U.S. patent application number 14/074752 was filed with the patent office on 2014-03-06 for electrode useable in electrochemical cell and method of making same.
This patent application is currently assigned to VANDERBILT UNIVERSITY. The applicant listed for this patent is VANDERBILT UNIVERSITY. Invention is credited to Shao-Hua Hsu, Weng Poo Kang, Supil Raina, Siyu Wei.
Application Number | 20140065299 14/074752 |
Document ID | / |
Family ID | 47219422 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140065299 |
Kind Code |
A1 |
Kang; Weng Poo ; et
al. |
March 6, 2014 |
ELECTRODE USEABLE IN ELECTROCHEMICAL CELL AND METHOD OF MAKING
SAME
Abstract
A method of making an electrode useable in an electrochemical
cell, includes the steps of (a) providing an electrically
conductive substrate; (b) forming nanostructured current collectors
on the conductive substrate; and (c) attaching nanoparticles of a
ternary orthosilicate composite to the nanostructured current
collectors. The ternary orthosilicate composite includes
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4, where x+y+z=1.
Inventors: |
Kang; Weng Poo; (Nashville,
TN) ; Raina; Supil; (Nashville, TN) ; Hsu;
Shao-Hua; (Nashville, TN) ; Wei; Siyu;
(Nashville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VANDERBILT UNIVERSITY |
Nashville |
TN |
US |
|
|
Assignee: |
VANDERBILT UNIVERSITY
Nashville
TN
|
Family ID: |
47219422 |
Appl. No.: |
14/074752 |
Filed: |
November 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13480860 |
May 25, 2012 |
8623555 |
|
|
14074752 |
|
|
|
|
61491096 |
May 27, 2011 |
|
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Current U.S.
Class: |
427/122 ;
427/126.1; 427/58 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 4/70 20130101; H01M 2010/0495 20130101; Y10T 29/49124
20150115; H01M 4/0404 20130101; H01M 4/5825 20130101; B82Y 30/00
20130101; H01M 4/136 20130101 |
Class at
Publication: |
427/122 ; 427/58;
427/126.1 |
International
Class: |
H01M 4/04 20060101
H01M004/04 |
Goverment Interests
STATEMENT AS TO RIGHTS UNDER FEDERALLY-SPONSORED RESEARCH
[0003] This invention was made with government support under
Contract No. N00014-11-M-0315 awarded by the Office of Navy
Research of the United States. The government has certain rights in
the invention.
Claims
1. A method of making an electrode useable in an electrochemical
cell, comprising the steps of: (a) providing an electrically
conductive substrate; (b) forming nanostructured current collectors
on the conductive substrate; and (c) attaching nanoparticles of a
ternary orthosilicate composite to the nanostructured current
collectors.
2. The method of claim 1, wherein the conductive substrate
comprises a film formed of an electrically conductive material.
3. The method of claim 2, wherein the film is flexible or
rigid.
4. The method of claim 1, wherein the nanostructured current
collectors comprise conductive nanotubes/fibers.
5. The method of claim 4, wherein the conductive nanotubes/fibers
comprie carbon nanotubes (CNTs) or carbon fibers (CFs).
6. The method of claim 4, wherein the forming step comprises
growing the conductive nanotubes/fibers on the conductive
substrate.
7. The method of claim 1, wherein the ternary orthosilicate
composite comprises Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4.
8. The method of claim 7, wherein x+y+z=1.
9. The method of claim 7, wherein the ternary orthosilicate
composite is synthesized by a hydrothermal process comprising: (a)
mixing starting precursors of lithium hydroxide, SiO.sub.2
particles, Fe(II) chloride tetrahydrate, manganese chloride, and
cobalt chloride, in a predetermined composition ratio to form a
mixture; (b) sealing the mixture under an Ar environment and baking
the sealed mixture at a predetermined temperature for a period of
time to form Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound;
(c) rinsing the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound
with de-ionized (DI) water; (d) drying rinsed
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound in vacuum; (e)
ball-milling the dried Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
compound into nanoparticles; and (f) calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powder in an inert or
reducing environment.
10. The method of claim 7, wherein the ternary orthosilicate
composite is synthesized by a Pechini process comprising: (a)
dispersing lithium acetate dehydrate, SiO.sub.2 particles, citric
acid, and ethylene glycol at a first predetermined composition
ratio in de-ionized (DI) water to form a first mixture, wherein the
mixture is sonicated for a period of time; (b) adding Fe(III)
citrate, manganese acetate, and cobalt carbonate at a second
predetermined composition ratio into the first mixture to form a
second mixture; (c) stirring and dwelling the second mixture to
form a Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel; (d) drying
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel to form
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound; (e) grinding
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders into
nanoparticles; and (f) heat-treating the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing atmosphere.
11. The method of claim 7, wherein the ternary orthosilicate
compound is synthesized by a sol-gel process comprising the steps
of: (a) dispersing lithium acetate, iron citrate, manganese acetate
and cobalt carbonate at a first predetermined composition ratio in
de-ionized (DI) water to form a first mixture; (b) adding citric
acid to the first mixture to form a second mixture, (c) adding
tetraethylorthosilicate (TEOS) and ethanol at a second
predetermined composition ratio to form a third mixture; (d)
stirring and dwelling the third mixture at a reflux station to form
a Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel; (e) drying the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound; (f) grinding
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound into
nanoparticles; and (g) calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
12. The method of claim 1, wherein the attaching step is performed
by a dripping/wetting process comprising: (a) preparing a
suspension of the nano-particles of the ternary orthosilicate
composite in a liquid medium; (b) dripping the suspension into the
nanostructured current collectors in electrical contact with the
conductive substrate; and (c) drying the suspension to attach the
nano-particles of the ternary orthosilicate composite onto the
nanostructured current collectors.
13. The method of claim 12, wherein the liquid medium comprises
acetone, water or other liquid media.
14. The method of claim 1, further comprising filling an
electrolyte solution in spaces defined among the nanostructured
current collectors and the nanoparticles of the active material.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a divisional application of and claims
the benefit of U.S. patent application Ser. No. 13/480,860, filed
May 25, 2012, entitled "ELECTRODE USEABLE IN ELECTROCHEMICAL CELL
AND METHOD OF MAKING SAME," by Weng Poo Kang, Supil Raina, Shao-Hua
Hsu and Siyu Wei, which status is allowed, which itself claims the
benefit, pursuant to 35 U.S.C. .sctn.119(e), of U.S. provisional
patent application Ser. No. 61/491,096, filed May 27, 2011,
entitled "LITHIUM-ION BATTERY CATHODE COMPRISING TERNARY COMPOSITE
OF NANOSTRUCTURED MATERIALS AND METHODS OF MAKING SAME," by Weng
Poo Kang, Siyu Wei and Supil Raina. Each of the above applications
is incorporated herein by reference in its entirety.
