U.S. patent application number 14/457994 was filed with the patent office on 2015-03-19 for carbon and carbon precursors in nanofibers.
This patent application is currently assigned to CORNELL UNIVERSITY. The applicant listed for this patent is CORNELL UNIVERSITY. Invention is credited to Yong Lak Joo, Kyoung Woo Kim, Yong Seok Kim.
Application Number | 20150076742 14/457994 |
Document ID | / |
Family ID | 51625350 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150076742 |
Kind Code |
A1 |
Joo; Yong Lak ; et
al. |
March 19, 2015 |
CARBON AND CARBON PRECURSORS IN NANOFIBERS
Abstract
Provided herein are nanofibers comprising carbon precursors,
nanofibers comprising carbon matrices, and processes for preparing
the same. In specific examples, provided herein are high
performance lithium ion battery anodic nanofibers comprising
non-aggregated silicon domains in a continuous carbon matrix.
Inventors: |
Joo; Yong Lak; (Ithaca,
NY) ; Kim; Kyoung Woo; (Ithaca, NY) ; Kim;
Yong Seok; (Ithaca, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNELL UNIVERSITY |
ITHACA |
NY |
US |
|
|
Assignee: |
CORNELL UNIVERSITY
ITHACA
NY
|
Family ID: |
51625350 |
Appl. No.: |
14/457994 |
Filed: |
August 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US14/25974 |
Mar 13, 2014 |
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14457994 |
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61781260 |
Mar 14, 2013 |
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61791619 |
Mar 15, 2013 |
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61894054 |
Oct 22, 2013 |
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Current U.S.
Class: |
264/433 |
Current CPC
Class: |
H01M 10/0525 20130101;
D01F 1/02 20130101; H01M 4/587 20130101; D01D 5/0069 20130101; Y02E
60/10 20130101; D01D 5/003 20130101; D04H 1/728 20130101; D01D 1/02
20130101; D01F 9/12 20130101; D01F 9/328 20130101; D01D 5/0015
20130101; D01F 9/20 20130101 |
Class at
Publication: |
264/433 |
International
Class: |
D01D 5/00 20060101
D01D005/00 |
Claims
1. A process for preparing a silicon-carbon nanocomposite
nanofiber, the process comprising: a. providing a fluid stock
comprising polyvinylalcohol, a plurality of silicon nanoparticles,
and a nanostructured carbon; b. electrospinning the fluid stock,
producing a nanofiber comprising the polyvinylalcohol, the silicon
nanoparticles, and the nanostructured carbon; and c. thermally
treating the nanofiber producing the silicon-carbon nanocomposite
nanofiber.
2. The process of claim 1, wherein the electrospinning is
gas-assisted.
3. The process of claim 2, wherein the electrospinning is coaxially
gas-assisted.
4. The process of claim 1, wherein the fluid stock is aqueous.
5. The process of claim 3, wherein the fluid stock is aqueous.
6. The process of claim 1, wherein the nanostructured carbon
comprises high aspect ratio nanostructured carbon, the aspect ratio
thereof being at least 10.
7. The process of claim 1, wherein the nanostructured carbon
comprises carbon black, graphene, or carbon nanotubes.
8. The process of claim 1, wherein the nanostructured carbon
comprises graphene or carbon nanotubes.
9. The process of claim 6, wherein the nanostructured carbon
comprises graphene or carbon nanotubes.
10. The process of claim 1, wherein the plurality of silicon
nanoparticles have an average diameter of less than 100 nm.
11. The process of claim 1, wherein the fluid stock comprises the
nanostructured carbon and the polyvinyl alcohol in a
weight-to-weight ratio of at least 1:10.
12. The process of claim 1, wherein the fluid stock comprises the
nanostructured carbon and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1.
13. The process of claim 3, wherein the fluid stock comprises the
nanostructured carbon and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1.
14. The process of claim 9, wherein the fluid stock comprises the
nanostructured carbon and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1.
15. The process of claim 1, wherein the fluid stock comprises the
silicon nanoparticles and the polyvinyl alcohol in a
weight-to-weight ratio of at least 1:10.
16. The process of claim 1, wherein the fluid stock comprises the
silicon nanoparticles and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1.
17. The process of claim 10, wherein the fluid stock comprises the
silicon nanoparticles and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1.
18. The process of claim 1, wherein the silicon-carbon
nanocomposite nanofiber comprises at least 60 elemental wt. %
silicon.
19. The process of claim 1, wherein the silicon-carbon
nanocomposite nanofiber comprises at least 75 elemental wt. %
silicon.
20. The process of claim 1, wherein the silicon-carbon
nanocomposite nanofiber comprises 5 wt. % to 25 wt. % carbon.
21. The process of claim 1, wherein thermally treating comprises
heating to a temperature between 400.degree. C. and 2000.degree.
C.
22. The process of claim 1, wherein the thermal treatment
carbonizes the polyvinylalcohol.
23. The process of claim 1, wherein the thermal treatment is
performed under inert or reducing conditions.
24. The process of claim 1, further comprising washing the
nanofiber prior to thermal treatment.
25. A process for preparing a silicon-carbon nanocomposite
nanofiber, the process comprising: a. providing an aqueous fluid
stock comprising polyvinylalcohol, a plurality of silicon
nanoparticles having an average diameter of less than 100 nm, and a
nanostructured carbon having an aspect ratio of at least 5, the
weight-to-weight ratio of silicon nanoparticles to polyvinylalcohol
being at least 1:10, and the weight-to-weight ratio of
nanostructured carbon to polyvinylalcohol being at least 1:10; b.
electrospinning the fluid stock, producing a nanofiber comprising
the polyvinylalcohol, the silicon nanoparticles, and the
nanostructured carbon, the electrospinning being coaxially gas
assisted; and c. thermally carbonizing the polyvinylalcohol of the
nanofiber, thereby producing the silicon-carbon nanocomposite
nanofiber.
26. The process of claim 25, wherein the fluid stock comprises the
silicon nanoparticles and the polyvinyl alcohol in a
weight-to-weight ratio of 1:4 to 4:1 and the nanostructured carbon
and the polyvinyl alcohol in a weight-to-weight ratio of 1:4 to
4:1.
27. The process of claim 25, wherein the nanostructured carbon
comprises carbon nanotubes or graphene.
28. The process of claim 25, wherein the silicon-carbon
nanocomposite nanofiber comprises at least 60 elemental wt. %
silicon and 5 wt. % to 25 wt. % carbon.
29. The process of claim 27, wherein the silicon-carbon
nanocomposite nanofiber comprises at least 60 elemental wt. %
silicon and 5 wt. % to 25 wt. % carbon.
30. A silicon-carbon nanocomposite nanofiber produced by the
process of claim 1.
Description
CROSS-REFERENCE
[0001] This application is a US Bypass continuation (CON)
application under 35 USC 111(a) and claims the benefit of
co-pending International Application No. PCT/US 14/25974 filed Mar.
13, 2014, which itself claims the benefit of U.S. Provisional
Application Nos. 61/781,260 filed Mar. 14, 2013, 61/791,619 filed
Mar. 15, 2013, and 61/894,054 filed on Oct. 22, 2013, which are all
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] Batteries comprise one or more electrochemical cell, such
cells generally comprising a cathode, an anode and an electrolyte.
Lithium ion batteries are high energy density batteries that are
fairly commonly used in consumer electronics and electric vehicles.
In lithium ion batteries, lithium ions generally move from the
negative electrode to the positive electrode during discharge and
vice versa when charging. In the as-fabricated and discharged
state, lithium ion batteries often comprise a lithium compound
(such as a lithium metal oxide) at the cathode (positive electrode)
and another material, generally carbon, at the anode (negative
electrode).
SUMMARY OF THE INVENTION
[0003] Provided herein is a carbon nanomaterials platform. In
specific instances, such carbon nanomaterials are carbon-silicon
nanocomposites comprising a carbon matrix material (e.g.,
continuous carbon matrix), with silicon domains (e.g.,
nanoparticles) embedded therein (e.g., a carbon-silicon composite).
In some embodiments, provided herein are processes for preparing
the same. In specific embodiments, the processes described herein
provide improved performance of the materials--e.g., improved
continuity and/or morphology control of the carbon matrix and,
thereby, improved electrochemical performance of the nanocomposite
materials. Also provided herein are nanomaterials comprising
polymer and nanostructured carbon (e.g., carbon allotrope) or
nanostructured carbon precursor (e.g., high aspect ratio carbon or
carbon precursor--such as having an aspect ratio of greater than 2,
5, 10 or the like). In specific instances, the nanomaterials
comprise polymer and nanostructured carbon (e.g., carbon
allotrope). In further or alternative specific instances, the
nanomaterials comprise polymer and nanostructured carbon precursor
(e.g., cellulose nanocrystals). In certain instances, such
nanomaterials (comprising polymer, and carbon precursor or carbon
nanostructure, and optional silicon domains (e.g., nanoparticles))
are precursor materials for (i.e., can be converted--e.g., through
thermal and/or chemical treatment) the carbon nanomaterials
provided herein.
[0004] In certain embodiments, provided herein is a process for
preparing a nanofiber (e.g., the nanofiber comprising a polymer or
carbon matrix (e.g., a continuous carbon matrix)), the process
comprising:
[0005] providing a fluid stock comprising (i) a polymer and (ii)
carbon (e.g., carbon allotrope, such as CNT) or a carbon precursor
(e.g., wherein the carbon and/or carbon precursor is high aspect
ratio, nanostructured carbon and/or carbon precursor); and
[0006] electrospinning the fluid stock (e.g., producing a nanofiber
comprising a polymer matrix with carbon and/or carbon precursor
nanostructures (e.g., high aspect ratio) embedded therein).
[0007] In more specific embodiments, provided herein is a process
for preparing a nanofiber, the nanofiber comprising a carbon matrix
(e.g., continuous carbon matrix), the process comprising:
[0008] providing a fluid stock comprising (i) a polymer and (ii)
carbon (e.g., a carbon allotrope) or a carbon precursor (e.g.,
wherein the carbon and/or carbon precursor is high aspect ratio,
nanostructured carbon and/or carbon precursor);
[0009] electrospinning the fluid stock, producing a first (e.g.,
as-spun) nanofiber; and
[0010] thermally treating the first (e.g., as-spun, including non-
and pre-treated) nanofiber (e.g., under inert or reducing
conditions), producing a second nanofiber comprising a continuous
carbon matrix.
