groups,
such as polyvinyl chloride). In some embodiments, the polymer is an
electrophilic polymer and a precursor (e.g., silicon and/or
optional metal precursor) is a nucleophilic precursor (e.g.,
metal-ligand complex comprising "ligands" with nucleophilic groups,
such as alcohols or amines). In specific embodiments, the
nucleophilic polymer and the precursor form a precursor-polymer
association in the fluid stock and/or the as-spun nanocomponsite
nanofiber and that association is a reaction product between an
electrophilic polymer and a nucleophilic first precursor.
[0300] For the purposes of this disclosure metal precursors include
both preformed metal-ligand associations (e.g., salts,
metal-complexes, or the like) (e.g., reagent precursors, such as
metal acetates, metal halides, or the like) and/or metal-polymer
associations (e.g., as formed following combination of reagent
precursor with polymer in an aqueous fluid).
[0301] Polymers of any suitable molecular weight may be utilized in
the processes and nanofibers described herein. In some instances, a
suitable polymer molecular weight is a molecular weight that is
suitable for electrospinning the polymer as a melt or solution
(e.g., aqueous solution or solvent solution--such as in dimethyl
formamide (DMF) or alcohol). In some embodiments, the polymer
utilized has an average atomic mass of 1 kDa to 1,000 kDa (or
more). In specific embodiments, the polymer utilized has an average
atomic mass of 10 kDa to 500 kDa. In more specific embodiments, the
polymer utilized has an average atomic mass of 10 kDa to 250 kDa.
In still more specific embodiments, the polymer utilized has an
average atomic mass of 50 kDa to 200 kDa.
[0302] In some embodiments, metal precursor comprise alkali metal
salts or complexes, alkaline earth metal salts or complexes,
transition metal salts or complexes, or the like. In specific
embodiments, the metal precursor comprises lithium precursor,
silicon precursor, iron precursor, a nickel precursor, a cobalt
precursor, a manganese precursor, a vanadium precursor, a titanium
precursor, a ruthenium precursor, a rhenium precursor, a platinum
precursor, a bismuth precursor, a lead precursor, a copper
precursor, an aluminum precursor, a combination thereof, or the
like. In specific embodiments, the optional or additional metal
precursor comprises a molybdenum precursor, niobium precursor,
tantalum precursor, tungsten precursor, iron precursor, nickel
precursor, copper precursor, cobalt precursor, manganese precursor,
titanium precursor, vanadium precursor, chromium precursor,
zirconium precursor, yttrium precursor, germanium precursor, tin
precursor, or a combination thereof. In specific embodiments, metal
(silicon, lithium, and other metals) precursors include metal salts
or complexes, wherein the metal is associated with any suitable
ligand or radical, or anion or other Lewis Base, e.g., a
carboxylate (e.g., --OCOCH.sub.3 or another --OCOR group, wherein R
is an alkyl, substituted alkyl, aryl, substituted aryl, or the
like, such as acetate), an alkoxide (e.g., a methoxide, ethoxide,
isopropyl oxide, t-butyl oxide, or the like), a halide (e.g.,
chloride, bromide, or the like), a diketone (e.g., acetylacetone,
hexafluoroacetylacetone, or the like), a nitrates, amines (e.g.,
NR'.sub.3, wherein each R'' is independently R or H or two R'',
taken together form a heterocycle or heteroaryl), and combinations
thereof.
[0303] In specific embodiments, (e.g., for the preparation of a
cathode material) the fluid stock comprises a lithium precursor and
at least one additional metal precursor, wherein the metal
precursor comprises an iron precursor, a nickel precursor, a cobalt
precursor, a manganese precursor, a vanadium precursor, a titanium
precursor, a ruthenium precursor, a rhenium precursor, a platinum
precursor, a bismuth precursor, a lead precursor, a copper
precursor, an aluminum precursor, a combination thereof, or the
like.
[0304] In more specific embodiments, the additional metal precursor
comprises an iron precursor, a nickel precursor, a cobalt
precursor, a manganese precursor, a vanadium precursor, an aluminum
precursor, or a combination thereof. In still more specific
embodiments, the additional metal precursor comprises an iron
precursor, a nickel precursor, a cobalt precursor, a manganese
precursor, an aluminum precursor, or a combination thereof. In yet
more specific embodiments, the additional metal precursor comprises
a nickel precursor, a cobalt precursor, a manganese precursor, or a
combination thereof. In still more specific embodiments, the
additional metal precursor comprises at least two metal precursors
from the group consisting of: a nickel precursor, a cobalt
precursor, and a manganese precursor. In more specific embodiments,
the additional metal precursor comprises a nickel precursor, a
cobalt precursor, and a manganese precursor.
[0305] In some embodiments, (e.g., where metal precursors are
utilized, such as a silicon or lithium precursor and one or more
additional metal precursor) the weight ratio of the metal
component(s) (including silicon or lithium and other metal
components, such as silicon and metal precursors) to polymer is at
least 1:5, at least 1:4, at least 1:3, at least 1:2, at least 1:1,
at least 1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at
least 3:1, or at least 4:1. In some instances, wherein the metal,
silicon, clay or ceramic component of a process, nanofiber, fluid
stock, or battery component described herein is a nanostructure or
nanoparticle, the component to polymer weight ratio is at least
1:5, at least 1:4, at least 1:3, at least 1:2, or the like. In some
instances, wherein the metal or silicon component of a process
described herein is a metal (including silicon) precursor, the
silicon component to polymer ratio is at least 1:3, at least 1:2,
at least 1:1, or the like. In some embodiments, the monomeric
residue (i.e., repeat unit) concentration of the polymer in the
fluid stock is at least 100 mM. In specific embodiments, the
monomeric residue (i.e., repeat unit) concentration of the polymer
in the fluid stock is at least 200 mM. In more specific
embodiments, the monomeric residue (i.e., repeat unit)
concentration of the polymer in the fluid stock is at least 400 mM.
In still more specific embodiments, the monomeric residue (i.e.,
repeat unit) concentration of the polymer in the fluid stock is at
least 500 mM. In some embodiments, the fluid stock comprises at
least about 0.5 weight %, at least about 1 weight %, at least about
2 weight %, at least about 5 weight %, at least about 10 weight %,
at least about 20 weight %, or at least 30 weight % polymer.
[0306] In some embodiments, the polymers described herein (e.g.,
hydrophilic or nucleophilic polymers) associate (e.g., through
ionic, covalent, metal complex interactions) with metal precursors
described herein when combined in a fluid stock. Thus, in certain
embodiments, provided herein is a fluid stock that comprises (a) at
least one polymer; (b) a metal precursor (e.g., a metal acetate or
metal alkoxide), or is prepared by combining (i) at least one
polymer; (ii) a metal precursor. In certain embodiments, upon
electrospinning of such a fluid stock, a nanofiber comprising a
polymer associated with the metal precursors is produced. For
example, provided in specific embodiments herein is a fluid stock
comprising PVA in association with a lithium precursor and at least
one additional metal precursor. In some embodiments, this
association is present in a fluid stock or in a nanofiber. In
specific embodiments, the association having the formula:
--(CH.sub.2--CHOM.sup.1).sub.n1-. In specific embodiments, each M
is independently selected from H, a metal ion, and a metal complex
(e.g., a metal halide, a metal carboxylate, a metal alkoxide, a
metal diketone, a metal nitrate, a metal amine, or the like).
[0307] In further embodiments, provided herein is a polymer (e.g.,
in a fluid stock or nanofiber) having the following formula:
(A.sub.dR.sup.1.sub.n--BR.sup.1.sub.mR.sup.2).sub.a. In some
embodiments, each of A and B are independently selected from C, O,
N, or S. In certain embodiments, at least one of A or B is C. In
some embodiments, each R.sup.1 is independently selected from H,
halo, CN, OH, NO.sub.2, NH.sub.2, NH(alkyl) or N(alkyl)(alkyl),
SO.sub.2alkyl, CO.sub.2-alkyl, alkyl, heteroalkyl, alkoxy, S-alkyl,
cycloalkyl, heterocycle, aryl, or heteroaryl. In certain
embodiments, the alkyl, alkoxy, S-alkyl, cycloalkyl, heterocycle,
aryl, or heteroaryl is substituted or unsubstituted. In some
embodiments, R.sup.2 is M.sup.1, OM.sup.1, NHM.sup.1, or SM.sup.1,
as described above. In specific embodiments, if R.sup.1 or R.sup.2
is M.sup.1, the A or B to which it is attached is not C. In some
embodiments, any alkyl described herein is a lower alkyl, such as a
C.sub.1-C.sub.6 or C.sub.1-C.sub.3 alkyl. In certain embodiments,
each R.sup.1 or R.sup.2 is the same or different. In certain
embodiments, d is 1-10, e.g., 1-2. In certain embodiments, n is 0-3
(e.g., 1-2) and m is 0-2 (e.g., 0-1). In some embodiments, a is
100-1,000,000. In specific embodiments, a substituted group is
optionally substituted with one or more of H, halo, CN, OH,
NO.sub.2, NH.sub.2, NH(alkyl) or N(alkyl)(alkyl), SO.sub.2alkyl,
CO.sub.2-alkyl, alkyl, heteroalkyl, alkoxy, S-alkyl, cycloalkyl,
heterocycle, aryl, or heteroaryl. In certain embodiments, the block
co-polymer is terminated with any suitable radical, e.g., H, OH, or
the like.
[0308] In specific embodiments, at least 5% of M.sup.1 are
Li.sup.+. In more specific embodiments, at least 10% of M.sup.1 are
Li.sup.+. In more specific embodiments, at least 15% of M.sup.1 are
Li.sup.+. In still more specific embodiments, at least 20% of
M.sup.1 are Li.sup.+. In more specific embodiments, at least 40% of
M.sup.1 are Li.sup.+. In further embodiments, at least 10% of
M.sup.1 are a non-lithium metal complex (e.g., iron acetate, cobalt
acetate, manganese acetate, nickel acetate, aluminum acetate, or a
combination thereof). In more specific embodiments, at least 15% of
M.sup.1 are non-lithium metal complex. In still more specific
embodiments, at least 20% of M.sup.I are non-lithium metal complex.
In more specific embodiments, at least 40% of M.sup.1 are
non-lithium metal complex.
[0309] In various embodiments, n1 is any suitable number, such as
1,000 to 1,000,000.
[0310] In some embodiments, the polymer is suitable for
electrospinning In some embodiments, the polymer is water soluble.
In some embodiments, the polymer is polyvinyl alcohol (PVA),
polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinyl
pyrrolidone (PVP), poly(phenylene oxide) (PPO), polystyrene (PS),
poly(methyl methacrylate) (PMMA), polycarbonate (PC), cellulose, or
any combination thereof.
[0311] In some embodiments, the polymer is a block co-polymer.
Without limitation, use of block co-polymers to produce porous
nanofibers is described in U.S. Provisional Patent Application No.
61/599,541 filed on Feb. 16, 2012. As described therein, co-axially
electrospinning a fluid stock comprising a block co-polymer
surrounded by a coating, then annealing to allow the blocks of the
block co-polymer to assembled ordered phase elements, followed by
selective removal of at least one of the phases produces ordered
porous nanofibers.