[0002] Some references, which may include patents, patent
applications and various publications, are cited and discussed in
the description of this invention. The citation and/or discussion
of such references is provided merely to clarify the description of
the present invention and is not an admission that any such
reference is "prior art" to the invention described herein. All
references cited and discussed in this specification are
incorporated herein by reference in their entireties and to the
same extent as if each reference was individually incorporated by
reference. In terms of notation, hereinafter, "[n]" represents the
nth reference cited in the reference list. For example, [1]
represents the 1st reference cited in the reference list, namely,
S. Wei, W. P. Kang, J. L. Davidson, B. R. Rogers, and J. H. Huang,
ECS Transactions 28, 97 (2010).
FIELD OF THE INVENTION
[0004] The present invention relates generally to a method of
making an electrode useable in an electrochemical cell, and more
particularly to a method of making a battery cathode material
including the steps of providing an electrically conductive
substrate, forming nanostructured current collectors on the
conductive substrate, and attaching (or coating) nanoparticles of a
ternary orthosilicate composite to the nanostructured current
collectors.
BACKGROUND OF THE INVENTION
[0005] Currently, a lithium-ion battery (LIB) is one of the most
promising battery technologies that can provide higher energy
density than other batteries. It also does not suffer from the
memory effect and the loss of charge is relatively slow when not in
use. Hence, high-performance LIB remains the preferred technology
that would address a much broader range of energy source/storage
for a variety of applications if advanced cathode material with
extreme operating capability could be realized.
[0006] Current lithium ion batteries mostly utilize metal oxides as
cathode material with LiCoO.sub.2 as the most popular and
commercially successful representative [2]. However, due to the
intrinsic material properties of these metal oxides, further
enhancement of LIB performance is limited. Specifically, the metal
oxides have limited average potential versus Li/Li.sup.+, mostly
well below 4V except LiMn.sub.2O.sub.4, and most of the metal
oxides have the specific capacity well below 180 mAh/g, with the
exception of LiNiO.sub.2. The metal oxides are also "hot" cathode
materials due to the thermal runaway reaction, so there is also a
concern for safety.
[0007] Another major group of cathode materials is LiMPO.sub.4,
where M=Co, Ni, Mn, or Fe. These materials have the electrode
potential in the range of about 3.5-5.2 V, but the capacity is
still limited below 150-170 mAh/g [3]. Further, these materials
have poor electrical conductivity, so they have to be made in the
form of tiny nanoparticles and coated with a carbon layer, which
increases the cost of the materials.
[0008] The Li.sub.2MSiO.sub.4 silicate family (where M=Co, Fe, or
Mn) has attracted research activities for the applications in LIB
only recently [4, 5] and much work needs to be done to thoroughly
understand its properties. The most significant advantage of this
group of materials is the polyanionic structure with two lithium
ions per formula unit. The theoretical capacity of these materials
is as high as about 330 mAh/g. Unfortunately, Co is an expensive
metal despite its high average voltage of about 4.3 V. Therefore,
pure Li.sub.2CoSiO.sub.4 is not an efficient and economic way for
making a cathode. Li.sub.2FeSiO.sub.4 has good cycle-ability, but
the average voltage is only about 3.1 V, far below 4 V. On the
contrary, Mn is an inexpensive and abundant element. The average
voltage of Li.sub.2MnSiO.sub.4 is about 4.2 V. The reported
specific capacity of Li.sub.2MnSiO.sub.4 is about 210 and about 250
mAh/g at room temperature and 55.degree. C., respectively [6].
However, it has to be noted that the entire family of
Li.sub.2MSiO.sub.4 silicates has poor electrical conductivity,
therefore Li.sub.2MnSiO.sub.4 has to be made into nanoparticles and
coated with carbon in order to improve the conductivity, similar to
the aforementioned LiMPO.sub.4. The additional carbon-coating
process is expensive.
[0009] Another major drawback of Li.sub.2MnSiO.sub.4 is its poor
cycle life characterized by the poor capacity retention and rate
performance. A recent report shows a 50% retained capacity at room
temperature after 20 cycles. The poor cycling performance is mainly
attributed to Jahn-Teller distortion, structural instability and
low electronic conductivity of the material. Another possible
attribution is the electrolyte degradation.
[0010] The presence of Mn.sup.3+ ions in the material system is
responsible for the dynamic Jahn-Teller distortion and manganese
dissolution, a situation similar to that of LiMn.sub.2O.sub.4
spinel cathode. Also, the structure of Li.sub.2MnSiO.sub.4 is prone
to collapsing upon delithiation. During delithiation, a phase
separation into MnSiO.sub.4 and Li.sub.2MnSiO.sub.4 may occur,
leading to the formation of an amorphous structure, which in turn
results in the drop of reversible capacity of the electrode during
the cycling.
[0011] An effective way to minimize the dynamic Jahn-Teller
distortion and prevent the collapse of Li.sub.2MnSiO.sub.4
structure is the utilization of a solid solution of
Li.sub.2MnSiO.sub.4 and Li.sub.2FeSiO.sub.4 as the cathode.
However, there is very limited research available on this topic. A
few literature reports do show that addition of Li.sub.2FeSiO.sub.4
has prevented Li.sub.2MnSiO.sub.4 from collapsing during
delithiation [7, 8]. Nonetheless, according to the reports, the
cyclic reversibility is still unacceptable.
[0012] Therefore, a heretofore unaddressed need exists in the art
to address the aforementioned deficiencies and inadequacies.
SUMMARY OF THE INVENTION
[0013] In one aspect, the present invention relates to an electrode
useable in an electrochemical cell. In one embodiment, the
electrode has an electrically conductive substrate, carbon
nanotubes (CNTs) in electrical contact with the conductive
substrate, and nanoparticles of a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite coated on the
CNTs, where x+y+z=1.
[0014] The conductive substrate includes a thin film formed of an
electrically conductive material, where the thin film is flexible
(or rigid). In one embodiment, the conductive material comprises a
metal, an alloy, a polymer, graphite, or a conducting oxide.
[0015] In one embodiment, the CNTs have tube diameters in a range
of about 1.0-1,000.0 nm and height in micrometer range. The
nanoparticles of the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite have diameters or sizes in a range of about 1.0-1000.0
nm.
[0016] Additionally, the electrode further has an electrolyte
solution filled in spaces among the CNTs and the nanoparticles of
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite.
[0017] In another aspect, the present invention relates to an
electrode useable in an electrochemical cell. In one embodiment,
the electrode has an electrically conductive substrate,
nanostructured current collectors formed on the conductive
substrate, and nanoparticles of a ternary orthosilicate composite
coated on the nanostructured current collectors.
[0018] The conductive substrate includes a thin film formed of an
electrically conductive material, where the thin film is flexible
(or rigid). In one embodiment, the conductive material comprises a
metal, an alloy, a polymer, graphite, or a conducting oxide.
[0019] The nanostructured current collectors in one embodiment
comprise conductive nanotubes/fibers in electrical contact with the
conductive substrate. In one embodiment, the conductive
nanotubes/fibers include carbon nanotubes (CNTs) or carbon
fibers/nanofibers (CFs). The ternary orthosilicate composite
comprises Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4, where
x+y+z=1.
[0020] Further, the electrode may also have an electrolyte solution
filled in spaces among the nanostructured current collectors and
the nanoparticles of the active material.
[0021] In yet another aspect, the present invention relates to an
electrochemical cell comprising the electrode as disclosed
above.