[0011] In still more specific embodiments, provided herein is a
process for preparing a nanofiber, the nanofiber comprising a
carbon matrix (e.g., continuous carbon matrix), the process
comprising:
[0012] providing a fluid stock comprising (i) a polymer, (ii)
carbon (e.g., such as a carbon allotrope) or a carbon precursor
(e.g., wherein the carbon and/or carbon precursor is high aspect
ratio, nanostructured carbon and/or carbon precursor), and (iii) a
metal component (e.g., a metal precursor or metal-containing
nanoparticle);
[0013] electrospinning the fluid stock, producing a first (e.g.,
as-spun nanofiber); and
[0014] thermally treating the first (e.g., as-spun) nanofiber
(e.g., under inert or reducing conditions), producing a second
nanofiber comprising a continuous carbon matrix (e.g., and metal
component embedded therein).
[0015] In further or alternative specific embodiments, provided
herein is a process for preparing a nanofiber, the nanofiber
comprising a carbon composite, the process comprising:
[0016] providing a fluid stock comprising (i) a polymer, (ii)
carbon (e.g., such as a carbon allotrope) or a carbon precursor
(e.g., wherein the carbon and/or carbon precursor is high aspect
ratio, nanostructured carbon and/or carbon precursor), and (iii) a
metal component (e.g., a metal precursor or metal-containing
nanoparticle);
[0017] electrospinning the fluid stock, producing first (e.g.,
as-spun) nanofiber; and
[0018] thermally treating the first (e.g., as-spun) nanofiber
(e.g., under inert or reducing conditions), producing a second
nanofiber, the second nanofiber being a carbon composite nanofiber
(e.g., comprising carbon, such as a continuous matrix of carbon,
and metal or metal oxide, such as nanoparticles or other
nanostructures thereof).
[0019] In still further or alternative specific embodiments,
provided herein is a process for preparing a composite nanofiber,
the process comprising:
[0020] providing a fluid stock comprising (i) a polymer, and (ii) a
high aspect ratio nanostructure (e.g., carbon (e.g., carbon
allotrope, such as CNT or graphene) or carbon precursor (e.g.,
CNC);
[0021] electrospinning the fluid stock, producing first (e.g.,
as-spun) nanofiber (e.g., comprising a polymer/nanostructure
composite material); and
[0022] optionally thermally treating the first (e.g., as-spun)
nanofiber (e.g., under inert or reducing conditions), producing a
second nanofiber (e.g., comprising a carbon/nanostructure composite
material).
[0023] In some embodiments, thermal treatment is optional or
omitted--e.g., to prepare a precursor nanofiber for a lithium ion
battery anode material (nanomaterial).
[0024] 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, polyvinylidene difluoride (PVDF),
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, or
the like) is optionally utilized.
[0025] In certain embodiments, the carbon precursor is an organic
nanomaterial (e.g., an organic crystalline nanomaterial). Carbon
precursors include any suitable material that may be converted to
carbon, such as abundant natural organic materials, e.g.,
cellulose, lignin, collagen, polysaccharide (e.g., maltodextrin),
keratin, protein, polymer (e.g., a second polymer, such as a
polymer that does not dissolve in the fluid stock medium), bamboo
fiber, or the like. In some embodiments, such carbon precursors are
nanostructured (e.g., high aspect ratio, nanostructured) materials.
In specific embodiments, the carbon precursor is cellulosic
nanomaterial, such as nanocrystalline cellulose (CNC--cellulose
nanocrystals). In other embodiments, the carbon is a non-organic
carbon (e.g., a carbon allotrope) nanomaterial--e.g., amorphous
carbon, carbon nanotubes (CNT), graphene, graphite, or the like. In
certain embodiments, the carbon and/or carbon precursor is
nanostructured--e.g., having at least one dimension (e.g.,
diameter) that is about 2000 microns or less, e.g., about 1000
microns or less. In certain embodiments, such nanostructures are
high aspect ratio, e.g., wherein the nanostructures have a second
dimension (e.g., length) that is at least 2.times., 5.times., or
10.times. the first dimension. In some embodiments, the
(nanostructured) carbon and/or carbon precursor is a nanomaterial
having an aspect ratio of at least 5. In more specific embodiments,
the carbon and/or carbon precursor is a nanomaterial having an
aspect ratio of at least 10. In certain instances, electrospinning
of a fluid stock comprising carbon and/or carbon precursors with a
larger aspect ratio provides nanofibers comprising such precursors
aligned lengthwise with the nanofiber. In some instances, thermal
treatment of such materials provides nanofiber having improved
morphology of the continuous carbon matrix and/or improved
performance (e.g., electrochemical performance, for example, as an
anode material in a lithium ion battery). In certain embodiments,
the as-spun nanofibers are optionally treated prior to thermal
treatment--e.g., washing with solvent or chemical reagent--such
pre-treated nanofibers are considered as-spun nanofibers (e.g.,
pre-treated as-spun nanofibers) for the purposes of the disclosure
herein.
[0026] In some embodiments, the metal component is a silicon
containing nanoparticle (e.g., comprising zero oxidation state
silicon). In other embodiments, the metal component is a silicon
precursor, such as silicon acetate. In other embodiments, the metal
component is a nanoparticle or precursor (e.g., alkoxide, halide or
acetate salt) of a lithium ion battery anode material (e.g., tin,
tin oxide, titanium dioxide, aluminum, or the like). In still other
embodiments, the metal component is a germanium containing
nanoparticle (e.g., comprising zero oxidation state germanium).
[0027] In certain embodiments, the fluid stock is aqueous. In
specific embodiments, the fluid stock is aqueous and comprises PVA.
In some embodiments, the fluid stock comprises an organic solvent.
In specific embodiments, the organic solvent is dimethylformamide
(DMF). In specific embodiments, the fluid stock comprises DMF as a
solvent and PAN as a polymer.
[0028] In some embodiments, the process comprises electrospinning
the fluid stock with gas assistance. In specific embodiments, the
process comprises electrospinning the fluid stock with coaxial gas
assistance. In some embodiments, the gas assistances is provided by
blowing gas (e.g., high velocity gas) along or around (i.e.,
coaxially) a longitudinal axis along which the fluid stock is
provided (e.g., along a common axis with which the fluid stock is
electrospun). In some embodiments, coaxial gas assistance comprises
providing a gas (e.g., pressurized or high velocity gas) centered
around the same longitudinal axis as the fluid stock is provided
and centered. FIG. 3 illustrates an exemplary nozzle for providing
coaxial-gas assisted electrospinning a fluid stock: the fluid stock
is electrospun along a longitudinal axis and providing the gas
around the same longitudinal axis. In other embodiments, coaxial
gas assistance comprises providing a gas (e.g., pressurized or high
velocity gas) around or along (but not necessarily centered around)
the longitudinal axis the fluid stock is provided and centered. In
some instances, coaxial gas assistance comprises providing a gas
(e.g., pressurized or high velocity gas) centered around a
different longitudinal axis as the fluid stock is provided and
centered. In some instances, coaxial gas assisted electrospinning
provided herein comprises providing a fluid stock along a first
longitudinal axis, providing a gas (e.g., pressurized or high
velocity gas) around a second longitudinal axis, and
electrospinning the fluid stock. In specific embodiments, the first
and second longitudinal axes are the same. In other embodiments,
the first and second longitudinal axes are different. In certain
embodiments, the first and second longitudinal axes are within 500
microns, within 100 microns, within 50 microns, or the like of each
other. In some embodiments, the first and second longitudinal axes
are aligned within 15 degrees, within 10 degrees, within 5 degrees,
within 3 degrees, within 1 degree, or the like of each other. In
some embodiments, the fluid stock is electrospun with a high
velocity gas flowing adjacent to and about or along the same axis
as the electrospun fluid stock (e.g., within 1, 5 or 10 degrees of
the axis along which the fluid stock is electrospun). FIG. 1 and
FIG. 3 illustrate exemplary systems for providing coaxial gas
assisted electrospinning of a fluid stock.
[0029] In some instances, e.g., wherein the metal component is a
silicon (or germanium) nanoparticle, such nanomaterials are
suitable for providing improved (e.g., silicon containing)
electrodes (e.g., for use in batteries, such as anode in lithium
ion batteries). For example, in some instances, provided herein are
nanofibers comprising metal component (e.g., silicon) distributed
along the length of a nanofiber (e.g., in a non-aggregated manner),
which, in some instances, facilitates high metal component (e.g.,
silicon) loading, and improved lithium ion uptake in the
nanofiber/electrode (e.g., with little to no pulverization of the
material). Provided herein are silicon nanofibers (including
treated and as-spun nanofibers), fluid stocks (e.g., for preparing
such nanofibers), and processes for preparing silicon nanofibers
(including treated and as-spun nanofibers).
[0030] In some embodiments, provided herein is a process for
preparing a nanofiber (e.g., the nanofiber comprising a polymer or
carbon matrix (e.g., a continuous carbon matrix) with silicon
nanoparticles embedded therein), the process comprising:
[0031] providing a fluid stock comprising (i) a polymer, (ii)
carbon (e.g., a nanostructured carbon allotrope) and/or a carbon
precursor (e.g., nanostructured cellulose), and (iii) a plurality
of silicon nanoparticles;
[0032] electrospinning the fluid stock, producing a first (e.g.,
as-spun) nanofiber (e.g., comprising a continuous matrix of (i)
polymer, (ii) carbon and/or carbon precursor, and (iii) silicon
nanoparticles).
[0033] In specific embodiments, the continuous matrix of polymer
comprises the silicon nanoparticles embedded therein (e.g.,
completely embedded therein). In more specific embodiments, the
continuous matrix of polymer comprises the silicon nanoparticles
and the carbon and/or carbon precursor (e.g., nanostructured
cellulose and/or a nanostructured carbon allotrope) embedded
therein. In certain embodiments, such nanofibers are a precursor
material, which is thermally treated to prepare nanofibers
comprising a continuous carbon matrix--e.g., with silicon
nanoparticles embedded therein (e.g., completely embedded therein,
such as wherein the surface of the silicon nanoparticles are
completely covered with carbon). In some instances, such materials
are suitable for use as high performance anode materials in lithium
ion batteries.
[0034] In some embodiments, provided herein is a process for
preparing a nanofiber (e.g., the nanofiber comprising silicon
nanoparticles embedded in a polymer or carbon matrix), the process
comprising:
[0035] providing a fluid stock comprising (i) a polymer, (ii)
carbon and/or a carbon precursor (e.g., nanostructured cellulose
and/or a carbon allotrope, such as a nanostructured carbon
allotrope), and (iii) a plurality of silicon nanoparticles; and
[0036] electrospinning the fluid stock, producing a first (e.g.,
as-spun) nanofiber.