[0312] In some embodiments, the polymer is a co-polymer (i.e., is a
polymer derived from two or more monomeric species, as opposed to a
homopolymer where only one monomer is used). Co-polymers comprising
incompatible monomer species (i.e., immiscible in each other)
microphase separate to form periodic nanostructures (i.e., phase
elements) in some embodiments. Generally, microphase separation is
understood to be distinct from phase separation (e.g., phase
separation of oil and water) because the incompatible monomers are
covalently bound to each other in the co-polymer and therefore
cannot macroscopically de-mix. In contrast to macroscopic
de-mixing, the monomers form small structures (i.e., phase
elements).
[0313] In some embodiments, the co-polymer is a graft co-polymer.
Graft co-polymers are a type of branched co-polymer where the side
chains are structurally distinct from the main chain. In some
embodiments, the main chain is a homo-polymer or a co-polymer. The
side chain(s) are homo-polymer(s) or co-polymer(s). Any arrangement
of main chain(s) and side chain(s) is suitable for forming ordered
phase elements and/or nanofibers having ordered pores.
[0314] Another suitable type of co-polymer is a "block co-polymer".
Block co-polymers are made up of blocks of different polymerized
monomers. For example, PS-b-PMMA is short for
polystyrene-b-poly(methyl methacrylate) and is usually made by
first polymerizing styrene, and then subsequently polymerizing MMA
from the reactive end of the polystyrene chains. This polymer is a
"diblock co-polymer" because it contains two different chemical
blocks. Triblocks, tetrablocks, multiblocks, etc. are also
suitable. Diblock co-polymers can be made using living
polymerization techniques, such as atom transfer free radical
polymerization (ATRP), reversible addition fragmentation chain
transfer (RAFT), ring-opening metathesis polymerization (ROMP), and
living cationic or living anionic polymerizations for example.
Another suitable technique is chain shuttling polymerization.
Another strategy for preparing block co-polymers is the
chemoselective stepwise coupling between polymeric precursors and
heterofunctional linking agents. In some instances, this method is
used to produce more complex structures such as tetrablock
quarterpolymers for example. Any suitable method for producing
block co-polymers is used to produce the ordered porous nanofibers
described herein.
[0315] In some embodiments, the block co-polymer comprises at least
two types of monomeric species designated "A" and "B". In some
embodiments, the blocks of the block co-polymer have a particular
size (e.g., number of polymerized "A" monomers per block of "A"
and/or number of polymerized "B" monomers per block of "B"). The
"A" block and/or "B" block can have a distribution of sizes, or can
be monodisperse (i.e., all "A" blocks have 20 polymerized "A"
monomers within a suitably low standard deviation (e.g., 5%, 10%,
20% or 50%)).
[0316] In some embodiments, the block co-polymer comprises 3 types
of monomeric species designated "A", "B" and "C". For example the
PI and PLA blocks of a PS-b-PI-b-PLA tri-block co-polymer are
removed, resulting in a nanofiber that is about 70% porous. In some
embodiments, greater numbers of monomeric species are used to
incorporate various materials (i.e., hybrid nanofibers) and/or
create more complex structures.
[0317] Depending on the relative size of each block, several
morphologies are obtained. In diblock copolymers, sufficiently
different block lengths lead to nanometer-sized spheres of one
block in a matrix of the second (for example PMMA in polystyrene).
Using less different block lengths, a "hexagonally packed cylinder"
geometry is obtained. In some embodiments, blocks of similar length
form layers (i.e., lamellar phase). In some embodiments, a gyroid
phase forms at block lengths intermediate between the cylindrical
and lamellar phase. The sizes of the blocks of the block co-polymer
are varied in any suitable manner to form phase elements and/or
nanofiber pores having a desired geometry. In some embodiments, the
block co-polymer is amphiphilic (e.g., has at least one hydrophobic
block and at least one hydrophilic block).
[0318] In one aspect, the method comprises selectively removing at
least part of the block co-polymer from the nanofiber (e.g.,
thereby producing an ordered mesoporous nanofiber). In some
embodiments, selectively removing at least part of the block
co-polymer comprises selectively degrading and/or removing one
block of the block co-polymer. In some embodiments, the block
co-polymer comprises a degradable block and/or a removable block.
For example, the degradable block is chemically degradable,
thermally degradable, or any combination thereof. Examples of
thermally or chemically degradable blocks include polyimide (PI),
polylactic acid (PLA), polyvinyl alcohol (PVA), polyethylene oxide
(PEO), polyvinylpyrrolidone (PVP), and polyacrylamide (PAA).
[0319] In some embodiments, the block co-polymer further comprises
a block that does not degrade under conditions suitable for
degrading and/or removing the degradable and/or removable block. In
some embodiments, the block co-polymer comprises a thermally stable
block and/or a chemically stable block. Examples of thermally or
chemically stable blocks include polystyrene (PS), poly(methyl
methacrylate) (PMMA), and polyacrylonitrile (PAN).
[0320] Exemplary block co-polymers suitable for use in the methods
described herein comprise PI-b-PS, PS-b-PLA, PMMA-b-PLA, PI-b-PEO,
PAN-b-PEO, PVA-b-PS, PEO-b-PPO-PEO, PPO-b-PEO-PPO, or any
combination thereof. The notation "-b-" indicates that the polymer
is a block co-polymer comprising the indicated blocks before and
after the "-b-".
High Energy Capacity Material
[0321] In one aspect, described herein are lithium-ion batteries
comprising an electrode and methods for making a lithium ion
battery comprising an electrode. In some embodiments, the electrode
comprises a plurality of nanofibers, the nanofibers comprising
domains of a high energy capacity material. In some embodiments,
the electrode comprises porous nanofibers, the nanofibers
comprising a high energy capacity material.
[0322] In another aspect, described herein is a method is described
for producing an electrode. In some embodiments the method
comprises electrospinning a fluid stock to form nanofibers, the
fluid stock comprising a high energy capacity material or precursor
thereof and a polymer. In another aspect, a method is described
comprising adding high energy capacity (e.g., nanoparticles) to
nanofibers.
[0323] In some embodiments, the high energy capacity material is
any material capable of intercalating and deintercalating lithium
ions. The high energy capacity material is in any suitable form in
the electrodes and methods described herein. In some embodiments,
the high energy capacity material comprises a powder or granules.
In some embodiments, the high energy capacity material comprises
nanoparticles of the high energy capacity material. In some
embodiments, the nanoparticles comprise Si, Ge, Sn, Ni, Co, Cu, Fe,
any oxidation state thereof, or any combination thereof.
[0324] In some embodiments, the fluid stock comprises a high energy
capacity material (e.g., in the form of a nanoparticle), or a
precursor thereof. In some embodiments, the high energy capacity
material is a metal.
[0325] In some embodiments, the precursor of the high energy
capacity material are metal acetates, metal nitrates, metal
acetylacetonates, metal chlorides, metal hydrides, hydrates
thereof, or any combination thereof.
[0326] In some embodiments, the high energy capacity material is a
ceramic (e.g., Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2), Si (e.g.,
amorphous silicon), Ge, Sn, metal (e.g., Fe, Cu, Co, Ag, Ni, Au),
any oxidation state thereof, or any combination thereof. In some
embodiments, the high energy capacity material comprises Si, Ge,
Sn, Fe, Co, Cu, Ni, LiCo.sub.xNi.sub.yMn.sub.zO.sub.2,
LiMn.sub.xNi.sub.yCo.sub.zV.sub.aO.sub.4, S, sulfur encapsulated in
carbon, Li.sub.2S, Fe.sub.xNi.sub.yCo.sub.zV.sub.aPO.sub.4,
LiFe.sub.xNi.sub.yCo.sub.zV.sub.aPO.sub.4, any oxidation state
thereof, or any combination thereof. Here, the subscript variables
(e.g., x, y, z, a) are any suitable integer or fraction.
Chemical Treatment/Thermal Treatment/Annealing
[0327] In one aspect, a method is described for producing an
electrode. In some embodiments the method comprises: (a)
electrospinning a fluid stock to form nanofibers, the fluid stock
comprising a high energy capacity material or precursor thereof and
a polymer; (b) heating the nanofibers; and (c) assembling the
nanofibers into an electrode.
[0328] The heating step performs any suitable function. In some
embodiments, the heating step carbonizes the polymer. In some
embodiments, the heating step removes the polymer. In some
embodiments, the heating step selectively removes a polymer phase.
In some embodiments, removing (e.g., selectively) the polymer
and/or polymer phase results in porous nanofibers. In some
embodiments, the heating step crystallizes the precursors and/or
nanoparticles (e.g., producing domains of high energy capacity
material). In some embodiments, the heating step determines the
oxidation state of the high energy capacity material, precursors
thereof and/or nanoparticles thereof, or any combination
thereof.
[0329] In some embodiments, the nanofibers are heated in the
presence of air, nitrogen, nitrogen/H.sub.2 (e.g., 95%/5%), argon,
argon/H.sub.2 (e.g., 96%/4%), or any combination thereof.
[0330] In some embodiments, heating removes the polymer from the
electrospun fluid stock. In some embodiments, the polymer is
removed by chemical means, including solubilizing the polymer,
chemically degrading the polymer, and the like. The polymer is
degraded in a strong acid or base for example.
[0331] In some embodiments, the heating converts the precursors to
a nanofiber. The conversion of precursors to nanofiber occurs
simultaneously with the removal of the polymer, or optionally
occurs at different times.
[0332] In some embodiments, the heating is performed in a gaseous
environment. If one does not want certain reactions such as
oxidation reactions to proceed in the calcination step, one chooses
an inert environment consisting of non-reactive gases in some
embodiments. The noble gases are particularly unreactive, so are
suitable. The noble gases include helium (He), neon (Ne), argon
(Ar), krypton (Kr), xenon (Xe), radon (Rn), or mixtures thereof.
While not a noble gas, another inert gas suitable for the present
invention is nitrogen (N.sub.2) gas, which constitutes the majority
of our atmosphere and is generally non-reactive.
[0333] Alternatively, in some instances certain chemical reactions
occur upon heating, optionally oxidation reactions. Oxidation
converts metal precursors to metal oxide or ceramic nanofibers for
example. Oxidative conditions are performed in an oxygen-rich
environment, such as air. In one particular example where the
nanofiber is a ceramic nanofiber, calcination is performed in air
at about 600.degree. C. for about 2 hours.
[0334] Reduction is the gain of electrons, which is the opposite
reaction from oxidation. In some instances, such as in the
production of pure metal nanofibers, reducing environments are
employed. In this case, the reductive environment prevents the
conversion of metal precursors to metal oxides. A mixture of inert
gas and hydrogen gas (H.sub.2) is one example of a reductive
environment. The strength of the reductive environment is varied by
blending with an inert gas in some embodiments. The present
disclosure encompasses hydrogen-nitrogen mixtures and the like.
Another reductive environment is any environment in which oxidation
is prevented, such as an environment substantially devoid of
oxygen. In some embodiments, the heating is performed under
vacuum.
[0335] In one particular instance, heating is performed under a
mixture of argon and hydrogen at about 800.degree. C. for about 2
hours to produce a metal nanofiber.
[0336] In some instances, heating is performed in a liquid
environment. The liquid environment is aqueous in some instances.
In other instances heating is performed in a different solvent than
water, such as an organic solvent. Oxidative, reductive, or inert
conditions are created in liquid environments. An exemplary
liquid-based reducing environment is a solution of NaOH or
NaBH.sub.4. An exemplary oxidizing solution comprises hydrogen
peroxide H.sub.2O.sub.2.
[0337] Heating is performed at any suitable temperature or time.
