U.S. patent application number 15/425696 was filed with the patent office on 2017-07-06 for silicon oxide based high capacity anode materials for lithium ion batteries.
The applicant listed for this patent is Envia Systems, Inc.. Invention is credited to Yogesh Kumar Anguchamy, Haixia Deng, Yongbong Han, Sujeet Kumar, Herman A. Lopez, Charan Masarapu.
Application Number | 20170194627 15/425696 |
Document ID | / |
Family ID | 47175147 |
Filed Date | 2017-07-06 |
United States Patent
Application |
20170194627 |
Kind Code |
A1 |
Deng; Haixia ; et
al. |
July 6, 2017 |
SILICON OXIDE BASED HIGH CAPACITY ANODE MATERIALS FOR LITHIUM ION
BATTERIES
Abstract
Silicon oxide based materials, including composites with various
electrical conductive compositions, are formulated into desirable
anodes. The anodes can be effectively combined into lithium ion
batteries with high capacity cathode materials. In some
formulations, supplemental lithium can be used to stabilize cycling
as well as to reduce effects of first cycle irreversible capacity
loss. Batteries are described with surprisingly good cycling
properties with good specific capacities with respect to both
cathode active weights and anode active weights.
Inventors: |
Deng; Haixia; (Fremont,
CA) ; Han; Yongbong; (San Francisco, CA) ;
Masarapu; Charan; (Fremont, CA) ; Anguchamy; Yogesh
Kumar; (Newark, CA) ; Lopez; Herman A.;
(Sunnyvale, CA) ; Kumar; Sujeet; (Newark,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Envia Systems, Inc. |
Newark |
CA |
US |
|
|
Family ID: |
47175147 |
Appl. No.: |
15/425696 |
Filed: |
February 6, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13108708 |
May 16, 2011 |
9601228 |
|
|
15425696 |
|
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|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/483 20130101;
H01B 1/122 20130101; H01M 2004/027 20130101; H01M 4/624 20130101;
H01M 10/0525 20130101; H01M 4/136 20130101; Y02E 60/10 20130101;
H01M 10/052 20130101; H01M 4/386 20130101; H01M 4/622 20130101;
H01M 4/505 20130101; H01M 10/0569 20130101; H01M 4/131 20130101;
H01M 4/583 20130101; H01M 4/525 20130101; H01M 4/625 20130101; H01M
4/134 20130101 |
International
Class: |
H01M 4/131 20060101
H01M004/131; H01M 10/0569 20060101 H01M010/0569; H01M 4/583
20060101 H01M004/583; H01M 4/525 20060101 H01M004/525; H01M 4/505
20060101 H01M004/505; H01M 10/0525 20060101 H01M010/0525; H01M
4/136 20060101 H01M004/136 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] Development of the inventions described herein was at least
partially funded with government support through U.S. Department of
Energy grant ARPA-E-DE-AR0000034, and the U.S. government has
certain rights in the inventions.
Claims
1. A lithium ion battery comprising a positive electrode comprising
a lithium metal oxide, a negative electrode comprising a silicon
oxide based active material, and a separator between the positive
electrode and the negative electrode, wherein after 50
charge-discharge cycles between 4.5V and 1.0V, the battery exhibits
at least about 750 mAh/g discharge capacity from negative electrode
active material and at least about 150 mAh/g discharge capacity
from positive electrode active material at a rate of C/3.
2. The lithium ion battery of claim 1 wherein the silicon oxide
based active material comprises silicon oxide with the structure of
SiO.sub.x, 0.1.ltoreq.x.ltoreq.1.5.
3. The lithium ion battery of claim 1 wherein the silicon oxide
based active material comprises a silicon oxide carbon composite
composition.
4. The lithium ion battery of claim 3 wherein the silicon oxide
carbon composite composition comprises elemental silicon.
5. The lithium ion battery of claim 1 wherein the negative
electrode further comprises pyrolytic carbon.
6. The lithium ion battery of claim 1 wherein the silicon oxide
based active material has a volume average particle size of not
more than about 8 microns.
7. The lithium ion battery of claim 1 wherein the negative
electrode further comprises carbon nanofibers.
8. The lithium ion battery of claim 1 wherein the negative
electrode further comprises graphite powder.
9. The lithium ion battery of claim 1 further comprising
supplemental lithium corresponding to at least about 10% of the
negative electrode capacity.
10. The lithium ion battery of claim 1 wherein after 50
charge-discharge cycles between 4.5V and 1.0V at a C/3 rate, the
battery exhibits at least about 800 mAh/g discharge capacity from
negative electrode active material and at least about 160 mAh/g
discharge capacity from positive electrode active material.
11. The lithium ion battery of claim 1 wherein the positive
electrode comprises a lithium metal oxide approximately represented
by the formula
Li.sub.1+bNi.sub..alpha.Mn.sub..beta.Co.sub..gamma.A.sub..delta.O.sub.2-z-
F.sub.z, where b ranges from about 0.01 to about 0.3, .alpha.
ranges from about 0 to about 0.4, .beta. range from about 0.2 to
about 0.65, .gamma. ranges from 0 to about 0.46, .delta. ranges
from 0 to about 0.15 and z ranges from 0 to about 0.2 with the
proviso that both .alpha. and .gamma. are not zero, and where A is
Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li
or combinations thereof.
12. A lithium ion battery comprising a positive electrode
comprising a lithium metal oxide, a negative electrode, a separator
between the positive electrode and the negative electrode, and an
electrolyte comprising lithium ions and a halogenated carbonate,
wherein the negative electrode comprises silicon oxide based active
material and wherein the battery discharge capacity decrease by no
more than about 15 percent at the 50th discharge cycle relative to
the 7th discharge cycle when discharged at a rate of C/3 from the
7th discharge to the 50th discharge.
13. The lithium ion battery of claim 12 wherein the silicon oxide
based active material comprises a silicon oxide carbon composite
composition.
14. The lithium ion battery of claim 12 wherein the negative
electrode comprises silicon oxide with the structure of SiO.sub.x,
0.1.ltoreq.x.ltoreq.1.5.
15. The lithium ion battery of claim 12 wherein the electrolyte
comprises from about 5 volume percent to about 25 volume percent
fluoroethylene carbonate, fluorinated vinyl carbonate, monochloro
ethylene carbonate, monobromo ethylene carbonate,
4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]dioxolan-2-one,
4-(2,3,3,3-tetrafluoro-2-trifluoro
methyl-propyl)-[1,3]dioxolan-2-one,
4-trifluoromethyl-1,3-dioxolan-2-one,
bis(2,2,3,3-tetrafluoro-propyl) carbonate,
bis(2,2,3,3,3-pentafluoro-propyl) carbonate, or mixtures
thereof.
16. The lithium ion battery of claim 12 wherein the electrolyte
comprises from about 5 volume percent to about 25 volume percent
fluoroethylene carbonate, and wherein the negative electrode has a
specific discharge capacity of at least about 700 mAh/g at a rate
of C/3 based on anode's mass discharged from 4.5V to 0.5V.
17. The lithium ion battery of claim 12 wherein the negative
electrode further comprises carbon nanofibers.
18. The lithium ion battery of claim 12 wherein the negative
electrode further comprises graphite powder.
19. The lithium ion battery of claim 12 further comprising
supplemental lithium corresponding to at least about 10% of the
negative electrode capacity.
20. The lithium ion battery of claim 12 the positive electrode
comprises a lithium metal oxide approximately represented by the
formula
Li.sub.1+bNi.sub..alpha.Mn.sub..beta.Co.sub..gamma.A.sub..delta.O.sub.2-z-
F.sub.z, where b ranges from about 0.01 to about 0.3, .alpha.
ranges from about 0 to about 0.4, .beta. range from about 0.2 to
about 0.65, .gamma. ranges from 0 to about 0.46, .delta. ranges
from 0 to about 0.15 and z ranges from 0 to about 0.2 with the
proviso that both .alpha. and .gamma. are not zero, and where A is
Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li
or combinations thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 13/108,708 filed May 16, 2011 to Haixia Deng
et al., entitled "Silicon Oxide Based High Capacity Anode Materials
For Lithium Ion Batteries" incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The invention relates to high capacity negative electrode
active materials based on silicon oxide for lithium ion batteries.
The invention further relates to batteries formed with silicon
and/or silicon oxide based negative electrode active materials and
high capacity lithium rich positive electrode active materials as
well as to silicon and/or silicon oxide-based lithium ion batteries
with a supplemental lithium source.
BACKGROUND
[0004] Lithium batteries have been used in various applications due
to their high energy density. For some current commercial
batteries, the negative electrode material can be graphite, and the
positive electrode materials can comprise of lithium cobalt oxide
(LiCoO.sub.2), lithium manganese oxide (LiMn.sub.2O.sub.4), lithium
iron phosphate (LiFePO.sub.4), lithium nickel oxide (LiNiO.sub.2),
lithium nickel cobalt oxide (LiNiCoO.sub.2), lithium nickel cobalt
manganese oxide (LiNiMnCoO.sub.2), lithium nickel cobalt aluminum
oxide (LiNiCoAlO.sub.2) and the like. For negative electrodes,
lithium titanate is an alternative to graphite with good cycling
properties, but it has a lower energy density. Other alternatives
to graphite, such as tin oxide and silicon, have the potential for
providing increased energy density. However, some high capacity
negative electrode materials have been found to be unsuitable
commercially due to high irreversible capacity loss and poor
discharge and recharge cycling related to structural changes and
anomalously large volume expansions, especially for silicon, that
are associated with lithium intercalation/alloying. The structural
changes and large volume changes can destroy the structural
integrity of the electrode, thereby decreasing the cycling
efficiency.
[0005] New positive electrode active materials are presently under
development that can significantly increase the corresponding
energy density and power density of the corresponding batteries.
Particularly promising positive electrode active materials are
based on lithium rich layered-layered compositions. In particular,
the improvement of battery capacities can be desirable for vehicle
applications, and for vehicle applications the maintenance of
suitable performance over a large number of charge and discharge
cycles is important.
SUMMARY OF THE INVENTION
[0006] In a first aspect, the invention pertains to a lithium ion
battery comprising a positive electrode comprising a lithium metal
oxide, a negative electrode, a separator between the positive
electrode and the negative electrode, and extractable supplemental
lithium wherein the negative electrode comprises silicon oxide
based active material.
[0007] In a further aspect, the invention pertains to a lithium ion
battery comprising a positive electrode comprising a lithium metal
oxide, a negative electrode, and a separator between the positive
electrode and the negative electrode, wherein the negative
electrode comprises silicon oxide based active material. The
negative electrode can comprise of a polymer binder having an
elongation of at least about 50% without tearing and a tensile
strength of at least about 100 MPa.
[0008] In another aspect, the invention pertains to a lithium ion
battery comprising a positive electrode comprising a lithium metal
oxide, a negative electrode comprising a silicon oxide based active
material, and a separator between the positive electrode and the
negative electrode, wherein after 50 charge-discharge cycles
between 4.5V and 1.0V, the battery exhibits at least about 750
mAh/g discharge capacity from negative electrode active material
and at least about 150 mAh/g discharge capacity from positive
electrode active material at a rate of C/3.
[0009] In additional aspects, the invention pertains to a composite
composition comprising silicon oxide with the structure of
SiO.sub.x, 0.1.ltoreq.x.ltoreq.1.9 and anode-inert elemental
metal.
[0010] In other aspects, the invention pertains to a lithium ion
battery comprising a positive electrode comprising a lithium metal
oxide, a negative electrode, a separator between the positive
electrode and the negative electrode, and an electrolyte comprising
lithium ions and a halogenated carbonate, wherein the negative
electrode comprises silicon oxide based active material. The
battery can exhibit a discharge capacity that decreases by no more
than about 15 percent at the 50th discharge cycle relative to the
7th discharge cycle when discharged at a rate of C/3 from the 7th
discharge to the 50th discharge.
[0011] Furthermore, the invention pertains to a lithium ion battery
comprising a positive electrode comprising a lithium metal oxide, a
negative electrode, and a separator between the positive electrode
and the negative electrode, wherein the negative electrode
comprises silicon oxide based active material having a specific
capacity of at least about 1000 mAh/g at a rate of C/3 based on
anode's mass.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic perspective view of a battery stack
with a cathode, an anode, and a separator between the cathode and
anode.
[0013] FIG. 2 is a plot of charge/discharge profiles of pristine
SiO in micron size.
[0014] FIG. 3 shows cycling performance of pristine SiO in micron
size at different loading density.
[0015] FIG. 4 shows x-ray diffraction (XRD) measurements of SiO
after different time periods of high-energy mechanical (HEMM)
milling at 300 rpm.
[0016] FIG. 5 is incremental volume percent versus particle
diameter graph showing particle size distribution of SiO after
different time periods of high-energy mechanical milling (HEMM) at
300 rpm.
[0017] FIG. 6 shows cycling performance of SiO after different time
periods of HEMM milled at 300 rpm.
[0018] FIG. 7 shows x-ray diffraction (XRD) measurements of SiO
after different heating and coating treatment conditions.
[0019] FIG. 8 shows cycling performance of SiO after different
heating and coating treatment conditions.
[0020] FIG. 9 shows the effect of 10, 15, 20 volume % of
fluorinated electrolyte additive (FEA) on Si-based electrode.
[0021] FIG. 10 shows effect of 10, 15, 20 volume % of fluorinated
electrolyte additive on SiO composite based electrode.
[0022] FIG. 11 shows effect of 10 volume % of fluorinated additive
on HCMR.TM. cathode material based electrode.
[0023] FIG. 12 shows x-ray diffraction measurements of SiO-graphite
samples after different time periods of milling at 300 rpm.
[0024] FIG. 13 shows cycling performance of SiO-graphite composite
at varied loading densities of 2.25-3.29 mg/cm.sup.2.
[0025] FIG. 14 shows charge/discharge profile of a battery with
SiO-graphite composite based anode and HCMR.TM. active material
based cathode.
[0026] FIG. 15 shows cycling performance of a battery with
SiO-Gr-HC composite based anode and HCMR.TM. active material based
cathode.
[0027] FIG. 16 shows the effect of supplemental lithium on
charge/discharge plots for SiO-based composite.
[0028] FIG. 17 shows XRD measurements of SiO-metal (SiO-M) and
SiO-metal-carbon nano fiber (SiO-M-CNF) composites.
[0029] FIG. 18 shows cycling performances of batteries with SiO-M
and SiO-M-CNF based electrode and lithium metal counter
electrode.
[0030] FIG. 19 shows cycling performance of a battery with
SiO-M-CNF based anode and HCMR.TM. cathode compared with a battery
with lithium metal anode and HCMR.TM. cathode.
[0031] FIG. 20 shows charge/discharge profile of a battery with
SiO-M-CNF based anode and HCMR.TM. cathode at different cycles.
[0032] FIG. 21 shows cycling performance of a battery with
SiO-M-CNF based anode and HCMR.TM. cathode.
[0033] FIG. 22 shows a graph of incremental volume percent versus
particle diameter showing the particle diameter profiles of
pristine SiO, SiO and SiO-M HEMM milled at 300 rpm, and SiO-M HEMM
milled mixed with CNF followed by additional milling at 300
rpm.
[0034] FIG. 23 shows scanning electron microscopy (SEM) images of
SiO-M-CNF composite at different magnifications.
[0035] FIG. 24 shows XRD measurements of SiO-Gr-HC--Si
composite.
[0036] FIG. 25a shows cycling performance of SiO-Gr-HC--Si
composite with or without carbon nano fibers.
[0037] FIG. 25b shows cycling performance of a battery with
SiO-Gr-HC--Si composite based anode and HCMR.TM. cathode based upon
the mass of the positive electrode active material.
[0038] FIG. 25c shows cycling performance of SiO-Gr-HC--Si
composites at different compositions.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0039] Silicon oxide based compositions have been formed into
composite materials with high capacities and very good cycling
properties. In particular, oxygen deficient silicon oxides can be
formed into composites with electrically conductive materials, such
as conductive carbons or metal powders, which surprisingly
significantly improve cycling while providing for high values of
specific capacity. Furthermore, the milling of the silicon oxides
into smaller particles, such as submicron structured materials, can
further improve the performance of the materials. The silicon oxide
based materials maintain their high capacities and good cycling as
negative electrode active materials when placed into lithium ion
batteries with high capacity lithium metal oxide positive electrode
active materials. The cycling can be further improved with the
addition of supplemental lithium into the battery and/or with an
adjustment of the balance of the active materials in the respective
electrodes. Supplemental lithium can replace at least some of the
lithium lost to the irreversible capacity loss due to the negative
electrode and can stabilize the positive electrode with respect to
cycling. Based on appropriate designs of the batteries, high energy
density batteries can be produced, and the batteries are suitable
for a range of commercial applications.
[0040] As with silicon, oxygen deficient silicon oxide, e.g.,
silicon oxide, SiO.sub.x, 0.1.ltoreq.x.ltoreq.1.5, can
intercalate/alloy with lithium such that the oxygen deficient
silicon oxide can perform as an active material in a lithium based
battery. The oxygen deficient silicon oxide can incorporate a
relatively large amount of lithium such that the material can
exhibit a large specific capacity. However, silicon oxide is
observed generally to have a capacity that fades quickly with
battery cycling, as is observed with elemental silicon. The
composite materials described herein can significantly address the
cycling fade of the silicon oxide based materials. In particular,
composites can be formed with electrically conductive components
that contribute to the conductivity of the electrode as well as the
stabilization of the silicon oxide during cycling.
[0041] Lithium has been used in both primary and secondary
batteries. An attractive feature of lithium metal for battery use
is its light weight and the fact that it is the most
electropositive metal, and aspects of these features can be
advantageously captured in lithium-based batteries also. Certain
forms of metals, metal oxides, and carbon materials are known to
incorporate lithium ions into its structure through intercalation,
alloying or similar mechanisms. The positive electrode of a lithium
based battery generally comprises an active material that
reversibly intercalates/alloys with lithium, e.g., a metal oxide.
Lithium ion batteries generally refer to batteries in which the
negative electrode active material is also a lithium
intercalation/alloying material.