[0037] In some embodiments, provided herein is a process for
preparing a nanofiber, the nanofiber comprising a continuous carbon
matrix with silicon nanoparticles embedded therein, the process
comprising:
[0038] providing a fluid stock comprising (i) a polymer, (ii)
carbon and/or a carbon precursor (e.g., nanostructured cellulose
and/or a carbon allotrope, such as a nanostructured carbon
allotrope), and (iii) a plurality of silicon nanoparticles;
[0039] electrospinning the fluid stock, producing a first (e.g.,
as-spun) nanofiber; and
[0040] thermally treating the first (e.g., as-spun) nanofiber
(e.g., under inert or reducing conditions), producing a second
nanofiber comprising a continuous carbon matrix with silicon
nanoparticles embedded therein.
[0041] In specific embodiments, nanofibers provided herein comprise
a carbon backbone (e.g., continuous matrix material), the carbon
backbone comprising nanoparticles embedded therein. In more
specific embodiments, the nanoparticles comprising silicon. In some
embodiments, the backbone is a core matrix material. In other
embodiments, the backbone comprises a hollow core--e.g., along at
least a portion of the nanofiber (e.g., with the nanoparticles
embedded within the matrix material rather than found within the
"hollow" center, such as illustrated in FIG. 2A).
[0042] In some embodiments, the backbone or matrix material of a
nanofiber described herein comprises amorphous carbon. In certain
embodiments, the backbone or matrix material of a nanofiber
described herein comprises crystalline carbon (e.g., graphite
and/or graphene). In further embodiments, the backbone or matrix
material of a nanofiber described herein comprises amorphous carbon
and crystalline carbon (e.g., wherein amorphous carbon arises from
carbonization of polymer and the carbon allotrope inclusion retains
its structure, or at least partially retains its structure).
[0043] In certain embodiments, the nanoparticles or discrete
domains of a nanofiber provided herein comprise silicon in a zero
oxidation state. In further embodiments, the nanoparticles or
discrete domains of a nanofiber provided herein comprise silicon in
a zero oxidation state (e.g., elemental silicon) and silicon in an
oxidized state (e.g., sub-stoiciometric silica (SiO.sub.x)
(0<x<2), silicon dioxide and/or silicon carbide). In specific
embodiments, the nanoparticles comprise elemental silicon and
silicon dioxide. In more specific embodiments, the nanoparticles
comprise elemental silicon, silicon dioxide, and silicon carbide.
In specific embodiments, the nanoparticles comprise elemental
silicon and sub-stoiciometric silica. In more specific embodiments,
the nanoparticles comprise elemental silicon, sub-stoiciometric
silica, and silicon carbide. In some embodiments, the nanofibers
comprises zero oxidation state silicon and greater than zero
oxidation state silicon in an elemental ratio of at least 5:1
(e.g., 10:1, 20:1, 30:1, or the like).
[0044] In certain embodiments, the nanoparticles or discrete
domains of a nanofiber provided herein have an average diameter of
less than 100 nm. In specific embodiments, the nanoparticles or
domains have an average diameter of 10 nm to 80 nm. In more
specific embodiments, the nanoparticles or domains have an average
diameter of 20 nm to 60 nm.
[0045] In some embodiments, a majority of the nanoparticles or
discrete domains comprise a surface that is at least 50% coated
with carbon. In specific embodiments, a majority of the
nanoparticles or discrete domains comprise a surface that is at
least 75% coated with carbon. In more specific embodiments, a
majority of the nanoparticles or discrete domains comprise a
surface that is at least 85% coated with carbon. In still more
specific embodiments, a majority of the nanoparticles or discrete
domains comprise a surface that is at least 90% coated with carbon.
In yet more specific embodiments, a majority of the nanoparticles
or discrete domains comprise a surface that is at least 95% coated
with 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 carbon.
[0046] In some embodiments, nanofibers provided herein comprise, on
average, less than 25 wt. % of carbon (e.g., as measured by TGA or
elemental analysis). In specific embodiments, the nanofibers
comprise, on average, 1 wt % to 25 wt % carbon. In more specific
embodiments, the nanofibers comprise, on average, 5 wt % to 25 wt %
carbon. In yet more specific embodiments, the nanofibers comprise,
on average, 5 wt % to 20 wt % carbon. In still more specific
embodiments, the nanofibers comprise, on average, 10 wt % to 20 wt
% carbon.
[0047] In some embodiments, nanofibers provided herein comprise, on
average, at least 50 elemental wt. % of silicon (e.g. in zero
and/or greater than zero oxidized state). In specific embodiments,
nanofibers provided herein comprise, on average, at least 60
elemental wt. % of silicon. In more specific embodiments,
nanofibers provided herein comprise, on average, at least 70
elemental wt. % of silicon. In still more specific embodiments,
nanofibers provided herein comprise, on average, at least 75
elemental wt. % of silicon. In yet more specific embodiments,
nanofibers provided herein comprise, on average, at least 80
elemental wt. % of silicon. In specific embodiments, nanofibers
provided herein comprise, on average, at least 85 elemental wt. %
of silicon. In some embodiments, nanofibers provided herein
comprise, on average, at least 50 wt. % of silicon (i.e., zero
oxidation/elemental silicon). In specific embodiments, nanofibers
provided herein comprise, on average, at least 60 wt. % of silicon
(i.e., zero oxidation/elemental silicon). In yet more specific
embodiments, nanofibers provided herein comprise, on average, at
least 70 wt. % of silicon (i.e., zero oxidation/elemental silicon).
In still more specific embodiments, nanofibers provided herein
comprise, on average, at least 75 wt. % of silicon (i.e., zero
oxidation/elemental silicon). In more specific embodiments,
nanofibers provided herein comprise, on average, at least 80 wt. %
of silicon (i.e., zero oxidation/elemental silicon). In still more
specific embodiments, nanofibers provided herein comprise, on
average, at least 85 wt. % of silicon (i.e., zero
oxidation/elemental silicon).
[0048] In certain embodiments, nanofibers provided herein (or
anodes comprising such nanofibers) have a specific energy capacity
of at least 1500 mAh/g on a first cycle at 0.1 C. In certain
embodiments, nanofibers provided herein (or anodes comprising such
nanofibers) have a specific energy capacity of at least 1200 mAh/g
on a first cycle at 0.1 C. In specific embodiments, nanofibers
provided herein (or anodes comprising such nanofibers) have a
specific energy capacity of at least 2000 mAh/g on a first cycle at
0.1 C. In some embodiments, nanofibers provided herein (or anodes
comprising such nanofibers) have a specific energy capacity of at
least 1200 mAh/g on a 10th cycle at 0.1 C. In specific embodiments,
nanofibers provided herein (or anodes comprising such nanofibers)
have a specific energy capacity of at least 1000 mAh/g on a 10th
cycle at 0.1 C. In some embodiments, nanofibers provided herein (or
anodes comprising such nanofibers) have a specific energy capacity
of at least 500 mAh/g on a 98th cycle at 0.1 C. In specific
embodiments, nanofibers provided herein (or anodes comprising such
nanofibers) have a specific energy capacity of at least 800 mAh/g
on a 98th cycle at 0.1 C. In some embodiments, provided herein is a
lithium ion battery comprising an anode comprising nanofibers
described herein and the anode having a specific capacity described
herein (e.g., at least 1200 mAh/g on a first cycle at 0.1 C).
[0049] In certain embodiments, the nanofiber(s) has an average
diameter of less than 1 micron (e.g., less than 800 nm). In some
embodiments, the nanofiber(s) has an average aspect ratio of at
least 100 (e.g., at least 1000 or at least 10,000). In some
embodiments, the nanofibers are cross-linked
[0050] Also provided herein is an electrode comprising a non-woven
mat of a plurality of nanofibers described herein. Further,
provided herein is a battery (e.g., lithium ion battery) comprising
such an electrode. In more specific embodiments, the lithium ion
battery comprises, such as in an initial or discharged state, a
positive electrode, a separator, and a negative electrode, the
negative electrode comprising any nanofiber as described herein, or
a woven mat comprising one or a plurality of such nanofibers.
[0051] Provided in certain embodiments herein is a process of
producing a nanofiber (e.g., as described above), the process
comprising electrospinning a fluid stock, the fluid stock
comprising or prepared by combining, in any order, a polymer,
carbon and/or a carbon precursor, a fluid, and an optional metal
component. In specific embodiments, the fluid comprises water or is
aqueous. In some embodiments, the polymer is a water-soluble
organic polymer. In some embodiments, the weight-to-weight ratio of
the carbon and/or carbon precursor to polymer is at least 1:10
(e.g., at least 1:5, at least 1:4, at least 1:3, at least 1:2, at
least 1:1, 1:10 to 1:1, or 1:5 to 1:1). In certain embodiments, the
weight-to-weight ratio of the metal component (e.g., silicon
nanoparticles) to polymer is at least 1:10 (e.g., at least 1:5, at
least 1:4, at least 1:3, at least 1:2, at least 1:1, 1:10 to 1:1,
or 1:5 to 1:1). In specific embodiments, the polymer-to-metal
component-to-carbon and/or carbon precursor ratio is about 1:1:1.
In certain embodiments, the weight ratio of the combination of the
metal component and the carbon and/or carbon precursor
component-to-polymer is at least 1:2 (e.g., at least 1:1, at least
3:2, at least 2:1 or the like). In some embodiments, the process
further comprises thermally treating the as-spun nanofiber. In some
embodiments, the thermal treatment occurs under inert conditions
(e.g., to carbonize the polymer and carbon precursor). In further
or alternative embodiments, the process further comprises reducing
the as-spun (or a previously treated, e.g., thermally treated)
nanofiber (e.g., concurrently with thermal treatment) (e.g., to
minimize oxidation of metal components).
[0052] In some embodiments, the process further comprises, to
prepare the fluid stock, comprises combining, in any order, the
carbon and/or carbon precursor, the optional metal component, the
polymer and a fluid medium (e.g., water or an aqueous
solution).
[0053] Provided in certain embodiments herein is a process for
preparing a nanofiber, the process comprising:
[0054] providing a fluid stock comprising a polymer and a high
aspect ratio nanostructure; and
[0055] electrospinning the fluid stock, producing a spun
nanofiber.