Higher temperature heating generally produce nanofibers of a
smaller diameter. Without being bound by theory, the temperature
and/or duration of heating governs the size and type of crystals in
the nanofiber. Low temperature and/or short time generates small
crystal domains in amorphous metal or metal oxides, while high
temperature calcination generally leads to nanofibers with pure
metal or pure metal oxide crystals. Without being bound by theory,
crystal size is thought to govern properties such as electric
conductivity or magnetic properties. In general, low temperature
heating of magnetically active metal or metal oxides generates
superparamagnetic nanofibers. In general, high temperature heating
produces metal nanofibers with increased electric conductivity.
[0338] In some embodiments, heating is performed at about
100.degree. C., about 150.degree. C., about 200.degree. C., about
300.degree. C., about 400.degree. C., about 500.degree. C., about
600.degree. C., about 700.degree. C., about 800.degree. C., about
900.degree. C., about 1,000.degree. C., about 1,500.degree. C.,
about 2,000.degree. C., and the like. In some embodiments, heating
is performed at a temperature of at least 100.degree. C., at least
150.degree. C., at least 200.degree. C., at least 300.degree. C.,
at least 400.degree. C., at least 500.degree. C., at least
600.degree. C., at least 700.degree. C., at least 800.degree. C.,
at least 900.degree. C., at least 1,000.degree. C., at least
1,500.degree. C., at least 2,000.degree. C., and the like. In some
embodiments, heating is performed at a temperature of at most
100.degree. C., at most 150.degree. C., at most 200.degree. C., at
most 300.degree. C., at most 400.degree. C., at most 500.degree.
C., at most 600.degree. C., at most 700.degree. C., at most
800.degree. C., at most 900.degree. C., at most 1,000.degree. C.,
at most 1,500.degree. C., at most 2,000.degree. C., and the like.
In some embodiments, heating is performed at a temperature of
between about 300.degree. C. and 800.degree. C., between about
400.degree. C. and 700.degree. C., between about 500.degree. C. and
900.degree. C., between about 700.degree. C. and 900.degree. C.,
between about 800.degree. C. and 1,200.degree. C., and the
like.
[0339] Heating is performed at a constant temperature, or the
temperature is changed over time. In one embodiment, the
temperature increases from a first temperature, optionally the
temperature of the electrospinning process, optionally room
temperature, to a second temperature. Heating then proceeds for a
given time at the second temperature, or the temperature continues
to vary. The rate of increase in temperature during heating is
varied in some embodiments. Any suitable rate of increase is
permissible and disclosed herein, whereby a nanofiber of the
desired properties is obtained. In certain embodiments, the rate of
temperature increase is about 0.1.degree. C./min, about 0.3.degree.
C./min, about 0.5.degree. C./min, about 0.7.degree. C./min, about
1.0.degree. C./min, about 1.5.degree. C./min, about 2.degree.
C./min, about 2.5.degree. C./min, about 3.degree. C./min, about
4.degree. C./min, about 5.degree. C./min, about 10.degree. C./min,
about 20.degree. C./min, and the like. In certain embodiments, the
rate of temperature increase is at least about 0.1.degree. C./min,
at least about 0.3.degree. C./min, at least about 0.5.degree.
C./min, at least about 0.7.degree. C./min, at least about
1.0.degree. C./min, at least about 1.5.degree. C./min, at least
about 2.degree. C./min, at least about 2.5.degree. C./min, at least
about 3.degree. C./min, at least about 4.degree. C./min, at least
about 5.degree. C./min, at least about 10.degree. C./min, at least
about 20.degree. C./min, and the like. In certain embodiments, the
rate of temperature increase is at most about 0.1.degree. C./min,
at most about 0.3.degree. C./min, at most about 0.5.degree. C./min,
at most about 0.7.degree. C./min, at most about 1.0.degree. C./min,
at most about 1.5.degree. C./min, at most about 2.degree. C./min,
at most about 2.5.degree. C./min, at most about 3.degree. C./min,
at most about 4.degree. C./min, at most about 5.degree. C./min, at
most about 10.degree. C./min, at most about 20.degree. C./min, and
the like. In yet other embodiments, the rate of temperature
increase is between about 0.1.degree. C./min and 0.5.degree.
C./min, between about 0.5.degree. C./min and 2.degree. C./min,
between about 2.degree. C./min and 10.degree. C./min, between about
0.1.degree. C./min and 2 l .degree. C./min, and the like.
[0340] Heating is performed for any suitable amount of time
necessary to arrive at a nanofiber with the desired properties. In
certain embodiments, the time and temperature of heating are
related to each other. For example, choice of a higher temperature
reduces, in some instances, the amount of time needed to produce a
nanofiber with a given property. In some instances, the converse is
also be true; increasing the time of calcination reduces the
necessary temperature. In some instances, this is advantageous if
the nanofiber includes temperature-sensitive materials for example.
In some embodiments, heating is performed for about 5 minutes,
about 15 minutes, about 30 minutes, about 1 hour, about 2 hours,
about 3 hours, about 4 hours, about 8 hours, about 12 hours, about
1 day, about 2 days, and the like. In some embodiments, heating is
performed for at least 5 minutes, at least 15 minutes, at least 30
minutes, at least 1 hour, at least 2 hours, at least 3 hours, at
least 4 hours, at least 8 hours, at least 12 hours, at least 1 day,
at least 2 days, and the like. In some embodiments, heating is
performed for at most 5 minutes, at most 15 minutes, at most 30
minutes, at most 1 hour, at most 2 hours, at most 3 hours, at most
4 hours, at most 8 hours, at most 12 hours, at most 1 day, at most
2 days, and the like. In yet other embodiments, heating is
performed for between about 10 minutes and 60 minutes, between
about 1 hour and about 5 hours, between about 5 hours and 1 day,
and the like.
[0341] In some embodiments, the nanofibers are heated in the
presence of a sacrificial oxidizer, thereby oxidizing the
sacrificial oxidizer and reducing (and/or not oxidizing) the high
energy capacity material. In some embodiments, the sacrificial
oxidizer comprises a material that is more readily oxidized than
the high energy capacity material (e.g., Mg when the high energy
capacity material is Si).
Calcination Reagents
[0342] In some embodiments, the fluid stock further comprises a
calcination reagent. In further or alternative embodiments, after
electrospinning, the nanofibers are thermally treated in
combination with a calcination reagent (e.g., air, or a reducing
agent, such as hydrogen or a sacrificial oxidation reagent like
Mg). In certain embodiments, the calcination reagent is a
phosphorus reagent (e.g., for preparing lithium metal phosphates or
phosphides upon thermal treatment/calcination of a nanofiber spun
from a fluid stock comprising lithium and at least one additional
metal precursors), a silicon reagent (e.g., for preparing lithium
metal silicates upon thermal treatment/calcination of a nanofiber
spun from a fluid stock comprising lithium and at least one
additional metal precursors), a sulfur reagent (e.g., for preparing
lithium metal sulfides or sulfates upon thermal
treatment/calcination of a nanofiber spun from a fluid stock
comprising lithium and at least one additional metal precursors),
or a boron reagent (e.g., for preparing lithium metal borates upon
thermal treatment/calcination of a nanofiber spun from a fluid
stock comprising lithium and at least one additional metal
precursors). In some embodiments, the reagent is elemental material
(e.g., phosphorus, sulfur) or any other suitable chemical compound.
In some embodiments, the calcination reagent has the formula:
X.sup.1R.sup.1.sub.q, wherein X.sup.1 is a non-metal (or
metalloid), such as S, P, N, B, Si, or Se; each R.sup.1 is
independently H, halo, CN, OH (or O--), NO.sub.2, NH.sub.2,
--NH(alkyl) or --N(alkyl)(alkyl), --SO.sub.2alkyl,
--CO.sub.2-alkyl, alkyl, heteroalkyl, alkoxy, --S-alkyl,
cycloalkyl, heterocycle, aryl, heteroaryl, oxide (.dbd.O); and q is
0-10 (e.g., 0-4). In certain embodiments, the alkyl, alkoxy,
S-alkyl, cycloalkyl, heterocycle, aryl, or heteroaryl is
substituted or unsubstituted. In specific embodiments, q is 0.
[0343] In some embodiments, R1 is alkoxy (e.g., wherein the
calcination reagent is triethylphosphite). In some embodiments
wherein metal oxides are prepared, an oxygen reagent is air, which
is provided in the atmosphere (e.g., which can react upon
sufficient thermal conditions with the metal precursors or calcined
metals). In certain embodiments, wherein metal carbides are
prepared, a carbon reagent (or carbon source) is the organic
polymer material (e.g., which can react upon sufficient thermal
conditions with the metal precursor(s)).
[0344] In some embodiments, the method comprises heating the
nanofibers in the presence of a calcining reagent, such as a
sacrificial oxidizer, wherein the sacrificial oxidizer becomes
oxidized. In some embodiments, the method further comprises
removing the oxidized sacrificial oxidizer (e.g., Mg) from the
nanofibers.
[0345] The sacrificial oxidizer is removed in any suitable manner.
In some embodiments, the nanofibers are contacted with a solution
comprising a strong acid. The acid is an acid vapor in some
embodiments. The acid is an aqueous solution in some embodiments.
The contacting is performed for any suitable amount of time. The
concentration of the acid is any suitable concentration.
[0346] The acid is any acid suitable for removing the sacrificial
oxidizer from the nanofibers. In some embodiments, the acid is a
weak acid such as acetic acid. In some embodiments, the acid is a
strong acid. In some embodiments, the acid comprises hydrochloric
acid (HCl). In some embodiments, the acid comprises hydrofluoric
acid (HF).
[0347] In one aspect, the electrodes described herein comprise
porous nanofibers. In some embodiments, removing the oxidized
sacrificial oxidizer increases the porosity of the nanofibers.
[0348] In some embodiments, the method further comprises reacting
and/or coating the nanofibers such that the nanofibers are not
capable of being oxidized. Methods for coating include dipping,
spraying, electrodepositing, and co-axial electrospinning The
method includes reacting and/or coating with any material suitable
for protecting the nanofibers from oxidation.
Electrodes
[0349] Without limitation, the batteries described herein comprise
electrodes (e.g., anode and cathode) comprising nanofibers.
Described herein are the batteries, the electrodes, the nanofibers,
methods for making the batteries, methods for making the
electrodes, methods for making the nanofibers, and the like. In one
aspect, a method is described for producing an electrode. In some
embodiments the method comprises: (a) electrospinning a fluid stock
to form nanofibers, the fluid stock comprising a high energy
capacity material or precursor thereof and a polymer; (b) treating
(e.g., thermally and/or chemically) the nanofibers; and (c)
assembling the nanofibers into an electrode. In certain
embodiments, a process of assembling an electrode herein comprises
assembling any nanofiber described herein into an electrode. In
some instances, provided herein is any electrode described herein
(e.g., in a battery, system or method herein). Further, in some
embodiments, such electrodes are lithium ion battery electrodes. In
some instances, such electrodes are thinner and lighter than those
currently commercially available (e.g., carbon electrodes). In some
embodiments, an electrode described herein comprises a porous
nanofiber (e.g., ceramic, metal, silicon, or hybrid thereof). In
further or alternative embodiments, electrodes provided herein
comprising domains of high energy capacity material. In certain
embodiments, such electrodes comprise further domains, such as
those that allow expansion of the nanofiber without pulverization,
degradation, or the like.