[0042] If elemental lithium metal itself is used as the anode or
negative electroactive material, the resulting battery generally is
referred to as a lithium battery. Lithium batteries can initially
cycle with good performance, but dendrites can form upon lithium
metal deposition that eventually can breach the separator and
result in failure of the battery. As a result, commercial
lithium-based secondary batteries have generally avoided the
deposition of lithium metal through the use of a negative electrode
active material that operates through intercalation/alloying or the
like and with a slight excess in negative electrode capacity
relative to the cathode or positive electrode to maintain the
battery from lithium plating on the anode. If the negative
electrode comprises a lithium intercalation/alloying composition,
the battery can be referred to as a lithium ion battery.
[0043] The batteries described herein are lithium based batteries
that use a non-aqueous electrolyte solution which comprises lithium
ions. For secondary lithium ion batteries during charge, oxidation
takes place in the cathode (positive electrode) where lithium ions
are extracted and electrons are released. During discharge,
reduction takes place in the cathode where lithium ions are
inserted and electrons are consumed. Similarly, during charge,
reduction takes place at the anode (negative electrode) where
lithium ions are taken up and electrons are consumed, and during
discharge, oxidation takes place at the anode with lithium ions and
electrons being released. Unless indicated otherwise, performance
values referenced herein are at room temperature. As described
below some of the testing of the silicon oxide based active
materials is performed in lithium and lithium ion batteries.
Generally, the lithium ion batteries are formed with lithium ions
in the positive electrode material such that an initial charge of
the battery transfers a significant fraction of the lithium from
the positive electrode material to the negative electrode material
to prepare the battery for discharge.
[0044] The word "element" is used herein in its conventional way as
referring to a member of the periodic table in which the element
has the appropriate oxidation state if the element is in a
composition and in which the element is in its elemental form,
M.sup.0, only when stated to be in an elemental form. Therefore, a
metal element generally is only in a metallic state in its
elemental form or a corresponding alloy of the metal's elemental
form. In other words, a metal oxide or other metal composition,
other than metal alloys, generally is not metallic.
[0045] When lithium ion batteries are in use, the uptake and
release of lithium from the positive electrode and the negative
electrode induces changes in the structure of the electroactive
material. As long as these changes are essentially reversible, the
capacity of the material does not change. However, the capacity of
the active materials is observed to decrease with cycling to
varying degrees. Thus, after a number of cycles, the performance of
the battery falls below acceptable values, and the battery is
replaced. Also, on the first cycle of the battery, generally there
is an irreversible capacity loss that is significantly greater than
per cycle capacity loss at subsequent cycles. The irreversible
capacity loss (IRCL) is the difference between the charge capacity
of the new battery and the first discharge capacity. The
irreversible capacity loss results in a corresponding decrease in
the capacity, energy and power for the battery due to changes in
the battery materials during the initial cycle.
[0046] The silicon oxide based materials exhibit a large
irreversible capacity loss, as described further below. In some
embodiments, the battery can comprise supplemental lithium, which
can compensate for the irreversible capacity loss of the silicon
oxide based materials as well as to surprisingly stabilize the
cycling of the battery. The supplemental lithium can replace some
or all of the active lithium removed from the cycling as a result
of the irreversible capacity loss of the silicon oxide based
material. In a traditional lithium ion battery, the lithium for
cycling is supplied only by a positive electrode active material
comprising lithium. The battery is initially charged to transfer
lithium from the positive electrode to the negative electrode where
it is then available for discharge of the battery. Supplemental
lithium results from a supply of active lithium other than the
positive electrode active material. It has also been found that
supplemental lithium can be very effective for the stabilization of
lithium rich high capacity positive electrode active materials.
See, copending U.S. patent application Ser. No. 12/938,073 now U.S.
Pat. No. 9,166,222 to Amiruddin et al., entitled, "Lithium Ion
Batteries With Supplemental Lithium," (hereinafter "the '073 patent
application") incorporated herein by reference. Thus, good cycling
has been obtained for realistic lithium ion batteries with
supplemental lithium to have relatively high specific capacities.
Supplemental lithium, for example, can be supplied by elemental
lithium, lithium alloys, a sacrificial lithium source or through
electrochemical lithiation of the negative electrode prior to
completion of the ultimate battery.
[0047] Silicon oxide based materials with greater capacity upon
cycling can be produced through the milling of the silicon oxide to
form smaller particles. In further embodiments, the silicon oxide
based materials can be formed into composites with electrically
conductive powders in combination with high energy mechanical
milling (HEMM) or the like. Alternatively or additionally, the
silicon oxide based materials can be subjected to high temperature
heat treatment. Smaller silicon oxide particles obtained from HEMM
treatment has shown greater capacity in either silicon oxide
electrode or electrodes with composites of silicon oxide-conductive
carbon particle, e.g., graphitic carbon, than commercial silicon
oxides with larger particle sizes. Pyrolytic carbon coated silicon
oxide composites showed improved conductivity and specific
capacity. Silicon oxide composites with inert metal particles with
or without a pyrolytic carbon coating have shown very good cycling
performance at high specific capacity. Suitable inert metal
particles are described further below. The milling of the silicon
oxide based materials with metal powders seems to reduce the
introduction of inert material from the grinding medium, e.g.,
zirconium oxide, into the product composite. Composites of silicon
oxide, graphite, and pyrolytic carbon in particular have shown
significantly improved specific capacity and cycling
performance.
[0048] HEMM and/or heat treatment under appropriate conditions can
result in some disproportionation of oxygen deficient silicon
oxides into SiO.sub.2 and elemental Si. Small crystalline silicon
peaks are observed under some processing conditions. It is possible
that the processed materials have some components of amorphous
elemental silicon and/or small crystallites within the structure.
However, it is believed that most of the silicon oxide based
materials herein have significant components of oxygen deficient
silicon oxide and amounts of elemental silicon have not been
quantified. In additional embodiments, elemental silicon powders,
such as submicron silicon particles, can be included in the
formation of composites with silicon oxide based materials. In
general, a range of composites are described herein, and these can
be summarized as
.alpha.SiO-.beta.Gr-.chi.HC-.delta.M-.epsilon.CNF-.phi.Si within
ranges of relative weights, as described further below. As used
herein, the reference to composites implies application of
significant combining forces, such as from HEMM milling, to
intimately associate the materials, in contrast with simple
blending, which is not considered to form composites.
[0049] When configured with high capacity lithium rich manganese
oxides based positive electrodes, the silicon oxide based electrode
can exhibit excellent cycling at reasonable rates. New electrolyte
with fluorinated additives has shown to further improve the battery
performance. High loading density electrodes with silicon oxide
based active materials can be achieved, for example, using a
polyimide binder.
[0050] Lithium rich layered-layered metal oxides have been found to
cycle with relatively high specific capacities as a positive
electrode active material. These layered-layered materials are
looking very promising for commercial applications as a new
generation of high capacity positive electrode active material. The
overall performance of the battery is based on the capacities of
both the negative and positive electrodes and their relative
balance. An improvement in the specific capacity of the negative
electrode active material can be more significant in the context of
overall battery design when a higher capacity positive electrode
active material is used in the battery. Having a high capacity
cathode material means that using only a fraction of the weight of
a high capacity cathode in a battery can result in the same energy
density as a LiCoO.sub.2 battery. Using less cathode material to
obtain the same performance reduces the price and weight of the
battery. From this perspective, the combination of the lithium rich
layered-layered positive electrode active material with high
capacity silicon oxide based negative electrode active material can
provide particularly desirable overall battery performance.
[0051] Supplemental lithium can replace lithium that does not cycle
due to an irreversible capacity loss of the negative electrode.
Furthermore, it has been discovered that the inclusion of
supplemental lithium can stabilize positive electrodes based on
lithium rich layered-layered lithium metal oxide compositions. In
particular, for these lithium rich metal oxides, the supplemental
lithium can stabilize the capacity of the positive electrode
compositions out to large number of cycles. This improvement in
cycling of the positive electrode active material is described
further in the copending '073 patent application.
[0052] The layered-layered lithium metal oxides, which provide a
relatively large specific capacity, exhibit a significant
irreversible capacity loss associated with changes to the material
during the initial charge of the battery. Irreversible capacity
loss associated with the positive electrode may result in lithium
that can get deposited in the negative electrode but which cannot
be later intercalated into the positive electrode active material.
This excess lithium from the positive electrode is separate from
any supplemental lithium introduced into the battery since the
battery is assembled with the lithium metal oxide fully loaded with
lithium pending the initial charge of the battery.
[0053] The supplemental lithium can be provided to the negative
electrode in various ways. In particular suitable approaches
include, for example, introducing elemental lithium into the
battery, the incorporation of a sacrificial material with active
lithium that can be transferred to the negative electrode active
material, or preloading of lithium into the negative electrode
active material. After the initial charge, supplemental lithium is
associated with the negative electrode active material although a
portion of the lithium can be associated with irreversible reaction
byproducts, such as the solid electrolyte interphase (SEI)
layer.
[0054] The introduction of elemental lithium in association with
the anode, i.e., negative electrode, can be an appropriate way to
introduce supplemental lithium. In particular, elemental lithium
powder or foil can be associated with the negative electrode to
supply the supplemental lithium. In some embodiments, an elemental
lithium powder can be placed on the surface of the electrode or on
the surface of the current collector. A supplemental lithium
source, such as elemental lithium, within the negative electrode
generally may initiate reaction with the silicon oxide based active
material upon contact of the electrode with electrolyte since the
reaction is spontaneous as long as electrical conductivity is
supported within the electrode structure.
[0055] In alternative or additional embodiments, a supplemental
lithium source can be associated with the positive electrode, i.e.,
cathode, or with a separate sacrificial electrode. If a
supplemental lithium source is associated with the positive
electrode or a separate sacrificial electrode, current flows
between the electrode with the supplemental lithium and the
negative electrode to support the respective half reactions that
ultimately results in the placement of the supplemental lithium
within the negative electrode active material, with possibly a
fraction of the supplemental lithium being consumed in side
reactions, such as formation of an SEI layer or other reactions
leading to irreversible capacity loss.
[0056] In further embodiments, the supplemental lithium can be
placed into the negative electrode active material prior to
construction of the battery. For example, prior to assembly of the
battery, supplemental lithium can be inserted into the active
material through electrochemical intercalation/alloying. To perform
the electrochemical deposition, the silicon oxide based electrode
can be assembled into a structure with electrolyte and the
supplemental lithium source, such as lithium foil. If the elemental
lithium is in electrical contact with the active material in the
presence of electrolyte, the reaction of the elemental lithium with
the active alloying/intercalation material can occur spontaneously.
Alternatively, the structure can be assembled into a cell with
electrolyte and a separator separating the silicon oxide based
electrode and an electrode with the supplemental lithium, such as a
lithium foil. Current flow through the cell can be controlled to
provide for the lithium incorporation into the silicon oxide based
electrode. In such a configuration, the silicon oxide based
electrode functions as a positive electrode of a lithium cell. This
cell can be cycled a few times to complete any formation of an SEI
layer as well as any other initial irreversible changes to the
electrode, prior to the deposition of a desired amount of
supplemental lithium into the electrode for transfer to the
ultimate battery. After deposition of a desired amount of lithium,
the silicon oxide based electrode can be taken and assembled into
the ultimate lithium ion battery.
[0057] For graphitic carbon based electrodes associated with
supplemental lithium, the electrodes are found to have extractable
lithium after essentially fully discharging the batteries having a
lithium metal oxide positive electrode active material after
cycling for relatively large numbers of cycles. The lithium is
supplied in the batteries from the positive electrode active
material as well as the supplemental lithium. This residual lithium
is found to stabilize the battery cycling when used with lithium
rich positive electrode active materials. Also, the amount of
residual lithium is found to gradually diminish with larger numbers
of cycles. See the '073 patent application referenced above. Based
on the measurements for the graphitic carbon electrodes, it is
anticipated that the silicon oxide based electrodes with
supplemental lithium can similarly exhibit residual lithium that
can be extracted from the electrodes after discharging the battery
with a lithium metal oxide positive electrode.
[0058] Silicon oxide has attracted significant amount of attention
as a potential negative electrode material due to its high specific
capacity with respect to intake and release of lithium and
promising cycling properties. See, for example, published U.S.
patent application 2004/0033419 to Funabiki, entitled "Negative
Electrode Active Material, Negative Electrode Using the Same,
Non-Aqueous Electrolyte Battery Using the Same, and Method for
Preparing the Same," incorporated herein by reference. It was
further recognized that association of conductive carbon with the
silicon oxide active material can improve the performance of the
silicon oxide material in a lithium ion battery. Composites with
electrically conductive materials and silicon oxide active material
described herein provide very good cycling performance.
[0059] As described herein, high energy milling is used to fracture
silicon oxide particles to a smaller size. The results herein
suggest that the smaller particles can cycle significantly better,
perhaps due to the ability of the smaller particles to accommodate
volume changes of the particles over cycling of the materials. The
milling process can incorporate electrically conductive diluents to
form an intimate composite through the milling process. Graphitic
carbon, e.g., nanostructured conductive carbon, can provide a good
electrically conductive medium for the formation of composites with
silicon oxide. Furthermore, it has been found that metal particles
provide desirable milling properties as well as a suitable
electrically conductive diluent for the formation of corresponding
composites. In particular, it has been found that milling with
metal powders can provide for the use of desirable milling
conditions while obtaining reduced amounts of milling media within
the product composite. High energy milling can generally be
performed with a hard ceramic milling media, such as zirconium
oxide particles. Milling can result in the incorporation of some
milling media into the product composite material. Since the
milling media is electrically insulating and electrochemically
inert, it is desirable to keep the amount of milling media in the
product composite material, after separation of the bulk quantities
of milling beads, to a low or possibly undetectable level.
[0060] The objective for the design of improved silicon oxide based
materials is to further stabilize the negative electrode materials
over cycling while maintaining a high specific capacity. Thus, high
energy milling can be performed to form composites with
electrically conductive materials. As described herein, pyrolytic
carbon coatings are also observed to stabilize silicon oxide based
materials with respect to battery performance. In particular, the
pyrolytic carbon coatings can be placed over the initially prepared
composites to provide an additional electrically conductive
component of the product material. The combination of the pyrolytic
carbon with a silicon oxide-particulate conductor composite
provides surprisingly improved performance in some embodiments.
[0061] With respect to the composite materials, silicon oxide
components can be combined with, for example, carbon nanoparticles
and/or carbon nanofibers. The components can be, for example,
milled to form the composite, in which the materials are intimately
associated. Generally, it is believed that the association has a
mechanical characteristic, such as the carbon coated over or
mechanically affixed with the silicon oxide materials. In
additional or alternative embodiments, the silicon oxide can be
milled with metal powders, in which the silicon oxide is milled to
a smaller particle size and the metal is intimately combined with
the silicon oxide material to form a composite material, for
example with a nanostructure. The carbon components can be combined
with the silicon-metal alloys to form multi-component composites.
The composite materials with intimately combined components are
distinguishable from simple blends of components held together with
a polymer binder, which lacks mechanical and/or chemical
interactions to form a single composite material.
[0062] Desirable carbon coatings can be formed by pyrolizing
organic compositions. The organic compositions can be pyrolyzed at
relatively high temperatures, e.g., about 800.degree. C. to about
900.degree. C., to form a hard amorphous coating. In some
embodiments, the desired organic compositions can be dissolved in a
suitable solvent, such as water and/or volatile organic solvents
for combining with the silicon oxide based component. The
dispersion can be well mixed with silicon oxide based composition.
After drying the mixture to remove the solvent, the dried mixture
can be heated in an oxygen free atmosphere to pyrolyze the organic
composition, such as organic polymers, some lower molecular solid
organic compositions and the like, and to form a carbon coating.
The carbon coating can lead to surprisingly significant improvement
in the capacity of the resulting material. Also, environmentally
friendly organic compositions, such as sugars and citric acid, can
be used as desirable precursors for the formation of pyrolytic
carbon coatings. In some embodiments, organic polymers can be
blended with the silicon oxide based materials for thermal
processing to form pyrolytic carbon. In further embodiments,
elemental metal coatings, such as silver or copper, can be applied
as an alternative to a pyrolytic carbon coating to provide
electrical conductivity and to stabilize silicon oxide based active
material. The elemental metal coatings can be applied through
solution based reduction of a metal salt.
[0063] The silicon oxide based materials can be incorporated into
suitable electrode structures generally with a suitable polymer
binder and optionally mixed with electrically conductive powders.
It has been found that polyimide binders are particularly desirable
for silicon oxide based materials. The high capacity silicon oxide
based materials are of particular value in combination with a high
capacity positive electrode active material. Traditionally, the
anode and cathode are relatively balanced so that the battery does
not involve significant waste with associated cost of unused
electrode capacity as well as for the avoidance of corresponding
weight and volume associated with unused electrode capacity. With
the materials described herein, it can be possible to get high
capacity results simultaneously for both electrodes in the lithium
ion battery. Furthermore, cycling capacity of both electrodes can
independently fade, and the capacities of both electrodes are
subject to irreversible capacity loss, and approaches to address
both of these issues are described herein. The positive electrodes
with lithium rich layered-layered compositions can exhibit a
significant first cycle irreversible capacity loss. However, high
capacity silicon oxide based anodes can generally exhibit
contributions to IRCL significantly greater than the positive
electrode active material.
[0064] The positive electrode active material can be designed to
reduce IRCL associated with the positive electrode, such as with a
coating applied to the positive electrode active material.
Furthermore, supplemental lithium can be used as a substitute for
additional capacity of the positive electrode to compensate for the
relatively large IRCL of the negative electrode. The supplemental
lithium can compensate for the large IRCL of the negative
electrode. Thus, if the supplemental lithium is selected to
appropriately compensate for the negative electrode IRCL, the
remaining observed IRCL can be attributed to the positive electrode
active material. With appropriate stabilization of the negative
electrode and positive electrode, a battery with high capacity
materials in both electrodes can exhibit high specific capacities
for both electrodes over at least a moderate number of cycles.
