U.S. patent application number 14/792932 was filed with the patent office on 2017-01-12 for nonaqueous electrolyte compositions.
The applicant listed for this patent is E I DU PONT DE NEMOURS AND COMPANY. Invention is credited to CHARLES J. DUBOIS, George K. KODOKIAN.
Application Number | 20170012321 14/792932 |
Document ID | / |
Family ID | 57731398 |
Filed Date | 2017-01-12 |
United States Patent
Application |
20170012321 |
Kind Code |
A1 |
DUBOIS; CHARLES J. ; et
al. |
January 12, 2017 |
NONAQUEOUS ELECTROLYTE COMPOSITIONS
Abstract
Electrolyte compositions containing a solvent, a co-solvent,
certain cyclic carboxylic acid anhydride additives, certain
phosphorus-containing additives, and an electrolyte salt are
described. The electrolyte compositions are useful in
electrochemical cells, such as lithium ion batteries where they
provide significantly improved cycle life with no loss of discharge
capacity.
Inventors: |
DUBOIS; CHARLES J.; (Orange,
TX) ; KODOKIAN; George K.; (Kennett Square,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPANY |
Wilmington |
DE |
US |
|
|
Family ID: |
57731398 |
Appl. No.: |
14/792932 |
Filed: |
July 7, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2300/004 20130101;
H01M 2300/0034 20130101; Y02E 60/10 20130101; H01M 10/0569
20130101; H01M 4/485 20130101; H01M 2300/0037 20130101; H01M
10/0525 20130101; H01M 4/583 20130101; H01M 4/525 20130101; H01M
10/0567 20130101; H01M 4/505 20130101 |
International
Class: |
H01M 10/0569 20060101
H01M010/0569; H01M 10/0525 20060101 H01M010/0525; H01M 4/587
20060101 H01M004/587; H01M 4/505 20060101 H01M004/505; H01M 4/133
20060101 H01M004/133; H01M 10/0567 20060101 H01M010/0567; H01M
4/131 20060101 H01M004/131 |
Claims
1. An electrolyte composition comprising: a) at least one solvent;
b) at least one co-solvent; c) at least one cyclic carboxylic acid
anhydride selected from the group consisting of ##STR00007##
wherein R.sup.7 to R.sup.14 are independently H, F, C.sub.1 to
C.sub.10 alkyl optionally substituted with fluorine, alkoxy, and/or
thioalkyl, C.sub.2 to C.sub.10 alkene, or C.sub.6 to C.sub.10 aryl;
d) at least one phosphorus-containing additive selected from the
group consisting of organic phosphates, organic phosphonates, and
partial salts thereof; and e) at least one electrolyte salt.
2. The electrolyte composition of claim 1, wherein the solvent is a
non-fluorinated solvent.
3. The electrolyte composition of claim 2, wherein the
non-fluorinated solvent is selected from the group consisting of
ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate,
propylene carbonate, and mixtures thereof.
4. The electrolyte composition of claim 1, wherein the solvent is a
fluorinated solvent selected from the group consisting of: a) a
fluorinated acyclic carboxylic acid ester represented by the
formula: R.sup.1--COO--R.sup.2 b) a fluorinated acyclic carbonate
represented by the formula: R.sup.3--OCOO--R.sup.4, and c) a
fluorinated acyclic ether represented by the formula:
R.sup.5--O--R.sup.6 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5, and R.sup.6, independently represent an alkyl group; the
sum of carbon atoms in any of R.sup.1 and R.sup.2, R.sup.3 and
R.sup.4, and R.sup.5 and R.sup.6 is 2 to 7; at least two hydrogens
in R.sup.1 and/or R.sup.2, R.sup.3 and/or R.sup.4, and R.sup.5
and/or R.sup.6 are replaced by fluorines; and neither R.sup.1,
R.sup.2, R.sup.3, R.sup.4, R.sup.5, nor R.sup.6 contains a
--CH.sub.2F or --CHF-- group.