[0350] Any method for assembling the nanofibers into an electrode
is suitable. In some embodiments, assembling the nanofibers into an
electrode comprises aligning the nanofibers. The nanofibers are
aligned in any suitable orientation. The nanofibers are disposed on
any suitable surface in some embodiments. In some instances, the
nanofibers are encapsulated in any suitable matrix material. The
nanofibers are assembled into an electrode such that lithium ions
are capable of intercalating and deintercalating from the high
energy capacity material, optionally at a high rate. In some
instances, the nanofibers are assembled into an electrode such that
operation of the battery delivers electricity to its intended
application (e.g., an electronic device such as a mobile phone, an
electric automobile, and the like).
System
[0351] In one aspect, described herein is a lithium ion battery
system, the system comprising: (a) an electrolyte; (b) an anode in
a first chamber, the anode comprising a plurality of first
nanofibers, the first nanofibers comprising a plurality of domains
of a first high energy capacity material, a plurality of
nanoparticles comprising the first high energy capacity material, a
plurality of pores, a core of high conductivity material, or any
combination thereof; (c) a cathode in a second chamber, the cathode
comprising a plurality of second nanofibers, the second nanofibers
comprising a plurality of domains of a second high energy capacity
material, a plurality of nanoparticles comprising the second high
energy capacity material, a plurality of pores, a core of high
conductivity material, or any combination thereof; and (d) a
separator between the first chamber and the second chamber, the
separator comprising a plurality of third nanofibers, the third
nanofibers comprising a polymer, and the separator allowing ion
transfer between the first chamber and second chamber in a
temperature dependent manner.
[0352] In one aspect, described herein is a system for producing
nanofibers for a lithium ion battery, the system comprising: (a) a
fluid stock comprising a polymer and inorganic precursors or
nanoparticles; (b) an electrospinner suitable for electrospinning
the fluid stock into nanofibers; (c) a heater suitable for heating
the nanofibers; and (d) optionally a module suitable for contacting
the nanofibers with an acid.
[0353] In some embodiments, electrospinning (e.g., with an aid of
gas stream--gas assisted) allows for the high throughput generation
of nanomaterials. Further, in some instances, gas assisted
electrospinning provides an ability to control the structure of
resultant as-spun nanofibers and calcined nanofibers (e.g., the
crystal structure thereof). In some embodiments, purely inorganic
or organic/inorganic hybrid (composite) nanofibers are generated by
inclusion of various metal/ceramic precursors (metal nitrate,
acetate, acetylacetonate, etc.) or preformed nanoparticles (Si, Ge,
Sn, Fe.sub.3O.sub.4, etc.) within a polymer (PVA, PAN, PEO, etc.)
solution, as shown in the schematic in FIG. 15. More specifically,
FIG. 15 illustrates one example of a process of preparing
nanofibers herein, beginning with the preparation of a fluid stock
1003 by combining 1002 polymer (e.g., PVA, PAN, PEO, or the like)
with a composite (e.g., metal, clay, ceramic) component 1001, such
as inorganic precursors (e.g., metal nitrate, acetate,
acetylacetonate, or the like) and/or pre-made nanoparticles (such
as Si, Ge, Sn, Fe.sub.3O.sub.4, or the like, or a nanoclay, or a
ceramic). The fluid stock 1003 is prepared for electrospinning by
any suitable process 1004, e.g., heating, mixing, or the like. The
fluid stock is provided to an electrospinning apparatus 1005 (or
prepared therein). The fluid stock is electrospun through an
electrospinning needle apparatus 1006 (e.g., the fluid is provided
to the tip of the needle whereupon a voltage is applied, overcoming
the surface tension of the fluid and providing an electrospun jet
1013). The needle apparatus 1006 is optionally monoaxial or
coaxial. A coaxial needle apparatus 1006 is illustrated with an
inner needle 1011 and outer needle 1012. In certain instances, the
outer needle provides a gas during electrospinning, providing for
coaxial gas assisted electrospinning of the fluid stock. The gas
(e.g., air) is provided to the needle from any suitable source,
such as a pump or gas canister (not shown). In other instances, the
inner needle 1011 provides a first fluid stock (e.g., from a first
syringe) and the outer needle 1012 provides a second fluid stock
(e.g., from a second syringe). The electrospun jet 1013 is then
collected on a collector 1007 as an as-spun nanofiber 1008. In some
instances, the as-spun nanofiber is collected in an aligned or
non-woven manner.
[0354] In some instances (e.g., in the preparation for anode or
cathode nanofibers provided herein) as-spun nanofiber 1008 is then
thermally treated to remove organics (e.g., polymer and/or
precursor ligands), calcine metal precursors, crystallize
inorganics, and/or combinations thereof. In other instances,
thermal treatment may be at a lower temperature, e.g., to anneal
the polymer component of the nanofiber. In certain instances, the
produced nanofibers have controlled porosity, conductivity,
etc.
[0355] In some embodiments, thermal treatment is of as-spun
nanofibers is used to carbonize polymers, remove polymers,
selectively remove a single polymer phase, and/or crystallize
included precursors or nanoparticles with controlled oxidation
state. In some embodiments, the morphology of resulting nanofibers,
as shown by TEM images and inlaid XRD patterns in FIGS. 1-3, vary
from single-phase high-capacity material (Si) to a high-capacity
secondary material in a nanofiber matrix (e.g., Ge in
Al.sub.2O.sub.3) as controlled by the number, type and
concentration of precursors and/or nanoparticles included in the
initial solutions and the thermal treatment procedure used. In some
instances, the use of a matrix increases cycle capability by
optimizing the concentration of high-capacity material to increase
capacity and decrease the impingement of multiple crystals on each
other during the volume expansion associated with intercalation or
alloying the high-capacity material with lithium. In some
embodiments, porosity in the nanofibers is controlled by the
removal of a polymer domain during thermal treatment, as
demonstrated in FIGS. 10-12 for mesoporous Si nanofibers, e.g., for
anode applications and FIGS. 30, 31, 33, 34, 36, 38, 39, 42-46 for
lithium containing nanofibers, e.g., for cathode application. In
some instances, this allows for greater surface area to volume
ratio and/or greater electrolyte contact increasing ion transfer,
while accommodating volume expansion during lithiation and
de-lithiation processes. In some instances, nanofiber electrical
conductivity is controlled by precursor selection for the substrate
as well as the core. Increased electrical conductivity allows for
greater electrical transfer and thus increased power density in
some embodiments. In some instances, core structures increase
mechanical stability and/or allow high capacity over many
charge/discharge cycles. In some embodiments, electrospun polymer
nanofibers (PVA, PAN, PEO, PVP, etc.) are used as the temperature
sensitive separator between the anode and cathode allowing for
electrolyte and ion transfer while limiting transfer at higher
temperatures when temperature overcomes polymer melting temperature
and results in nanofiber morphology collapsing.
[0356] In other embodiments, provided herein are systems comprising
any lithium ion battery described herein. In some instances, such
systems include a battery described herein with a device or system
operated and/or powered by a battery. In some instances, such a
device is an electric vehicle. In some instances, an electric
vehicle comprising a battery described herein is capable of
travelling at least 300 miles, at least 400 miles, at least 500
miles, or more on a single charge (or without needing to recharge
the battery).
Certain Definitions
[0357] The articles "a", "an" and "the" are non-limiting. For
example, "the method" includes the broadest definition of the
meaning of the phrase, which can be more than one method.
[0358] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only.
[0359] Numerous variations, changes, and substitutions will now
occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
[0360] The term "alkyl" as used herein, alone or in combination,
refers to an optionally substituted straight-chain, or optionally
substituted branched-chain saturated or unsaturated hydrocarbon
radical. Examples include, but are not limited to methyl, ethyl,
n-propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl,
2-methyl-1-butyl, 3-methyl- 1-butyl, 2-methyl-3-butyl,
2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,
4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,
4-methyl-2-pentyl, 2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl,
2-ethyl-1-butyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl,
isopentyl, neopentyl, tert-amyl and hexyl, and longer alkyl groups,
such as heptyl, octyl and the like.
[0361] Whenever it appears herein, a numerical range such as
"C.sub.1-C.sub.6 alkyl," means that: in some embodiments, the alkyl
group consists of 1 carbon atom; in some embodiments, 2 carbon
atoms; in some embodiments, 3 carbon atoms; in some embodiments, 4
carbon atoms; in some embodiments, 5 carbon atoms; in some
embodiments, 6 carbon atoms. The present definition also covers the
occurrence of the term "alkyl" where no numerical range is
designated. In certain instances, "alkyl" groups described herein
include linear and branched alkyl groups, saturated and unsaturated
alkyl groups, and cyclic and acyclic alkyl groups.
[0362] The term "aryl" as used herein, alone or in combination,
refers to an optionally substituted aromatic hydrocarbon radical of
six to about twenty ring carbon atoms, and includes fused and
non-fused aryl rings. A fused aryl ring radical contains from two
to four fused rings, where the ring of attachment is an aryl ring,
and the other individual rings are alicyclic, heterocyclic,
aromatic, heteroaromatic or any combination thereof. Further, the
term aryl includes fused and non-fused rings containing from six to
about twelve ring carbon atoms, as well as those containing from
six to about ten ring carbon atoms. A non-limiting example of a
single ring aryl group includes phenyl; a fused ring aryl group
includes naphthyl, phenanthrenyl, anthracenyl, azulenyl; and a
non-fused bi-aryl group includes biphenyl.
[0363] The term "heteroaryl" as used herein, alone or in
combination, refers to optionally substituted aromatic monoradicals
containing from about five to about twenty skeletal ring atoms,
where one or more of the ring atoms is a heteroatom independently
selected from among oxygen, nitrogen, sulfur, phosphorous, silicon,
selenium and tin but not limited to these atoms and with the
proviso that the ring of the group does not contain two adjacent O
or S atoms. Where two or more heteroatoms are present in the ring,
in some embodiments, the two or more heteroatoms are the same as
each another; in some embodiments, some or all of the two or more
heteroatoms are be different from the others. The term heteroaryl
includes optionally substituted fused and non-fused heteroaryl
radicals having at least one heteroatom. The term heteroaryl also
includes fused and non-fused heteroaryls having from five to about
twelve skeletal ring atoms, as well as those having from five to
about ten skeletal ring atoms. In some embodiments, bonding to a
heteroaryl group is via a carbon atom; in some embodiments, via a
heteroatom. Thus, as a non-limiting example, an imidiazole group is
attached to a parent molecule via any of its carbon atoms
(imidazol-2-yl, imidazol-4-yl or imidazol-5-yl), or its nitrogen
atoms (imidazol-1-yl or imidazol-3-yl). Further, in some
embodiments, a heteroaryl group is substituted via any or all of
its carbon atoms, and/or any or all of its heteroatoms. A fused
heteroaryl radical contains from two to four fused rings, where the
ring of attachment is a heteroaromatic ring. In some embodiments,
the other individual rings are alicyclic, heterocyclic, aromatic,
heteroaromatic or any combination thereof. A non-limiting example
of a single ring heteroaryl group includes pyridyl; fused ring
heteroaryl groups include benzimidazolyl, quinolinyl, acridinyl;
and a non-fused bi-heteroaryl group includes bipyridinyl. Further
examples of heteroaryls include, without limitation, furanyl,
thienyl, oxazolyl, acridinyl, phenazinyl, benzimidazolyl,
benzofuranyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl,
benzothiophenyl, benzoxadiazolyl, benzotriazolyl, imidazolyl,
indolyl, isoxazolyl, isoquinolinyl, indolizinyl, isothiazolyl,
isoindolyloxadiazolyl, indazolyl, pyridyl, pyridazyl, pyrimidyl,
pyrazinyl, pyrrolyl, pyrazinyl, pyrazolyl, purinyl, phthalazinyl,
pteridinyl, quinolinyl, quinazolinyl, quinoxalinyl, triazolyl,
tetrazolyl, thiazolyl, triazinyl, thiadiazolyl and the like, and
their oxides, such as for example pyridyl-N-oxide.