[0065] To achieve cycling of the battery without lithium plating,
the negative electrode generally is balanced to at least about 100%
of the positive electrode capacity. The electrode capacities are
evaluated independently against a lithium metal electrode, as
described further below. On the other hand, for embodiments with
supplemental lithium, the supplemental lithium can be designed to
compensate for the IRCL such that the cycling capacities of the
negatives electrode and positive electrode can be roughly balanced
or with some excess negative electrode capacity, although a greater
amount of supplemental lithium can be used if desired.
[0066] Improved performance of silicon oxide based batteries is
also observed with the addition of a halogenated carbonates as an
additive to the electrolyte. For example, fluoroethylene carbonate
(FEC) has been proposed to improve the safety of batteries due to
its nonflammability, to expand the operating cell voltage due to
its high oxidation resistance, to improve cycle performance by
forming an electrochemically stable SEI that included LiF and
silicon (Si) fluorides on a Si-based anode, and many other
advantages [1-6]. 1. R. McMillan, H. Slegr, Z. X. Shu, and W. Wang,
J. Power Sources, 81, 20 (1999). 2. N.-S. Choi, K. H. Yew, K. Y.
Lee, M. Sung, H. Kim, and S.-S. Kim, J. Power Sources, 161, 1254
(2006). 3. I. A. Profatilova, S.-S. Kim, and N.-S. Choi,
Electrochim. Acta, 54, 4445 (2009). 4. T. Achiha, T. Nakajima, Y.
Ohzawa, M. Koh, A. Yamauchi, M. Kagawa, and H. Aoyama, J.
Electrochem. Soc., 156, A483 (2009). 5. J. Yamaki, S. Yamami, T.
Doi, and S. Okada, Electrochem. Soc., 602, 263 (2006). 6. K. Naoi,
E. Iwama, N. Ogihara, Y. Nakamura, H. Segawa, and Y. Ino, J.
Electrochem. Soc., 156, A272 (2009). A halogenated carbonate
additive has been found to provide surprisingly significant
improvement in the performance of the batteries based on silicon
oxide active materials.
Lithium Ion Battery Structure
[0067] Lithium ion batteries generally comprise a positive
electrode (cathode), a negative electrode (anode), a separator
between the negative electrode and the positive electrode and an
electrolyte comprising lithium ions. The electrodes are generally
associated with metal current collectors, such as metal foils.
Lithium ion batteries refer to batteries in which the negative
electrode active material is a material that takes up lithium
during charging and releases lithium during discharging. Referring
to FIG. 1, a battery 100 is shown schematically having a negative
electrode 102, a positive electrode 104, and a separator 106
between negative electrode 102 and positive electrode 104. A
battery can comprise multiple positive electrodes and multiple
negative electrodes, such as in a stack, with appropriately placed
separators. Electrolyte in contact with the electrodes provides
ionic conductivity through the separator between electrodes of
opposite polarity. A battery generally comprises current collectors
108, 110 associated respectively with negative electrode 102 and
positive electrode 104. The basic battery structures and
compositions are described in this section and modifications
related to incorporation of supplemental lithium are described
further below.
[0068] The nature of the positive electrode active material and the
negative electrode active material influences the resulting voltage
of the battery since the voltage is the difference between the half
cell potentials at the cathode and anode. Suitable positive
electrode active materials are described below, and the materials
of particular interest are lithium metal oxides. In general,
suitable negative electrode lithium intercalation/alloying
compositions can include, for example, graphite, synthetic
graphite, coke, fullerenes, other graphitic carbons, niobium
pentoxide, tin alloys, silicon, silicon oxide, silicon alloys,
silicon-based composites, titanium oxide, tin oxide, and lithium
titanium oxide, such as Li.sub.xTiO.sub.2, 0.5<x.ltoreq.1 or
Li.sub.1+xTi.sub.2-xO.sub.4, 0.ltoreq.x.ltoreq.1/3. Graphitic
carbon and metal oxide negative electrode compositions take up and
release lithium through an intercalation or similar process.
Silicon and tin alloys form alloys with the lithium metal to take
up lithium and release lithium from the alloy to correspondingly
release lithium. Negative electrode active materials of particular
interest herein are silicon oxide based materials described in
detail below. In general, if the battery does not include
supplemental lithium, the positive electrode and negative electrode
are balanced such that the capacities of the negative electrode
active material is from about 100 to about 110 percent of the
capacity of the positive electrode active material. The positive
electrode active material capacity can be estimated from the
theoretical capacity of the material, and the negative electrode
capacity can be measured by cycling the material against lithium
metal foil. The balancing of the battery when supplemental lithium
is present is described further below.
[0069] The positive electrode active compositions and negative
electrode active compositions generally are powder compositions
that are held together in the corresponding electrode with a
polymer binder. The binder provides ionic conductivity to the
active particles when in contact with the electrolyte. Suitable
polymer binders include, for example sodium carboxy methyl
cellulose (CMC), polyvinylidine fluoride (PVDF), polyimide,
polyethylene oxide, polyethylene, polypropylene,
polytetrafluoroethylene, polyacrylates, rubbers, e.g.
ethylene-propylene-diene monomer (EPDM) rubber or styrene butadiene
rubber (SBR), copolymers thereof, or mixtures thereof. In
particular, thermally curable polyimide polymers have been found
desirable, which may be due to their high mechanical strength.
Table I provides suppliers of polyimide polymers, and names of
corresponding polyimide polymers.
TABLE-US-00001 TABLE I Supplier Binder New Japan Chemical Co., Ltd.
Rikacoat PN-20 Rikacoat EN-20 Rikacoat SN-20 HD MicroSystems
PI-2525 PI-2555 PI-2556 PI-2574 AZ Electronic Materials PBI
MRS0810H Ube Industries. Ltd. U-Varnish S U-Varnish A Maruzen
Petrochemical Co., Ltd. Bani-X (Bis-allyl-nadi-imide) Toyobo Co.,
Ltd. Vyromax HR16NN
[0070] With respect to polymer properties, some significant
properties for electrode application are summarized in Table
II.
TABLE-US-00002 TABLE II Tensile Elastic Elongation Strength Modulus
Viscosity Binder (%) (MPa) (psi) (P) PVDF 5-20 31-43 160000 10-40
Polyimide 70-100 150-300 40-60 CMC 30-40 10-15 30
[0071] The elongation refers to the percent elongation prior to
tearing of the polymer. In general, to accommodate the silicon
oxide based materials, it is desirable to have an elongation of at
least about 50% and in further embodiments at least about 70%.
Similarly, it is desirable for the polymer binder to have a tensile
strength of at least about 100 MPa and in further embodiments at
least about 150 MPa. Tensile strengths can be measured according to
procedures in ASTM D638-10 Standard Test Method for Tensile
Properties of Plastics, incorporated herein by reference. A person
of ordinary skill in the art will recognize that additional ranges
of polymer properties within the explicit ranges above are
contemplated and are within the present disclosure. The particle
loading in the binder can be large, such as greater than about 80
weight percent up to about 97 percent or more. To form the
electrode, the powders can be blended with the polymer in a
suitable liquid, such as a solvent for the polymer. The resulting
paste can be pressed into the electrode structure.
[0072] The positive electrode composition, and possibly the
negative electrode composition, generally also comprises an
electrically conductive powder distinct from the electroactive
composition. Suitable supplemental electrically conductive powders
include, for example, graphite, carbon black, metal powders, such
as silver powders, metal fibers, such as stainless steel fibers,
and the like, and combinations thereof. Generally, a positive
electrode can comprise from about 1 weight percent to about 25
weight percent, and in further embodiments from about 2 weight
percent to about 15 weight percent distinct electrically conductive
powder. While the negative electrode can comprise an electrically
conductive material incorporated into the composite, the negative
electrode can further comprise an electrically conductive material
that is simply blended into the blend with the polymer such that
the additional conductor is not intimately combined with the
silicon oxide. With respect to the blended electrically conductive
compositions, the negative electrode can comprise from about 1
weight percent to about 30 weight percent additional conductor and
in further embodiments from about 2 weight percent to about 15
weight percent additional electrical conductor. A person of
ordinary skill in the art will recognize that additional ranges of
amounts of electrically conductive powders and polymer binders
within the explicit ranges above are contemplated and are within
the present disclosure.
[0073] The electrode generally is associated with an electrically
conductive current collector to facilitate the flow of electrons
between the electrode and an exterior circuit. The current
collector can comprise metal, such as a metal foil or a metal grid.
In some embodiments, the current collector can be formed from
nickel, aluminum, stainless steel, copper or the like. The
electrode material can be cast as a thin film onto the current
collector. The electrode material with the current collector can
then be dried, for example in an oven, to remove solvent from the
electrode. In some embodiments, the dried electrode material in
contact with the current collector foil or other structure can be
subjected to a pressure, such as, from about 2 to about 10
kg/cm.sup.2 (kilograms per square centimeter).
[0074] The separator is located between the positive electrode and
the negative electrode. The separator is electrically insulating
while providing for at least selected ion conduction between the
two electrodes. A variety of materials can be used as separators.
Commercial separator materials are generally formed from polymers,
such as polyethylene and/or polypropylene that are porous sheets
that provide for ionic conduction. Commercial polymer separators
include, for example, the Celgard.RTM. line of separator material
from Hoechst Celanese, Charlotte, N.C. Also, ceramic-polymer
composite materials have been developed for separator applications.
These composite separators can be stable at higher temperatures,
and the composite materials can significantly reduce the fire risk.
The polymer-ceramic composites for separator materials are
described further in U.S. patent application 2005/0031942A to
Hennige et al., entitled "Electric Separator, Method for Producing
the Same and the Use Thereof," incorporated herein by reference.
Polymer-ceramic composites for lithium ion battery separators are
sold under the trademark Separion.RTM. by Evonik Industries,
Germany.
[0075] We refer to solutions comprising solvated ions as
electrolytes, and ionic compositions that dissolve to form solvated
ions in appropriate liquids are referred to as electrolyte salts.
Electrolytes for lithium ion batteries can comprise one or more
selected lithium salts. Appropriate lithium salts generally have
inert anions. Suitable lithium salts include, for example, lithium
hexafluorophosphate, lithium hexafluoroarsenate, lithium
bis(trifluoromethyl sulfonyl imide), lithium trifluoromethane
sulfonate, lithium tris(trifluoromethyl sulfonyl) methide, lithium
tetrafluoroborate, lithium perchlorate, lithium
tetrachloroaluminate, lithium chloride, lithium difluoro oxalato
borate, and combinations thereof. Traditionally, the electrolyte
comprises a 1 M concentration of the lithium salts, although
greater or lesser concentrations can be used. Particularly useful
electrolytes for high voltage lithium-ion batteries are described
further in copending U.S. patent application Ser. No. 12/630,992
filed on Dec. 4, 2009 now U.S. Pat. No. 8,993,177 to Amiruddin et
al. (the '992 application), entitled "Lithium Ion Battery With High
Voltage Electrolytes and Additives," incorporated herein by
reference.
[0076] For lithium ion batteries of interest, a non-aqueous liquid
is generally used to dissolve the lithium salt(s). The solvent
generally does not dissolve the electroactive materials.
Appropriate solvents include, for example, propylene carbonate,
dimethyl carbonate, diethyl carbonate, 2-methyl tetrahydrofuran,
dioxolane, tetrahydrofuran, methyl ethyl carbonate,
.gamma.-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,
dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),
diglyme (diethylene glycol dimethyl ether), DME (glyme or
1,2-dimethyloxyethane or ethylene glycol dimethyl ether),
nitromethane and mixtures thereof. Particularly useful solvents for
high voltage lithium-ion batteries are described further in the
copending '992 application.
[0077] Additives to the electrolytes can further provide
performance improvements. In particular, the performance of silicon
oxide based batteries can have significant performance improvements
with the addition of halogenated carbonates to the electrolyte.
Suitable halogenated carbonates include, for example,
fluoroethylene carbonate (C.sub.3H.sub.3FO.sub.3), fluorinated
vinyl carbonate, monochloro ethylene carbonate, monobromo ethylene
carbonate,
4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]dioxolan-2-one,
4-(2,3,3,3-tetrafluoro-2-trifluoro
methyl-propyl)-[1,3]dioxolan-2-one,
4-trifluoromethyl-1,3-dioxolan-2-one,
bis(2,2,3,3-tetrafluoro-propyl) carbonate,
bis(2,2,3,3,3-pentafluoro-propyl) carbonate, mixtures thereof and
the like. Note that ethylene carbonate is also known by its IUPAC
name of 1,3-dioxolan-2-one. In general, the electrolyte can
comprise from about 1 volume percent to about 35 volume percent
halogenated carbonate, in further embodiments from about 2 volume
percent to about 30 volume percent and in other embodiments from
about 3 volume percent to about 25 volume percent halogenated
carbonate in the electrolyte. A person of ordinary skill in the art
will recognize that additional ranges of halogenated carbonate
concentrations within the explicit ranges above are contemplated
and are within the present disclosure. As described further in the
Examples below, the incorporation of halogenated carbonate into the
electrolyte has been observed to significantly improve the specific
capacity and the cycling properties of batteries incorporating
silicon oxide active materials.
[0078] The electrodes described herein can be incorporated into
various commercial battery designs, such as prismatic shaped
batteries, wound cylindrical batteries, coin batteries or other
reasonable battery shapes. The batteries can comprise a single
electrode stack or a plurality of electrodes of each charge
assembled in parallel and/or series electrical connection(s).
Appropriate electrically conductive tabs can be welded or the like
to the current collectors, and the resulting jellyroll or stack
structure can be placed into a metal canister or polymer package,
with the negative tab and positive tab welded to appropriate
external contacts. Electrolyte is added to the canister, and the
canister is sealed to complete the battery. Some presently used
rechargeable commercial batteries include, for example, the
cylindrical 18650 batteries (18 mm in diameter and 65 mm long) and
26700 batteries (26 mm in diameter and 70 mm long), although other
battery sizes can be used. Pouch batteries can be constructed as
described in published U.S. patent application 2009/0263707 to
Buckley et al, entitled "High Energy Lithium Ion Secondary
Batteries", incorporated herein by reference.
Positive Electrode Active Compositions
[0079] In general, the lithium ion battery positive electrode
materials can be any reasonable positive electrode active material,
such as stoichiometric layered cathode materials with hexagonal
lattice structures, such as LiCoO.sub.2, LiNiO.sub.2, LiMnO.sub.2,
Li(CoNiMn).sub.1/3O.sub.2, Li(CoNiMnAl).sub.1/4O.sub.2 or the like;
cubic spinel cathode materials such as LiMn.sub.2O.sub.4,
LiNi.sub.0.5Mn.sub.1.5O.sub.4, Li.sub.4Mn.sub.5O.sub.12, or the
like; olivine LiMPO.sub.4 (M=Fe, Co, Mn, combinations thereof and
the like) type materials; layered cathode materials such as
Li.sub.1+x(NiCoMn).sub.0.33-xO.sub.2 (0.ltoreq.x<0.3) systems;
layer-layer composites, such as xLi.sub.2MnO.sub.3.(1-x)LiMO.sub.2
where M can be Ni, Co, Mn, combinations thereof and the like; and
composite structures like layered-spinel structures such as
LiMn.sub.2O.sub.4.LiMO.sub.2. In additional or alternative
embodiments, a lithium rich composition can be referenced relative
to a composition LiMO.sub.2, where M is one or more metals with an
average oxidation state of +3. Generally, the lithium rich
compositions can be represented approximately with a formula
Li.sub.1+xM.sub.1-yO.sub.2-zF.sub.z where M is one or more metal
elements, x is from about 0.01 to about 0.33, y is from about x-0.2
to about x+0.2 with the proviso that y.gtoreq.0, and z is from 0 to
about 0.2. In the layered-layered composite compositions, x is
approximately equal to y. In general, the additional lithium in the
lithium rich compositions is accessed at higher voltages such that
the initial charge takes place at a relatively higher voltage to
access the additional capacity.
[0080] Lithium rich positive electrode active materials of
particular interest can be represented approximately by a formula
Li.sub.1+bNi.sub..alpha.Mn.sub..beta.Co.sub..gamma.A.sub..delta.O.sub.2-z-
F.sub.z, where b ranges from about 0.01 to about 0.3, .alpha.
ranges from about 0 to about 0.4, .beta. range from about 0.2 to
about 0.65, .gamma. ranges from 0 to about 0.46, .delta. ranges
from 0 to about 0.15 and z ranges from 0 to about 0.2 with the
proviso that both .alpha. and .gamma. are not zero, and where A is
Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li
or combinations thereof. A person of ordinary skill in the art will
recognize that additional ranges of parameter values within the
explicit compositional ranges above are contemplated and are within
the present disclosure. To simplify the following discussion in
this section, the optional fluorine dopant is not discussed
further. Desirable lithium rich compositions with a fluorine dopant
are described further in published U.S. patent application
2010/0086854 to Kumar et al., entitled "Fluorine Doped Lithium Rich
Metal Oxide Positive Electrode Battery Materials With High Specific
Capacity and Corresponding Batteries," incorporated herein by
reference. Compositions in which A is lithium as a dopant for
substitution for Mn are described in published U.S. patent
application 2011/0052989 to Venkatachalam et al., entitled "Lithium
Doped Cathode Material," incorporated herein by reference. The
specific performance properties obtained with +2 metal cation
dopants, such as Mg.sup.+2, are described in copending U.S. patent
application Ser. No. 12/753,312 now U.S. Pat. No. 8,741,484 to
Karthikeyan et al., entitled "Doped Positive Electrode Active
Materials and Lithium Ion Secondary Batteries Constructed
Therefrom," incorporated herein by reference.
[0081] If b+.alpha.-.beta.+.gamma.+.delta. approximately equals to
1, the positive electrode material with the formula above can be
represented approximately in two component notation as x
Li.sub.2M'O.sub.3.(1-x)LiMO.sub.2 where 0<x<1, M is one or
more metal cations with an average valance of +3 within some
embodiments at least one cation being a Mn ion or a Ni ion and
where M' is one or more metal cations with an average valance of +4
such as Mn.sup.+4. It is believed that the layered-layered
composite crystal structure has a structure with the excess lithium
supporting the stability of the material. For example, in some
embodiments of lithium rich materials, a Li.sub.2MnO.sub.3 material
may be structurally integrated with a layered LiMO.sub.2 component
where M represents selected non-lithium metal elements or
combinations thereof. These compositions are described generally,
for example, in U.S. Pat. No. 6,680,143 to Thackeray et al.,
entitled "Lithium Metal Oxide Electrodes for Lithium Cells and
Batteries," incorporated herein by reference.