[0022] In a further aspect, the present invention relates to a
method of making an electrode useable in an electrochemical cell.
In one embodiment, the method includes the steps of providing an
electrically conductive substrate, forming nanostructured current
collectors on the conductive substrate, and attaching (or coating)
nanoparticles of a ternary orthosilicate composite to the
nanostructured current collectors.
[0023] The method may further include the step of filling an
electrolyte solution in spaces among the nanostructured current
collectors and the nanoparticles of the active material
[0024] The conductive substrate comprises a thin film formed of an
electrically conductive material. In one embodiment, the thin film
is flexible (or rigid).
[0025] In one embodiment, the nanostructured current collectors
comprise conductive nanotubes/fibers. The conductive
nanotubes/fibers in one embodiment include carbon nanotubes (CNTs)
or carbon fibers/nanofibers (CFs).
[0026] In one embodiment, the forming step comprises synthesizing
or growing the conductive nanotubes/fibers, such as CNTs or CFs or
other types of conductive nanotubes/fibers on the conductive
substrate.
[0027] In one embodiment, the ternary orthosilicate composite
comprises Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4, where
x+y+z=1.
[0028] In one embodiment, the ternary orthosilicate composite is
synthesized by a hydrothermal process comprising the steps of
mixing starting precursors of lithium hydroxide, SiO.sub.2
particles, Fe(II) chloride tetrahydrate, manganese chloride, and
cobalt chloride, in a predetermined composition ratio to form a
mixture, sealing the mixture under an Ar (or inert) environment and
baking the sealed mixture at a predetermined temperature for a
period of time to form Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
compound, rinsing the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
compound with de-ionized (DI) water, drying rinsed
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound in vacuum,
ball-milling the dried Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
compound into nanoparticles, and calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
[0029] In another embodiment, the ternary orthosilicate compound is
synthesized by Pechini process comprising the steps of dispersing
lithium acetate, SiO.sub.2 particles, citric acid, and ethylene
glycol at a first predetermined composition ratio in de-ionized
(DI) water to form a first mixture, wherein the mixture is
sonicated for a period of time, adding Fe(III) citrate, manganese
acetate, and cobalt carbonate at a second predetermined composition
ratio into the first mixture to form a second mixture, stirring and
dwelling the second mixture at a reflux station to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel, drying the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel, grinding the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 into nanoparticles, and
calcining the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in
an inert or reducing environment.
[0030] In another embodiment, the ternary orthosilicate compound is
synthesized by a sol-gel process comprising the steps of dispersing
lithium acetate, iron citrate, manganese acetate, and cobalt
carbonate at a first predetermined composition ratio in de-ionized
(DI) water to form a first mixture, adding citric acid to the first
mixture to form a second mixture, adding tetraethylorthosilicate
(TEOS) and ethanol at a second predetermined composition ratio to
form third mixture, stirring and dwelling the third mixture at a
reflux station to form a Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
gel, drying the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel to
form a Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound, grinding
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound into
nanoparticles, and calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
[0031] In one embodiment, the attaching (or coating) step is
performed by a dripping/wetting process comprising the steps of
preparing a suspension of the nano-particles of the ternary
orthosilicate composite in a liquid medium, dripping the suspension
into the nanostructured current collectors in electrical contact
with the conductive substrate, and drying the suspension to attach
(or coat) the nano-particles of the ternary orthosilicate composite
onto the nanostructured current collectors. The liquid medium
comprises acetone, water or other liquid media.
[0032] These and other aspects of the present invention will become
apparent from the following description of the preferred embodiment
taken in conjunction with the following drawings, although
variations and modifications therein may be affected without
departing from the spirit and scope of the novel concepts of the
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The accompanying drawings illustrate one or more embodiments
of the invention and together with the written description, serve
to explain the principles of the invention. Wherever possible, the
same reference numbers are used throughout the drawings to refer to
the same or like elements of an embodiment.
[0034] FIG. 1A shows schematically a cross-sectional view of a
lithium-ion battery cathode according to one embodiment of the
present invention.
[0035] FIG. 1B shows schematically a cross-sectional view of the
vertical-aligned CNTs according to one embodiment of the present
invention.
[0036] FIG. 1C shows a scanning electron microscope (SEM) diagram
of vertical-aligned CNTs according to one embodiment of the present
invention.
[0037] FIG. 1D shows an SEM image of a side view of the
vertical-aligned CNTs according to one embodiment of the present
invention.
[0038] FIG. 1E shows a Raman spectroscopy diagram of
vertical-aligned, multi-walled conductive CNTs according to one
embodiment of the present invention.
[0039] FIG. 1F shows a flowchart of a method of making a
lithium-ion battery cathode according to one embodiment of the
present invention.
[0040] FIG. 2 shows schematically a cross-sectional view of a
lithium-ion battery using a cathode according to one embodiment of
the present invention.
[0041] FIG. 3A shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a hydrothermal process according
to one embodiment of the present invention.
[0042] FIG. 3B shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a Pechini process according to
one embodiment of the present invention.
[0043] FIG. 3C shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a sol-gel process according to
one embodiment of the present invention.
[0044] FIG. 3D shows SEM images of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite coated CNTs at
different magnifications according to one embodiment of the present
invention.
[0045] FIG. 4A shows an SEM image of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.25, y=0.5, and
z=0.25.
[0046] FIG. 4B shows an SEM image of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.1, y=0.8, and
z=0.1.
[0047] FIG. 5A shows an energy-dispersive X-ray spectroscopy (EDS)
spectrum of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.25, y=0.5, and
z=0.25.
[0048] FIG. 5B shows an EDS spectrum of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.1, y=0.8, and
z=0.1.
[0049] FIG. 6A shows a DSC plot of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.25, y=0.5, and
z=0.25.
[0050] FIG. 6B shows a DSC plot of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.1, y=0.8, and
z=0.1.
[0051] FIG. 7 shows XRD spectra of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention, where x=0.25, y=0.5, and
z=0.25 and according to second embodiment of the present invention,
where x=0.1, y=0.8, and z=0.1.
[0052] FIG. 8A shows a Nyquist plot of the impedance of the cathode
with the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite at 3V
according to one embodiment of the present invention, where x=0.1,
y=0.8, and z=0.1.
[0053] FIG. 8B shows a Nyquist plot of the impedance of the cathode
with the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite at
4.7V according to one embodiment of the present invention, where
x=0.1, y=0.8, and z=0.1.
[0054] FIG. 9A shows a plot of the cell performance of the lithium
ion battery using the cathode with the
Li.sub.2Mn.sub.0.25Fe.sub.0.5Co.sub.0.25SiO.sub.4 composite with
the weight of 4.0 mg according to one embodiment of the present
invention.
[0055] FIG. 9B shows a plot of the cell performance of the lithium
ion battery using the cathode with the
Li.sub.2Mn.sub.0.25Fe.sub.0.5Co.sub.0.25SiO.sub.4 composite with
the weight of 1.6 mg according to one embodiment of the present
invention.
[0056] FIG. 9C shows a plot of the cell performance of the lithium
ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 3.9 mg according to one embodiment of the present
invention.
[0057] FIG. 9D shows a plot of the cell performance of the lithium
ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 1.4 mg and the discharge voltage window of 4.7-2.0 V
according to one embodiment of the present invention.