[0364] The term "heteroalkyl" as used herein refers to optionally
substituted alkyl structure, as described above, in which one or
more of the skeletal chain carbon atoms (and any associated
hydrogen atoms, as appropriate) are each independently replaced
with a heteroatom (i.e. an atom other than carbon, such as though
not limited to oxygen, nitrogen, sulfur, silicon, phosphorous, tin
or combinations thereof), or heteroatomic group such as though not
limited to --O--O--, --S--S--, --O--S--, --S--O--, .dbd.N--N.dbd.,
--N.dbd.N--, --N.dbd.N--NH--, --P(O)2-, --O--P(O)2-, --P(O)2-O--,
--S(O)--, --S(O)2-, --SnH2- and the like.
[0365] The term "heterocyclyl" as used herein, alone or in
combination, refers collectively to heteroalicyclyl groups. Herein,
whenever the number of carbon atoms in a heterocycle is indicated
(e.g., C1-C6 heterocycle), at least one non-carbon atom (the
heteroatom) must be present in the ring. Designations such as
"C1-C6 heterocycle" refer only to the number of carbon atoms in the
ring and do not refer to the total number of atoms in the ring.
Designations such as "4-6 membered heterocycle" refer to the total
number of atoms that are contained in the ring (i.e., a four, five,
or six membered ring, in which at least one atom is a carbon atom,
at least one atom is a heteroatom and the remaining two to four
atoms are either carbon atoms or heteroatoms). For heterocycles
having two or more heteroatoms, in some embodiments, those two or
more heteroatoms are the same; in some embodiments, they are
different from one another. In some embodiments, heterocycles are
substituted. Non-aromatic heterocyclic groups include groups having
only three atoms in the ring, while aromatic heterocyclic groups
must have at least five atoms in the ring. In some embodiments,
bonding (i.e. attachment to a parent molecule or further
substitution) to a heterocycle is via a heteroatom; in some
embodiments, via a carbon atom.
EXAMPLES
Example 1
Tin Oxide Matrix
[0366] A first composition is prepared by combining 0.5 g PVA (79
kDa, 88% hydrolyzed) with 4.5 g water. The first composition is
heated to 95 C for at least 8 hours. A second composition is
prepared by combining 1 g water, 0.5 g acetic acid, 3 drops x-100
surfactant, tin acetate. The second composition is mixed for at
least 4 hours. The first and second compositions are combined and
mixed for at least 2 hours to form a fluid stock.
[0367] The fluid stock is electrospun in a coaxial gas assisted
manner, using a flow rate of 0.005 to 0.02 mL/min, a voltage of
10-20 kV and a tip to collector distance of 10-20 cm.
Electrospinning of the fluid stock prepares an as-spun precursor
nanofiber, which is subsequently thermally treated at a temperature
of 500 C-1000 C in air.
[0368] FIG. 1 illustrates an SEM image of a nanofiber comprising a
continuous matrix of (crystalline) SnO.sub.2 (panel A).
Example 2
Germanium Matrix
[0369] A fluid stock is prepared according to Example 1, using
germanium acetate in place of tin acetate. Electrospinning and
thermal treatment are as set forth in Example 1, with the exception
that thermal treatment occurs under inert or reducing conditions.
FIG. 1 illustrates an SEM image of a nanofiber comprising a
continuous matrix of Ge (panel B).
Example 3
Silicon Matrix
[0370] A fluid stock is prepared according to Example 1, using
germanium acetate in place of tin acetate. Electrospinning and
thermal treatment are as set forth in Example 1. The resultant
nanofibers comprise a continuous matrix of silica, which are
treated with Mg (sacrificial oxidizing agent) under vacuum,
followed by treatment with HCl (to remove Mg oxide). FIG. 10
illustrates SEM (a-b) and TEM (c-e) images of the nanofibers
including images of (a) the as-spun fiber, (b) fiber heated in air,
(c) fiber heated in air, (d) fiber heated under vacuum with Mg, and
(e) HCl treated fiber. FIG. 11 illustrates the schematic of the
synthetic process. FIG. 12 illustrates X-Ray Diffraction of the
nanofibers at various stages of the synthetic process. Table 1
demonstrates the specific capacities of the pre- and post-HCl
treated fibers.
TABLE-US-00001 TABLE 1 Si/MgO Si/MgO Pure Si Pure Si @400 mA/g
@1000 mA/g @400 mA/g @1000 mA/g (mAh/g) (mAh/g) (mAh/g) (mAh/g) 1
995.9 826.1 4352.2 3529.4 2 711.7 605.9 3156.3 2515.7 3 588.3 491.1
2398.9 1882.6 4 491.5 238.0 1901.5 1492.0 5 409.3 178.2 1550.4
1232.3 6 325.0 145.0 1305.9 1030.6 7 268.0 134.1 1104.8 885.7 8
222.4 130.7 953.0 773.1 9 193.7 128.6 818.9 681.7 10 179.3 127.5
702.6 609.4 11 171.3 127.3 614.1 549.1 12 166.1 127.0 540.7 488.6
13 162.6 127.0 486.7 429.1 14 159.1 127.3 441.5 394.6 15 156.5
127.5 411.5 362.0 16 155.2 127.3 390.7 343.7 17 153.3 128.0 369.6
324.6 18 152.2 128.0 355.2 310.6 19 150.9 128.0 343.7 294.9 20
150.4 128.0 333.7 286.3 21 150.0 128.0 323.7 276.9 22 149.1 128.2
315.6 271.7 23 148.7 128.0 308.1 266.3 24 147.8 127.5 301.1 259.4
25 147.2 127.5 294.8 254.3 26 146.3 127.3 290.0 247.4 27 146.1
126.8 284.1 244.0 28 145.4 127.0 280.0 237.1 29 144.6 126.8 275.6
231.1 30 142.6 126.6 271.1 226.3
Example 4
Tin in Tin Matrix
[0371] A fluid stock is prepared according to Example 1, also
including tin nanoparticles in the second composition.
Electrospinning and thermal treatment are as set forth in Example
1, with the exception that thermal treatment occurs under inert or
reducing conditions, followed by thermal treating in air (to remove
carbon). FIG. 2 illustrates an SEM image of a nanofiber comprising
(crystalline) Sn in a continuous matrix of (amorphous) Sn (panel
A).
Example 5
Tin in Carbon Matrix
[0372] A fluid stock is prepared according to Example 4, excluding
the tin acetate in the second composition. Electrospinning and
thermal treatment are as set forth in Example 1, with the exception
that thermal treatment occurs under inert or reducing conditions.
FIG. 2 illustrates an SEM image of a nanofiber comprising
(crystalline) Sn in a continuous matrix carbon (panel B).
Example 6
Tin in Alumina Matrix
[0373] A fluid stock is prepared according to Example 1, including
tin nanoparticles and aluminum acetate (instead of tin acetate) in
the second composition. Electrospinning and thermal treatment are
as set forth in Example 1. FIG. 2 illustrates an SEM image of a
nanofiber comprising (crystalline) Sn in a continuous matrix of
alumina (Al.sub.2O.sub.3) (panel C).
Example 7
Tin in Zirconia Matrix
[0374] A fluid stock is prepared according to Example 1, including
tin nanoparticles and zirconium acetate (instead of tin acetate) in
the second composition. Electrospinning and thermal treatment are
as set forth in Example 1. FIG. 2 illustrates an SEM image of a
nanofiber comprising (crystalline) Sn in a continuous matrix of
zirconia (ZrO.sub.2) (panel D).
Example 8
Germanium in Carbon Matrix
[0375] A fluid stock is prepared according to Example 1, including
polyacrylonitrile (PAN) in dimethylformamide (DMF) instead of
PVA/water in the first composition and germanium nanoparticles and
DMF (instead of tin acetate/water) in the second composition.
Electrospinning and thermal treatment are as set forth in Example
1, with the exception that it is performed under inert or reducing
conditions. FIG. 3 illustrates an SEM image of a nanofiber
comprising (crystalline) Ge in a continuous matrix of carbon (panel
A).
Example 8
Germanium in Alumina Matrix
[0376] A fluid stock is prepared according to Example 1, including
germanium nanoparticles and aluminum acetate (instead of tin
acetate) in the second composition. Electrospinning and thermal
treatment are as set forth in Example 1. FIG. 3 illustrates an SEM
image of a nanofiber comprising (crystalline) Ge in a continuous
matrix alumina (Al.sub.2O.sub.3) (panel B).
Example 8
Germanium in Alumina Matrix
[0377] A fluid stock is prepared according to Example 1, including
germanium nanoparticles and zirconium acetate (instead of tin
acetate) in the second composition. Electrospinning and thermal
treatment are as set forth in Example 1. FIG. 3 illustrates an SEM
image of a nanofiber comprising (crystalline) Ge in a continuous
matrix of zirconia (ZrO.sub.2) (panel C).
Example 9
Half Cell Performance of Ge-- and Sn-Containing Nanofibers
[0378] Anode half-cell tests with nanofibers with discrete Ge and
Sn crystal domains were performed. FIG. 13 shows energy capacity
over many cycles. As seen in FIG. 13, alumina or carbon nanofibers
with discrete Sn or Ge crystal domains maintain 40% to 80% of
theoretical capacity after 100 cycles, resulting in 800-1100 mAh/g
of energy capacity, which is two to three times greater than
current carbon with theoretical capacity of 372 mAh/g. This
demonstrates the use of the substrate structure with discrete high
energy capacity crystal domains can drastically reduce
pulverization issues.
Example 10
Preparing a Fluid Stock of Silicon Nanoparticles and PVA
[0379] 0.5 grams of preformed silicon nanoparticles (100 nm average
diameter), the silicon component, is suspended in 20 ml of 1 molar
acetic acid solution with X-100 surfactant. The solution is stirred
for 2 hours to create a suspension of silicon nanoparticles.
[0380] In a second solution, 1 gram of hydrolyzed (e.g., 88% or
99.7%) polyvinyl alcohol (PVA) with an average molecular weight of
79 kDa and polydispersity index of 1.5 is dissolved in 10 ml of
de-ionized water. The polymer solution is heated to a temperature
of 95.degree. C. and stirred for 2 hours to create a homogenous
solution.
[0381] The silicon nanoparticle suspension is then combined with
the PVA solution to create a fluid stock. In order to distribute
the nanoparticles substantially evenly in the fluid stock, the
nanoparticle suspension is added gradually to the polymer solution
while being continuously vigorously stirred for 2 hours. The mass
ratio of nanoparticles to polymer for the fluid feed (based on
silicon nanoparticle mass) is 1:4.
Example 11
Preparing Silicon/Polymer and Silicon/Carbon Nanocomposite
Nanofiber
[0382] The fluid stock is co-axially electrospun with gas using a
coaxial needle apparatus similar to the one depicted in FIG. 14 and
FIG. 15 (where 1006 illustrates the needle). The center conduit
contains silicon suspension fluid stock of Example 10 and the outer
conduit contains air. The electrospun hybrid fluid stock is
calcinated by heating for 2 hours at 600.degree. C. in an inert
atmosphere (e.g., argon).