[0082] Recently, it has been found that the performance properties
of the positive electrode active materials can be engineered around
the specific design of the composition stoichiometry. The positive
electrode active materials of particular interest can be
represented approximately in two component notation as x
Li.sub.2MnO.sub.3.(1-x) LiMO.sub.2, where M is one or more metal
elements with an average valance of +3 and with one of the metal
elements being Mn and with another metal element being Ni and/or
Co. In general, 0<x<1, but in some embodiments
0.03.ltoreq.x.ltoreq.0.55, in further embodiments
0.075.ltoreq.x.ltoreq.0.50, in additional embodiments
0.1.ltoreq.x.ltoreq.0.45, and in other embodiments
0.15.ltoreq.x.ltoreq.0.425. A person of ordinary skill in the art
will recognize that additional ranges within the explicit ranges of
parameter x above are contemplated and are within the present
disclosure. For example, M can be a combination of nickel, cobalt
and manganese, which, for example, can be in oxidation states
Ni.sup.+2, Co.sup.+3, and Mn.sup.+4 within the initial lithium
manganese oxides. The overall formula for these compositions can be
written as
Li.sub.2(i+x)/(2+x)Mn.sub.2x/(2+x)M.sub.(2-2x)/(2+x)O.sub.2. In the
overall formula, the total amount of manganese has contributions
from both constituents listed in the two component notation. Thus,
in some sense the compositions are manganese rich.
[0083] In some embodiments, M can be written as
Ni.sub.uMn.sub.vCo.sub.wA.sub.y. For embodiments in which y=0, this
simplifies to Ni.sub.uMn.sub.vCo.sub.w. If M includes Ni, Co, Mn,
and optionally A the composition can be written alternatively in
two component notation and single component notation as the
following.
xLi.sub.2MnO.sub.3(1-x)LiNi.sub.uMn.sub.vCo.sub.wA.sub.yO.sub.2,
(1)
Li.sub.1+bNi.sub..alpha.Mn.sub..beta.Co.sub..gamma.A.sub..delta.O.sub.2,
(2)
[0084] with u+v+w+y.apprxeq.1 and
b+a+.beta.+.gamma.+.delta..apprxeq.1. The reconciliation of these
two formulas leads to the following relationships:
b=x/(2+x),
.alpha.=2u(1-x)/(2+x),
.beta.=2x/(2+x)+2v(1-x)/(2+x),
.gamma.=2w(1-x)/(2+x),
.delta.=2y(1-x)/(2+x),
and similarly,
x=2b/(1-b),
u=.alpha./(1-3b),
v=((.beta.-2b)/(1-3b),
w=.gamma./(1-3b),
y=.delta./(1-3b).
[0085] In some embodiments, it may be desirable to have
u.apprxeq.v, such that LiNi.sub.uMn.sub.vCo.sub.wA.sub.yO.sub.2
becomes approximately LiNi.sub.uMn.sub.uCo.sub.wA.sub.yO.sub.2. In
this composition, when y=0, the average valance of Ni, Co and Mn is
+3, and if u.apprxeq.v, then these elements can have valances of
approximately Ni.sup.+2, Co.sup.+3 and Mn.sup.+4 to achieve the
average valance. When the lithium is hypothetically fully
extracted, all of the elements go to a +4 valance. A balance of Ni
and Mn can provide for Mn to remain in a +4 valance as the material
is cycled in the battery. This balance avoids the formation of
Mn.sup.+3, which has been associated with dissolution of Mn into
the electrolyte and a corresponding loss of capacity.
[0086] In further embodiments, the composition can be varied around
the formula above such that
LiNi.sub.u+.DELTA.Mn.sub.u-.DELTA.Co.sub.wA.sub.yO.sub.2, where the
absolute value of .DELTA. generally is no more than about 0.3
(i.e., -0.3.ltoreq..DELTA..ltoreq.0.3), in additional embodiments
no more than about 0.2 (-0.2.ltoreq..DELTA..ltoreq.0.2) in some
embodiments no more than about 0.175
(-0.175.ltoreq..DELTA..ltoreq.0.175) and in further embodiments no
more than about 0.15 (-0.15.ltoreq..DELTA..ltoreq.0.15). Desirable
ranges for x are given above. With 2u+w+y.apprxeq.1, desirable
ranges of parameters are in some embodiments 0.ltoreq.w.ltoreq.1,
0.ltoreq.u.ltoreq.0.5, 0.ltoreq.y.ltoreq.0.1 (with the proviso that
both u+A and w are not zero), in further embodiments,
0.1.ltoreq.w.ltoreq.0.6, 0.1.ltoreq.u.ltoreq.0.45,
0.ltoreq.y.ltoreq.0.075, and in additional embodiments
0.2.ltoreq.w.ltoreq.0.5, 0.2.ltoreq.u.ltoreq.0.4,
0.ltoreq.y.ltoreq.0.05. A person of ordinary skill in the art will
recognize that additional ranges of composition parameters within
the explicit ranges above are contemplated and are within the
present disclosure. As used herein, the notation
(value1.ltoreq.variable.ltoreq.value2) implicitly assumes that
value 1 and value 2 are approximate quantities. The engineering of
the composition to obtain desired battery performance properties is
described further in published U.S. patent application number
2011/0052981 to Lopez et al., entitled "Layer-Layer Lithium Rich
Complex Metal Oxides With High Specific Capacity and Excellent
Cycling," incorporated herein by reference.
[0087] The formulas presented herein for the positive electrode
active materials are based on the molar quantities of starting
materials in the synthesis, which can be accurately determined.
With respect to the multiple metal cations, these are generally
believed to be quantitatively incorporated into the final material
with no known significant pathway resulting in the loss of the
metals from the product compositions. Of course, many of the metals
have multiple oxidation states, which are related to their activity
with respect to the batteries. Due to the presence of the multiple
oxidation states and multiple metals, the precise stoichiometry
with respect to oxygen generally is only roughly estimated based on
the crystal structure, electrochemical performance and proportions
of reactant metals, as is conventional in the art. However, based
on the crystal structure, the overall stoichiometry with respect to
the oxygen is reasonably estimated. All of the protocols discussed
in this paragraph and related issues herein are routine in the art
and are the long established approaches with respect to these
issues in the field.
[0088] A co-precipitation process has been performed for the
desired lithium rich metal oxide materials described herein having
nickel, cobalt, manganese and additional optional metal cations in
the composition and exhibiting the high specific capacity
performance. In addition to the high specific capacity, the
materials can exhibit a good tap density which leads to high
overall capacity of the material in fixed volume applications.
Specifically, lithium rich metal oxide compositions formed by the
co-precipitation process were used in coated forms to generate the
results in the Examples below.
[0089] Specifically, the synthesis methods based on
co-precipitation have been adapted for the synthesis of
compositions with the formula
Li.sub.1+bNi.sub..alpha.Mn.sub..beta.Co.sub..gamma.A.sub..delta.O.sub.2-z-
F.sub.z, as described above. In the co-precipitation process, metal
salts are dissolved into an aqueous solvent, such as purified
water, with a desired molar ratio. Suitable metal salts include,
for example, metal acetates, metal sulfates, metal nitrates, and
combination thereof. The concentration of the solution is generally
selected between 1M and 3M. The relative molar quantities of metal
salts can be selected based on the desired formula for the product
materials. Similarly, the dopant elements can be introduced along
with the other metal salts at the appropriate molar quantity such
that the dopant is incorporated into the precipitated material. The
pH of the solution can then be adjusted, such as with the addition
of Na.sub.2CO.sub.3 and/or ammonium hydroxide, to precipitate a
metal hydroxide or carbonate with the desired amounts of metal
elements. Generally, the pH can be adjusted to a value between
about 6.0 to about 12.0. The solution can be heated and stirred to
facilitate the precipitation of the hydroxide or carbonate. The
precipitated metal hydroxide or carbonate can then be separated
from the solution, washed and dried to form a powder prior to
further processing. For example, drying can be performed in an oven
at about 110.degree. C. for about 4 to about 12 hours. A person of
ordinary skill in the art will recognize that additional ranges of
process parameters within the explicit ranges above are
contemplated and are within the present disclosure.
[0090] The collected metal hydroxide or carbonate powder can then
be subjected to a heat treatment to convert the hydroxide or
carbonate composition to the corresponding oxide composition with
the elimination of water or carbon dioxide. Generally, the heat
treatment can be performed in an oven, furnace or the like. The
heat treatment can be performed in an inert atmosphere or an
atmosphere with oxygen present. In some embodiments, the material
can be heated to a temperature of at least about 350.degree. C. and
in some embodiments from about 400.degree. C. to about 800.degree.
C. to convert the hydroxide or carbonate to an oxide. The heat
treatment generally can be performed for at least about 15 minutes,
in further embodiments from about 30 minutes to 24 hours or longer,
and in additional embodiments from about 45 minutes to about 15
hours. A further heat treatment can be performed at a second higher
temperature to improve the crystallinity of the product material.
This calcination step for forming the crystalline product generally
is performed at temperatures of at least about 650.degree. C., and
in some embodiments from about 700.degree. C. to about 1200.degree.
C., and in further embodiments from about 700.degree. C. to about
1100.degree. C. The calcination step to improve the structural
properties of the powder generally can be performed for at least
about 15 minutes, in further embodiments from about 20 minutes to
about 30 hours or longer, and in other embodiments from about 1
hour to about 36 hours. The heating steps can be combined, if
desired, with appropriate ramping of the temperature to yield
desired materials. A person of ordinary skill in the art will
recognize that additional ranges of temperatures and times within
the explicit ranges above are contemplated and are within the
present disclosure.
[0091] The lithium element can be incorporated into the material at
one or more selected steps in the process. For example, a lithium
salt can be incorporated into the solution prior to or upon
performing the precipitation step through the addition of a
hydrated lithium salt. In this approach, the lithium species is
incorporated into the hydroxide or carbonate material in the same
way as the other metals. Also, due to the properties of lithium,
the lithium element can be incorporated into the material in a
solid state reaction without adversely affecting the resulting
properties of the product composition. Thus, for example, an
appropriate amount of lithium source generally as a powder, such as
LiOH.H.sub.2O, LiOH, Li.sub.2CO.sub.3, or a combination thereof,
can be mixed with the precipitated metal carbonate or metal
hydroxide. The powder mixture is then advanced through the heating
step(s) to form the oxide and then the crystalline final product
material.
[0092] Further details of the hydroxide co-precipitation process
are described in published U.S. patent application 2010/0086853A to
Venkatachalam et al. entitled "Positive Electrode Material for
Lithium Ion Batteries Having a High Specific Discharge Capacity and
Processes for the Synthesis of these Materials", incorporated
herein by reference. Further details of the carbonate
co-precipitation process are described in published U.S. patent
application 2010/0151332A to Lopez et al. entitled "Positive
Electrode Materials for High Discharge Capacity Lithium Ion
Batteries," incorporated herein by reference.
[0093] Also, it has been found that coating the positive electrode
active materials can improve the cycling of lithium-based
batteries. The coating can also be effective at reducing the
irreversible capacity loss of the battery as well as increasing the
specific capacity generally. The amount of coating material can be
selected to accentuate the observed performance improvements.
Suitable coating materials, which are generally believed to be
electrochemically inert during battery cycling, can comprise metal
fluorides, metal oxides, metal non-fluoride halides or metal
phosphates. The results in the Examples below are obtained with
materials coated with metal fluorides.
[0094] For example, the general use of metal fluoride compositions
as coatings for cathode active materials, specifically LiCoO.sub.2
and LiMn.sub.2O.sub.4, is described in published PCT application WO
2006/109930A to Sun et al., entitled "Cathode Active Material
Coated with Fluorine Compound for Lithium Secondary Batteries and
Method for Preparing the Same," incorporated herein by reference.
Improved metal fluoride coatings with appropriately engineered
thicknesses are described in published U.S. patent application
number 2011/0111298 to Lopez et al, (the '298 application) entitled
"Coated Positive Electrode Materials for Lithium Ion Batteries,"
incorporated herein by reference. Suitable metal oxide coatings are
described further, for example, in published U.S. patent
application number 2011/0076556 to Karthikeyan et al. entitled
"Metal Oxide Coated Positive Electrode Materials for Lithium-Based
Batteries", incorporated herein by reference. The discovery of
non-fluoride metal halides as desirable coatings for cathode active
materials is described in copending U.S. patent application Ser.
No. 12/888,131 now U.S. Pat. No. 8,663,849 to Venkatachalam et al.,
entitled "Metal Halide Coatings on Lithium Ion Battery Positive
Electrode Materials and Corresponding Batteries," incorporated
herein by reference. In general, the coatings can have an average
thickness of no more than 25 nm, in some embodiments from about 0.5
nm to about 20 nm, in other embodiments from about 1 nm to about 12
nm, in further embodiments from 1.25 nm to about 10 nm and in
additional embodiments from about 1.5 nm to about 8 nm. A person of
ordinary skill in the art will recognize that additional ranges of
coating material within the explicit ranges above are contemplated
and are within the present disclosure.
[0095] A metal fluoride coating can be deposited using a solution
based precipitation approach. A soluble composition of the desired
metal can be dissolved in a suitable solvent, such as an aqueous
solvent. Then, NH.sub.4F can be gradually added to the
dispersion/solution to precipitate the metal fluoride. The total
amount of coating reactants can be selected to form the desired
thickness of coating, and the ratio of coating reactants can be
based on the stoichiometry of the coating material. After removing
the coated electroactive material from the solution, the material
can be dried and heated, generally above about 250.degree. C., to
complete the formation of the coated material. The heating can be
performed under a nitrogen atmosphere or other substantially oxygen
free atmosphere.
[0096] An oxide coating is generally formed through the deposition
of a precursor coating onto the powder of active material. The
precursor coating is then heated to form the metal oxide coating.
Suitable precursor coating can comprise corresponding metal
hydroxides, metal carbonates or metal nitrates. The metal
hydroxides and metal carbonate precursor coating can be deposited
through a precipitation process since the addition of ammonium
hydroxide and/or ammonium carbonate can be used to precipitate the
corresponding precursor coatings. The precursor coating can be
heated, generally above about 250.degree. C., to decompose the
precursor to form the oxide coating.
Negative Electrode Active Materials
[0097] Desirable high capacity negative electrode active materials
can comprise silicon oxide based materials, such as composites with
nanostructured carbon materials or metal powders. In general, the
silicon oxide materials have been found to have significantly
improved performance if they are milled to a small particle size,
whether or not formed into a composite. In particular, active
silicon oxide based material can comprise oxygen deficient silicon
oxide, i.e., that the material has a formula SiO.sub.x where
x<2. The oxygen deficient silicon oxide can take up and release
lithium with a large specific capacity and as described herein this
material can be incorporated into lithium ion batteries with good
cycling properties. Oxygen deficient silicon oxide can be unstable
with respect to a disproportionation reaction to form elemental
silicon and silicon dioxide, although this reaction does not seem
to take place without the application of heat or with significant
milling times. The processing to form desired forms of silicon
oxide based materials can result in some formation of elemental
silicon, which is electroactive, and silicon dioxide, which is
believed to be inert in a lithium ion battery. The structure of the
oxygen deficient silicon oxide has been debated, and evidence
suggests the formation of amorphous domains of elemental silicon
surrounded by amorphous domains of silicon dioxide, but the
particular microscopic structure of the oxygen deficient silicon
oxide material is not particularly relevant for the present
discussion. In general, processing is performed under conditions in
which only small amounts of crystalline silicon is observed in
x-ray diffractograms, such that it is believed that a significant
majority of the material remains as an active silicon oxide that is
oxygen deficient relative to SiO.sub.2. In general, it is desirable
to mill the material to form smaller particles of the silicon oxide
based material, and in some embodiments it may be desirable to form
a composite with an electrically conductive component.
[0098] Suitable composites as described herein can comprise silicon
oxide, carbon components, such as graphitic particles (Gr), inert
metal powders (M), elemental silicon (Si), especially
nanoparticles, pyrolytic carbon coatings (HC), carbon nano fibers
(CNF), or combinations thereof. Thus, the general compositions of
the composites can be represented as
.alpha.SiO-.beta.Gr-.chi.HC-.delta.M-.epsilon.CNF-.phi.Si, where
.alpha., .beta., .gamma., .delta., .epsilon., and .phi. are
relative weights that can be selected such that
.alpha.+.beta.+.gamma.+.delta.+.epsilon.+.phi.=1. Generally
0.35<.alpha.<1, 0.ltoreq..beta.<0.6,
0.ltoreq..chi.<0.65, 0.ltoreq..delta.<0.65,
0.ltoreq..epsilon.<0.65, and 0.ltoreq..phi.<0.65. Certain
subsets of these composite ranges are of particular interest. In
some embodiments, composites with SiO and one or more carbon based
components are desirable, which can be represented by a formula
.alpha.SiO-.beta.Gr-.chi.HC-.epsilon.CNF, where
0.35<.alpha.<0.9, 0.ltoreq..beta..ltoreq.0.6,
0.ltoreq..chi.<0.65 and 0.ltoreq..epsilon..ltoreq.0.65
(.delta.=0 and .phi.=0), in further embodiments
0.35<.alpha.<0.8, 0.1.ltoreq..beta.<0.6,
0.0.ltoreq..chi.<0.55 and 0.ltoreq..epsilon.<0.55, in some
embodiments 0.35<.alpha.<0.8, 0.ltoreq..beta.<0.45,
0.0.ltoreq..chi.<0.55 and 0.1.ltoreq..epsilon.<0.65, and in
additional embodiments 0.35<.alpha.<0.8,
0.ltoreq..beta.<0.55, 0.1.ltoreq..chi.<0.65 and
0.ltoreq..epsilon.<0.55. In additional or alternative
embodiments, composites with SiO, inert metal powders and
optionally one or more conductive carbon components can be formed
that can be represented by the formula
.alpha.SiO-.beta.Gr-.chi.HC-.delta.M-.epsilon.CNF, where
0.35<.alpha.<1, 0.ltoreq..beta.<0.55,
0.ltoreq..chi.<0.55, 0.1.ltoreq..delta.<0.65, and
0.ltoreq..epsilon.<0.55. In further additional or alternative
embodiments, composites of SiO with elemental silicon and
optionally one or more conductive carbon components can be formed
that can be represented by the formula
.alpha.SiO-.beta.Gr-.chi.HC-.epsilon.CNF-.phi.Si, where
0.35<.alpha.<1, 0.ltoreq..beta.<0.55,
0.ltoreq..chi.<0.55, 0.ltoreq..epsilon.<0.55, and
0.1.ltoreq..phi.<0.65 and in further embodiments
0.35<.alpha.<1, 0.ltoreq..beta.<0.45,
0.1.ltoreq..chi.<0.55, 0.ltoreq..epsilon.<0.45, and
0.1.ltoreq..phi.<0.55. A person or ordinary skill in the art
will recognize that additional ranges within the explicit ranges
above are contemplated and are within the present disclosure.