[0058] FIG. 9E shows a plot of the cell performance of the lithium
ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 1.4 mg and the discharge voltage window of 4.7-2.4 V
according to one embodiment of the present invention.
[0059] FIG. 10 shows a plot of the discharge capacity-cycle number
relationship of the lithium ion batteries of FIGS. 9A-9E according
to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0060] The present invention is more particularly described in the
following examples that are intended as illustrative only since
numerous modifications and variations therein will be apparent to
those skilled in the art. Various embodiments of the invention are
now described in detail. Referring to the drawings, like numbers
indicate like components throughout the views. As used in the
description herein and throughout the claims that follow, the
meaning of "a", "an", and "the" includes plural reference unless
the context clearly dictates otherwise. Also, as used in the
description herein and throughout the claims that follow, the
meaning of "in" includes "in" and "on" unless the context clearly
dictates otherwise. Moreover, titles or subtitles may be used in
the specification for the convenience of a reader, which shall have
no influence on the scope of the present invention. Additionally,
some terms used in this specification are more specifically defined
below.
Definitions
[0061] The terms used in this specification generally have their
ordinary meanings in the art, within the context of the invention,
and in the specific context where each term is used. Certain terms
that are used to describe the invention are discussed below, or
elsewhere in the specification, to provide additional guidance to
the practitioner regarding the description of the invention. For
convenience, certain terms may be highlighted, for example using
italics and/or quotation marks. The use of highlighting has no
influence on the scope and meaning of a term; the scope and meaning
of a term is the same, in the same context, whether or not it is
highlighted. It will be appreciated that same thing can be said in
more than one way. Consequently, alternative language and synonyms
may be used for any one or more of the terms discussed herein, nor
is any special significance to be placed upon whether or not a term
is elaborated or discussed herein. Synonyms for certain terms are
provided. A recital of one or more synonyms does not exclude the
use of other synonyms. The use of examples anywhere in this
specification including examples of any terms discussed herein is
illustrative only, and in no way limits the scope and meaning of
the invention or of any exemplified term. Likewise, the invention
is not limited to various embodiments given in this
specification.
[0062] It will be understood that when an element is referred to as
being "on" another element, it can be directly on the other element
or intervening elements may be present therebetween. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present. As used herein,
the term "and/or" includes any and all combinations of one or more
of the associated listed items.
[0063] It will be understood that, although the terms first,
second, third etc. may be used herein to describe various elements,
components, regions, layers and/or sections, these elements,
components, regions, layers and/or sections should not be limited
by these terms. These terms are only used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of the present invention.
[0064] Furthermore, relative terms, such as "lower" or "bottom" and
"upper" or "top," may be used herein to describe one element's
relationship to another element as illustrated in the Figures. It
will be understood that relative terms are intended to encompass
different orientations of the device in addition to the orientation
depicted in the Figures. For example, if the device in one of the
figures is turned over, elements described as being on the "lower"
side of other elements would then be oriented on "upper" sides of
the other elements. The exemplary term "lower", can therefore,
encompasses both an orientation of "lower" and "upper," depending
of the particular orientation of the figure. Similarly, if the
device in one of the figures is turned over, elements described as
"below" or "beneath" other elements would then be oriented "above"
the other elements. The exemplary terms "below" or "beneath" can,
therefore, encompass both an orientation of above and below.
[0065] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0066] As used herein, "around", "about" or "approximately" shall
generally mean within 20 percent, preferably within 10 percent, and
more preferably within 5 percent of a given value or range.
Numerical quantities given herein are approximate, meaning that the
term "around", "about" or "approximately" can be inferred if not
expressly stated.
[0067] As used herein, if any, the term "scanning electron
microscope" or its abbreviation "SEM" refers to a type of electron
microscope that images the sample surface by scanning it with a
high-energy beam of electrons in a raster scan pattern. The
electrons interact with the atoms that make up the sample producing
signals that contain information about the sample's surface
topography, composition and other properties such as electrical
conductivity.
[0068] As used herein, if any, the term "energy-dispersive X-ray
spectroscopy" or its abbreviation "EDS" refers to an analytical
technique used for the elemental analysis or chemical
characterization of a sample. It relies on the investigation of an
interaction of some source of X-ray excitation and a sample. Its
characterization capabilities are due in large part to the
fundamental principle that each element has a unique atomic
structure allowing unique set of peaks on its X-ray spectrum.
[0069] As used herein, if any, the term "X-ray diffraction" or its
abbreviation "XRD" refers to a method of determining the
arrangement of atoms within a crystal or solid, in which a beam of
X-rays strikes a crystal and diffracts into many specific
directions. From the angles and intensities of these diffracted
beams, a crystallographer can produce a three-dimensional picture
of the density of electrons within the crystal. From this electron
density, the mean positions of the atoms in the crystal can be
determined, as well as their chemical bonds, their disorder and
various other information. In an X-ray diffraction measurement, a
crystal or solid sample is mounted on a goniometer and gradually
rotated while being bombarded with X-rays, producing a diffraction
pattern of regularly spaced spots known as reflections. The
two-dimensional images taken at different rotations are converted
into a three-dimensional model of the density of electrons within
the crystal using the mathematical method of Fourier transforms,
combined with chemical data known for the sample.
[0070] As used herein, if any, the term "differential scanning
calorimetry" or its abbreviation "DSC" refers to a thermoanalytical
technique in which the difference in the amount of heat required to
increase the temperature of a sample and reference is measured as a
function of temperature. Both the sample and reference are
maintained at nearly the same temperature throughout the
experiment. Generally, the temperature program for a DSC analysis
is designed such that the sample holder temperature increases
linearly as a function of time. The reference sample should have a
well-defined heat capacity over the range of temperatures to be
scanned.
[0071] As used herein, "nanoscopic-scale", "nanoscopic",
"nanometer-scale", "nanoscale", "nanocomposites", "nanoparticles",
the "nano-" prefix, and the like generally refers to elements or
articles having widths or diameters of less than about 1 .mu.m,
preferably less than about 100 nm in some cases. In all
embodiments, specified widths can be smallest width (i.e. a width
as specified where, at that location, the article can have a larger
width in a different dimension), or largest width (i.e. where, at
that location, the article's width is no wider than as specified,
but can have a length that is greater).
[0072] As used herein, a "nanostructure" refers to an object of
intermediate size between molecular and microscopic
(micrometer-sized) structures. In describing nanostructures, the
sizes of the nanostructures refer to the number of dimensions on
the nanoscale. For example, nanotextured surfaces have one
dimension on the nanoscale, i.e., only the thickness of the surface
of an object is between 1.0 and 1000.0 nm. Nanotubes have two
dimensions on the nanoscale, i.e., the diameter of the tube is
between 1.0 and 1000.0 nm; its length could be much greater.
Finally, sphere-like nanoparticles have three dimensions on the
nanoscale, i.e., the particle is between 1.0 and 1000.0 nm in each
spatial dimension. A list of nanostructures includes, but not
limited to, nanoparticle, nanocomposite, quantum dot, nanofilm,
nanoshell, nanofiber, nanoring, nanorod, nanowire, nanotube, and so
on.