[0056] In specific embodiments, the high aspect ratio nanostructure
has an aspect ratio of at least 2. In more specific embodiments,
the high aspect ratio nanostructure has an aspect ratio of at least
5. In still more specific embodiments, the high aspect ratio
nanostructure has an aspect ratio of at least 10.
[0057] In certain embodiments, the polymer is polyvinyl alcohol,
polyvinyl acetate, polyethylene oxide, polyvinyl ether, polyvinyl
pyrrolidone, polyglycolic acid, polyvinylidene difluoride,
polyacrylonitrile, polyacrylic acid, polymethylmethacrylate, or a
combination thereof, or any polymer described herein. In some
embodiments, the fluid stock further comprises water, alcohol,
hydrocarbon solvent, DMF, or a combination thereof, or any other
solvent described herein. In certain embodiments, the
electrospinning is gas assisted, e.g., according to any
electrospinning process described herein. In specific embodiments,
the electrospinning is coaxially gas assisted.
[0058] Disclosure of characteristics of a single nanofiber
described herein includes the disclosure of a plurality of
nanofibers having the average characteristic described. Similarly,
disclosure of an average characteristic of a plurality of
nanofibers includes the disclosure of a single nanofiber having the
characteristic described.
[0059] In some embodiments, nanofibers provided herein or prepared
according to a process herein comprise a continuous polymer matrix
and a carbon nanoinclusion (e.g., precursor (e.g., nanostructured
cellulose) or carbon allotrope (e.g., nanostructured graphene or
carbon nanotubes)). In specific embodiments, the carbon
nanoinclusions are embedded within the polymer matrix. In some
embodiments, the polymer matrix has carbon nanoinclusions on the
surface of and embedded within the matrix thereof. In certain
embodiments, the nanoinclusions have an aspect ratio of greater
than 1, and an axis along the length (longest dimension) of the
nanostructure (the length being the longest dimension of the
nanostructure). In specific embodiments, the nanoinclusions are
substantially aligned along the same longitudinal axis the
nanofiber (i.e., the axis running along the length of the
nanofiber). In certain embodiments, at least 30% (e.g., at least
50%, or at least 75%) of the nanoinclusions are aligned within 15
degrees (e.g., within 10 degrees, or within 5 degrees) of the
nanofiber axis.
[0060] In specific embodiments, the nanofibers provided herein have
a polymer matrix and carbon nanotube inclusions. In more specific
embodiments, the nanotube inclusions are substantially aligned
along the same longitudinal axis of the nanofiber.
[0061] In further embodiments, nanofibers provided herein or
prepared according to a process herein comprise a continuous
polymer matrix, a carbon nanoinclusion (e.g., precursor (e.g.,
nanostructured cellulose) or carbon allotrope (e.g., nanostructured
graphene or carbon nanotubes)), and a metal component (e.g., metal,
metalloid, metal oxide, ceramic, or the like). In specific
embodiments, the metal component is a nanostructured metal
inclusion (e.g., silicon nanoparticles). In specific embodiments,
the carbon nanoinclusions and metal nanoinclusions are embedded
within the polymer matrix. In some embodiments, the polymer matrix
has carbon nanoinclusions and metal nanoinclusions on the surface
of and embedded within the matrix thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] 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:
[0063] FIG. 1 describes a system for preparing a nanofiber wherein
electrospinning of such a nanofiber, or precursor of such a
nanofiber, is coaxially gas assisted.
[0064] FIG. 2A illustrates a nanofiber, with a cross-sectional view
(right panel), comprising (i) a hollow core, (ii) discrete domains
of a first material in the sheath layer, and (iii) a continuous
matrix (e.g., core matrix) of a second material in the sheath
layer. FIG. 2B illustrates a nanofiber, with a cross-sectional view
(right panel), comprising (i) discrete domains of a first material,
and (ii) a continuous matrix (e.g., core matrix) of a second
material.
[0065] FIG. 3 illustrates a bi-layered co-axial electrospinning
apparatus (with a cut-out of the outer needle), having an inner
needle and an outer needle coaxially aligned about a common axis.
In some instances, the inner and outer needles are configured to
electrospin a first fluid stock along with a gas (e.g., in a gas
assisted manner when the gas is in the outer layer or to provide
hollow nanofibers when the gas is in the inner/core layer).
[0066] FIG. 4: (A) illustrates as-spun carbon (CNT) and
nanoparticles (Si NP) in polymer matrix nanofibers, (C) an
increased magnification image over image (A), (B) thermally treated
nanofibers therefrom, and (D) an increased magnification image over
image (B).
[0067] FIG. 5 illustrates as-spun carbon precursor (CNC) and
nanoparticles (Si NP) in polymer matrix nanofibers (Panel A)
(10:10:2, polymer:NP:carbon precursor) and thermally treated
nanofibers (panel B) therefrom.
[0068] FIG. 6: (A) illustrates as-spun carbon precursor (CNC) and
nanoparticles (Si NP) in polymer matrix nanofibers (1:1:1), (B)
thermally treated nanofibers therefrom, (C) surface TEM image, and
(D) microtomed TEM image thereof.
[0069] FIG. 7 illustrates as-spun carbon precursor (CNC) and
nanoparticles (Si NP) in polymer matrix nanofibers (Panel A)
(1:1:1) and thermally treated nanofibers (panel B) therefrom.
[0070] FIG. 8: (A) illustrates as-spun nanoparticles (Si NP) in
polymer matrix nanofibers (1:1), (B) thermally treated nanofibers
therefrom, (C) surface TEM image, and (D) microtomed TEM image
thereof.
[0071] FIG. 9 illustrates the performance of various anodes
prepared from carbon precursor containing nanofibers (e.g., Si/C
nanofiber prepared from nanofibers comprising carbon precursor) to
other anode systems (e.g., pure Si nanoparticles, and Si/C
nanofibers prepared without the use of carbon precursor).
[0072] FIG. 10 illustrates a sodium form of cellulose
nanocrystals.
[0073] FIG. 11: (A) illustrates an SEM image of carbon
allotrope/polymer composite nanofibers, and (B) carbon nanofibers
prepared by carbonizing such nanofibers.
DETAILED DESCRIPTION OF THE INVENTION
[0074] Provided herein are nanofibers and nanofiber mats and
processes for preparing nanofibers and nanofiber mats. In some
embodiments, a nanofiber provided herein comprises a continuous
polymer matrix and carbon and/or a carbon precursor embedded
therein. In more specific embodiments, the nanofiber comprises a
continuous polymer matrix, carbon (e.g., nanostructured carbon
allotrope, such as CNT or graphene) and/or carbon precursor (e.g.,
nanostructured carbon precursor, such as CNC) embedded in the
polymer matrix, and metal component (e.g., silicon) nanoparticles
embedded in the polymer matrix (e.g., PVA or PAN). In further
embodiments, a nanofiber provided herein comprises a carbon matrix,
e.g., wherein the carbon matrix is prepared by thermal treatment of
a continuous polymer matrix with carbon precursor embedded therein.
In more specific embodiments, a nanofiber provided herein comprises
a carbon matrix with a plurality of silicon nanoparticles embedded
therein, e.g., wherein the carbon matrix is prepared by thermal
treatment of a continuous polymer matrix with carbon precursor
embedded therein. Also provided herein are processes, apparatuses,
and systems for preparing such nanofibers.
[0075] FIG. 1 illustrates an as-spun nanofiber 108 and thermally
treated nanofiber 110 provided herein and a process for preparing
the same. In some instances, the as-spun nanofiber 108 comprises a
polymer matrix, carbon and/or carbon precursor embedded in the
polymer matrix, and an optional metal component embedded within the
polymer matrix. FIG. 1 illustrates an exemplary system or schematic
of a process described herein, particularly a system or process for
preparing a nanofiber (e.g., by a coaxial gas assisted
electrospinning process). In some instances, a fluid stock 104
(e.g., comprising (i) carbon and/or a carbon precursor, (ii) a
polymer, and (iii) an optional metal component) is prepared by
combining 102 carbon (e.g., CNT) and/or a carbon precursor (e.g.,
CNC) 101 with polymer and optional metal component (e.g., silicon
nanoparticles). In some embodiments, the fluid stock is provided
104 to an electrospinning apparatus 105 having a needle apparatus
106. In some instances, the fluid stock is optionally electrospun
through a needle apparatus 106, with an optional cross section
illustrated by 111. In some instances, the fluid stock is
electrospun through either of layers 112, or 113. In certain
instances, the electrospinning is gas assisted and the gas, if
present, is electrospun through any other of layers 112, or 113.
Optionally, an additional coaxial layer providing gas may be
utilized (e.g., if a hollow nanofiber is prepared, coaxial gas may
be flowed through an inner and an outer needle in the needle
apparatus 111). In some instances, such techniques provide a gas
assisted electrospinning process or system. The fluid stocks may be
provided to an electrospinning apparatus (e.g., an electrospinning
needle apparatus with voltage supplied thereto--e.g., voltage
sufficient to overcome the surface tension of a liquid polymer or
polymer solution to produce a jet) by any device, e.g., by a
syringe 105 or a pump. A gas may be provided to an electrospinning
needle apparatus 106, 111 from any source (e.g., air pump). 111 is
representative of an exemplary cross section of a coaxial needle
apparatus or a coaxially layered nanofiber. For example, exemplary
co-axial needles comprise an outer sheath tube (which would be
represented by 112) at least one inner or core tube (which would be
represented by 113). In specific embodiments, such tubes are
aligned along a common axis (e.g., aligned within 5 degrees of one
another). In some instances, the tubes are slightly offset, but the
angle of the tubes is substantially aligned (e.g., within 5 degrees
of one another). The electrospun jet 114 is collected on a
collector 107 as an as-spun (hybrid or nanocomposite) nanofiber
108, which is optionally thermally treated 109 to produce
carbonized nanofibers 110.
[0076] In some embodiments, gas assisted electrospinning processes
or apparatus described herein providing a device configured to
provide a flow of gas along the same axis as an electrospun fluid
stock. 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. 3 illustrates co-axial electrospinning
apparatus 300. The coaxial needle apparatus comprises an inner
needle 301 and an outer needle 302, both of which needles are
coaxially aligned around a similar axis 303 (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 301 and 302, which are aligned around the axis
303 (e.g., as illustrated in FIG. 1). In some instances, the
termination of the needles is optionally offset 304.