[0099] Nanostructured materials can provide high surface areas
and/or high void volume relative to a corresponding bulk material,
such as a silicon oxide based material. By adapting to volume
changes of the material, it is believed that nanostructured silicon
oxide based material, e.g., nano particulates, can provide at least
some accommodation for volume expansion and reduced stress on the
material during silicon-lithium alloying. Furthermore, the
adaptability of nano structured silicon oxide based materials can
result in a corresponding decrease in irreversible structural
changes in the material upon cycling such that the performance of
the negative electrode degrades more slowly upon cycling, and a
battery formed with the negative electrode can have satisfactory
performance over a larger number of battery cycles. As described
herein milling can be a suitable process for the formation of
nanostructures silicon oxide based materials, and the milling
process can be combined with the formation of a composite with a
selected electrically conductive component.
[0100] Oxygen deficient silicon oxide with its high specific
capacity with respect to intake and release of lithium and
relatively lower volume change compared to silicon has been studied
as negative electrode material. As used herein unless specifically
noted otherwise, the term "silicon oxide" in reference to a lithium
active material as well as "oxygen deficient silicon oxide" refers
to amorphous oxygen deficient silicon oxides generally represented
by formula SiO.sub.x where 0.1.ltoreq.x.ltoreq.1.9, in further
embodiments 0.15.ltoreq.x.ltoreq.1.8, in other embodiments
0.2.ltoreq.x.ltoreq.1.6 and in additional embodiments
0.25.ltoreq.x.ltoreq.1.5. In some embodiments, the x.apprxeq.1 and
the silicon oxide is represented by formula SiO. A person of
ordinary skill in the art will recognize that additional ranges of
silicon oxide stoichiometry within the explicit ranges above are
contemplated and are within the present disclosure. Silicon oxide
based materials can contain various amounts of silicon, silicon
oxide, and silicon dioxide. In general, silicon oxide measured or
tested as control without prior treatment is referred to as the
"pristine" sample throughout the specification. The word "pristine"
used herein thus refers to untreated control sample instead of
indicating the purity or condition of the control sample.
[0101] In some embodiments, the negative electrode active material
comprises a composite of an initially particulate carbon material
and a silicon oxide based material. After forming the composite,
the silicon oxide based material can be nanostructured. For
example, the components of the composite can be milled together to
form the composite, in which the constituent materials are
intimately associated, but generally not alloyed or otherwise
chemically reacted. The nanostructure characteristics are generally
expected to manifest themselves in the composite, although
characterization of the composites may be less established relative
to the characterization of the component materials. Specifically,
the composite material may have dimensions, porosity or other high
surface area characteristics that are manifestations of the
nano-scale of the initial materials and/or properties of the
material resulting from milling or other process used in forming
the composite. In some embodiments, the negative electrode active
material can comprise a silicon oxide based material in a composite
with carbon nanofibers and/or carbon nanoparticles, which is
achieved using high energy mechanical milling.
[0102] In some embodiments, the silicon-based negative electrode
active material can comprise a silicon oxide-metal composite.
Silicon oxide-metal composites can be formed from a variety of
elemental metals and generally the elemental metals do not alloy
with lithium during cycling of the corresponding battery. A wide
range of metals can be used, as described further below.
[0103] Also, carbon coatings can be applied over the silicon oxide
based materials to improve electrical conductivity, and the carbon
coatings seem to also stabilize the silicon oxide based material
with respect to improving cycling and decreasing irreversible
capacity loss. In embodiments of particular interest, an organic
composition dissolved in a suitable solvent can be mixed with the
active composition and dried to coat the active composition with
the carbon coating precursor. The precursor coated composition can
then be pyrolyzed in an oxygen free atmosphere to convert the
organic precursor into a carbon coating, such as a hard carbon
coating. The carbon coated compositions have been found to improve
the performance of the negative electrode active material.
[0104] Without being limited by a theory, it is believed that
carbon coatings and/or composite formulations, especially in a
nanostructured form, can provide structural stability to the
expanding and contracting silicon oxide during silicon
oxide-lithium intercalation/alloying and corresponding release of
lithium. Desirable battery performance has been observed with
nanostructured silicon oxide composites as well as with carbon
coated silicon oxide based materials.
[0105] Based on the combination of improved parameters described
herein, the silicon oxide based active materials can be introduced
to form improved electrode structures. In particular, the selection
of desirable electrically conductive components can provide for
improved electrode design and the desirable polymer binders can
provide desired mechanical properties suitable for the electrode
design in view of significant active material changes during
cycling. Based on these combined features, silicon oxide based
electrodes can be formed with densities of active silicon oxide
based materials, e.g., composite materials with electrically
conductive components, with at least reasonable performance of at
least about 0.6 g/cm.sup.3, in further embodiments at least about
0.7 g/cm.sup.3 and in further embodiments at least about 0.75
g/cm.sup.3. Similarly, the silicon oxide based electrodes can have
an average dried thickness of at least about 25 microns, in further
embodiments at least about 30 microns and in additional embodiments
at least about 50 microns, which can correspond to active material
loadings of at least about 2 mg/cm.sup.2. The resulting silicon
oxide based electrodes can exhibit capacities per unit area of at
least about 3.5 mAh/cm.sup.2, in further embodiments at least about
4.5 mAh/cm.sup.2 and in additional embodiments at least about 6
mAh/cm.sup.2. A person of ordinary skill in the art will recognize
that additional ranges of negative electrode parameters within the
explicit ranges above are contemplated and are within the present
disclosure.
[0106] Silicon Oxide
[0107] In general, any reasonable method can be used to synthesize
the silicon oxide for use in the silicon oxide based materials
described herein. At least SiO is available commercially from
Sigma-Aldrich. Furthermore, silicon oxide may be produced, for
example, by heating a mixture of silicon dioxide and metallic
silicon to produce silicon monoxide gas and cooling the gas for
precipitation as described for example in, U.S. Pat. No. 6,759,160
to Fukuoka et al. entitled "Silicon oxide powder and making method"
and U.S. Patent Application No. 2007/0259113 to Kizaki et al.
entitled "Silicon monoxide vapor deposition material, silicon
powder for silicon monoxide raw material, and method for producing
silicon monoxide", both are incorporated herein by reference.
Alternatively, molten silicon can react with molecular oxygen to
form silicon oxide material according to a process described in
U.S. Pat. No. 6,759,160 to Iwamoto et al. entitled "Negative
electrode active material and negative electrode using the same and
lithium ion secondary battery" and U.S. Patent Application No.
2007/0099436 to Kogetsu et al. entitled "Method of producing
silicon oxide, negative electrode active material for lithium ion
secondary battery and lithium ion secondary battery using the
same", both are incorporated herein by reference.
[0108] A silicon-silicon oxide (SiO.sub.x) composite with
0<O/Si<1.0 was discussed in U.S. Patent Application No.
2010/0243951 to Watanabe et al. (herein after Watanabe '951
application) entitled "Negative electrode material for nonaqueous
electrolyte secondary battery, making method and lithium ion
secondary battery", incorporated herein by reference. The SiO has
been prepared by etching silicon oxide particles in an acidic
atmosphere. The SiO formed is then coated with carbon using
CH.sub.4 gas at elevated temperature. The composites in Watanabe
'951 application showed improved IRCL, specific capacity, as well
as cycling performance compared to samples formed without the
acidic etching. A modified procedure where etching is conducted
after carbon coating formation is described in U.S. Patent
Application No. 2010/0288970 to Watanabe et al. (herein after
Watanabe '970 application) entitled "Negative electrode material
for nonaqueous electrolyte secondary battery, making method and
lithium ion secondary battery", incorporated herein by reference.
The composites in Watanabe '970 application showed improved IRCL
and specific capacity and comparable cycling performance compared
to samples formed without acidic etching. Earlier work utilized a
vapor deposition process to produce SiO.sub.x in U.S. Patent
Application No. 2007/0254102 to Fukuoka et al (herein after
Fukuoka) entitled "Method for producing SiO.sub.x (x<1)",
incorporated herein by reference. The Watanabe documents and the
Fukuoka do not teach the specific composites described herein or
the corresponding processes.
[0109] The formation of lithium silicates has been described in the
context of materials for lithium ion batteries. For example,
Silicon-Silicon oxide-lithium (Si--SiO--Li) composite has been
discussed in U.S. Pat. No. 7,776,473 to Aramata et al. (herein
after Aramata) entitled "Silicon-Silicon Oxide-Lithium composite,
making method, and non-aqueous electrolyte secondary cell negative
electrode material", incorporated herein by reference. In Aramata,
silicon oxide is mixed with metallic lithium to undergo
disproportionation into silicon and silicon dioxide doped with
lithium and concomitant formation of Li.sub.4SiO.sub.4. The
formation of lithium silicate correspondingly is believed to result
in formation of a portion of elemental silicon, which can then act
as an active material in a lithium based battery. The composite
formed in Aramata has improved cycle performance and decreased IRCL
compared to the silicon oxide material without lithium while the
specific capacity however has decreased significantly. The use of
supplemental lithium with silicon oxide based materials is not
believed to result in substantial formation of lithium silicate.
During electrochemical lithiation, the lithium intercalates and
de-intercalates into and out from the amorphous silicon oxide
structure in contrast with the formation of the stable crystalline
lithium silicate structure. However, the formation of some lithium
silicate as a byproduct of the lithiation process herein has not
been ruled out, although even with the formation of such
byproducts, the lithiation processes described herein are
substantially different from the processes and compositions
described in Aramata.
[0110] An early description of oxygen deficient silicon oxide as an
active material for a lithium ion battery is described in U.S. Pat.
No. 6,083,644 to Watanabe et al. entitled "Non-aqueous electrolyte
secondary battery," incorporated herein by reference. Synthesis of
silicon oxide with various amount of carbon coating were discussed
in U.S. Patent Application No. 2004/0033419 to Funabiki et al.
(herein after Funabiki) entitled "Negative active material,
negative electrode using the same, non-aqueous electrolyte battery
using the same, and method for preparing the same", incorporated
herein by reference. In Funabiki, silicon oxide was heat treated to
form a composite SiO.sub.x followed by itching with hydrofluoric
acid to remove any SiO.sub.2 in the product material.
[0111] Composites of Silicon oxide-graphite (SiO--C) with optional
carbon coating were discussed in U.S. Pat. No. 6,638,662 to Kaneda
et al. (herein after Kaneda) entitled "Lithium secondary battery
having oxide particles embedded in particles of carbonaceous
material as a negative electrode material", incorporated herein by
reference. In Kaneda, silicon oxide is ball milled extensively with
graphite, which is in turn optionally coated with carbon through
the heating of the silicon oxide with a carbon precursor in an
inert atmosphere.
[0112] Lim et al. discussed the use of silicon, silicon oxide, or
silicon alloy with carbon in U.S. Patent Application No.
2009/0325061 entitled "Secondary battery", incorporated herein by
reference. Jeong et al. discussed the use of silicon based compound
alloyed with metal mixed with a carbonaceous material in U.S. Pat.
Nos. 7,432,015 and 7,517,614, both entitled "Negative active
material for a rechargeable lithium battery, a method of preparing
the same, and a rechargeable lithium battery comprising the same",
both incorporated herein by reference. The silicon oxide used is
formed by heating silicon dioxide with silicon at elevated
temperature. Similarly, Lee et al. discussed the use of silicon
based compound alloyed with metal mixed with a carbonaceous
material in U.S. Patent Application No. 2005/0233213, entitled
"Negative active material for a rechargeable lithium battery, a
method of preparing the same, and a rechargeable lithium battery
comprising the same", incorporated herein by reference. The silicon
oxide used is formed by heating silicon dioxide with silicon at
elevated temperature. Mah et al. disclosed synthesis of SiO.sub.x
(0<x<0.8) from silane compound in U.S. Patent Application No.
2008/0193831 entitled "Anode active material, method of preparing
the same, anode and lithium battery containing the material",
incorporated herein by reference. Kim et al. disclosed synthesis of
SiO.sub.x (0<x<2) by sintering hydrogen silsesquioxane in
U.S. Pat. No. 7,833,662 entitled "Anode active material, method of
preparing the same, and anode and lithium battery containing the
material", incorporated herein by reference.
Composites with Carbon Particles and/or Nano-Scale Carbon
Fibers
[0113] Carbon nanofibers and/or carbon nanoparticles provide for
good electrical conductivity and can provide a support structure
for nano-structured silicon oxide such that the stress of alloy
formation with lithium can be reduced. Carbon nanofibers can be
obtained or can be synthesized using a vapor organic composition
and a catalyst in a suitable thermal reaction. One approach for the
synthesis of carbon nanofibers are described in published U.S.
patent application 2009/0053608 to Choi et al., entitled "Anode
Active Material Hybridizing Carbon Nanofiber for Lithium Secondary
Battery," incorporated herein by reference. Carbon fibers are
available commercially from a variety of suppliers. Suitable
suppliers are summarized in Table 3, which has parts A and B.
[0114] In general, suitable carbon nanofibers can have average
diameters of about 25 nm to about 250 nm and in further
embodiments, from about 30 nm to about 200 nm, and with average
lengths from about 2 microns to about 50 microns, and in further
embodiments from about 4 microns to about 35 microns. A person of
ordinary skill in the art will recognize that additional ranges of
nanofiber average diameters and lengths within the explicit ranges
above are contemplated and are within the present disclosure.
[0115] Similarly, pyrolytic carbon particles, e.g., carbon blacks,
can be used as a support in appropriate composites. Carbon black
can have average particle sizes of no more than about 250 nm, and
in some embodiments no more than about 100 nm, as well as suitable
subranges within these ranges. Carbon blacks are readily available
from a variety of suppliers, such as Cabot Corporation and Timcal,
Ltd, Switzerland (acetylene black, Super P.TM.).
[0116] Graphite (Gr), a polymorph of the element carbon, is a
semimetal and electrically conductive. Graphite is also called
graphitic carbon or graphitic particles and can be crystalline with
isolated, flat, plate-like particles. Graphite can be milled with
silicon oxide with or without additional material to form
composites having improved capacity. In some embodiments, the
composites may contain 0 to 60% wt, 5 to 55% wt, or 10 to 45% wt
graphitic carbon. A person or ordinary skill in the art will
recognize that additional ranges within the explicit ranges above
are contemplated and are within the present disclosure. Graphite
powders are readily available from a variety of suppliers, such as
natural graphite from Superior Graphite, MAGD.TM. and MAGE.TM.
artificial graphite from Hitachi Chemical, MPG-13.TM. from
Mitsubishi, and MCMB.TM. graphite from Nippon Carbon.
[0117] It can be desirable to form composites of nano-scale carbon
particles and/or fibers with silicon oxide. To form the composites,
the constituent materials are obtained and/or prepared and combined
to introduce strong mechanical interactions between the material
components. While not wanted to be limited by theory, the composite
may comprise, for example, at least a fraction of the carbon
composition coated onto silicon oxide that is milled to a submicron
scale from the processing. In general, the types of interactions
between the constituents of the composites do not need to be well
characterized. Nevertheless, the composites are distinct in
composition and properties from simple blends of the constituent
materials that may be held together with a binder. The composites
though are found to exhibit desirable battery performance in a
lithium ion battery. In general, the composite can comprise at
least about 5 weight percent silicon oxide, in further embodiments,
from about 7.5 weight percent to about 95 weight percent and in
additional embodiments from about 10 weight percent to about 90
weight percent silicon oxide. A person of ordinary skill in the art
will recognize that additional ranges of silicon oxide composition
within the explicit ranges above are contemplated and are within
the present disclosure.
[0118] In some embodiments, silicon oxide composites can be formed
by milling silicon oxide with carbon fibers and/or carbon
nanoparticles. The milling process can comprise, for example, jar
milling and/or ball milling, such as planetary ball milling. Ball
milling and similarly jar milling may involve grinding using a
grinding medium, such as ceramic particles, which can then be
substantially removed from the ground material. A planetary ball
mill is a type of ball milling in which the mill comprises a
sun-wheel, at least one grinding jar mounted eccentrically on the
sun-wheel, and a plurality of mixing balls within the grinding jar.
In operation, the grinding jar rotates about its own axis and in
the opposite direction around the common axis of the sun-wheel.
[0119] Desirable ball milling rotation rates and ball milling times
can be selected based on the desired silicon oxide composite
composition and structure. For the formation of silicon oxide
composites described herein, suitable ball milling rotation rates
generally can be from about 25 rpm to about 1000 rpm and in further
embodiments from about 50 rpm to about 800 rpm. Furthermore,
desirable ball milling times can be from about 10 minutes to about
20 hour, in further embodiments from about 20 minutes to about 15
hours, in additional embodiments from about 1 hour to 5 hours. A
person of ordinary skill in the art will recognize that additional
ranges of milling rates and times within the explicit ranges above
are contemplated and are within the present disclosure. The mill
container can be filled with an inert gas to avoid oxidizing the
contents of the container during milling. Examples of suitable
grinding media include, for example, particles of zirconia,
alumina, tungsten carbide or the like.