[0073] As used herein, "plurality" means two or more.
[0074] As used herein, the terms "comprising", "including",
"carrying", "having", "containing", "involving", and the like are
to be understood to be open-ended, i.e., to mean including but not
limited to.
OVERVIEW OF THE INVENTION
[0075] The present invention relates to electrodes useable in an
electrochemical cell, methods of making the same, and applications
of the same. In one embodiment, the electrochemical cell is
corresponding to a battery, and the electrode is utilized for a
lithium-ion battery cathode and includes a composite of
nanostructured materials.
[0076] In one aspect of the present invention, an electrode usable
for a battery cathode has an electrically conductive substrate,
nanostructured current collectors in electrical contact with the
conductive substrate, and nanoparticles of a ternary orthosilicate
composite coated on the nanostructured current collectors. The
conductive substrate includes a thin film formed of an electrically
conductive material. Preferably, the thin film is flexible. The
conductive material includes a metal, an alloy, a polymer,
graphite, or a conducting oxide. The nanostructured current
collectors include CNTs or carbon fibers/nanofibers (CFs), where
the CNTs or CFs are in electrical contact with the conductive
substrate. The ternary orthosilicate composite includes
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4, where x+y+z=1. The CNTs
have diameters or thicknesses in a range of about 1.0-1,000.0 nm.
The nanoparticles of the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite have diameters or sizes in a range of about 1.0-1000.0
nm.
[0077] In addition, the electrode further includes an electrolyte
solution filled in spaces among the CNTs and the nanoparticles of
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite.
[0078] In one embodiment, CNTs are utilized as an array of
nano-architecture current collectors formed directly on a
conductive substrate, which can be a flexible (or rigid) conducting
foil (e.g. metal, graphite). Vertical-aligned CNTs impregnated with
MnO.sub.2 nano-particles as electrodes [1] have been used for
electrochemical supercapacitors recently, which resulted in
excellent performance of about 1,000 F/cm.sup.3. In the present
invention, the material coated on the CNT array is a
high-performance active layer of ternary orthosilicate compound
with composition of Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4,
where x+y+z=1. The electrode using such nanostructured CNTs
provides a high surface area of attachment for
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4nanoparticles, which
minimizes the contact resistance at the active material/current
collector interface, and thereby maximizes the charge efficiency
and the energy density of the cathode.
[0079] The electrode of the present invention is a high-voltage,
high-capacity, and inexpensive cathode for lithium-ion batteries
(LIBs) capable of supporting high transient and pulsed loads while
offering enhanced safety and lifecycle performance. Currently LIB
is one of the most promising battery technologies that can provide
higher energy density than other battery technologies. It also does
not suffer from the memory effect and the loss of charge is
relatively slow when not in use. Hence, with the electrode of the
present invention, high-performance LIB can be realized to address
a much broader range of energy source/storage for both military and
civil applications.
[0080] Li.sub.2MSiO.sub.4, where M=Mn, Fe, and/or Co, is similar to
olivine phosphate (LiFePO.sub.4) and has low electron conductivity.
Fabrication processes of the LIB cathode structures utilizing such
materials usually involve making the active material in the form of
tiny nanoparticles, mixing them with carbon or coating them with a
conductive carbon layer, and then pasting the mixture onto a
conductive substrate (e.g., an aluminum foil) with a binder
material. However, the electron conductivity of the mixture is
limited by the high resistivity of the binder material and the high
ohmic contact resistance between the cathode material and the
substrate. In addition, the heat transfer between the cathode
material and the substrate is also less than optimal, leading to
elevated cathode temperature under heavy load.
[0081] Accordingly, the present invention utilizes a ternary
orthosilicate composite, such as the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite, for the
cathode active material, which would lead to a cathode with high
voltage (.gtoreq.4V), high capacity (.gtoreq.180 mAh/g), excellent
cycle life, and low cost. To achieve the present invention,
synthesis of high performance ternary orthosilicate composite of
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 must be realized such
that the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite can be
attached to the CNTs structure. Thus, the cathode obtained would
have enhanced specific area and minimized interface resistance,
thereby maximizing the charge transfer efficiency and specific
power-energy densities.
[0082] In a further aspect of the present invention, a method of
making a cathode useable in a battery includes the steps of
providing an electrically conductive substrate, forming
nanostructured current collectors on the conductive substrate, and
attaching nanoparticles of a ternary orthosilicate composite to the
nanostructured current collectors.
[0083] In one embodiment, the ternary orthosilicate composite is
synthesized by a hydrothermal process comprising the steps of
mixing starting precursors of lithium hydroxide, SiO.sub.2
particles, Fe(II) chloride tetrahydrate, manganese chloride, and
cobalt chloride, in a predetermined composition ratio to form a
mixture, sealing the mixture under an Ar environment and baking the
sealed mixture at a predetermined temperature for a period of time
to form Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound, rinsing
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound with
de-ionized (DI) water, drying rinsed
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound in vacuum,
ball-milling the dried Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
powders into nanoparticles, and calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
[0084] In another embodiment, the ternary orthosilicate composite
is synthesized by a Pechini process comprising the steps of
dispersing lithium acetate, SiO.sub.2 particles, citric acid, and
ethylene glycol at a first predetermined composition ratio in
de-ionized (DI) water to form a first mixture, wherein the mixture
is sonicated for a period of time, adding Fe(III) citrate,
manganese acetate, and cobalt carbonate at a second predetermined
composition ratio into the first mixture to form a second mixture,
stirring and dwelling the second mixture to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel, drying the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel, grinding the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound into
nanoparticles, and calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
[0085] In another embodiment, the ternary orthosilicate compound is
synthesized by a sol-gel process comprising the steps of dispersing
lithium acetate, iron citrate, manganese acetate, and cobalt
carbonate at a first predetermined composition ratio in de-ionized
(DI) water to form a first mixture, adding citric acid to the first
mixture to form a second mixture, adding tetraethylorthosilicate
(TEOS) and ethanol at a second predetermined composition ratio to
form third mixture, stirring and dwelling the third mixture at a
reflux station to form a Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
gel, drying the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel,
grinding the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 into
nanoparticles, and calcining the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders in an inert or
reducing environment.
[0086] The attaching step, in one embodiment, is performed by a
dripping/wetting process comprising the steps of preparing a
suspension of the nano-particles of the ternary orthosilicate
composite in a liquid medium, dripping the suspension into the
nanostructured current collectors in electrical contact with the
conductive substrate, and drying the suspension to attach the
nano-particles of the ternary orthosilicate composite onto the
nanostructured current collectors. The liquid medium comprises
acetone, water or other liquid media.
[0087] The present invention in one aspect also relates to a
battery comprising the cathode as disclosed above.
[0088] These and other aspects of the present invention are more
specifically described below.
IMPLEMENTATIONS AND EXAMPLES OF THE INVENTION
[0089] Without intent to limit the scope of the invention,
exemplary methods and their related results according to the
embodiments of the present invention are given below. Note that
titles or subtitles may be used in the examples for convenience of
a reader, which in no way should limit the scope of the invention.