[0383] FIG. 4 illustrates silicon/polymer and silicon/carbon
nanocomposite nanofibers prepared according to a method such as set
for above. Panel A illustrates an SEM image of the as-spun
polymer/Si nanoparticle nanocomposite nanofibers. Panel B
illustrates an SEM image of the heat treated carbon/Si nanoparticle
nanocomposite nanofibers. Panel C illustrates a TEM image of the
heat-treated carbon/Si nanoparticle nanocomposite nanofibers.
Example 12
Silicon Nanocomposite Nanofibers--Thermal Treatment
[0384] Fluid stock: 0.5 g PVA (88% hydrolyzed, 78 kDa) was combined
with 4.5 g water and heated at 95 C for at least 8 hours. Silicon
nanoparticles (purchased from Silicon and Amorphous Materials,
Inc., 20-30 nm (actual average size about 50 nm)) added to the
polymer solution and sonicated at room temperature for 4 hours.
Heated and mixed at 50 C for 4 hours. Silicon nanoparticles are
added in ratios of polymer:Si of 2:1.
[0385] Nanofibers: the fluid stock is gas-assisted electrospun from
a needle apparatus having an inner needle and an outer needle
coaxially aligned, the inner needle providing the fluid stock, the
outer needle providing the gas. The fluid stock is provided at a
flow rate of 0.01 mL/min; the voltage used is 20 kV, the needle
apparatus tip to collector distance is 15 cm.
[0386] The electrospun nanofiber is a polymer-Si (nanoparticle)
nanocomposite nanofiber illustrated in FIG. 16 (Panel A). The
nanofibers are then treated with heat under Argon: at 500.degree.
C., 700.degree. C., 900.degree. C., and 1200.degree. C. (heat and
cool rate of 2.degree. C./minute). FIG. 16 (panel B) illustrates an
SEM image of a silicon/carbon nanocomposite nanofiber prepared by
treatment at 900.degree. C.; FIG. 16 (panel C) illustrates an SEM
image of a silicon/carbon nanocomposite nanofiber prepared by
treatment at 1200.degree. C. FIG. 17 illustrates normalized XRD
peaks for the nanocomposite nanofibers prepared at 500, 700, and
900.degree. C. FIG. 18 illustrates SEM images for silicon/carbon
nanocomposite nanofibers prepared by treatment at 500.degree. C.
(panel A), 700.degree. C. (panel B), and 900.degree. C. (panel C).
FIG. 5 illustrates a TEM image for silicon/carbon nanocomposite
nanofibers prepared by treatment at 900.degree. C. FIG. 19
illustrates TGA curves for Super P (Timcal) carbon (a) compared to
silicon/carbon nanocomposite nanofibers prepared by treatment at
900.degree. C. (b) and 1200.degree. C. (c). FIG. 20 illustrates
Raman spectra for Super P (Timcal) carbon (a) compared to
silicon/carbon nanocomposite nanofibers prepared by treatment at
900.degree. C. (b) and 1200.degree. C. (c). XRD done using Scintag
2-theta diffractometer; SEM with Leica 440 SEM; TEM with FEI Spirit
TEM.
Example 13
Silicon Nanocomposite Nanofibers--Polymer Loading
[0387] Fluid stock: 0.5 g PVA (88% hydrolyzed, 78 kDa) was combined
with 4.5 g water and heated at 95 C for at least 8 hours. Silicon
nanoparticles (purchased from Silicon and Amorphous Materials,
Inc., 20-30 nm (actual average size about 50 nm)) added to the
polymer solution and sonicated at room temperature for 4 hours.
Heated and mixed at 50 C for 4 hours. Silicon nanoparticles are
added in ratios of polymer:Si of 20:1, 4:1, 2:1, and 1:1.
[0388] Nanofibers: the fluid stock is gas-assisted electrospun from
a needle apparatus having an inner needle and an outer needle
coaxially aligned, the inner needle providing the fluid stock, the
outer needle providing the gas. The fluid stock is provided at a
flow rate of 0.01 mL/min; the voltage used is 20 kV, the needle
apparatus tip to collector distance is 15 cm.
[0389] The electrospun nanofiber is a polymer-Si (nanoparticle)
nanocomposite nanofiber illustrated in FIG. 21 (panel A for 20:1;
panel B for 2:1; panel C for 1:1). The nanofibers are then treated
with heat under Argon: at 900.degree. C. (heat and cool rate of
2.degree. C./minute). FIG. 21 also illustrates an SEM image of a
silicon/carbon nanocomposite nanofibers prepared by such thermal
treatment (panels D for 20:1, panel E for 2:1, panel F for 1:1).
Table 2 demonstrates components of the produced nanocomposite
nanofibers (as determined by TGA; calculation based on assumption
of no Si nanoparticle loss):
TABLE-US-00002 TABLE 2 Polymer/Si NC NF Si/C NC NF PVA Si Carbon Si
PVA/Si (1:1) 50% 50% 1.3% 98.7% PVA/Si (2:1) 67% 33% 14.9% 85.1%
PVA/Si (4:1) 80% 20% 19.3% 80.7% PVA/Si (20:1) 95% 5% 50.1%* 49.9%*
*Nanofiber morphology not observed.
Example 14
Si/C Nanocomposite Nanofibers as Negative Electrode in Lithium Ion
Battery
[0390] Coin cell-typed Li-ion batteries were fabricated by using
various Si--C nanofibers. The C-SiNPs nanofibers were blended with
Super P (Timcal) and poly(acrylic acid) (PAA, Mw=3,000,000) for
70:15:15 wt % in 1-Methyl-2-pyrrolidinone (NMP, Aldrich) in order
to make a homogeneous slurry without breaking the 1-D
nanostructures. After the slurries were dropped on a current
collector with 9 .mu.m thickness (Cu foil, MTI), the working
electrodes using C-SiNPs nanofibers were dried in the vacuum oven
at 80.degree. C. to remove the NMP solvent.
[0391] For fabricating the half cells, Li metal was used as a
counter electrode and polyethylene (ca. 25 .mu.m thickness) was
inserted as a seperator between working electrode and counter
electrode. The mass of working electrode was 3-4 mg/cm.sup.2. The
coin cell-typed Li-ion batteries were assembled in Ar-filled glove
box with electrolyte.
[0392] The cut off voltage during the galvanostatic tests was
0.01-2.0 V for anode and 2.5-4.2 V by using battery
charge/discharge cyclers from MTI. Full cells are prepared in a
similar manner, and are composed of C--Si nanofibers as anode and
stock-LiCoO.sub.2 as cathode. The cut off voltage during the
galvanostatic tests was 2.5-4.5 V. The impedance measurements for
all battery cells were performed from 1 Hz to 10 kHz frequency
under potentiostatic mode at open circuit voltages of the
cells.
[0393] The electrochemical properties of Si--C nanofibers were
characterized by cyclic voltammetry and electrochemical impedance
spectroscopy. FIG. 8 (panel A) illustrates cyclic voltammograms of
Si nanoparticles and Si--C nanofibers (prepared according to
Example 13 using a polymer-to-Si nanoparticle ratio of 2:1).
Delithiation is observed at 0.3 V (vs. Li/Li.sup.+) and lithiation
is observed at 0.15 V (vs. Li/Li.sup.+). Charge transport
resistance of C--Si nanofibers in the Nyquist plots of FIG. 8
(panel B) obtained from AC impedance, is greatly reduced to about
60 12, compared with that of Si nanoparticles (about 220 12).
Furthermore, the solution (polarization) resistance in C--Si
nanofibers is decrease by 4.112 from 7.412 of pure silicon
nanoparticles.
[0394] The cells were cycled for 25 cycles as shown in FIG. 6 and
FIG. 7. FIG. 6 (panel A) illustrates that Nancomposite Si--C
nanofibers show an initial discharge capacity of 1,844 mAh/g, while
SiNPs has an initial discharge capacity of 3,325 mAh/g. The
discharge capacity of SiNPs is dramatically decreased to 50 mAh/g
after 25 cycles. Si--C nanocomposite nanofibers have a discharge
capacity of 1,452 mAh/g after 25 cycles. FIG. 6 (panel B)
illustrate that the coulombic efficiencies of Si--C nanocomposite
nanofibers are maintained over 90% during 25 cycles. FIG. 7
illustrates that Si--C nanocomposite nanofibers have outstanding
cyclabilities from 0.1 to 1 C. Conversely, SiNPs have very low
capacities (e.g., about 50 mAh/g at 0.5 C, 0.8 C, and 1 C). The
discharge capacities of the prepared Si--C nanocomposite nanofibers
are 1,150 mAh/g at 0.5 C and 1,000 mAh/g at 0.8 C.
[0395] Table 3 illustrates cycling performance (at 0.1 C) of
various Si/C nanocomposite nanofibers prepared according to the
Examples.
TABLE-US-00003 TABLE 3 Carbon content Specific capacity (mAh/g)
(from 1st 10.sup.th TGA) Cycle Cycle 20.sup.th 50.sup.th 98.sup.th
Si NP 0% 3,310 509 131 22 13 PVA/Si 3% 2,548 1,446 1,161 908 463
(1:1) PVA/Si 8% 2,091 1,851 1,607 1,011 286 (2:1) PVA/Si 14% 1,845
1,688 1,540 1,074 411 (4:1)
Example 15
Si/C Nanocomposite Nanofibers without Gas Assistance
[0396] Using a procedure similar to that set forth in Examples 10
and 11, nanocomposite nanofibers comprising silicon nanofibers were
prepared without gas assistance. FIG. 22 (panels A and B)
illustrate TEM images of the resultant Si/polymer (PVA)
nanocomposite nanofibers.
Example 16
Si/C Nanocomposite Nanofibers from PAN/DMF Stock
[0397] Fluid stock: is prepared similar to as set forth in Example
10 and Example 12, using polyacrylonitrile (PAN) as the polymer and
dimethylformamide (DMF) as the solvent. Polyacrylonitrile (PAN) is
combined with DMF. Silicon nanoparticles are added to the polymer
solution, mixed and heated.
[0398] Nanofibers: the fluid stock is gas-assisted electrospun from
a needle apparatus having an inner needle and an outer needle
coaxially aligned, the inner needle providing the fluid stock, the
outer needle providing the gas. The fluid stock is provided at a
flow rate of 0.01 mL/min; the voltage used is 20 kV, the needle
apparatus tip to collector distance is 15 cm.
Example 17
Si/C Nanocomposite Nanofibers without as Assistance
[0399] Using a procedure similar to that set forth in Example 16,
nanocomposite nanofibers comprising silicon nanofibers were
prepared without gas assistance. FIG. 22 (panels C and D)
illustrate TEM images of the resultant Si/polymer (PAN)
nanocomposite nanofibers.
[0400] Using a procedure similar to that set forth in Examples 10,
12, and 16, PAN/Si and PVA/Si polymer/Si nanocomposite nanofibers
are prepared without gas assistance. The Si nanoparticles utilized
in the fluid stock have an average diameter of about 100 nm.
Thermal treating to carbonize the polymer is performed at 500 C.
Table 4 illustrates the charge capacities of the resultant
nanofibers (as lithium ion half cell anodes) at 400 mA/g.