[0120] The milling of the silicon oxide based materials results in
a reduced particle size that seems to contribute significantly to
performance based on the milling of the particles. The desirable
performance can be achieved similarly with the performance of the
milling with electrically conductive particles for the formation of
a composite. In general, the milled particles can be evaluated with
respect to size by forming a dispersion and using light scattering
to measure particle size. Direct measurements by dynamic light
scattering (DLS) are intensity weighted particle size
distributions, and these can be converted to volume based
distributions using conventional techniques. The volume-average
particle size can be evaluated from the volume-based particle size
distribution. Suitable particle size analyzers include, for
example, a Microtrac UPA instrument from Honeywell and Saturn
DigiSizer.TM. from Micromeritics based on dynamic light scattering,
a Horiba Particle Size Analyzer from Horiba, Japan and ZetaSizer
Series of instruments from Malvern based on Photon Correlation
Spectroscopy. The principles of dynamic light scattering for
particle size measurements in liquids are well established. The
volume average particle sizes can be no more than about 10 microns,
in other embodiments no more than about 8 microns and in further
embodiments no more than about 7 microns. A person of ordinary
skill in the art will recognize that additional ranges of average
particle size within the explicit ranges above are contemplated and
are within the present disclosure.
[0121] Metal Particle--Silicon Oxide Composites
[0122] Inert metal particles are also useful for the formation of
composites with the silicon oxide materials. The incorporation of
the metal into the composite can improve the electrical
conductivity of the composite material. The metal for these
composites is generally selected to be inert with respect to
reaction both with silicon oxide so that the metal does not reduce
the silicon oxide and with lithium so that the metal does not alloy
with lithium under conditions to be experienced in the batteries.
The composites are formed through high energy milling or the like
to intimately combine the materials in the composite so that the
materials are distinctly different from simple blend of the
material that may be held together by a polymer. In the composite
materials, while not wanting to be limited by theory, the more
malleable metal may be spread over the silicon oxide material
during the formation of the composite.
[0123] The inert metal-silicon oxide composites are found to
exhibit desirable battery performance in a lithium ion battery.
Suitable metals include, for example, nickel, iron, vanadium,
cobalt, titanium, zirconium, silver, manganese, molybdenum,
gallium, chromium and combinations thereof. In general, the
composite can comprise at least about 5 weight percent silicon
oxide, in further embodiments, from about 7.5 weight percent to
about 95 weight percent and in additional embodiments from about 10
weight percent to about 90 weight percent silicon oxide. Similarly,
in some embodiments, the composite can comprise from about 5 to
about 45 weight percent inert metal and in further embodiments from
about 7 to about 40 weight percent inert metal. A person of
ordinary skill in the art will recognize that additional ranges of
silicon oxide composition within the explicit ranges above are
contemplated and are within the present disclosure.
[0124] The inert-metal-silicon oxide composites can be formed using
high energy mechanical milling similar to the formation of the
carbon-silicon oxide composites. A ball media generally is used
with the metal particles to facilitate the milling process.
Desirable milling rotation rates and milling times can be selected
based on the desired inert metal-silicon oxide composite
composition and structure. For the formation of silicon oxide
composites described herein, suitable milling rotation rates
generally can be from about 25 rpm to about 1000 rpm and in further
embodiments from about 50 rpm to about 800 rpm. Furthermore,
desirable milling times can be from about 10 minutes to about 50
hour and in further embodiments from about 20 minutes to about 20
hours. A person of ordinary skill in the art will recognize that
additional ranges of milling rates and times within the explicit
ranges above are contemplated and are within the present
disclosure. The mill container can be filled with an inert gas to
avoid oxidizing the contents of the container during milling.
[0125] Pyrolytic Carbon Coatings
[0126] Carbon coatings can be applied to silicon oxide based
material to increase electrical conductivity and/or to provide
structural support to the resulting materials. In general, the
carbon coatings can be applied to silicon oxide, for example, after
milling the silicon oxide, silicon oxide carbon particle
composites, silicon oxide-metal particle composites or the like.
The carbon coatings can be formed from pyrolyzed organic
compositions under oxygen free atmospheres. Hard carbon coatings
are generally formed at relatively high temperatures. The
properties of the coatings can be controlled based on the
processing conditions. In particular, carbon coatings can have a
high hardness and generally can comprise significant amorphous
regions possible along with graphitic domains and diamond
structured domains.
[0127] Carbon coatings formed from coal tar pitch is described in
published PCT patent application WO 2005/011030 to Lee et al.,
entitled "A Negative Active Material for Lithium Secondary Battery
and a Method for Preparing Same," incorporated herein by reference.
In contrast, as described herein, an organic composition is
dissolved in a suitable solvent and mixed with the active material.
The solvent is removed through drying to form a solid precursor
coated active material. This approach with a solvent for delivering
a solid pyrolytic carbon precursor can facilitate formation of a
more homogenous and uniform carbon coating. Then, the precursor
coated material is heated in an effectively oxygen free environment
to form the pyrolytic carbon coating.
[0128] The heating is generally performed at a temperature of at
least about 500.degree. C., and in further embodiments at least
about 700.degree. C. and in other embodiments, from about
750.degree. C. to about 1350.degree. C. Generally, if temperatures
are used above about 800.degree. C., a hard carbon coating is
formed. The heating can be continued for a sufficient period of
time to complete the formation of the carbon coating. In some
embodiments, it is desirable to use pyrolytic carbon precursors
that can be delivered in a solvent to provide for good mixing of
the precursors with the silicon oxide based materials and to
provide for a range of desired precursor compounds. For example,
desirable precursors can comprise organic compositions that are
solids or liquids at room temperature and have from two carbon
atoms to 40 carbon atoms, and in further embodiments from 3 carbon
atoms to 25 carbon atoms as well as other ranges of carbon atoms
within these ranges, and generally these molecules can comprise
other atoms, such as oxygen, nitrogen, sulfur, and other reasonable
elements. Specifically, suitable compounds include, for example,
sugars, other solid alcohols, such as furfuryl alcohol, solid
carboxylic acids, such as citric acid, polymers, such as
polyacrylonitrile, and the like. The coated materials generally
comprise no more than about 50 weight percent pyrolytic carbon, in
further embodiments no more than about 40 weight percent, and in
additional embodiments, from about 1 weight percent to about 30
weight percent. A person of ordinary skill in the art will
recognize that additional ranges within the explicit ranges above
of amounts of coating composition are contemplated and are within
the present disclosure.
[0129] Metal Coatings
[0130] As an alternative or in addition to carbon coatings,
elemental metal can be coated onto the silicon oxide based
material. For example, the metal coatings can be applied to
silicon-oxide carbon composites, silicon oxide-metal particle
composites or the like. Suitable elemental metals include metals
that can be reduced under reasonable conditions to form an inert
metal in the battery. In particular, silver and copper can be
reduced to deposit the metal coating. The elemental metal coating
can be expected to increase electrical conductivity and to
stabilize the silicon oxide based material during the lithium
alloying and de-alloying process. In general, the coated material
can comprise no more than about 25 weight percent metal coating and
in further embodiments from about 1 weight percent to about 20
weight percent metal coating. A person of ordinary skill in the art
will recognize that additional ranges of metal coating composition
within the explicit ranges above are contemplated and are within
the present disclosure. A solution based approach can be used to
apply the metal coating. For example, the silicon oxide based
material to be coated can be mixed with a solution comprising
dissolved salt of the metal, such as silver nitrate, silver
chloride, copper nitrate, copper chloride or the like, and a
reducing agent can be added to deposit the metal coating. Suitable
reducing agents include, for example, sodium hypophosphite, sodium
borohydride, hydrazine, formaldehyde and the like.
Supplemental Lithium
[0131] Various approaches can be used for the introduction of
supplemental lithium into the battery, although following
corresponding initial reactions and/or charging, the negative
electrode becomes associated with excess lithium for cycling from
the supplemental lithium. With respect to the negative electrode in
batteries having supplemental lithium, the structure and/or
composition of the negative electrode can change relative to its
initial structure and composition following the first cycle as well
as following additional cycling. Depending on the approach for the
introduction of the supplemental lithium, the positive electrode
may initially include a source of supplemental lithium and/or a
sacrificial electrode can be introduced comprising supplemental
lithium. The supplemental lithium is introduced into the negative
electrode using electrochemical methods in contrast with purely
chemical or mechanical methods. Chemical methods or mechanical
methods, such as milling, may lead to effectively irreversible
formation of lithium silicate, while the electrochemical method
does not seem to result in lithium silicate formation. In
particular, the electrochemical introduction of lithium in general
results in reversible lithium incorporation, although lithium can
be consumed in an initial formation of a solvent electrolyte
interphase (SEI) layer. With respect to initial structure of the
negative electrode, in some embodiments, the negative electrode has
no changes due to the supplemental lithium. In particular, if the
supplemental lithium is initially located in the positive electrode
or a separate electrode, the negative electrode can be an unaltered
form with no lithium present until the battery is charged or at
least until the circuit is closed between the negative electrode
and the electrode with the supplemental lithium in the presence of
electrolyte and a separator. For example, the positive electrode or
supplemental electrode can comprise elemental lithium, lithium
alloy and/or other sacrificial lithium source.
[0132] If sacrificial lithium is included in the positive
electrode, the lithium from the sacrificial lithium source is
loaded into the negative electrode during the charge reaction. The
voltage during the charging based on the sacrificial lithium source
may be significantly different than the voltage when the charging
is performed based on the positive electrode active material. For
example, elemental lithium in the positive electrode can charge the
negative electrode active material without application of an
external voltage since oxidation of the elemental lithium drives
the reaction. For some sacrificial lithium source materials, an
external voltage is applied to oxidize the sacrificial lithium
source in the positive electrode and drive lithium into the
negative electrode active material. The charging generally can be
performed using a constant current, a stepwise constant voltage
charge or other convenient charging scheme. However, at the end of
the charging process, the battery should be charged to a desired
voltage, such as 4.5V.
[0133] In further embodiments, at least a portion of the
supplemental lithium is initially associated with the negative
electrode. For example, the supplemental lithium can be in the form
of elemental lithium, a lithium alloy or other lithium source that
is more electronegative than the negative electrode active
material. After the negative electrode is in contact with
electrolyte, a reaction can take place, and the supplemental
lithium is transferred to the negative electrode active material.
During this process, the solid electrolyte interface (SEI) layer is
also formed. Thus, the supplemental lithium is loaded into the
negative electrode active material with at least a portion consumed
in formation of the SEI layer. The excess lithium released from the
lithium rich positive electrode active material is also deposited
into the negative electrode active material during eventual
charging of the battery. The supplemental lithium placed into the
negative electrode should be more electronegative than the active
material in the negative electrode since there is no way of
reacting the supplemental lithium source with the active material
in the same electrode through the application of a voltage.
[0134] In some embodiments, supplemental lithium associated with
the negative electrode can be incorporated as a powder within the
negative electrode. Specifically, the negative electrode can
comprise an active negative electrode composition and a
supplemental lithium source within a polymer binder matrix, and any
electrically conductive powder if present. In additional or
alternative embodiments, the supplemental lithium is placed along
the surface of the electrode. For example, the negative electrode
can comprise an active layer with an active negative electrode
composition and a supplemental lithium source layer on the surface
of active layer. The supplemental lithium source layer can comprise
a foil sheet of lithium or lithium alloy, supplemental lithium
powder within a polymer binder and/or particles of supplemental
lithium source material embedded on the surface of the active
layer. In an alternative configuration, a supplemental lithium
source layer is between the active layer and current collector.
Also, in some embodiments, the negative electrode can comprise
supplemental lithium source layers on both surfaces of the active
layer.
[0135] In additional embodiments, at least a portion of the
supplemental lithium can be supplied to the negative electrode
active material prior to assembly of the battery. In other words,
the negative electrode can comprise partially lithium-loaded
silicon oxide based active material, in which the partially loaded
active material has a selected degree of loading of lithium through
intercalation/alloying or the like. For example, for the preloading
of the negative electrode active material, the negative electrode
active material can be contacted with electrolyte and a lithium
source, such as elemental lithium, lithium alloy or other
sacrificial lithium source that is more electronegative than the
negative electrode active material.
[0136] An arrangement to perform such a preloading of lithium can
comprise an electrode with silicon oxide based active material
formed on a current collector, which are placed in vessel
containing electrolyte and a sheet of lithium source material
contacting the electrode. The sheet of lithium source material can
comprise lithium foil, lithium alloy foil or a lithium source
material in a polymer binder optionally along with an electrically
conductive powder, which is in direct contact with the negative
electrode to be preloaded with lithium such that electrons can flow
between the materials to maintain electrical neutrality while the
respective reactions take place. In the ensuing reaction, lithium
is loaded into the silicon oxide based active material through
intercalation, alloying or the like. In alternative or additional
embodiments, the negative electrode active material can be mixed in
the electrolyte and the lithium source material for incorporation
of the supplemental lithium prior to formation into an electrode
with a polymer binder so that the respective materials can react in
the electrolyte spontaneously.
[0137] In some embodiments, the lithium source within an electrode
can be assembled into a cell with the electrode to be preloaded
with lithium. A separator can be placed between the respective
electrodes. Current can be allowed to flow between the electrodes.
Depending on the composition of the lithium source it may or may
not be necessary to apply a voltage to drive the lithium deposition
within the silicon oxide based active material. An apparatus to
perform this lithiation process can comprise a container holding
electrolyte and a cell, which comprises an electrode, to be used as
a negative electrode in an ultimate battery, a current collector, a
separator and a sacrificial electrode that comprises the lithium
source, where the separator is between the sacrificial electrode
and the electrode with the silicon-based active material. A
convenient sacrificial electrode can comprise lithium foil, lithium
powder embedded in a polymer or lithium alloys, although any
electrode with extractable lithium can be used. The container for
the lithiation cell can comprise a conventional battery housing, a
beaker, or any other convenient structure. This configuration
provides the advantage of being able to measure the current flow to
meter the degree of lithiation of the negative electrode.
Furthermore, the negative electrode can be cycled once or more than
once in which the negative electrode active material is loaded
close to full loading with lithium. In this way, an SEI layer can
be formed with a desired degree of control during the preloading
with lithium of the negative electrode active material. Then, the
negative electrode is fully formed during the preparation of the
negative electrode with a selected preloading with lithium.
[0138] In general, the lithium source can comprise, for example,
elemental lithium, a lithium alloy or a lithium composition, such
as a lithium metal oxide, that can release lithium from the
composition. Elemental lithium can be in the form of a thin film,
such as formed by evaporation, sputtering or ablation, a lithium or
lithium alloy foil and/or a powder. Elemental lithium, especially
in powder form, can be coated to stabilize the lithium for handling
purposes, and commercial lithium powders, such as powders from FMC
Corporation, are sold with proprietary coatings for stability. The
coatings generally do not alter the performance of the lithium
powders for electrochemical applications. Lithium alloys include,
for example, lithium silicon alloys and the like. Lithium
composition with intercalated lithium can be used in some
embodiments, and suitable compositions include, for example,
lithium titanium oxide, lithium tin oxide, lithium cobalt oxide,
lithium manganese oxide, and the like.
[0139] In general, for embodiments in which supplemental lithium is
used, the amount of supplemental lithium preloaded or available to
load into the active composition can be in an amount of at least
about 2.5% of capacity, in further embodiments from about 3 percent
to about 90 percent of capacity, in additional embodiments from
about 5 percent to about 80 percent of capacity, and in some
embodiments at least 10% of the negative electrode active material
capacity. The supplemental lithium can be selected to approximately
balance the IRCL of the negative electrode, although other amounts
of supplemental lithium can be used as desired. Thus, the
contribution to the IRCL of the negative electrode can be
effectively reduced or removed due to the addition of the
supplemental lithium such that the measured IRCL of the battery
represents partially or mostly contributions from the IRCL of the
positive electrode, which is not diminished due to the presence of
supplemental lithium. In some embodiments, the IRCL can be reduced
to no more than about 20% of the initial negative electrode
capacity, in further embodiments no more than about 15%, in
additional embodiments no more than about 10%. A person of ordinary
skill in the art will recognize that additional ranges of IRCL
within the explicit ranges above are contemplated and are within
the present disclosure.
[0140] Another parameter of interest relates to the total balance
of the capacity of the negative electrode active material against
the positive electrode theoretical capacity, when supplemental
lithium is present. It has been observed that the inclusion of
additional negative electrode capacity can be desirable when
supplemental lithium is present to compensate for all or some of
the IRCL of the negative electrode. In some embodiments, the
balance expressed as a ratio of negative electrode capacity divided
by positive electrode capacity expressed as a percent can be from
about 95 to about 180 percent of the negative electrode capacity,
in further embodiments from about 100 to about 160 percent and in
other embodiments, from about 110 percent to about 150 percent.
Furthermore, increased values of average voltage are observed when
the battery comprises supplemental lithium. Specifically, for
batteries with SiO based active materials a supplemental lithium,
the average voltage can be at least about 3.3V, in further
embodiments at least above 3.35V and in other embodiments from
3.37V to about 3.45V when cycled between 4.5V and 2.0V at rates of
C/3. A person of ordinary skill in the art will recognize that
additional ranges of battery balance within the explicit ranges
above are contemplated and are within the present disclosure.
Battery Performance
[0141] Batteries formed from lithium rich positive electrode active
materials, silicon oxide based negative electrode active materials,
with or without supplemental lithium have demonstrated promising
performance under realistic discharge conditions. Specifically, the
silicon oxide based negative electrode active materials have
demonstrated a high specific capacity upon cycling of the batteries
at moderate discharge rates and with realistic cathodes with
cycling over a voltage range with a high voltage cutoff. In
particular, desirable specific capacities can be obtained based on
both the masses of the positive electrode active material and the
negative electrode active material such that the results correspond
with a high overall capacity of the batteries. Silicon based
negative electrode composites described herein can exhibit
reasonable irreversible capacity losses, and in some embodiments
supplemental lithium can be successfully used to reduce the
irreversible capacity loss. Electrode balance to reduce
irreversible capacity loss is described above. Relatively stable
cycling of the silicon based negative electrode material at high
specific capacities can be obtained for a modest number of cycles
against a positive electrode with lithium rich high capacity
lithium metal oxides.