Moreover, certain theories are proposed and disclosed herein;
however, in no way they, whether they are right or wrong, should
limit the scope of the invention so long as the invention is
practiced according to the invention without regard for any
particular theory or scheme of action. It should be appreciated
that while these techniques are exemplary of preferred embodiments
for the practice of the invention, those of skill in the art, in
light of the present disclosure, will recognize that numerous
modifications can be made without departing from the spirit and
intended scope of the invention.
Example One
The Cathode Structure and Method of Making the Same
[0090] FIG. 1A shows schematically a cross-sectional view of a
lithium-ion battery cathode according to one embodiment of the
present invention. In FIG. 1A, the cathode 100 is a novel CNT-based
cathode structure, which includes an electrically conductive
substrate 110, single walled or multi-walled CNTs 120 in electrical
contact with the conductive substrate 110, and nanoparticles 130 of
an Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite attached to
the CNTs 120.
[0091] In one embodiment, the cathode 100 further includes an
electrolyte solution 140 filled in spaces among the CNTs 120 and
the nanoparticles 130 of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite.
[0092] In one embodiment, the conductive substrate 110 can be a
flexible (or rigid) thin film formed of an electrically conductive
material, such as a metal, an alloy, a polymer, graphite, or a
conducting oxide. For example, the conductive substrate 110 can be
a flexible (or rigid) thin film aluminum or graphite foil.
[0093] The CNTs 120 serve as nanostructured current collectors of
the cathode. In one embodiment, the CNTs 120 are grown directly on
the conductive substrate 110. The direct growth of the CNTs 120 on
the conductive substrate 110 provides strong chemical bonding at
the interface between the CNTs 120 and the conductive substrate 110
such that the contact resistance is minimized. In one embodiment,
the CNTs 120 have diameters or thicknesses in a range of about
1.0-1,000.0 nm. For example, FIG. 1B shows schematically a
cross-sectional view of the CNTs according to one embodiment of the
present invention. As shown in FIG. 1B, the CNTs 120 have diameters
of about 30 nm, and the distance between adjacent CNTs 120 is about
40 nm. FIGS. 1C and 1D show scanning electron microscope (SEM)
images of vertical-aligned CNTs according to one embodiment of the
present invention.
[0094] The CNTs, particularly multi-walled CNTs, are highly
conductive. FIG. 1E shows a Raman spectroscopy diagram of
vertical-aligned, multi-walled conductive CNTs according to one
embodiment of the present invention. As shown in FIG. 1E, the
strongest peak at 1327 cm.sup.-1 corresponds to the D-band in the
CNT structures, and the second strongest band at 1587 cm.sup.-1
corresponds to G-band graphite mode. The other bands located at
2654 and 2915 cm.sup.-1 are due to the second-order combinations of
2D and D+G, respectively.
[0095] The Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite is a
ternary orthosilicate composite in the group of Li.sub.2MSiO.sub.4,
where M=Mn, Fe, or Co. In one embodiment, x+y+z=1. In one
embodiment, the nanoparticles 130 of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite have diameters
or sizes in a range of about 1.0-1,000.0 nm.
[0096] As stated above, due to the extremely high surface area of
the CNTs 120 (or the nanostructured current collectors), the total
surface area of the current collectors of the cathode 100 becomes
three-dimensional instead of two-dimensional and increases
thousands of times. As a result, both electric charge and heat
transfer of the cathode 100 become much more efficient, and
capacity and safety against overheating of the cathode 100 are thus
improved.
[0097] In some embodiments, carbon fibers/nanofibers (CFs) may
replace the CNTs as the nanostructured current collectors. The
structure and performance of the CFs are similar to those of the
CNTs, and detailed description of the CFs is hereafter omitted.
[0098] In some embodiments, other type of nanotubes/fibers (such as
conductive metal-oxide nanotubes/fiber) may replace the CNTs as the
nanostructured current collectors, with the structure and
performance similar to those of the CNTs.
[0099] FIG. 1F shows a flowchart of a method of making a
lithium-ion battery cathode according to one embodiment of the
present invention. According to FIG. 1F, an electrically conductive
substrate, such as the conductive substrate 110 in FIG. 1, is
provided (step S110), and nanostructured current collectors, such
as the CNTs 120 in FIG. 1A or the CFs, are formed or vertically in
electrical contact with the conductive substrate (step S120). Then,
nanoparticles of a ternary orthosilicate composite, such as the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite, are attached
to the nanostructured current collectors (step S130) to form the
cathode. In some embodiments, a further step can be added to fill
an electrolyte solution in spaces among the nanostructured current
collectors and the nanoparticles of the active material.
[0100] The forming or growing of the CNTs can be performed, for
example, by a microwave plasma-enhanced chemical vapor deposition
(CVD) process. To assist the forming of the CNTs, a thin layer of
Ni or Co or a suitable catalyst can be deposited on the conductive
substrate as catalyst. In one embodiment, hydrogen-diluted methane
or a suitable hydrocarbon can be used as the carbon source.
Example Two
Lithium-Ion Battery Comprising the Cathode
[0101] FIG. 2 shows schematically a cross-sectional view of a
lithium-ion battery using a cathode according to one embodiment of
the present invention. In FIG. 2, the battery 200 includes a
cathode 202, an anode 204, and a separator 206 between the cathode
202 and the anode 204. The cathode 202 is similar to the cathode
100 in FIG. 1A, which includes an electrically conductive substrate
210, CNTs 220 in electrical contact with the conductive substrate
210, nanoparticles 230 of an
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite attached to the
CNTs 220, and an electrolyte solution 240 filled in spaces among
the CNTs 220 and the nanoparticles 230 of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite. The anode 204
includes an electrically conductive substrate 250, anode structures
260 in electrical contact with the conductive substrate 250, and an
electrolyte solution 270 filled in spaces among the anode
structures 260.
[0102] In one embodiment, the conductive substrate 210 of the
cathode 202 can be a flexible (or rigid) thin film formed of an
electrically conductive material, such as a metal, an alloy, a
polymer, graphite, or a conducting oxide. For example, the
conductive substrate 210 can be a flexible (or rigid) thin film
aluminum or graphite foil.
[0103] The CNTs 220 serve as nanostructured current collectors of
the cathode. In one embodiment, the CNTs 220 are single walled or
multi-walled conductive CNTs formed directly on the conductive
substrate 210. In one embodiment, the CNTs 220 have diameters or
thicknesses in a range of about 1.0-1,000.0 nm.
[0104] The Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite is a
ternary orthosilicate composite. In one embodiment, x+y+z=1. In one
embodiment, the nanoparticles 230 of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite nanoparticles
have diameters or sizes in a range of about 1.0-1,000.0 nm.
[0105] The anode 204 can be any type of anode. In one embodiment,
the conductive substrate 250 of the anode 204 can be a flexible (or
rigid) thin film formed of an electrically conductive material,
such as a metal, an alloy, a polymer, graphite, or a conducting
oxide. For example, the conductive substrate 250 can be a flexible
(or rigid) thin film copper foil.
[0106] The anode structures 260 serve as nanostructured current
collectors of the anode. In one embodiment, the anode structures
can be formed of high capacity anode materials, such as silicon
nanowires.