[0077] FIG. 2A illustrates a nanofiber 200 comprising (i) a hollow
core, (ii) discrete domains of a metal component 201 embedded in
(iii) a continuous carbon matrix 202 (sheath layer). As illustrated
in the cross-sectional view 203, the discrete domains of silicon
material 204 may penetrate into the core 205 of the nanofiber. FIG.
2B illustrates a nanofiber 206 comprising (i) discrete domains of
silicon material 207 in/on a (ii) a continuous core matrix 208
layer. As illustrated in the cross-sectional view 209, the discrete
domains of metal component 210 may penetrate into the core 211 of
the nanofiber. In some instances, the nanofibers comprise metal
component on the surface of the nanofiber. And in some instances,
the nanofibers comprise or further comprise discrete domains of
metal component completely embedded within the core matrix
material.
[0078] In certain embodiments, continuous matrix materials of any
nanofiber described herein is continuous over at least a portion of
the length of the 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).
[0079] In some embodiments, a nanofiber provide herein comprises
discrete domains within the nanofiber. In specific embodiments, the
discrete domains comprise a silicon 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.
[0080] In some embodiments, the metal component 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.
[0081] In some embodiments, the carbon and/or carbon precursor is a
nanostructured material and is present in a polymer-matrix
containing nanofiber, the carbon and/or carbon precursor being
non-aggregated. In specific embodiments, the nanofibers comprises
less than 50% of carbon and/or carbon precursor nanostructures
(e.g., CNC) that are aggregated. In specific embodiments, the
nanofibers comprises less than 40% of carbon and/or carbon
precursor nanostructures (e.g., CNC) that are aggregated. In
specific embodiments, the nanofibers comprises less than 25% of
carbon and/or carbon precursor nanostructures (e.g., CNC) that are
aggregated. In specific embodiments, the nanofibers comprises less
than 10% of carbon and/or carbon precursor nanostructures (e.g.,
CNC) that are aggregated. In specific embodiments, the nanofibers
comprises less than 5% of carbon and/or carbon precursor
nanostructures (e.g., CNC) that are aggregated.
[0082] In some embodiments, a nanofiber provided herein comprises
nanoparticles (e.g., silicon or germanium) present in a matrix
(e.g., polymer or carbon matrix), the nanoparticles being
non-aggregated. In specific embodiments, less than 50% of
nanoparticles are aggregated (in the nanofiber). In specific
embodiments, less than 40% of nanoparticles are aggregated. In
specific embodiments, less than 25% of nanoparticles are
aggregated. In specific embodiments, less than 10% of nanoparticles
are aggregated. In specific embodiments, less than 5% of
nanoparticles are aggregated. In some embodiments, a nanofiber
provided herein comprises (i) nanostructured carbon or carbon
precursor and (ii) nanoparticles (e.g., silicon or germanium)
present in a matrix (e.g., polymer or carbon matrix), the
nanostructures and nanoparticles being non-aggregated. In specific
embodiments, less than 50% of nanostructures and nanoparticles are
aggregated (in the nanofiber). In specific embodiments, less than
40% of nanostructures and nanoparticles are aggregated. In specific
embodiments, less than 25% of nanostructures and nanoparticles are
aggregated. In specific embodiments, less than 10% of
nanostructures and nanoparticles are aggregated. In specific
embodiments, less than 5% of nanostructures and nanoparticles are
aggregated.
Matrix Material
[0083] In certain embodiments, nanofibers provided and/or prepared
according to processes described herein comprise a matrix material,
such as polymer or carbon.
[0084] In some embodiments, a nanofiber provided herein comprises a
polymer matrix and a carbon precursor. In certain embodiments,
additional materials are optionally present (e.g., a metal
component, such as silicon nanoparticles). In some embodiments, the
nanofiber comprises at least 15 wt. %, at least 30 wt. %, at least
50 wt. %, or the like of the matrix material (e.g., polymer).
[0085] In some embodiments, a polymer in a process 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. 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 other instances, solvent soluble polymers are utilized. In
specific embodiments, polyacrylonitrile ("PAN") is optionally
utilized (e.g., with DMF as a solvent). In other instances, a
polyacrylate (e.g., polyalkacrylate, polyacrylic acid,
polyalkylalkacrylate, or the like) is optionally utilized.
[0086] 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. 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.
[0087] In certain embodiments, a nanofiber provided herein
comprises a carbon matrix (e.g., prepared from thermal
treatment--such as under inert or reducing conditions--of a polymer
matrix and carbon and/or carbon precursor). In certain embodiments,
additional materials are optionally present (e.g., a metal
component, such as silicon nanoparticles). In some embodiments, the
nanofiber comprises at least 3%, at least 5%, at least 10%, at
least 15%, at least 20%, at least 30% or the like of the matrix
material (e.g., carbon). In further or alternative embodiments, the
nanofiber comprises less than 50 wt. %, less than 30 wt. %, less
than 20 wt. %, or the like of the matrix material (e.g., carbon).
In certain embodiments, the nanofibers comprise about 1 wt % to
about 70 wt %, or about 5 wt % to about 50 wt %, or about 5 wt % to
about 20 wt % of the matrix material (e.g., carbon or polymer).
[0088] In some embodiments, the matrix material is a continuous
matrix material, such as a continuous core matrix or a continuous
sheath matrix (e.g., surrounding a hollow core).
Carbon/Carbon Precursor
[0089] In various embodiments, the carbon precursor is any suitable
carbon or organic material. In some embodiments, the carbon and/or
carbon precursor is a nanostructured. In some instances, the carbon
is a nanostructured carbon material, such as carbon nanotubes,
graphitic nanoparticles, or the like. In some instances, the carbon
is a non-organic carbon nanomaterial--e.g., a carbon allotrope,
such as amorphous carbon, carbon nanotubes, graphene, graphite, or
the like. In other embodiments, the nanostructured carbon precursor
is a nanostructured organic compound. In specific embodiments, the
nanostructured organic compound is a nanocrystal. In more specific
embodiments, the nanostructured organic compound is a cellulose
nanocrystal (CNC). In still more specific embodiments, the CNC is a
sodium form of cellulose nanocrystals--e.g., as illustrated in FIG.
9 (repeat unit is illustrated--bond to the cell is absent in the
CNC structures).
[0090] In certain embodiments, carbon precursors are compounds that
are converted to carbon upon high temperature thermal treatment
(e.g., under inert conditions).
[0091] In some embodiments, the carbon nanoinclusion provided
herein is a carbon allotrope, such as carbon nanotubes, graphene,
graphite, or the like. In certain embodiments, such carbon
allotropes are optionally functionalized, e.g., with carboxyl
groups (COOR), hydroxyl groups, alkoxyl groups (OR), amino groups
(NR.sub.2), thio groups (SR), combinations thereof, or the like
(e.g., wherein each R is independently selected from H, alkyl,
heteroalkyl, aryl, or heterocycle, in particular, H or alkyl). In
the case of carbon nanotubes, the nanotubes are optionally single
or multi-walled. In the case of graphene, the graphene is obtained
by any suitable process, such as cutting open nanotubes, from
(e.g., sonicating) graphite, carbon dioxide reduction, by the
reduction of ethanol by sodium metal, followed by pyrolysis of the
ethoxide product, or the like.
[0092] In some embodiments, nanostructured carbon and/or carbon
precursors provided herein have an aspect ratio of at least 2. In
certain embodiments, nanostructured carbon precursors with an high
aspect ratio align lengthwise in the same direction as an as-spun
nanofiber having a polymer matrix. In some instances upon thermal
treatment and conversion of the polymer and the carbon precursor to
a carbon matrix, the lengthwise alignment of the carbon precursor
provides a more uniform and higher performance carbon nanofiber. In
certain embodiments, nanostructured carbon and/or carbon precursors
provided herein have an aspect ratio of at least 5. In more
specific embodiments, nanostructured carbon and/or carbon
precursors provided herein have an aspect ratio of at least 10.
[0093] In certain embodiments, nanostructured carbon and/or carbon
precursors have any suitable dimensions, such as diameters, e.g.,
an average diameter of less than 50 nm. In more specific
embodiments, nanostructured carbon and/or carbon precursors have an
average diameter of less than 25 nm. In still more specific
embodiments, nanostructured carbon and/or carbon precursors have an
average diameter of less than 20 nm. In certain embodiments,
nanostructured carbon and/or carbon precursors have an average
diameter of 2 nm to 20 nm. In specific embodiments, nanostructured
carbon and/or carbon precursors have an average diameter of 4 nm to
12 nm.
[0094] In certain embodiments, nanostructured carbon and/or carbon
precursors have any suitable second dimension, such as length,
e.g., an average length of at least 25 nm. In more specific
embodiments, nanostructured carbon and/or carbon precursors have an
average length of at least 50 nm. In still more specific
embodiments, nanostructured carbon and/or carbon precursors have an
average length of at least 100 nm. In certain embodiments,
nanostructured carbon and/or carbon precursors have an average
diameter of 50 nm to 300 nm. In specific embodiments,
nanostructured carbon and/or carbon precursors have an average
diameter of 100 nm to 250 nm.
[0095] In specific embodiments, nanostructured carbon (e.g., CNT,
graphite, graphene) and/or carbon precursors (e.g., CNC) provided
herein have an average diameter of 2 nm to 20 nm and an average
length of 50 nm to 300 nm. In more specific embodiments,
nanostructured carbon and/or carbon precursors (e.g., CNC) provided
herein have an average diameter of 4 nm to 12 nm and an average
length of 100 nm to 250 nm. In still more specific embodiments,
nanostructured carbon and/or carbon precursors (e.g., CNC) provided
herein have an average diameter of about 7-9 nm and an average
length of about 90-110 nm. In other specific embodiments,
nanostructured carbon and/or carbon precursors (e.g., CNC) provided
herein have an average diameter of about 9-11 nm and an average
length of about 140-160 nm. In still other specific embodiments,
nanostructured carbon and/or carbon precursors (e.g., CNC) provided
herein have an average diameter of about 5-7 nm and an average
length of about 150-250 nm.