TABLE-US-00004 TABLE 4 From From PAN/Si PVA/Si Cycle (mAh/g)
(mAh/g) 1 382.1 49.2 2 117.9 40.8 3 89.3 38.3 4 78.6 36.7 5 75.0
35.8 6 71.4 34.2 7 71.4 33.3 8 67.9 33.3 9 67.9 32.5 10 67.9 31.7
11 64.3 31.7 12 64.3 30.8 13 64.3 30.0 14 64.3 30.0 15 64.3 29.2 16
64.3 29.2 17 60.7 28.3 18 60.7 28.3 19 60.7 28.3 20 60.7 27.5
Example 18
Hollow Si/C Nanocomposite Nanofibers
[0401] Fluid stock: is prepared similar to as set forth in Example
10, Example 12, and Example 16 using polyacrylonitrile (PAN) as the
polymer and dimethylformamide (DMF) as the solvent.
Polyacrylonitrile (PAN) is combined with DMF. Silicon nanoparticles
are added to the polymer solution, mixed and heated.
[0402] Nanofibers: the fluid stock is gas-assisted electrospun from
a needle apparatus having an inner needle and an outer needle
coaxially aligned, the inner needle providing air, the outer needle
providing the fluid stock. Additional gas assistance surrounding
the fluid needle is optionally utilized. The gas and fluid stock is
provided at a flow rate of 0.008 mL/min to 0.017 mL/min; the
voltage used is 10-15 kV, the needle apparatus tip to collector
distance is 10-15 cm.
[0403] FIG. 24 illustrates as spun nanofibers using a polymer:Si
nanoparticle ratio of 5:1, and Si nanoparticles having an average
diameter of about 100 nm. The as-spun nanofibers are calcined under
argon, producing carbon-silicon nanocomposite nanofibers having a
carbon:silicon ratio of 1.9:1. Panel A illustrates SEM images of
as-spun nanofibers; panel B illustrates SEM images of calcined
nanofibers.
[0404] FIG. 25 illustrates as spun nanofibers using a polymer:Si
nanoparticle ratio of 3.2:1, and Si nanoparticles having an average
diameter of about 100 nm. The as-spun nanofibers are calcined under
argon, producing carbon-silicon nanocomposite nanofibers having a
carbon:silicon ratio of 1.2:1. Panel A illustrates SEM images of
as-spun nanofibers; panel B illustrates SEM images of calcined
nanofibers.
[0405] FIG. 26 illustrates as spun nanofibers using a polymer:Si
nanoparticle ratio of 1.84:1, and Si nanoparticles having an
average diameter of about 100 nm. The as-spun nanofibers are
calcined under argon, producing carbon-silicon nanocomposite
nanofibers having a carbon:silicon ratio of 0.7:1. Panel A
illustrates SEM images of as-spun nanofibers; panel B illustrates
SEM images of calcined nanofibers.
[0406] FIG. 27 illustrates a TEM image of microtomed hollow Si/C
nanocomposite nanofibers described herein (from Si nanoparticles
having an average diameter of 100 nm).
[0407] FIG. 28 illustrates as spun nanofibers using Si
nanoparticles having an average diameter of about 50 nm. The
as-spun nanofibers are calcined under argon, producing
carbon-silicon nanocomposite nanofibers having a carbon:silicon
ratio of 1:1. Panel A illustrates SEM images of as-spun nanofibers;
panel B illustrates SEM images of calcined nanofibers.
[0408] FIG. 29 illustrates TEM images of microtomed hollow Si/C
nanocomposite nanofibers described herein (from Si nanoparticles
having an average diameter of 50 nm).
[0409] Hollow nanofibers prepared using Si nanoparticles with an
average diameter of 50 nm are described in Table 5 (32 wt % Si in
carbon matrix):
TABLE-US-00005 TABLE 5 All Materials Silicon Discharge Charge
Discharge Charge Cycles (mAh/g) (mAh/g) (mAh/g) (mAh/g) 1 1381.4
1062.3 4256.4 3273.3 2 1086.8 1045.0 3348.7 3220.1 3 1104.8 1070.8
3404.1 3299.4 4 1092.0 1063.4 3364.9 3276.7 5 1081.6 1059.6 3332.6
3265.0 6 1082.2 1060.3 3334.5 3267.1 7 1097.8 1075.6 3382.5 3314.4
8 1079.1 1056.7 3324.9 3256.1 9 1175.3 1146.1 3621.5 3531.6 10
1360.0 1318.3 4190.7 4062.1 11 1349.7 1315.4 4148.7 4053.0 12
1316.5 1291.8 4056.6 3980.5 13 1317.9 1289.9 4060.8 3974.7 14
1303.9 1271.7 4017.6 3918.6 15 1295.6 1261.1 3992.2 3885.8 16
1276.9 1246.5 3934.6 3841.0
[0410] Hollow nanofibers prepared using Si nanoparticles with an
average diameter of 100 nm are described in Table 6 (50 wt % Si in
carbon matrix):
TABLE-US-00006 TABLE 6 All materials Silicon DChg Chg DChg Chg
Cycles (mAh/g) (mAh/g) (mA/gh) (mAh/g) 1 1171.5 878.1 2332.7 1748.6
2 977.4 928.6 1946.1 1849.0 3 982.9 944.3 1957.2 1880.3 4 989.4
958.9 1970.1 1909.4 5 992.1 963.0 1975.4 1917.6 6 997.0 968.9
1985.3 1929.2 7 993.0 973.6 1977.4 1938.7 8 996.2 977.0 1983.6
1945.4 9 996.4 971.1 1984.1 1933.8 10 994.1 973.5 1979.5 1938.5 11
988.2 967.4 1967.7 1926.4 12 984.1 964.0 1959.6 1919.5 13 975.2
954.9 1941.9 1901.4 14 969.1 947.9 1929.6 1887.5 15 967.6 946.0
1926.7 1883.7 16 958.9 934.7 1909.4 1861.2 17 958.2 932.0 1908.0
1855.9 18 954.3 926.7 1900.2 1845.3 19 947.4 920.7 1886.6 1833.3 20
945.1 924.8 1881.9 1841.4 21 931.7 906.7 1855.2 1805.4 22 926.9
902.0 1845.6 1796.1 23 922.6 897.3 1837.1 1786.7 24 911.4 882.4
1814.7 1757.1 25 901.0 875.3 1794.0 1742.9 26 891.6 865.1 1775.4
1722.5 27 879.7 850.9 1751.7 1694.3 28 870.2 842.2 1732.7 1677.1 29
856.4 829.9 1705.4 1652.5 30 849.1 821.7 1690.8 1636.2 31 837.1
805.8 1666.9 1604.6 32 827.8 798.8 1648.2 1590.6
Example 19
Nanofiber Having a Continuous Core Matrix of a Lithium (Metal
Oxide)-Containing-Material
[0411] A first composition is prepared by combining 0.5 g PVA (79
kDa, 88% hydrolyzed) with 4.5 g water. The first composition is
heated to 95 C for at least 8 hours. A second composition is
prepared by combining 1 g water, 0.5 g acetic acid, 3 drops x-100
surfactant, lithium acetate (hydrate) and one or more metal
precursor (e.g., cobalt acetate (hydrate), manganese acetate
(hydrate), nickel acetate (hydrate)). The second composition is
mixed for at least 4 hours. The first and second compositions are
combined and mixed for at least 2 hours to form a fluid stock.
[0412] The fluid stock is electrospun in a coaxial gas assisted
manner, using a flow rate of 0.01 mL/min, a voltage of 20 kV and a
tip to collector distance of 15 cm. The fluid stock is also
electrospun without coaxial gas assistance, using a flow rate of
0.005 mL/min, a voltage of 20 kV and a tip to collector distance of
18 cm. Electrospinning of the fluid stock prepares an as-spun
precursor nanofiber, which is subsequently thermally treated.
[0413] A one step thermal treatment procedure involves treating the
as-spun nanofibers in air at about 700 C (with a heat/cool rate of
2 C/min) for 5 hours. A two step thermal treatment procedure
involves a first thermal treatment under argon at about 700 C (with
a heat/cool rate of 2 C/min) for 5 hours, and a second thermal
treatment under air at about 500 C (with a heat/cool rate of 2
C/min).
Example 20
LiCoO Nanofibers
[0414] Using a gas assisted procedure of Example 19, wherein cobalt
acetate is utilized as the metal precursor, lithium cobalt oxide
nanofibers are prepared. Nanofibers are prepared using 1:1, 1:1.5,
and 1:2 molar ratios of cobalt acetate-to-lithium acetate.
[0415] FIG. 30 illustrates an SEM image of such nanofibers (panel
A). FIG. 30 (panel B) also illustrates SEM images such nanofibers
prepared using 1:1, 1:1.5, and 1:2 molar ratios of cobalt
acetate-to-lithium acetate (ratios in the figure are inverted).
FIG. 31 (panel A) illustrates the XRD pattern for the lithium
cobalt oxide nanofibers and illustrates the XRD pattern (panel B)
for nanofibers prepared using 1:1, 1:1.5, and 1:2 molar ratios of
cobalt acetate-to-lithium acetate (ratios in the figure are
inverted). FIG. 32 illustrates the charge/discharge capacities for
lithium cobalt oxide prepared using a one step thermal process
(panel A) and a two step thermal process (panel B). The lithium
cobalt oxide nanofibers produced is observed to have an initial
capacity of about 120 mAh/g at 0.1 C.
[0416] Table 7 illustrates charge capacities determined using the
various lithium-metal ratios and the one and two step thermal
treatment processes.
TABLE-US-00007 TABLE 7 Li:Co Charge capacity (ratio for stock)
Thermal Treatment (mAh/g) 1:1 700 C./air N/A 1.5:1 700 C./air 67
2:1 700 C./air 89 2:1 1. 700 C./Ar 50 2. 300 C./air 2:1 1. 700
C./Ar 110 2. 700 C./air
Example 21
Li(Ni.sub.xCo.sub.yMn.sub.z)O.sub.2 Nanofibers
[0417] Using a gas assisted procedure of Example 19, wherein nickel
acetate, cobalt acetate, and manganese acetate are utilized as the
metal precursor, Li.sub.a(Ni.sub.xCo.sub.yMn.sub.z)O.sub.2
nanofibers are prepared. Nanofibers are prepared using 1:1, 1:1.5,
and 1:2 molar ratios of the combined nickel/cobalt/manganese
acetate-to-lithium acetate. Various molar ratios of nickel acetate
(x) to cobalt acetate (y) to manganese acetate (z) are
utilized.
[0418] FIG. 33 (panel A) illustrates an SEM image of as-spun
nanofibers prepared using a 1:1:1 ratio of x:y:z. Panel B
illustrates an SEM image of thermally treated
(Li(Ni.sub.1/3Co.sub.1/3Mn.sub.1/3)O.sub.2) nanofibers (treated at
650 C in air). Panel C illustrates a TEM image of the thermally
treated nanofibers. FIG. 34 illustrates the XRD pattern for the
thermally treated nanofibers. FIG. 35 illustrates the
charge/discharge capacities for 1:1:1 (x:y:z) nanofibers prepared.
The nanofibers produced is observed to have an initial capacity of
about 180 mAh/g at 0.1 C.
[0419] Using similar procedures,
Li[Li.sub.0.2Mn.sub.0.56Ni.sub.0.16Co.sub.0.08]O.sub.2 nanofibers
are also prepared. FIG. 36 illustrates the as-spun and thermally
treated (900 C for 5 hours under argon) nanofibers. FIG. 37
illustrates the charge/discharge capacities for nanofibers
prepared. The nanofibers produced is observed to have an initial
capacity of about 90 mAh/g at 0.1 C.