[0142] In general, various similar testing procedures can be used
to evaluate the capacity performance of the battery. The silicon
oxide based electrodes can be tested against a lithium foil
electrode to evaluate the capacity and the IRCL. However, more
meaningful testing can be performed with a realistic positive
electrode since then the battery is cycled over appropriate voltage
ranges for cycling in a useful battery. Suitable testing procedures
are described in more detail in the examples below. Specifically,
batteries assembled with a lithium foil electrode are cycled with
the silicon oxide based electrode functioning as a positive
electrode (cathode) and the lithium foil functions as the negative
electrode (anode). The batteries with a lithium foil electrode can
be cycled over a voltage range, for example, from 0.005V to 1.5 V
at room temperature. Alternatively, batteries can be formed with a
positive electrode comprising a layered-layered lithium rich metal
oxide in which the silicon oxide based electrode is then the
negative electrode, and the battery can then be cycled between 4.5
volts and 1.0 volt at room temperature. For the batteries with a
lithium metal oxide-based positive electrode, the first cycle can
be charged and discharged at a rate of C/20 and subsequent cycling
can be at a rate of C/3 unless specified otherwise with charging at
C/3. The specific discharge capacity is very dependent on the
discharge rate. The notation C/x implies that the battery is
discharged at a rate to fully discharge the battery to the selected
voltage minimum in x hours.
[0143] The specific capacity of the silicon oxide based negative
electrode can be evaluated in configurations with either a
lithium-foil counter-electrode or with a lithium metal oxide based
counter electrode. For the batteries formed with a lithium metal
oxide based positive electrode, the specific capacity of the
battery can be evaluated against the weights of both anode active
material and cathode active material, which involved division of
the capacity by the respective weights. If supplemental lithium is
included in the battery, the weight of the negative electrode
active material includes the weight of the supplemental lithium.
Using a high capacity positive electrode active material, the
overall benefits of using a high capacity silicon oxide based
negative electrode active material becomes even more beneficial.
Based on the capacity of the battery, the specific capacities can
be obtained by dividing the respective weight of the active
materials in each electrode. It can be desirable to have high
specific capacities for both electrodes. The advantages of high
specific capacity for each electrode with respect to the overall
specific capacity of the battery is described in an article by
Yoshio et al., Journal of Power Sources 146 (June 2005) pp 10-14,
incorporated herein by reference.
[0144] In general, it can be desirable for the negative electrode
to have a specific capacity at the tenth cycle of at least about
500 mAh/g, in further embodiments at least about 700 mAh/g, in some
embodiments at least about 850 mAh/g, in additional embodiments at
least about 1000 mAh/g, and in some embodiments at least about 1100
mAh/g at a discharge rate of C/3 when cycled between 4.5V and 1.0V
based on the anode active weight. Depending on the specific silicon
oxide based active material, the lower voltage cutoff can be
selected to be 2.0V, 1.5V, 1.0V or 0.5V. In general, the lower
voltage cutoff can be selected to extract a selected portion of the
electrode capacity from about 92% to about 99%, and in further
embodiments from about 95% to about 98% of the total capacity of
the positive electrode. As noted above, it can be desirable to have
a relatively high specific capacity for both electrodes when the
positive electrode comprises a lithium rich metal oxide, and the
battery can exhibit at a discharge rate of C/3 at the 50th cycle a
positive electrode specific capacity of at least about 150 mAh/g
and a negative electrode specific capacity of at least about 750
mAh/g, in further embodiments a positive electrode specific
capacity of at least about 160 mAh/g and a negative electrode
specific capacity of at least about 800 mAh/g, and in additional
embodiments a positive electrode specific capacity of at least
about 170 mAh/g and a negative electrode specific capacity of at
least about 1000 mAh/g, when cycled between 4.5V and 1.0V. The
batteries with lithium rich metal oxides and silicon oxide based
materials can exhibit desirable cycling properties, and in
particular the batteries can exhibit a discharge capacity decrease
of no more than about 15 percent at the 50th discharge cycle
relative to the 7th discharge cycle and in further embodiments no
more than about 10 percent when discharged at a rate of C/3 from
the 7th cycle to the 50th cycle. A person of ordinary skill in the
art will recognize that additional ranges of specific capacity and
other battery parameters within the explicit ranges above are
contemplated and are within the present disclosure. In some
embodiments, the batteries further include supplemental lithium to
reduce the irreversible capacity loss and to stabilize the cycling
of lithium rich metal oxides.
EXAMPLES
[0145] A significant variety of silicon oxide based active negative
electrode materials were tested in batteries to evaluate their
performance. Many of these samples comprised silicon oxide and some
of these samples were formed into composites with carbon and/or
metal powders. Generally, the samples were formed into coin cells
to test the performance of materials with respect to lithium
alloying/intercalation. Coin cells were formed either with lithium
foil as the counter electrode such that the silicon oxide based
electrode functioned as a positive electrode against the lithium
foil or with a positive electrode comprising a lithium rich mixed
metal oxide such that the resulting battery had a realistic
formulation for cycling over a relevant voltage range for a
commercial battery. The general procedure for formation of the coin
cells is described in the following discussion and the individual
examples below describe formulation of the silicon oxide based
materials and the performance results from batteries formed from
the silicon oxide materials. The batteries described herein in
general were cycled by charging and discharging between 4.6V and
1.0V in the first formation cycle and between 4.5V and 1.0V in the
cycle testing for batteries with HCMR.TM. positive electrode or
between 0.005V-1.5V for batteries with lithium foil counter
electrode at a rate of C/20, C/10, C/5, and C/3 for the 1st and 2nd
cycles, for the 3rd and 4th cycles, for the 5th and 6th cycles, and
for subsequent cycles, respectively.
[0146] To test particular samples, electrodes were formed from the
samples of silicon oxide based active materials. In general, a
powder of silicon oxide based active material was mixed thoroughly
with acetylene black (Super P.RTM. from Timcal, Ltd., Switzerland)
to form a homogeneous powder mixture. Separately, polyimide binder
was mixed with N-methyl-pyrrolidone ("NMP") (Sigma-Aldrich) and
stirred overnight to form a polyimide-NMP solution. The homogenous
powder mixture was then added to the polyimide-NMP solution and
mixed for about 2 hours to form a homogeneous slurry. The slurry
was applied onto a copper foil current collector to form a thin,
wet film and the laminated current collector was dried in a vacuum
oven to remove NMP and to cure the polymer. The laminated current
collector was then pressed between rollers of a sheet mill to
obtain a desired lamination thickness. The dried laminate contained
at least 75 wt % silicon oxide based active material and at least 2
wt % polyimide binder. The resulting electrodes were assembled with
either a lithium foil counter electrode or with a counter electrode
comprising a lithium metal oxide (LMO).
[0147] For a first set of batteries with the lithium foil counter
electrodes, the silicon oxide based electrodes were placed inside
an argon filled glove box for the fabrication of the coin cell
batteries. Lithium foil (FMC Lithium) having thickness of roughly
125 micron was used as a negative electrode. A conventional
electrolyte comprising carbonate solvents, such as ethylene
carbonate, diethyl carbonate and/or dimethyl carbonate, was used. A
trilayer (polypropylene/polyethylene/polypropylene) micro-porous
separator (2320 from Celgard, LLC, NC, USA) soaked with electrolyte
was placed between the positive electrode and the negative
electrode. A few additional drops of electrolyte were added between
the electrodes. The electrodes were then sealed inside a 2032 coin
cell hardware (Hohsen Corp., Japan) using a crimping process to
form a coin cell battery. The resulting coin cell batteries were
tested with a Maccor cycle tester to obtain charge-discharge curve
and cycling stability over a number of cycles.
[0148] For a second set of batteries, the silicon oxide based
electrodes were used as negative electrode, and the positive
electrodes comprised a high capacity lithium rich composition. The
resulting positive electrodes are referred to as high capacity
manganese rich ("HCMR.TM.") electrodes. LMO composite active
materials were synthesized using a selected co-precipitation
process. The synthesis of similar compositions by a hydroxide
co-precipitation process have been described in published U.S.
patent application 2010/0086853A to Venkatachalam et al. entitled
"Positive Electrode Material for Lithium Ion Batteries Having a
High Specific Discharge Capacity and Processes for the Synthesis of
these Materials", and the synthesis of similar compositions by a
carbonate co-precipitation process have been described in published
U.S. patent application 2010/0151332A to Lopez et al. entitled
"Positive Electrode Materials for High Discharge Capacity Lithium
Ion Batteries", both of which are incorporated herein by reference.
In particular, the LMO powder was synthesized that is approximately
described by the formula xLi.sub.2MnO.sub.3.(1-x)Li
Ni.sub.uMn.sub.vCo.sub.wO.sub.2 where x=0.5. A discussion of the
design of HCMR.TM. compositions to achieve particular performance
results are described in detail in published U.S. patent
application number 2011/0052981 filed Aug. 27, 2010 to Lopez et
al., entitled "Layer-Layer Lithium Rich Complex Metal Oxides With
High Specific Capacity and Excellent Cycling," incorporated herein
by reference.
[0149] Electrodes were formed from the synthesized HCMR.TM. powder
by initially mixing it thoroughly with conducting carbon black
(Super P.TM. from Timcal, Ltd, Switzerland) and graphite (KS 6.TM.
from Timcal, Ltd) to form a homogeneous powder mixture. Separately,
Polyvinylidene fluoride PVDF (KF1300.TM. from Kureha Corp., Japan)
was mixed with N-methyl-pyrrolidone (Sigma-Aldrich) and stirred
overnight to form a PVDF-NMP solution. The homogeneous powder
mixture was then added to the PVDF-NMP solution and mixed for about
2 hours to form homogeneous slurry. The slurry was applied onto an
aluminum foil current collector to form a thin, wet film and the
laminated current collector was dried in vacuum oven at 110.degree.
C. for about two hours to remove NMP. The laminated current
collector was then pressed between rollers of a sheet mill to
obtain a desired lamination thickness. The dried electrode
comprised at least about 75 weight percent active metal oxide, at
least about 1 weight percent graphite, and at least about 2 weight
percent polymer binder.
[0150] Some of the batteries fabricated from a silicon oxide based
negative electrode and a HCMR.TM. positive electrode further
comprised supplemental lithium. In particular, a desired amount of
SLMP.RTM. powder (FMC Corp., stabilized lithium metal powder) was
loaded into a vial and the vial was then capped with a mesh
comprising nylon or stainless steel with a mesh size between about
40 .mu.m to about 80 .mu.m. SLMP.RTM. (FMC corp.) was then
deposited by shaking and/or tapping the loaded vial over a formed
silicon oxide based negative electrode. The coated silicon oxide
based negative electrode was then compressed to ensure mechanical
stability.
[0151] Batteries fabricated from a silicon oxide based negative
electrode and a HCMR.TM. positive electrode were balanced to have
excess negative electrode material. Specific values of the negative
electrode balance are provided in the specific examples below. For
batteries containing supplemental lithium, balancing was based on
the ratio of the first cycle lithium insertion capacity of the
silicon oxide based negative electrode to the theoretical capacity
of the HCMR.TM. positive electrode. The amount of supplemental
lithium was selected to approximately compensate for the
irreversible capacity loss of the negative electrode. For batteries
without supplemental lithium, balancing was calculated as the first
cycle lithium insertion capacity of the silicon oxide based
negative electrode to the theoretical capacity of the HCMR.TM.
positive electrode as well. In particular, for a given silicon
oxide based active composition, the insertion and extraction
capacities of the silicon oxide based composition can be evaluated
with the battery having a positive electrode comprising the silicon
oxide based active material and a lithium foil negative electrode
where lithium is intercalated/alloyed to the silicon oxide based
electrode to 5 mV and de-intercalated/de-alloyed to 1.5V at a rate
of C/20.
[0152] Coin cell batteries were formed by placing the silicon oxide
based electrode and the HCMR.TM. electrode inside an argon filled
glove box. An electrolyte was selected to be stable at high
voltages, and appropriate electrolytes are described in copending
U.S. patent application Ser. No. 12/630,992 now U.S. Pat. No.
8,993,177 to Amiruddin et al., entitled "Lithium Ion Battery With
High Voltage Electrolytes and Additives," incorporated herein by
reference. Based on these electrodes and the high voltage
electrolyte, the coin cell batteries were completed with separator
and hardware as described above for the batteries with the lithium
foil electrode. During the first cycle, the batteries were charged
to 4.6V, and in subsequent cycles, the batteries were charged to
4.5V.
Example 1: Silicon Oxide Based Anode Material
[0153] This example studies the effect of high energy mechanical
milling (HEMM) and heat treatment on the silicon oxide based
electrode active material. The silicon oxide starting materials
used herein are 325 mesh particles from Sigma-Aldrich. In general,
HEMM was used to reduce particle size of the starting SiO
materials. HEMM process was found to not only reduce the size of
SiO but also partially crystallize amorphous SiO to form a material
comprising some crystalline Si. High temperature heat treatment of
silicon oxide based anode active material has also been shown to
partially crystallize amorphous SiO to form some crystalline Si as
well as carbonize a carbon precursor coating material to pyrolytic
carbon concomitantly. HEMM has been used in the subsequent examples
below to form composites of silicon oxide powder (325 mesh) with
conductive material such as graphite, hard carbon, carbon
nano-fiber, and metal to increase the performance and the loading
level of silicon oxide based electrode active materials.
[0154] Micron size silicon oxide (325 mesh) was incorporated into
coin cells with a lithium foil electrode to evaluate its capacity
and cycling behavior. FIG. 2 is plots of the 1.sup.st and 2.sup.nd
cycle charge and discharge profile of micron size silicon oxide
without milling, showing large irreversible capacity loss (IRCL).
Electrode with micron size silicon oxide at different loading
densities 2.73 mg/cm.sup.2, 4.48 mg/cm.sup.2, and 5.26 mg/cm.sup.2
were cycled and the results are shown in FIG. 3. Batteries
incorporating electrodes with silicon oxide loading density of 2.73
mg/cm.sup.2 were observed to have better specific capacity than
batteries having electrodes with silicon oxide loading densities of
4.48 mg/cm.sup.2 and 5.26 mg/cm.sup.2. Although significant
capacity loss and generally poor cycling behavior has been observed
for electrodes with all three loading densities for these active
materials.
[0155] Pristine silicon oxide (325 mesh, Sigma Aldrich) was HEMM
ball milled at 300 rpm (revolutions per minute) for 1 to 24 h in
ethanol and the physical and cycling behavior of the resulted
materials were studied. XRD measurements of these materials with
milling times t1-t4 with 1 h<t1<t2<t3<t4<24 h shown
in FIG. 4 revealed peaks for crystalline silicon (indicated by
black dot) in t2, t3, and t4 samples, indicating at least partial
conversion of the amorphous silicon oxide to crystalline silicon
after sufficient hours of milling. At extended HEMM ball milling
time of t4, ZrO.sub.2 contaminants from the HEMM media was observed
in the treated sample, indicating the prolonged milling condition
may not be favored since ZrO.sub.2 would correspond to an inert
contaminant in the active material.
[0156] The size distribution of these silicon oxide materials was
studied and the results are shown in FIG. 5. The particle sizes
were measured using dynamic light scattering for particle
dispersions. Specifically, longer time HEMM such as t2 or t3 has
produced silicon oxide composite with reduced particle size,
including particles with less than micron size. Coin cell batteries
were formed with these silicon oxide based materials with a lithium
foil counter electrode. The cycling performance of the batteries
with these silicon oxide based materials was evaluated and the
results are shown in FIG. 6. Milling at 300 rpm for t1 and t2 has
produced silicon oxide composite materials with comparable cycling
performance, which is significantly better than untreated silicon
oxide (labeled pristine). Milling at 300 rpm for t3 produced
silicon oxide composite materials with the highest specific
capacity, better than t1 and t2 samples, although the battery with
the t3 sample experienced the largest percent capacity fade.
Prolonged milling at t4 resulted in a material with poorer battery
performance, again indicating the prolonged milling condition is
not favored. HEMM milling at appropriate rate and length of time
therefore improves the cycling behavior of silicon oxide. As micron
size silicon oxide particles have shown above in FIGS. 2 and 3 to
have poor cycling behavior, HEMM milling has been demonstrated to
significantly improve the battery performance of the material,
although it is not clear if this improvement is a result of the
decrease in particle size and change in the crystal structure or a
combination of factors.
[0157] To study the effect of heat treatment, silicon oxide and
silicon oxide coated with an appropriate carbon source were heated
in a furnace in an inert atmosphere per condition provided in table
4. Examples of suitable carbon source are polyvinyl chloride,
poly(vinyl chloride)-co-vinyl acetate, polyacrylonitrile (PAN),
glucose, sucrose, polymerized furfuryl alcohol, poly[(o-cresyl
glycidyl ether)-co-formaldehyde resin, poly(methacrylo-nitrile).
The desired organic compositions can be dissolved in a suitable
solvent, such as water and/or volatile organic solvents, such as
NMP (N-Methyl-2-pyrrolidone) and/or THF (tetrahydrofuran).
TABLE-US-00003 TABLE 4 Temperature Time Condition 1 600.degree. C.
to 1200.degree. C. 1 hr to 24 hr (No Carbon coating) Condition 2
600.degree. C. to 1200.degree. C. 1 hr to 24 hr (Coated with carbon
source)
[0158] Silicon oxide coated with the appropriate carbon source is
known to form silicon oxide coated pyrolytic carbon, e.g., hard
carbon, under the specified heat treatment conditions to form a
SiO--HC composite material. Heat treated samples together with
untreated (pristine) silicon oxide are evaluated with XRD
measurements and the results are shown in FIG. 7. Silicon oxide
particles without the heat treatment appear to comprise largely of
amorphous silicon oxide. Heat treated silicon oxide appear to have
similar XRD profile to SiO--HC material, with at least some of the
amorphous silicon oxide reduced to crystalline silicon (indicated
by black dots). The cycling performance of the heat treated and
untreated samples are measured, and the results are shown in FIG.