Metal Component
[0096] In various embodiments, the metal component in a nanofiber
provided herein is any suitable metal material (e.g., a metal
containing nanoparticle, such as a silicon nanoparticle). In some
embodiments, the metal component comprises a transition metal, an
alkali metal, an alkaline earth metal, a metalloid, or the like. In
certain embodiments, the metal component comprises metal precursor
(e.g., metal ions (e.g., from disassociated metal salt), metal
salt, (such as metal acetate, metal nitrate, metal halide, or the
like), nanoparticles (e.g., metal, metalloid, metal oxide, ceramic,
or the like nanoparticles), or the like. In specific embodiments,
the metal component comprises silicon, such as silicon, or a
silicon alloy (e.g., a silicon metal oxide). In some embodiments,
the metal component comprises silicon in a zero oxidation state
(e.g., elemental silicon), a positive (greater than zero) oxidation
state (e.g., sub-stoiciometric silica, silicon dioxide and/or
silicon carbide), or a combination thereof. In certain embodiments,
the silicon material is a material suitable for use in a lithium
ion battery anode or negative electrode. In some embodiments, the
silicon material 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 silicon of the
silicon material is in a crystalline state. In various embodiments,
the silicon of the silicon material is in a zero oxidation state, a
positive oxidation state, or a combination thereof. In specific
embodiments, the silicon of the silicon 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). In certain
embodiments, the metal component is a metal precursor, such as a
metal precursor of a material suitable for use as an anode material
in a lithium ion battery. In some embodiments, metal precursors
include, by way of non-limiting example, silicon precursors (e.g.,
silicon acetate), titanium precursors (e.g., titanium acetate), tin
precursors (e.g., tin acetate), aluminum precursors (e.g., aluminum
acetate), bismuth precursors (e.g., bismuth acetate), combinations
thereof, or the like.
[0097] In specific embodiments, a nanofiber provided herein
comprises silicon nanoparticles. In specific embodiments, the
silicon nanoparticles comprise at least 70 wt. % zero oxidation
silicon and less than 30 wt % silicon dioxide. In more specific
embodiments, the silicon nanoparticles comprise at least 90 wt. %
zero oxidation silicon and less than 10 wt % silicon dioxide. In
still more specific embodiments, the silicon nanoparticles comprise
70-99 wt. % zero oxidation silicon and 0.01 (or 0.1) wt % to 30 wt
% silicon dioxide. In certain embodiments, the silicon
nanoparticles comprise zero oxidation state elemental silicon,
silicon dioxide, and silicon carbide. In specific embodiments, a
nanofiber provided herein comprises silicon nanoparticles. In
specific embodiments, the silicon nanoparticles comprise at least
70 wt. % zero oxidation silicon and less than 30 wt % SiOy
(0<y.ltoreq.2). In more specific embodiments, the silicon
nanoparticles comprise at least 90 wt. % zero oxidation silicon and
less than 10 wt % SiOy (0<y.ltoreq.2). In still more specific
embodiments, the silicon nanoparticles comprise 70-99 wt. % zero
oxidation silicon and 0.01 (or 0.1) wt % to 30 wt % SiOy
(0<y.ltoreq.2). In certain embodiments, the silicon
nanoparticles comprise zero oxidation state elemental silicon, SiOy
(0<y.ltoreq.2), and silicon carbide.
[0098] In certain embodiments, the discrete silicon 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.
[0099] In certain embodiments, provided herein are nanofibers
comprising a silicon material, the silicon material comprising
silicon (and other optional elements). In specific embodiments, the
nanofibers comprise at least 25% by weight of the silicon material
(e.g., on average for a plurality of nanofibers). In more specific
embodiments, the nanofibers comprise at least 50% by weight of the
silicon 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 silicon material (e.g., on average for a
plurality of nanofibers). In yet more specific embodiments, the
nanofibers comprise at least 70% by weight of the silicon material
(e.g., on average for a plurality of nanofibers). In specific
embodiments, the nanofibers comprise at least 80% by weight of the
silicon material (e.g., on average for a plurality of
nanofibers).
[0100] 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 nanofibers comprise at least 50% by weight of the silicon
(e.g., on average for a plurality of nanofibers). In more specific
embodiments, the nanofibers comprise at least 75% by weight of
silicon (e.g., on average for a plurality of nanofibers). In yet
more specific embodiments, the nanofibers comprise at least 90% by
weight of silicon (e.g., on average for a plurality of nanofibers).
In specific embodiments, the nanofibers comprise at least 95% by
weight of silicon (e.g., on average for a plurality of
nanofibers).
[0101] In some embodiments, the silicon material comprises silicon,
silicon oxide, sub-stoiciometric silica, 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.
Nanofibers
[0102] In certain embodiments, nanofiber provided herein have any
suitable characteristic.
[0103] In some embodiments, a nanofiber provided herein has a
diameter of less than 2 microns (e.g., an average diameter of a
plurality of nanofibers). In specific embodiments, a nanofiber
provided herein has a diameter of less than 1.5 microns (e.g., an
average diameter of a plurality of nanofibers). In more specific
embodiments, a nanofiber provided herein has a diameter of less
than 1 micron (e.g., an average diameter of a plurality of
nanofibers). In still more specific embodiments, a nanofiber
provided herein has a diameter of less than 750 nm (e.g., an
average diameter of a plurality of nanofibers). In yet more
specific embodiments, a nanofiber provided herein has a diameter of
less than 500 nm (e.g., an average diameter of a plurality of
nanofibers). In more specific embodiments, a nanofiber provided
herein has a diameter of less than 250 nm (e.g., an average
diameter of a plurality of nanofibers).
[0104] In some embodiments, nanofibers provided herein have a
(e.g., average) length of at least 1 .mu.m, at least 10 .mu.m, at
least 20 .mu.m, at least 100 .mu.m, at least 500 .mu.m, at least
1,000 .mu.m, at least 5,000 .mu.m, at least 10,000 .mu.m, or the
like.
[0105] In some embodiments, a nanofiber provided herein has an
aspect ratio of greater than 10 (e.g., an average aspect ratio of a
plurality of nanofibers). In specific embodiments, a nanofiber
provided herein has an aspect ration of greater than 100 (e.g., an
average aspect ratio of a plurality of nanofibers). In more
specific embodiments, a nanofiber provided herein has an aspect
ration of greater than 500 (e.g., an average aspect ratio of a
plurality of nanofibers). In still more specific embodiments, a
nanofiber provided herein has an aspect ration of greater than 1000
(e.g., an average aspect ratio of a plurality of nanofibers). In
yet more specific embodiments, a nanofiber provided herein has an
aspect ration of greater than 10.sup.4 (e.g., an average aspect
ratio of a plurality of nanofibers).
[0106] 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 silicon, carbon, and oxygen, 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 silicon and carbon, when taken together,
by mass (e.g., elemental mass).
Batteries and Electrodes
[0107] 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).
[0108] 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 1200 mAh/g on a first cycle at 0.1 C
(e.g., as determined by half cell or full cell testing). 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 1050
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 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 750
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 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.
[0109] In some embodiments, negative electrodes provided herein are
prepared by depositing high energy (anodic) capacity nanofibers
(e.g., comprising a carbon matrix with silicon nanoparticles
embedded therein) 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. In further or alternative
specific embodiments, the composition further comprises a
conductive material (e.g., carbon black)--e.g., to improve electron
mobility.
Process
[0110] In certain embodiments, provided herein is a process for
preparing a nanofiber, the process comprising:
[0111] providing a fluid stock comprising a polymer and carbon
and/or a carbon precursor; and
[0112] electrospinning the fluid stock.
[0113] In certain embodiments, provided herein is a process for
preparing a nanofiber, the process comprising:
[0114] providing a fluid stock comprising a polymer and a high
aspect ratio nanostructure; and
[0115] electrospinning the fluid stock.
[0116] In certain embodiments, such a nanofiber comprises a
continuous polymer matrix with carbon and/or carbon precursor
(e.g., nanostructured carbon and/or carbon precursor) embedded
therein. In some embodiments, the nanostructured carbon precursor
has an aspect ratio of greater than 2 (e.g., greater than 10). In
specific embodiments, a plurality or a majority of the
nanostructured carbon and/or carbon precursors are aligned (i.e.,
along the length of the nanostructured carbon precursor) with
(i.e., in the same direction, e.g., within 5 or 10 degrees of
parallel) the nanofiber (i.e., along the length of the nanofiber).
In some embodiments, the fluid stock comprises polymer:carbon
precursor (e.g., CNC) in a wt. to wt. ratio of 4:1 to 1:4, e.g.,
2:1 to 1:2. In some embodiments, the fluid stock comprises
polymer:carbon (e.g., CNT) in a wt. to wt. ratio of 4:1 to 1:4,
e.g., 2:1 to 1:2.
[0117] In certain embodiments, provided herein is a process for
preparing a nanofiber, the nanofiber comprising a continuous carbon
matrix, the process comprising:
[0118] providing a fluid stock comprising (i) a polymer and (ii)
carbon and/or a carbon precursor;
[0119] electrospinning the fluid stock, producing an as-spun
nanofiber; and
[0120] thermally treating the as-spun nanofiber (e.g., under inert
or reducing conditions), producing a nanofiber comprising a
continuous carbon matrix.
[0121] In some embodiments, the nanostructured carbon and/or carbon
precursor has an aspect ratio of greater than 2 (e.g., greater than
10). In specific embodiments, a plurality or a majority of the
nanostructured carbon and/or carbon precursors are aligned (i.e.,
along the length of the nanostructured carbon precursor) with
(i.e., in the same direction, e.g., within 5 or 10 degrees of
parallel) the as-spun nanofiber (i.e., along the length of the
nanofiber). In some embodiments, the fluid stock comprises
polymer:carbon precursor (e.g., CNC) in a wt. to wt. ratio of 4:1
to 1:4, e.g., 2:1 to 1:2. In some embodiments, the fluid stock
comprises polymer:carbon (e.g., CNT) in a wt. to wt. ratio of 4:1
to 1:4, e.g., 2:1 to 1:2.
[0122] In some embodiments, provided herein is a process for
preparing a nanofiber, the nanofiber comprising a continuous carbon
matrix, the process comprising:
[0123] providing a fluid stock comprising a polymer, carbon and/or
a carbon precursor, and a metal component (e.g., a metal precursor
or metal-containing nanoparticle);
[0124] electrospinning the fluid stock, producing an as-spun
nanofiber; and
[0125] thermally treating the as-spun nanofiber (e.g., under inert
or reducing conditions), producing a nanofiber comprising a
continuous carbon matrix.