[0420] Using similar procedures,
Li.sub.0.8Mn.sub.0.4Ni.sub.0.4Co.sub.0.4O.sub.2 nanofibers are
prepared. FIG. 38 (panel A) illustrates as-spun nanofibers and
(panel B) thermally treated (900 C for 5 hours under argon)
nanofibers.
Example 22
LiMn.sub.2O.sub.4 Nanofibers
[0421] Using a gas assisted procedure of Example 19, wherein
manganese acetate is utilized as the metal precursor,
LiMn.sub.2O.sub.4 nanofibers are prepared. Nanofibers are prepared
using 2:1, 3:2 (50% excess lithium acetate), and 1:1 (100% excess
lithium acetate) molar ratios of the manganese acetate-to-lithium
acetate. FIG. 39 (panel A) illustrates an SEM image of as-spun
nanofibers. Panel B illustrates an SEM image of thermally treated
nanofibers (treated at 650 C in air). Panel C illustrates a TEM
image of the thermally treated nanofibers. FIG. 40 illustrates the
XRD pattern for the thermally treated nanofibers. FIG. 41
illustrates the charge/discharge capacity of the nanofibers for
about 40 cycles. The lithium manganese oxide nanofibers produced is
observed to have an initial capacity of about 95 mAh/g at 0.1
C.
Example 23
Li(Ni.sub.xMn.sub.z)O.sub.4 Nanofibers
[0422] Using a gas assisted procedure of Example 19, wherein nickel
acetate and manganese acetate are utilized as the metal precursor,
Li(Ni.sub.xMn.sub.z)O.sub.4 nanofibers are prepared. Nanofibers are
prepared using 2:1, 3:2, and 1:1 molar ratios of the combined
nickel/manganese acetate-to-lithium acetate. Various molar ratios
of nickel acetate (x) to manganese acetate (z) are utilized (e.g.,
1:3 for Li(Ni.sub.0.5Mn.sub.1.5)O.sub.4). FIG. 42 illustrates the
XRD pattern for the thermally treated nanofibers.
Example 24
Nanofiber having a Continuous Core Matrix of a Lithium (Metal
Phosphate)-Containing-Material
[0423] A first composition is prepared by combining 0.5 g PVA (79
kDa, 88% hydrolyzed) with 4.5 g water. The first composition is
heated to 95 C for at least 8 hours. A second composition is
prepared by combining 1 g water, 0.5 g acetic acid, 3 drops x-100
surfactant, lithium acetate (hydrate), one or more metal precursor
(e.g., iron acetate (hydrate), cobalt acetate (hydrate), manganese
acetate (hydrate), nickel acetate (hydrate)), and a phosphorus
precursor (e.g., triethylphosphite). The second composition is
mixed for at least 4 hours. The first and second compositions are
combined and mixed for at least 2 hours to form a fluid stock.
[0424] The fluid stock is electrospun in a coaxial gas assisted
manner, using a flow rate of 0.01 mL/min, a voltage of 20 kV and a
tip to collector distance of 15 cm. The fluid stock is also
electrospun without coaxial gas assistance, using a flow rate of
0.005 mL/min, a voltage of 20 kV and a tip to collector distance of
18 cm. Electrospinning of the fluid stock prepares an as-spun
precursor nanofiber, which is subsequently thermally treated.
[0425] A one step thermal treatment procedure involves treating the
as-spun nanofibers in air at about 700 C (with a heat/cool rate of
2 C/min) for 5 hours. A two step thermal treatment procedure
involves a first thermal treatment under argon at about 700 C (with
a heat/cool rate of 2 C/min) for 5 hours, and a second thermal
treatment under air at about 500 C (with a heat/cool rate of 2
C/min).
Example 25
LiFePO.sub.4 Nanofibers
[0426] Using a gas assisted procedure of Example 6, wherein iron
acetate is utilized as the metal precursor, lithium iron phosphate
nanofibers are prepared. Nanofibers are prepared using 1:1, 1:1.5,
and 1:2 molar ratios of iron acetate-to-lithium acetate.
[0427] FIG. 43 illustrates an SEM image of the as-spun nanofibers
(panel A) and thermally treated nanofibers (panel B). FIG. 44
illustrates the XRD pattern for the lithium iron phosphate
nanofibers.
Example 26
Nanofiber having a Lithium
(Sulfide/Sulfate)-Containing-Material
[0428] A first composition is prepared by combining 0.5 g PVA (79
kDa, 88% hydrolyzed) with 4.5 g water. The first composition is
heated to 95 C for at least 8 hours. A second composition is
prepared by combining 1 g water, 0.5 g acetic acid, 3 drops x-100
surfactant, lithium acetate (hydrate), and a sulfur precursor
(e.g., elemental sulfur, such as sulfur nanoparticles). The second
composition is mixed for at least 4 hours. The first and second
compositions are combined and mixed for at least 2 hours to form a
fluid stock.
[0429] The fluid stock is electrospun in a coaxial gas assisted
manner, using a flow rate of 0.01 mL/min, a voltage of 20 kV and a
tip to collector distance of 15 cm. The fluid stock is also
electrospun without coaxial gas assistance, using a flow rate of
0.005 mL/min, a voltage of 20 kV and a tip to collector distance of
18 cm. Electrospinning of the fluid stock prepares an as-spun
precursor nanofiber, which is subsequently thermally treated.
[0430] The thermal treatment occurs under argon at about 1000 C
(with a heat/cool rate of 2 C/min) for 5 hours for preparation of
lithium sulfide containing fibers (Li.sub.2S/Carbon
nanocomposites). Subsequent air oxidation provides lithium sulfate
containing fibers (Li.sub.2SO.sub.4/Carbon nanocomposites). FIG. 45
illustrates an SEM image of the as-spun nanofibers (panel A) and
thermally treated nanofibers (panel B). Panel C illustrates a TEM
image of the thermally treated nanofibers. FIG. 46 illustrates the
XRD pattern for the oxidized nanofibers.
[0431] For fabricating the half cells, Li metal is used as a
counter electrode and polyethylene (ca. 25 .mu.m thickness) is
inserted as a separator between working electrode and counter
electrode. The mass of working electrode is 3-4 mg/cm.sup.2. The
coin cell-typed Li-ion batteries are assembled in Ar-filled glove
box with electrolyte. The cut off voltage during the galvanostatic
tests is 0.01-2.0 V for anode and 2.5-4.2 V by using battery
charge/discharge cyclers from MTI.
Example 27
Nanoclay in Polymer Matrix
[0432] A first composition is prepared by combining preformed
nanoclay (e.g., montmorillonite clay, Bentonite Nanomer.RTM. PGV)
or nanoceramic with a solvent. In one example, 0.03 g of clay is
suspended in 1 g DMF. A second composition is prepared by combining
a polymer and a solvent. In one example, 0.63 g polyacrylonitrile
(PAN) (e.g., MW=1,000 to 1,000,000, such as 150,000 g/mol) is
combined with 5 g DMF. The first and second compositions are
combined and mixed (e.g., stirring, sonication, or the like).
[0433] The solution is mixed for 5 hours to create a fluid
stock.
[0434] The fluid stock is electrospun using a flow rate of 0.005 to
0.04 mL/min, a voltage of 10-20 kV and a tip to collector distance
of 10-20 cm. Electrospinning is optionally gas assisted.
Electrospinning of the fluid stock prepares an as-spun
polymer/(nanoclay/nanoceramic) nanocomposite nanofiber.
[0435] FIG. 53 illustrates nanofibers prepared with a PAN:nanoclay
ratio of 91/9, 9.5 wt % pan in DMF. FIG. 54 illustrates nanofibers
prepared without nanoclay (10 wt % PAN in DMF).
Example 28
Nanoclay in Polymer Matrix--Compressed Mats
[0436] Nanocomposite (nanoclay or nanoceramic in polymer matrix)
nanofibers are prepared according to a process of Example 27 in a
non-woven mat and compressed. FIG. 55 illustrates SEM images of
PAN/nanoclay (95.5/4.5 wt %) nanofibers compressed at 1 Mpa for 15
seconds. FIG. 56 illustrates SEM images of PAN/nanoclay (95.5/4.5
wt %) nanofibers compressed at 3 Mpa for 15 seconds. FIG. 57
illustrates SEM images of PAN/nanoclay (95.5/4.5 wt %) nanofibers
compressed at 5 Mpa for 15 seconds. Panel A illustrates an SEM
image of a front view and Panel B illustrates an SEM image of a
back view of the compressed mat.
[0437] The nanofibers are optionally annealed at 150 C for 3 hours,
before or after compression.
[0438] FIG. 47 illustrates the narrow pore size distribution for
various PAN systems. The porosity is illustrated pure PAN,
PAN/nanoclay nanocomposites compressed at 5 MPa, and PAN/nanoclay
nanocomposites annealed and compressed at 5 Mpa. FIG. 48
illustrates the good resistance profile of the nanofibers systems
provided herein. Nyquist plots are illustrated for pure PAN, and
various PAN/nanoclay nanocomposites--fresh state cell test
(constant voltage=VOC(1.7-2.0V)), stock LiCoO.sub.2 electrode (32
mg) and Li metal). FIG. 49 illustrates charge capacity cycle tests
for commercial polyethylene films compared to various PAN/NC
nanofibers mats described herein. The first (top) line illustrates
capacity retention of compressed PAN/NC separators; the second
(from top) line illustrates capacity retention of annealed and
compressed PAN/NC separators; the third (second from bottom) line
illustrates capacity retention of not-compressed, not-annealed
PAN/NC separators; and the four (bottom) illustrates capacity
retention of commercial PE separator. FIG. 50 illustrates nanofiber
stability/solvent analysis by TGA of annealed versus not annealed
PAN/NC nanofibers. Observed range is from room temperature to 200 C
at 2 C/min, under air flow with 20 mL/min. FIG. 51 illustrates C
rate capacity tests for discharge capacity of half cells using 32
mg LiCoO.sub.2 and Li metal. Programmed C rates are 0.63 mA for 5
cycles, 1.02 mA for 5 cycles, 2.30 mA for 5 cycles, and 6.90 mA for
5 cycles, repeat. The voltage sweep is between 2.5 V and 4.0 V. As
seen in FIG. 51, the PAN/NC separators provided herein demonstrate
improved performance over commercial PE separator. Similarly, FIG.
52 illustrates C rate capacity tests for discharge capacity of half
cells--this time using 32.8 mg LiMn.sub.2O.sub.4 and Li metal.
Programmed C rates are 0.46 mA for 5 cycles, 0.92 mA for 5 cycles,
1.38 mA for 5 cycles, 2.3 mA for 5 cycles, and 4.5 mA for 5 cycles.
As seen in FIG. 52, the PAN/NC separators provided herein
demonstrate improved performance over commercial PE separator.
Example 29
Full Cell Testing
[0439] Full cells are prepared using Si/C nanofibers provided
herein as the anode/negative electrode and lithium-containing
nanofibers provided herein as the cathode/positive electrode. The
cells are prepared using a anode:cathode weight ratio of 1:1. FIG.
59 illustrates the full cell performance of Si/C nanofibers with
(Li(Ni.sub.1/3Co.sub.1/3Mn.sub.1/3)O.sub.2) nanofibers. Initial
capacity of some of such cells are 157 mAh per gram of anode. FIG.
60 illustrates the full cell performance of Si/C nanofibers with
Li[Li.sub.0.2Mn.sub.0.56Ni.sub.0.16Co.sub.0.08]O.sub.2 nanofibers.
Initial capacity of some of such cells are 150 mAh per gram of
anode.
* * * * *