8. Batteries formed with heat treated silicon oxide sample without
carbon coating were observed to have worse cycling performance than
batteries formed with untreated silicon oxide samples, while
batteries formed with the SiO--HC material has shown significantly
improved cycling behavior compared to batteries formed with the
untreated sample.
Example 2: Effect of Fluorinated Electrolyte Additive (FEA)
[0159] Varied amount of fluorinated electrolyte additive was added
to the electrolyte to investigate the effect of the additive on
battery performance. Various fluorine containing additives can be
used, including fluorine compounds with carbonate structures, such
as fluoro ethylene carbonate, fluorine-containing vinyl carbonate,
4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]dioxolan-2-one,
4-(2,2,3,3-tetrafluoro-2-trifluoromethyl-propyl)-[1,3]dioxolan-2-one,
bis(2,2,3,3-tetrafluoro-propyl) carbonate,
bis(2,2,3,3,3-pentafluoro-propyl) carbonate, or a combination
thereof. Positive effect of fluorinated electrolyte additive on
both anode and cathode materials has been observed.
[0160] Table 5 below shows the effect of fluorinated electrolyte
additive (FEA) on the ion conductivity of electrolytes E03 and E07,
which contain different ratios of common organic carbonate solvents
such as ethylene carbonate (EC), diethyl carbonate (DEC), and
dimethyl carbonate (DMC) along with a suitable electrolyte salt.
Appropriate electrolytes are described in copending U.S. patent
application Ser. No. 12/630,992 now U.S. Pat. No. 8,993,177 to
Amiruddin et al., entitled "Lithium Ion Battery With High Voltage
Electrolytes and Additives," incorporated herein by reference. It
appears that reasonable amounts of fluorinated electrolyte additive
do not significantly alter the ionic conductivity of the
electrolytes, which is measured in milli-Siemens per
centimeter.
[0161] The effect of FEA on E03 as base electrolyte in batteries
with various active materials has been evaluated. The effect of 10,
15, and 20 vol % of FEA on silicon based Si-Gr electrode material
has been evaluated together with no additive sample (pristine) in
batteries, using a lithium counter electrode and the results are
shown in FIG. 9. At all three volume percentages, the additive has
appeared to significantly improve the cycling performance of the
batteries with silicon oxide based materials compared to the sample
with no additive. Similar effect has been observed when silicon
oxide composite was used and the results are shown in FIG. 10. The
silicon oxide composite material is formed from HEMM at 300 rpm of
silicon oxide and graphite followed by blending with a carbon
source and heating at 900.degree. C. to form a hard carbon coating
to produce the SiO-Gr-HC composite material. FIG. 11 showed the
effect of 10 vol % FEA on HCMR.TM. cathode with lithium anode
counter electrode in batteries. FEA added battery has demonstrated
higher specific capacity and longer cycling life than the battery
without the additive. In general 10 vol % FEA additives showed the
best stability and conductivity and was used as a standard amount
in high voltage electrolyte used in some of the following
examples.
Example 3: Silicon Oxide-Graphite (SiO-Gr) Composites
[0162] Silicon oxide particles are HEMM milled with graphite to
form a SiO-Gr composite. The physical properties and cycling
behaviour of the composites were evaluated together with untreated
silicon oxide.
[0163] Pristine silicon oxide particles (Sigma-Aldrich-325 mesh)
were mixed with graphite at 300 rpm using planetary ball milling
for three different times t1, t2, and t3, with 1
hr<t1<t2<t3<24 hrs, in a dry state to form SiO-Gr
samples. XRD measurements of the samples are shown in FIG. 12. XRD
of the t1 sample comprises primarily of crystalline carbon peaks.
Longer time milling for t2 has led to the carbon to become less
crystalline such that the amorphous SiO background becomes more
visible. At longest milling time of t3, an amorphous SiO-Gr
composite has formed with no observable crystalline carbon
peaks.
[0164] As noted above, pre-milled silicon oxide showed improved
electrochemical performance relative to pristine silicon oxide. So
for the following samples, silicon oxide particles that had been
pre-milled in ethanol for t5 hours at 300 rpm by HEMM were mixed
with graphite at 300 rpm with HEMM ball milling for t4, t5, t6 or
more hours to form SiO-Gr composite samples (1
hr<t4<t5<t6<24 hrs). The composites were used to form
four electrodes with loading densities between 2.25 to 3.29
mg/cm.sup.2, which is used to build batteries with lithium counter
electrode. Specifically, sample 1 composite was milled t5 hours and
the loading density of the electrode formed was 2.25 mg/cm.sup.2.
Sample 2 composite was milled for t6 hours and the loading density
of the electrode formed was 2.24 mg/cm.sup.2. Sample 3 was milled
for t5 hours and the loading density of the electrode formed was
3.16 mg/cm.sup.2. Sample 4 was milled for t4 hours and the loading
density of the electrode formed was 3.29 mg/cm.sup.2.
[0165] FEA (10 vol %) has been added into the electrolyte used in
the battery comprising E03. The cycling performance of these
batteries evaluated and the results are shown in FIG. 13. The
SiO-Gr composites have demonstrated improved cycling performance
compared to the untreated silicon oxide material.
[0166] Also, silicon oxide particles (55-70 wt %, Sigma-Aldrich,
325 mesh) were mixed with graphite (30-45 wt %) at 300 rpm with
HEMM ball milling for t1 hr to form a SiO-Gr composite sample. The
composites were used to form electrodes, which is used to build a
battery with HCMR.TM. used as the active material for the positive
electrode. The battery was cycled between 4.5V to 0.5V after the
first cycle charge to 4.6V, at a balance of anode capacity to
cathode capacity of 142% and the 1.sup.st and the 10.sup.th cycles
charge-discharge profiles based on cathode are shown in FIG. 14.
The SiO-Gr composite has maintained about 85% of capacity at the
10.sup.th cycle compared to the 1.sup.st cycle.
Example 4: Silicon Oxide-Hard Carbon Composites
[0167] This example demonstrates the performance of coin cell
batteries fabricated from electrodes formed from negative electrode
active materials comprising SiO-hard carbon composites
(SiO--HC).
[0168] Composite precursor materials were prepared by ball milling.
In particular, an appropriate amount of powdered silicon oxide
particles (Sigma-Aldrich, 325 mesh) is subjected to ball milling
for 1 hr to 24 hr at a milling rate of 300 rpm. For a given amount
of silicon oxide, to obtain the appropriate amount by weight of
carbon coating (3%-35%), the required amount of carbon source is
dissolved in tetrahydrofuran (THF) to form a solution. The ball
milled silicon oxide particles is added to the solution and mixed
thoroughly for 2 hrs to 12 hrs with a magnetic stirrer. The mixture
is then dried over night to evaporate all the THF. The solid
obtained is transferred into an alumina boat and heat treated in a
tube furnace between 700.degree. C. to 1200.degree. C. for 1 hr to
24 hr under argon atmosphere. The SiO--HC composite material is
then collected and sieved.
[0169] A battery was assembled with an anode comprising the SiO--HC
composite across from a high capacity HCMR.TM. cathode in a coin
cell The anode was coated with supplemental lithium to compensate
for the first cycle IRCL of the anode. The cycling performance of
the battery is plotted in FIG. 15 showing 400 charge-discharge
cycles, where cycle 1 is cycled at a C/20 rate, cycles 2-3 at C/10,
cycles 4-5 at C/5 and cycles 6-400 at a C/3 rate. The first
discharge capacity of the coin cell at C/3 is about 235 mAh/g with
a capacity retention of about 80% in 380 cycles.
Example 5: Effect of Pre-lithiation
[0170] The effect of SLMP.TM. on the charge/discharge profile and
cycling performance of SiO-Gr-HC composite based anodes were
studied and the results are shown in FIG. 16 and the Tables 6 and 7
below.
[0171] SiO-Gr-HC composite was used to form an electrode with 3.7
mg/cm2 density and supplemental lithium (SLMP.TM.) on the 1.54
cm.sup.2 electrode. The SiO-Gr-HC composite based electrode was
cycled against a HCMR.TM. cathode and the results are shown in
Tables 6 and 7 below for specific capacity data obtained based on
cathode active material mass or anode active material mass,
respectively. Similar to the results obtained for SiO-Gr based
electrode, the addition of SLMP.TM. on SiO-Gr-HC based electrode
has shown to increase the charge discharge capacity and increase
the average voltage of the battery at different cycling rate. The
charge-discharge plots at a C/20 rate are shown in FIG. 16. The
average voltages from the results in FIG. 16 are 2.90V (pristine,
4.6V-0.5V), 2.94V (83% compensated, 4.6V-0.5V), 3.18V (100%
compensated, 4.6V-1.V) and 3.63 (Li anode). It can be seen that the
SLMP.TM. can effective eliminate the IRCL from the anode since
results comparable to those obtained with a Li anode were obtained.
The remaining IRCL can be attributed to the cathode.
TABLE-US-00004 TABLE 6 With Without Supplemental Li Supplemental Li
Based on Cathode (4.6/4.5 V-2.0 V) (4.6/4.5 V-1.5 V) Avg. V-C/20
3.50 3.13 (1st cycle, 4.6 V) Avg. V-C/10 (4.5 V) 3.465 3.14 Avg.
V-C/3 (4.5 V) 3.42 3.10 Charge Capacity-C/20 329 298 Discharge
Capacity-C/20 268 214 Charge Capacity-C/3 238 224 Discharge
Capacity-C/3 225 183 Excess anode % 11% 25%
TABLE-US-00005 TABLE 7 With Without Supplemental Li Supplemental Li
Based on Anode (4.6/4.5 V-2.0 V) (4.6/4.5 V-1.5 V) Charge
Capacity-C/20 1436 1443 (1st cycle-4.6 V) Discharge Capacity-C/20
1170 1036 Charge Capacity-C/3 (4.5 V) 1039 1084 Discharge
Capacity-C/3 982 886
A small portion of the average voltage differences in performance
noted in Tables 6 and 7 can be attributed to the difference in
voltage ranges, but significant portion of the differences are due
to the presence of supplemental lithium.
Example 6: SiO-Carbon Nanofiber (SiO--CNF) Based Composites
[0172] This example demonstrates the performance of coin cell
batteries fabricated from electrodes formed from negative electrode
active materials comprising SiO-Carbon nanofiber (SiO--CNF) based
composites.
[0173] Carbon nanofibers (CNFs) were added to silicon oxide to
enhance rate capability and the cycling stability of the composite
electrodes. Specifically, .alpha.SiO-.epsilon.CNF (where
0.5<.alpha.<0.95 and 0.05<.epsilon.<0.50) is formed by
mixing appropriate amount silicon oxide particles with carbon
nanofibers using a jar mill. The required materials were mixed in a
plastic jar with some zirconia milling balls. The jar was allowed
to mix for one hour and the contents of the jar were collected for
anode preparation process. There is no sieving step involved after
the Jarmill mixing process.
[0174] The SiO--CNF composite negative electrode active material
was formed into SiO--CNF electrode as describe above. For
comparison, pristine SiO powder was also formed into SiO electrode.
The cycling performances of these two electrodes are evaluated in
batteries with lithium foil counter electrode described above and
the results are shown in Table 8 below. The SiO--CNF battery
exhibited significant improvement with capacity retention both at
initial C/3 cycle and after cycling for 50 cycles.
TABLE-US-00006 TABLE 8 Specific Capacity Capacity at Initial Fade
C/3 Cycle After 50 Sample IRCL (mAh/g) Cycles SiO 33% 136 90%
SiO--CNF 40% 1083 24%
Example 7: SiO--Metal Based Composite Materials with or without
CNF
[0175] This example studies the performance of silicon oxide based
composites with inert metal powders, as described above. A
composite of .alpha.SiO-.delta.M where 0.5<.alpha.<0.95 and
0.05<.delta.<0.55 was prepared by HEMM ball milling at a
speed of 300 rpm for 1-24 hr to form a first composite. An
appropriate amount of carbon nanofiber (CNF) was added to the first
composite and milled for an additional 1-24 hours at 300 rpm to
form a second composite with .alpha.SiO-.delta.M-.epsilon.CNF where
0.5<.alpha.<0.9, 0.05<.delta.<0.35 and
0.05<.epsilon.<0.50). FIG. 17 showed the XRD of SiO-M
composite and SiO-M-CNF composite. No crystalline SiO-M was
observed in either composite sample.
[0176] The SiO-M composite and the SiO-M-CNF composite were formed
into electrodes and the electrochemical performances of the
electrodes were evaluated against lithium foil and the results are
shown in FIG. 18. The SiO-M-CNF based electrode appears to have
improved IRCL and overall cycling specific capacity compared to
SiO-M based electrode.
[0177] The SiO-M-CNF composite was also evaluated against HCMR.TM.
cathode and the results are shown in FIG. 19 and FIG. 20. The anode
has a SiO-M-CNF loading density of 2.1 mg/cm.sup.2 with
supplemental lithium powder (SLMP.TM.) lithium powder added on the
surface of anode as described above and a balance of 150% anode
capacity compared to cathode capacity. The electrolyte used in the
battery comprised 10 vol % fluorinated electrolyte additive in the
electrolyte. FIG. 19 showed the cycling performance of SiO-M-CNF
based electrode against the HCMR.TM. cathode calculated based on
the weight of cathode active material. The same HCMR.TM. cathode
cycled against lithium foil electrode is also included for
comparison. The SiO-M-CNF based electrode appears to have
comparable cycling performance as the lithium foil against the
HCMR.TM. based cathode, maintaining specific cycling capacity above
225 mAh/g beyond 100 cycles.
[0178] The detailed charge/discharge profile of the SiO-M-CNF/HCMR
battery based on the weight of cathode active material was
additionally shown in FIG. 19. FIG. 20 showed the cycling
performance of SiO-M-CNF based electrode against the HCMR.TM.
cathode calculated based on the weight of anode active material.
The SiO-M-CNF based electrode appears to maintain specific cycling
capacity above 1150 mAh/g after 55 cycles. The irreversible
capacity loss appeared to be 85 mAh/g (<200 mAh/g). The capacity
retention after 50 cycles at a C/3 rate is 97%. FIG. 21 shows
charge/discharge profiles for the 1st, 10th, 20th and 50th cycles
of the battery, indicating that it has comparable charge and
discharge profiles at the 10th, 20th and 50th cycles.
[0179] A separate study was performed to evaluate the effect of
milling on the size of the particles and the results are shown in
FIG. 22. After milling at 300 rpm for 1-24 hours, the size of
silicon oxide particles is reduced significantly compared to the
pristine sample, which is consistent with the milling studies
carried out in Example 1. The SiO-M sample showed similar size
distribution after adding 10% CNF and milling for additional 1-24
hours at 300 rpm to form SiO-M-CNF composites. The SiO-M-CNF
composite thus formed is studies with SEM at different
magnifications and the results are shown in FIG. 23.
Example 8: SiO-Gr-HC--Si Composite with and without CNF
[0180] This example is directed to examining active material
composites with both silicon oxide and silicon. Silicon oxide
milled at 300 rpm HEMM was combined with nano amorphous silicon and
graphite and milled for at 300 rpm by HEMM. The resulting mixture
is then carbonized at 900.degree. C. for 1-24 h in an Argon
environment with the appropriate hard carbon source, such as poly
vinyl chloride, poly(vinyl chloride)-co-vinyl acetate,
polyacrylonitrile, glucose, sucrose, polymerized furfuryl alcohol,
poly[(o-cresyl glycidyl ether)-co-formaldehyde resin,
poly(methacrylo-nitrile), a combination thereof to form a composite
material. XRD measurements of the composite material are shown in
FIG. 24, and these results reveal the formation of at least some
crystalline silicon in the composite. The resulting composite can
be represented by a formula .alpha.SiO-.beta.Gr-.chi.HC-.phi.Si
where 0.4<.alpha.<0.75, 0.05<.beta.<0.25,
0.01<.chi.<0.20, and 0.01<.phi.<0.50. A portion of the
SiO-Gr-HC--Si composite material was then mixed with CNF and jar
milled to form a .alpha.SiO-.beta.Gr-.chi.HC-.epsilon.CNF-.phi.Si
composite where 0.4<.alpha.<0.75, 0.05<13<0.25,
0.01<.chi.<0.2, 0.01<.epsilon.<0.2 and
0.01<.phi.<0.5. Both the SiO-Gr-HC--Si composite and the
SiO-Gr-HC--CNF--Si composite were formed into electrodes and cycled
against a lithium foil electrode and the results are shown in FIG.
25a. The SiO-Gr-HC--CNF--Si composite formed electrode appeared to
have improved cycling performance compared to the SiO-Gr-HC--Si
composite formed electrode. The SiO-Gr-HC--CNF--Si composite was
additionally cycled against a HCMR.TM. cathode and the results are
shown in FIG. 25b.
[0181] Two composite materials with varied amounts of SiO, Si, Gr,
and HC were synthesized: sample 1 has a composition with relatively
less Si relative to SiO and sample 2 has a composition containing
higher silicon concentration relative to SiO. Samples 1 and 2 had
similar amounts of Gr and HC. The cycling performance of electrodes
formed from samples 1 and 2 were tested against a lithium foil
counter electrode and the results are shown in FIG. 25c. The sample
with higher silicon ratio, sample 2, appears to have better cycling
performance, maintaining specific capacity above 1600 mAh/g after
60 cycles. All tested batteries had 10 vol % fluorinated additive
added to the electrolyte used in the battery.
[0182] The embodiments above are intended to be illustrative and
not limiting. Additional embodiments are within the claims. In
addition, although the present invention has been described with
reference to particular embodiments, those skilled in the art will
recognize that changes can be made in form and detail without
departing from the spirit and scope of the invention. Any
incorporation by reference of documents above is limited such that
no subject matter is incorporated that is contrary to the explicit
disclosure herein.
[0183] This document was prepared as a result of work sponsored by
the California Energy Commission. It does not necessarily represent
the views of the Energy Commission, its employees, or the State of
California. The Commission, the State of California, its employees,
contractors, and subcontractors make no warranty, express or
implied, and assume no legal liability for the information in this
document; nor does any party represent that the use of this
information will not infringe upon privately owned rights.
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