[0126] In certain embodiments, such a nanofiber comprises a
continuous carbon matrix with metal component domains therein
(e.g., metal containing nanoparticles, such as silicon
nanoparticles, embedded therein). In some embodiments, the
nanostructured carbon and/or carbon precursor has an aspect ratio
of greater than 2 (e.g., greater than 10). In specific embodiments,
a plurality or a majority of the nanostructured carbon and/or
carbon precursors are aligned (i.e., along the length of the
nanostructured carbon precursor) with (i.e., in the same direction,
e.g., within 5 or 10 degrees of parallel) the nanofiber (i.e.,
along the length of the nanofiber). In some embodiments, the fluid
stock comprises polymer:carbon precursor (e.g., CNC) in a wt. to
wt. ratio of 4:1 to 1:4, e.g., 2:1 to 1:2. In some embodiments, the
fluid stock comprises polymer:carbon (e.g., CNT) in a wt. to wt.
ratio of 4:1 to 1:4, e.g., 2:1 to 1:2. In certain embodiments, the
fluid stock comprises polymer:(carbon (e.g., CNT) plus metal
component (e.g., Si NP)) in a wt. to wt. ratio of 4:1 to 1:4, e.g.,
2:1 to 1:2.
[0127] In specific 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 an organic solvent, such as
dimethylformamide (DMF).
[0128] In some embodiments, thermal treatment of the as-spun
nanofiber comprises thermally treating the as-spun nanofiber under
inert conditions (e.g., argon or nitrogen). In still other specific
embodiments, thermal treatment of the as-spun nanofiber comprises
thermally treating the as-spun nanofiber under reducing conditions
(e.g., hydrogen, or a hydrogen/argon blend). In certain
embodiments, the as-spun nanofiber is heated to a temperature of
about 500.degree. C. to about 2000.degree. 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).
[0129] 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.
[0130] 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.
[0131] In certain embodiments, provided herein are nanofibers and
fluid stocks wherein the carbon and/or carbon precursor (e.g.,
nanostructured carbon or carbon precursor, such as CNC or CNT) to
polymer weight ratio is at least 1:10, at least 1:5, at least 1:4,
at least 1:3, at least 1:2, or the like. In some instances,
provided herein are nanofibers and fluid stocks wherein the metal
component of a process described herein is a preformed nanoparticle
(e.g., silicon nanoparticle), the metal 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 certain embodiments, the total inclusion (e.g., metal
component and carbon and/or carbon precursor) to polymer ratio is
about 1:99 to about 95:5 in a fluid stock or of a nanofiber (e.g.,
comprising a polymer matrix--such as a precursor nanofiber)
provided herein. In some embodiments, the total inclusion to
polymer ratio is about 33:67 to about 90:10 in a fluid stock or
nanofiber provided herein. In specific embodiments, the total
inclusion to polymer ratio is about 50:50 to about 80:20 in a fluid
stock or nanofiber provided herein.
[0132] 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 %, or at least about 20 weight polymer.
Electrospinning
[0133] In some embodiments, the process comprises electrospinning a
fluid stock. Any suitable method for electrospinning is used.
[0134] In some embodiments, provided herein is a process for
preparing a nanofiber, the process comprising:
[0135] providing a fluid stock to a first conduit of an
electrospinning nozzle apparatus, the first conduit being enclosed
along the length of the conduit by a first wall having an interior
and an exterior surface, the first conduit having a first inlet end
and a first outlet end, and the first conduit having a first
diameter; and
[0136] providing a gas (e.g., a pressurized or high speed gas) to a
second conduit of an electrospinning apparatus, the second conduit
being enclosed along the length of the conduit by a second wall
having an interior surface, the second conduit having a second
inlet end and a second outlet end, and the second conduit having a
second diameter.
[0137] In certain embodiments, the first and second conduit having
a conduit overlap length (for example, FIG. 3 illustrates a portion
of the overlap of two conduits 301 and 302). In some embodiments,
the first conduit (e.g., 301 in FIG. 3) is positioned inside the
second conduit (e.g., 302 in FIG. 3), the exterior surface of the
first wall and the interior surface of the second wall being
separated by a conduit gap. In certain embodiments, the first
outlet end protruding beyond the second outlet end by a protrusion
length (an example of which is illustrated by 304 in FIG. 3). In
some instances, the ratio of the conduit overlap length-to-second
diameter is about 10 or more (e.g., about 13 or more, or about 18
or more). In further or alternative embodiments, the ratio of the
average conduit gap-to-second diameter about 0.2 or less (e.g.,
about 0.1 or less, or about 0.05 or less). In further or
alternative embodiments, the ratio of the protrusion
length-to-second diameter is about 0.3 or less. In certain
embodiments, the fluid stock is provided to the first conduit at
any suitable rate, e.g., at a rate of at least 0.05 mL/min (e.g.,
about 0.05 mL/min to about 3 mL/min). In more specific embodiments,
the rate is at least 0.5 mL/min (e.g., about 0.5 mL/min to about
2.5 mL/min) In some embodiments, the gas is provided to the second
conduit at any suitable speed or pressure. In specific embodiments,
the gas is provided at a pressure of about 15 to about 30 psi,
e.g., about 25 psi. In certain embodiments, the conduits have any
suitable shape, such as conical (e.g., circular or elliptical),
conical (e.g., circular or elliptical), prismatic, or the like. In
specific instances, the first conduit and the first wall, taken
together, form a first needle, and the second conduit and the
second wall, taken together, form a second needle. In various
embodiments, any suitable first and second diameter is utilized.
For example, in specific instances, the first diameter being about
0.05 mm to about 3 mm. In further or alternative embodiments, the
second diameter is about 0.1 mm to about 5 mm. In certain
embodiments, the conduit gap is on average 0.5 mm or less (e.g.,
about 0.01 mm to about 0.5 mm) In some embodiments, a voltage is
applied to the nozzle apparatus to electrospin the fluid stock. Any
suitable voltage is optionally applied to the nozzle, such as about
5 kV to about 50 kV. In specific embodiments, the voltage is about
20 kV to about 30 kV, such as about 25 kV. Further and more
specific embodiments are described in U.S. Provisional Patent
Application 61/7981,260 and the corresponding PCT application(s)
claiming priority thereto, all of which are incorporated herein for
such disclosure.
[0138] In some instances, elevated temperature electrospinning is
utilized. Exemplary methods for comprise methods for
electrospinning at elevated temperatures as disclosed in U.S. Pat.
No. 7,326,043 and U.S. Pat. No. 7,901,610, which are incorporated
herein for such disclosure. In some embodiments, elevated
temperature electrospinning improves the homogeneity of the fluid
stock throughout the electrospinning process.
[0139] In some embodiments, gas assisted electrospinning is
utilized (e.g., about a common axis with the jet electrospun from a
fluid stock described herein). Exemplary methods of gas-assisted
electrospinning are described in PCT Patent Application
PCT/US2011/024894 ("Electrospinning apparatus and nanofibers
produced therefrom"), which is incorporated herein for such
disclosure. In gas-assisted embodiments, the gas is optionally air
or any other suitable gas (such as an inert gas, oxidizing gas, or
reducing gas). In some embodiments, gas assistance increases the
throughput of the process and/or reduces the diameter of the
nanofibers. In some instances, gas assisted electrospinning
accelerates and elongates the jet of fluid stock emanating from the
electrospinner. In some instances, gas assisted electrospinning
disperses silicon material in nanofibers. For example, in some
instances, gas assisted electrospinning (e.g., coaxial
electrospinning of a gas--along a substantially common axis--with a
fluid stock comprising Si nanoparticles) facilitates dispersion or
non-aggregation of the Si nanoparticles in the electrospun jet and
the resulting as-spun nanofiber (and subsequent nanofibers produced
therefrom). In some embodiments, incorporating a gas stream inside
a fluid stock produces hollow nanofibers. In some embodiments, the
fluid stock is electrospun using any suitable technique.
[0140] In specific embodiments, the process comprises coaxial
electrospinning (electrospinning two or more fluids about a common
axis). As described herein, coaxial electrospinning a first fluid
stock as described herein (e.g., comprising carbon/carbon precursor
and polymer) with a second fluid is used to add coatings, make
hollow nanofibers, make nanofibers comprising more than one
material, and the like. In various embodiments, the second fluid is
either outside (i.e., at least partially surrounding) or inside
(e.g., at least partially surrounded by) the first fluid stock. In
some embodiments, the second fluid is a gas (gas-assisted
electrospinning) In some embodiments, gas assistance increases the
throughput of the process, reduces the diameter of the nanofibers,
is used to produce hollow nanofibers, and/or reduces nanostructure
and/or nanoparticle aggregation in as-spun nanofibers. In some
embodiments, the method for producing nanofibers comprises
coaxially electrospinning the first fluid stock and a gas.
[0141] The term "alkyl" as used herein, alone or in combination,
refers to an optionally substituted straight-chain, optionally
substituted branched-chain or optionally substituted carbocyclic
saturated or unsaturated hydrocarbon radical. Examples include, but
are not limited to methyl, ethyl, propyl, butyl, pentyl, hexyl, and
longer alkyl groups, such as heptyl, octyl and the like. certain
instances, "alkyl" groups described herein include linear and
branched alkyl groups, saturated and unsaturated alkyl groups, and
cyclic and acyclic alkyl groups.
[0142] 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 non-limiting example of a single ring aryl
group includes phenyl; a fused ring aryl group includes
naphthyl.
[0143] The term "heterocycle" as used herein, alone or in
combination, refers to optionally substituted cyclic 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.
EXAMPLES
Example 1
Preparing an Electrospinning Fluid Stock
[0144] 1 grams of preformed nanostructured carbon and/or carbon
precursor is suspended in 20 ml of 1 molar acetic acid solution
with X-100 surfactant. The combination is optionally stirred for 2
hours, sonicated, or the like to create a first composition.
[0145] In a second composition, 1 gram of 99.7% hydrolyzed
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 optionally heated to a temperature
of 95.degree. C. and stirred for 2 hours to create a homogenous
solution.
[0146] The first and second compositions are then combined to
create a fluid stock. In order to distribute the carbon/carbon
precursor substantially evenly in the fluid stock, the first
composition is optionally added gradually to the second composition
while being continuously vigorously stirred for 2 hours. The mass
ratio of carbon/carbon precursor to polymer for the fluid stock is
1:1.
Example 2
Preparing Polymer Composite Nanofiber and Carbon Nanofiber
[0147] The fluid stock is co-axially electrospun with gas using a
coaxial needle apparatus similar to the one depicted in FIG. 1
(where 111 illustrates the needle apparatus). The center conduit
contains fluid stock of Example 1 and the outer conduit contains
air. The electrospun fluid stock (as-spun nanofiber) is calcinated
by heating for 2 hours at 400-1200.degree. C. in an inert
atmosphere (e.g., argon).