[0107] In one embodiment, the electrolyte solutions 240 and 270 can
be the same electrolyte solution, such as lithium
bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte.
Example Three
[0108] Synthesis of Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 Solid
Solution
[0109] An advantage of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite as the ternary
orthosilicate composite used in the cathode exists in that both the
average potential difference of the cathode and the specific
capacity of the cathode can be increased. As indicated above,
conventional metal oxides used as cathode materials have limited
average potential versus Li/Li.sup.+, mostly well below 4V, and
most of the metal oxides have the specific capacity well below 180
mAh/g. In other words, these metal oxide cathode materials cannot
meet both the requirements of the average potential difference
being larger than 4V and the specific capacity being larger than
180 mAh/g.
[0110] In contrast, the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite not only allows the specific capacity to reach about 330
mAH/g and provides adequate average potential difference of at
least 4V, but also has a satisfactory cycle life with original
capacity. Thus, using the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite as the cathode material may lead to better performance
and longer life cycle of the battery.
[0111] There are three major synthesis methods of the ternary
orthosilicate composite, such as the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite. One is a
hydrothermal synthesis process, the second is the Pechini synthesis
process, and the third is the sol-gel process.
[0112] FIG. 3A shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a hydrothermal process according
to one embodiment of the present invention. As shown in FIG. 3A,
starting precursors of lithium hydroxide, SiO.sub.2 particles,
Fe(II) chloride tetrahydrate, manganese chloride, and cobalt
chloride are mixed together in a predetermined composition ratio to
form a mixture (step S310). Then the mixture is sealed under an Ar
environment, and the sealed mixture is baked at a predetermined
temperature for a period of time to form
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound (step S312). The
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound is then rinsed
with de-ionized (DI) water (step S314), and the rinsed
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound is dried in
vacuum (step S316). The dried
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound is ball-milled
into nanoparticles (step S318) and finally, the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders are calcined in
an inert or reducing environment (step S319).
[0113] FIG. 3B shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a Pechini process according to
one embodiment of the present invention. As shown in FIG. 3B,
lithium acetate, SiO.sub.2 particles, citric acid, and ethylene
glycol are dispersed at a first predetermined composition ratio in
de-ionized (DI) water to form a first mixture, and the first
mixture is sonicated for a period of time (step S320). Then Fe(III)
citrate, manganese acetate, and cobalt acetate at a second
predetermined composition ratio are added into the first mixture to
form a second mixture (step S322). The second mixture is then
stirred and dwelled to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel (step S324), and the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 sol-gel is dried to form
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound (step S326). The
dried Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound are
grounded into nanoparticles (step S328). Finally, the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders are calcined in
an inert or reducing environment (step S330).
[0114] FIG. 3C shows a flowchart of a method of synthesizing the
ternary orthosilicate composite by a sol-gel-process according to
one embodiment of the present invention. As shown in FIG. 3C, at
step S340, lithium acetate, iron citrate, manganese acetate and
cobalt carbonate are dispersed at a first predetermined composition
ratio in de-ionized (DI) water to form a first mixture. At step
S341, citric acid is added to the first mixture to form a second
mixture. Then tetraethylorthosilicate (TEOS) and ethanol are added
at a second predetermined composition ratio to form a third mixture
(at step S342). At step S343, the third mixture at a reflux station
is stirred and dwelled to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel. At step S344, the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 gel is dried to form a
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound. At step $345,
the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 compound is grinded
into nanoparticles. Then, the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 powders are calcined in
an inert or reducing environment.
[0115] An example of synthesis of Li.sub.2FeSiO.sub.4 is used to
describe the three synthesis processes as follows.
[0116] For the hydrothermal process, the starting precursors of
lithium hydroxide, SiO.sub.2 particles, and Fe(II) chloride
tetrahydrate are mixed in the predetermined composition ratio of
4:1:1 to form the mixture. The mixture is sealed under the Ar
environment and baked at 150.degree. C. for 14 days to form the
Li.sub.2FeSiO.sub.4 powders. The Li.sub.2FeSiO.sub.4 powders are
then rinsed with de-ionized (DI) water, dried in vacuum, and
ball-milled into nanoparticles.
[0117] For the Pechini process, lithium acetate, SiO.sub.2
particles, citric acid, and ethylene glycol are dispersed at the
first predetermined composition ratio of 2:1:2:1 in the DI water to
form the first mixture, and the first mixture is sonicated for 2
hours. Then Fe(III) citrate is added to the first mixture (at the
second predetermined composition ratio of 1:0:0 since neither Mn
nor Co is used) to form the second mixture. After further stirring
and dwelling of the second mixture, the Li.sub.2FeSiO.sub.4 gel is
formed, which is then dried and ground into nanoparticles. Finally,
the Li.sub.2FeSiO.sub.4 powders are heat treated in the CO/CO.sub.2
environment to generate the end product.
[0118] For the sol-gel process, lithium acetate and iron citrate
are dispersed at the pre-determined ratio of 2:1 in de-ionized (DI)
water to form a first mixture. Saturated solution of citric acid is
added to the first mixture to form a second mixture.
Tetraethylorthosilicate (TEOS) and ethanol are added at a second
predetermined composition ratio to form third mixture which is
stirred at 80.degree. C. for 14 hours at a reflux station to form
Li.sub.2FeSiO.sub.4 gel. The Li.sub.2FeSiO.sub.4 gel is dried and
ground into nanoparticles. Finally, the Li.sub.2FeSiO.sub.4 powder
is calcined in an Argon atmosphere.
[0119] The three processes can be applied for the synthesis of the
ternary orthosilicate composite, such as
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4, where Mn, Fe and Co all
exist in the composite. In one embodiment, the ternary
orthosilicate composite obtained can be subsequently dispersed onto
the CNTs by a dripping or wetting method. Specifically, a
suspension of the nanoparticles of the ternary orthosilicate
composite can be prepared in a liquid medium. Then, by dripping the
suspension into the nanostructured current collectors in electrical
contact with the conductive substrate and drying the suspension,
the nanoparticles of the ternary orthosilicate composite are coated
onto the nanostructured current collectors. By varying the number
of droplets applied in the dripping process, the mass ratio of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite to the CNTs can
be controlled.
[0120] In one embodiment, the liquid medium includes acetone, water
or other liquid media.
[0121] FIG. 3D shows SEM images of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite attached to the
CNTs at different magnifications according to one embodiment of the
present invention.
[0122] The performance of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite can be verified
with material characterization analysis, such as SEM,
energy-dispersive X-ray spectroscopy (EDS), differential scanning
calorimetry (DSC) and X-ray diffraction (XRD) analysis.
[0123] FIGS. 4A and 4B show two SEM images of nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite according to
one embodiment of the present invention. The two figures represent
two embodiments. In FIG. 4A, x=0.25, y=0.5, and z=0.25, referring
to the ternary orthosilicate composite of
Li.sub.2Mn.sub.0.25Fe.sub.0.5Co.sub.0.25SiO.sub.4. In FIG. 4B,
x=0.1, y=0.8, and z=0.1, referring to the ternary orthosilicate
composite of Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4. FIGS.