Example 3
Preparing CNC/Polymer Composite Nanofibers and Nanofibers Having
Carbon Matrix
Example 3A
[0148] Using a process similar to Example 1, a fluid stock is
prepared using 0.2 g of cellulose nanocrystal (CNC) (8 nm average
diameter, 100 nm average length) as the carbon precursor. The
resultant polymer:precursor weight ratio is 5:1. The fluid stock is
electrospun according to a process of Example 2.
Example 3B
[0149] Using a process similar to Example 1, a fluid stock is
prepared using 0.1 g of cellulose nanocrystal (CNC) (8 nm average
diameter, 100 nm average length) as the carbon precursor. The
resultant polymer:precursor weight ratio is 10:1. The fluid stock
is electrospun according to a process of Example 2.
Example 4
Preparing CNT/Si NP/Polymer Composite Nanofibers and Si/C Composite
Nanofibers
[0150] Using a process similar to Example 1, a fluid stock is
prepared using 0.1 g of carbon nanotubes as a carbon inclusion. In
addition, 1 gram of preformed silicon nanoparticles (.about.50 nm
average diameter) is added to the first composition. The resultant
polymer:nanoparticle:precursor weight ratio is 10:10:1.
[0151] The fluid stock is electrospun according to a process of
Example 2. FIG. 4(A) illustrates as-spun nanofibers and
nanoparticles (Si NP) in polymer matrix nanofibers; FIG. 4(C) is an
increased magnification image over image (A); FIG. 4(B) illustrates
thermally treated (at 900.degree. C. for 5 hours under argon)
nanofibers therefrom; and FIG. 4(D) an increased magnification
image over image (B).
Example 5
Preparing Carbon Allotrope/Polymer Composite Nanofibers
[0152] Using a process similar to Example 1, a fluid stock is
prepared using 0.1 g of carbon nanotubes as a carbon precursor. The
resultant polymer:precursor weight ratio is 10:1.
[0153] Also, using a process similar to Example 1, a fluid stock is
prepared with carbon black (Super P) and PVA at various PVA:Super P
molar ratios (e.g., 2.1, 3.14 and >3.14). The fluid stock is
electrospun and carbonized. FIG. 11(A) illustrates an SEM image of
electrospun carbon allotrope/polymer composite nanofibers; and FIG.
11(B) illustrates carbonized nanofibers prepared by carbonizing
such nanofibers.
Example 6
Preparing CNC/Si NP/Polymer Composite Nanofibers and Si/C Composite
Nanofibers
Example 6A
[0154] Using a process similar to Example 1, a fluid stock is
prepared using 0.2 g of cellulose nanocrystal (CNC) (8 nm average
diameter, 100 nm average length) as the carbon precursor. In
addition, 1 gram of preformed silicon nanoparticles (.about.50 nm
average diameter) is added to the first composition. The resultant
polymer:nanoparticle:precursor weight ratio is 10:10:2.
[0155] The fluid stock is electrospun according to a process of
Example 2. FIG. 5 illustrates as-spun nanofibers (Panel A) and
thermally treated (at 900.degree. C. for 5 hours under argon)
nanofibers (panel B).
Example 6B
[0156] Using a process similar to Example 1, a fluid stock is
prepared using 1 g of cellulose nanocrystal (CNC) (8 nm average
diameter, 100 nm average length) as the carbon precursor. In
addition, 1 gram of preformed silicon nanoparticles (.about.50 nm
average diameter) is added to the first composition. The resultant
polymer:nanoparticle:precursor weight ratio is 1:1:1.
[0157] The fluid stock is electrospun according to a process of
Example 2. FIG. 6(A) illustrates as-spun carbon precursor (CNC) and
nanoparticles (Si NP) in polymer matrix nanofibers (1:1:1); FIG. 6
(B) illustrates thermally treated nanofibers therefrom; FIG. 6 (C)
shows a surface TEM image; and FIG. 6 (D) shows a microtomed TEM
image thereof.
Example 6C
[0158] Using a process similar to Example 1, a fluid stock is
prepared using 0.1 g of cellulose nanocrystal (CNC) (8 nm average
diameter, 100 nm average length) as the carbon precursor. In
addition, 1 gram of preformed silicon nanoparticles (.about.50 nm
average diameter) is added to the first composition. The resultant
polymer:nanoparticle:precursor weight ratio is 10:10:1.
[0159] The fluid stock is electrospun according to a process of
Example 2. FIG. 7 illustrates as-spun nanofibers (Panel A) and
thermally treated (at 900.degree. C. for 5 hours under argon)
nanofibers (panel B).
Example 6D
[0160] Nanofibers are also prepared without additional carbon
precursor, using PVA and Si nanoparticles in a process similar to
that described in Examples 5A-5C. FIG. 8: (A) illustrates as-spun
nanoparticles (Si NP) in polymer matrix nanofibers (1:1), (B)
thermally treated nanofibers therefrom, (C) surface TEM image, and
(D) microtomed TEM image thereof.
[0161] Comparing FIG. 6 and FIG. 8 panels C and D illustrate the
comparison of distribution of Si NPs in carbon matrix nanofibers
for those nanofibers prepared with and without carbon precursor,
respectively. Si NPs are more randomly distributed in carbon
nanofibers from the PVA/Si NP system, whereas Si NPs are more
uniformly dispersed in carbon nanofibers from the PVA/Si/CNC
systems. The microtomed TEM image of cross-section of the nanofiber
in FIG. 6, Panel D shows encapsulation of Si NP by carbon. In some
instances, this configuration will reduce or prevent the Si--C
hybrid/composite anode from pulverization during the
lithiation/delithiation process.
[0162] Table 1 illustrates yields of nanofibers prepared herein as
well as yields of similar nanofibers prepared in the absence of
carbon precursor. Yield measurements are determined by the
following analysis: wt. thermally treated NF/wt. pre-thermal
treatment (i.e., spun) NF.
TABLE-US-00001 900.degree. C. * 5 h, Cal- Calcined 2.degree. C./m
Constituents cination nanofibers (under argon) PVA Si CNC Yield Si
Carbon PVA 100.0% 6.5% 100.0% CNC 100.0% 27.3% 100.0% PVA/Si(1/1)
50.0% 50.0% 51.3% 97.4% 2.6% PVA/Si/CNC 47.6% 47.6% 4.8% 47.3%
91.9% 8.1% (10/10/1) PVA/Si/CNC 45.5% 45.5% 9.1% 42.9% 90.6% 9.4%
(10/10/2) PVA/Si/CNC 33.3% 33.3% 33.3% 38.8% 85.9% 14.1%
(10/10/10)
[0163] Table 2 illustrates cycling performance of nanofibers
constructed as an anode in a lithium ion battery half cell.
TABLE-US-00002 TABLE 2 Specific Capacity (mAh/g) Anode 1.sup.st
cycle 50.sup.th cycle 98.sup.th cycle Si NP 3,310 22 13 Thermally
treated NF 2,091 1,011 286 from PVA/Si (1:1) Thermally treated NF
2,250 1,253 814 from PVA/Si/CNC (1:1:1)
[0164] Further, FIG. 9 illustrates discharge cyclability (0.1 C) of
various nanofibers prepared from spun nanofibers with and without
nanostructured carbon precursors. FIG. 10 illustrates the improved
performance of anodes prepared from nanofibers prepared from spun
nanofibers having nanostructured carbon precursors.
[0165] Si nanoparticles show very high initial capacity, but show
drastic decrease in capacity as charge/discharge cycle. Polymer
(PVA)/Si NP system shows much stable behavior than Si nanoparticles
in the cycle performance. As increasing the polymer (PVA) contents,
the content of carbon increases and cycle performance becomes more
stable, but still shows rapid decrease in capacity. By addition of
CNC, anode shows higher capacity and more stable cyclability than
PVA/Si system.
Example 7
[0166] Polyvinyl alcohol (PVA) (M.sub.w 78,000) was provided from
Polyscience Inc., and Si nanoparticles with the size of 20.about.30
nm were supplied by Nanostructured & Amorphous Materials, Inc.
CNC has a Na form which is pH.about.7.
[0167] We dispersed CNCs in the water with concentration of
8.about.12%, and mixed PVA with the ratio of PVA/CNC=1/1, 5/1 and
10/1. And Si nanoparticles were added in the PVA/CNC solution to
prepare PVA/Si/CNC solution. The weight ratios of PVA/Si/CNC was
10/10/10 and to prevent the aggregation of nanoparticles PVA/Si/CNC
solution was sonicated for 3.about.5 hrs.
[0168] The prepared polymer solution was pumped into the needle for
electrospinning. The distance between the nozzle and collection
plate was kept to 10.about.20 cm, and the flow rate of
0.05.about.0.015 ml/min was maintained. A charge of +15 to +25 kV
was maintained at the needle. However, these variables could be
appropriately changed with the resin to obtain the right morphology
of the fibers as well as to fine tune their properties.
[0169] SEM images of carbon precursor nanofibers show very good
morphologies even at very high content of CNC. Calcined nanofibers
also show good fiber morphologies.
Example 8
[0170] PVA is charged in CNC containing composition with the ratio
of PVA/CNC 10/1, 10/2, 10/10 and then sonicated (e.g., for the
distribution of CNC). Si nanoparticles are added in these
composition to form PVA/Si/CNC (e.g., with ratios of PVA/Si=1/1,
2/1, 4/1 and 8/1). For the homogenization this composition is
sonicated again for a long time to distribute all the nanoparticles
well. When the composition is homogenized well, electrospinnability
of these solutions is good, providing very good fiber morphologies
even at very high content of CNC
[0171] To make carbon/Si nanocomposite nanofibers, as-spun fibers
are heat-treated under inert (e.g., argon) gas (e.g., at around 900
C.), providing nanofibers with good fiber morphologies. The
theoretical calcination yield of PVA is 54.5%, but experimental
yield is just 5.about.7% at 900 C. under argon. CNC of sodium form
shows low theoretical calcination yield of 36.4%, but experimental
yield is 26.about.28% at the same condition.
[0172] The obtained carbon/Si nanocomposite nanofibers are mixed
with conductor (Super P) and binder (PVDF), and then changed to
slurry with the help of solvent (NMP). This slurry is coated on the
copper foil and then dried in the vacuum oven. To calculate the
precise weight of activated materials, the weight of copper foil is
checked before and after coating. Dried anode is assembled into
coin type half cell with lithium metal foil as a cathode. Cell
performance is tested with the half cell.
* * * * *