5A and 5B shows energy-dispersive X-ray spectroscopy (EDS) diagrams
of the nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite in FIGS. 4A and
4B, respectively. FIGS. 6A and 6B shows differential scanning
calorimetry (DSC) diagrams of the nanoparticles of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite in FIGS. 4A and
4B, respectively.
[0124] An expected composite ratio in the form of Mn:Fe:Co of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite in FIGS. 4A and
5A is 1:2:1 (0.25:0.5:0.25). However, as shown in FIG. 5A,
quantitative analysis of the EDS data shows that the composite
ratio is about 1.6:1:1.5. An expected composite ratio in the form
of Mn:Fe:Co of the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite in FIGS. 4B and 5B is 1:8:1 (0.1:0.8:0.1). However, as
shown in FIG. 5A, quantitative analysis of the EDS data shows that
the composite ratio is about 1:10:1. Both FIGS. 6A and 6B show
that, under calorimetric measurements, the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composites have good
thermal behavior with negligible exothermic release at the
temperature under 500.degree. C.
[0125] FIG. 7 shows XRD spectra of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composites according to
two embodiments of the present invention, where x=0.25, y=0.50,
z=0.25 and, where x=0.1, y=0.8, z=0.1.
[0126] FIGS. 8A and 8B show diagrams of the impedance of the
cathode with the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4
composite at 3V and 4.7V, respectively, according to one embodiment
of the present invention, where x=0.1, y=0.8, and z=0.1. Excess
coating of the Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite
on the CNTs would lead to high equivalent series resistance (ESR)
and degrading discharge capacity.
Example Four
Performance of the LIB
[0127] In order to show the performance of the LIB of the present
invention, five embodiments of the LIB using cathodes with
different composition ratio and weight of the
Li.sub.2Mn.sub.xFe.sub.yCo.sub.zSiO.sub.4 composite and different
discharge voltage window are provided.
[0128] FIG. 9A shows a diagram of the cell performance of the
lithium ion battery using the cathode with the
Li.sub.2Mn.sub.0.25Fe.sub.0.5Co.sub.0.25SiO.sub.4 composite with
the weight of 4.0 mg according to one embodiment of the present
invention. In this embodiment, the discharge voltage window is
4.7-2.0 V. For the performance obtained, the discharge capacity is
63-80 mAh/g, the specific energy is 180-263 Wh/kg, and the specific
power is 178 W/kg. As shown in FIG. 9A, the cathode performance of
this embodiment is unsatisfactory due to the composition ratio and
too thick amount by weight of the ternary orthosilicate composite
coating on the CNTs.
[0129] FIG. 9B shows a diagram of the cell performance of the
lithium ion battery using the cathode with the
Li.sub.2Mn.sub.0.25Fe.sub.0.5Co.sub.0.25SiO.sub.4 composite with
the weight of 1.6 mg according to one embodiment of the present
invention. In this embodiment, the discharge voltage window is
4.7-2.0 V. For the performance obtained, the discharge capacity is
100-109 mAh/g, the specific energy is 337-369 Wh/kg, and the
specific power is 439 W/kg. As shown in FIG. 9B, the cathode
performance of this embodiment is improved comparing to the
embodiment of FIG. 9A due to thinner amount by weight of the
ternary orthosilicate composite coating on the CNTs.
[0130] FIG. 9C shows a diagram of the cell performance of the
lithium ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 3.9 mg according to one embodiment of the present
invention. In this embodiment, the discharge voltage window is
4.7-2.0 V. For the performance obtained, the discharge capacity is
150-163 mAh/g, the specific energy is 467-518 Wh/kg, and the
specific power is 178 W/kg. As shown in FIG. 9C, the cathode
performance of this embodiment is improved comparing to the
embodiment of FIG. 9A due to adjustment of the composite ratio of
the ternary orthosilicate composite coating on the CNTs.
[0131] FIG. 9D shows a diagram of the cell performance of the
lithium ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 1.4 mg and the discharge voltage window of 4.7-2.0 V
according to one embodiment of the present invention. In this
embodiment, the discharge voltage window is 4.7-2.0 V. For the
performance obtained, the discharge capacity is 288-325 mAh/g, the
specific energy is 919-984 Wh/kg, and the specific power is 489
W/kg. As shown in FIG. 9D, the cathode performance of this
embodiment is greatly improved comparing to the previous
embodiments of FIGS. 9A-9C due to adjustment of the composite ratio
and thinner amount by weight of the ternary orthosilicate composite
coating on the CNTs.
[0132] FIG. 9E shows a diagram of the cell performance of the
lithium ion battery using the cathode with the
Li.sub.2Mn.sub.0.1Fe.sub.0.8Co.sub.0.1SiO.sub.4 composite with the
weight of 1.4 mg and the discharge voltage window of 4.7-2.4 V
according to one embodiment of the present invention. In this
embodiment, the discharge voltage window is 4.7-2.4 V. For the
performance obtained, the discharge capacity is 182-209 mAh/g, the
specific energy is 695-764 Wh/kg, and the specific power is 485
W/kg. The average voltage of the battery is 4.0-4.05 V. As shown in
FIG. 9E, the cathode performance of this embodiment is also greatly
improved comparing to the previous embodiments of FIGS. 9A-9C. The
high discharge capacity is larger than 180 mAh/g and the specific
energy is larger than 600 Wh/kg at the average voltage of larger
than 4V. Further, the battery is stable in that the discharge
capacity maintains more than 90% of its original discharge capacity
of 209 mAh/g at the voltage range of 4.7-2.4 V within 10 cycles.
The discharge capacity is also close to its theoretical limit of
330 mAh/g for 4 cycles in the voltage range of 4.7-2.1 V.
[0133] FIG. 10 shows a diagram of the discharge capacity-cycle
number relationship of the lithium ion batteries of FIGS. 9A-9E
according to one embodiment of the present invention. In FIG. 10,
the lines 1010, 1020, 1030, 1040 and 1050 respectively represent
the lithium ion batteries of FIGS. 9A-9E. As shown by the lines
1040 and 1050 in FIG. 10, high performance lithium ion batteries,
such as the batteries in FIGS. 9D and 9E, can achieve extremely
high discharge capacity of larger than 180 mAh/g within 10 cycles
at voltage range of 4.7-2.4 V, which is larger than 90% of its
original first discharge capacity of 209 mAh/g. Further, the
battery of FIG. 9E can achieve deep discharge capacity of about 330
mAh/g in the voltage range of 4.7-2.1V, which is close to its
theoretical limit of 330 mAh/g.
[0134] The foregoing description of the exemplary embodiments of
the invention has been presented only for the purposes of
illustration and description and is not intended to be exhaustive
or to limit the invention to the precise forms disclosed. Many
modifications and variations are possible in light of the above
teaching.
[0135] The embodiments were chosen and described in order to
explain the principles of the invention and their practical
application so as to enable others skilled in the art to utilize
the invention and various embodiments and with various
modifications as are suited to the particular use contemplated.
Alternative embodiments will become apparent to those skilled in
the art to which the present invention pertains without departing
from its spirit and scope. Accordingly, the scope of the present
invention is defined by the appended claims rather than the
foregoing description and the exemplary embodiments described
therein.
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