5. The electrolyte composition of claim 4, wherein the fluorinated
acyclic carboxylic acid ester is selected from one or more members
of the group consisting of CH.sub.3--COO--CH.sub.2CF.sub.2H,
CH.sub.3CH.sub.2--COOCH.sub.2CF.sub.2H,
F.sub.2CHCH.sub.2--COO--CH.sub.3,
F.sub.2CHCH.sub.2--COO--CH.sub.2CH.sub.3,
CH.sub.3--COO--CH.sub.2CH.sub.2CF.sub.2H,
CH.sub.3CH.sub.2--COO--CH.sub.2CH.sub.2CF.sub.2H,
F.sub.2CHCH.sub.2CH.sub.2--COO--CH.sub.2CH.sub.3, and
CH.sub.3--COO--CH.sub.2CF.sub.3.
6. The electrolyte composition of claim 5, wherein the fluorinated
acyclic carboxylic acid ester is 2,2-difluoroethyl acetate or
2,2-difluoroethyl propionate, or a mixture thereof.
7. The electrolyte composition of claim 1, wherein the co-solvent
is selected from one or more members of the group consisting of
ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate,
butylene carbonate, ethylene carbonate, and ethyl methyl
sulfone.
8. The electrolyte composition of claim 7, wherein the co-solvent
is ethylene carbonate.
9. The electrolyte composition of claim 1, wherein the cyclic
carboxylic acid anhydride is selected from one or more members of
the group consisting of maleic anhydride, succinic anhydride,
glutaric anhydride, 2,3-dimethylmaleic anhydride, citraconic
anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride,
2,3-diphenylmaleic anhydride, 3,4,5,6-tetrahydrophthalic anhydride,
2,3-dihydro-1,4-dithiiono-[2,3-c] furan-5,7 dione, and phenylmaleic
anhydride.
10. The electrolyte composition of claim 9, wherein the cyclic
carboxylic acid anhydride is maleic anhydride.
11. The electrolyte composition of claim 1, wherein the organic
phosphates are represented by the formula: ##STR00008## wherein
R.sup.15, R.sup.16, and R.sup.17 are each independently linear or
branched C.sub.1 to C.sub.10 alkyl or fluoroalkyl, C.sub.3 to
C.sub.10 cyclic alkyl, C.sub.2 to C.sub.10 ether, C.sub.2 to
C.sub.10 ether wherein at least one of the hydrogens is replaced
with a fluorine, R.sup.15 and R.sup.16, R.sup.16 and R.sup.17, or
R.sup.15 and R.sup.17 may be joined to form a ring.
12. The electrolyte composition of claim 11, wherein the organic
phosphate is selected from the group consisting of
tris(1,1,1,3,3,3-hexafluoropropan-2yl) phosphate,
tris(2,2,2-trifluoroethyl) phosphate,
tri(2,2,3,3,3-pentafluoropropyl) phosphate,
tris(2,2,3,3-tetrafluoropropyl) phosphate, triethyl phosphate,
trimethyl phosphate, tripropyl phosphate, triisopropyl phosphate,
tris(2,2,3,3,4,4,5,5,6,6-decafluorohexyl) phosphate, and
tris(2,2-difluoroethyl) phosphate.
13. The electrolyte composition of claim 1, wherein the partial
salt of an organic phosphate is represented by the following
formulae ##STR00009## wherein R.sup.15 and R.sup.16, are each
independently linear or branched C.sub.1 to C.sub.10 alkyl or
fluoroalkyl, C.sub.3 to C.sub.10 cyclic alkyl, C.sub.2 to C.sub.10
ether, C.sub.2 to C.sub.10 ether wherein at least one of the
hydrogens is replaced with a fluorine, R.sup.15 and R.sup.16 may be
joined to form a ring, M.sup.+ is a cation selected from the group
consisting of lithium, sodium, potassium, rubidium, and cesium, and
M.sup.+2 is cation selected from the group consisting of beryllium,
magnesium, calcium, strontium, and barium.
14. The electrolyte composition of claim 1, wherein the organic
phosphonates are represented by the formula: ##STR00010## wherein
R.sup.15, R.sup.16, and R.sup.17 are each independently linear or
branched C.sub.1 to C.sub.10 alkyl or fluoroalkyl, C.sub.3 to
C.sub.10 cyclic alkyl, C.sub.2 to C.sub.10 ether, C.sub.2 to
C.sub.10 ether wherein at least one of the hydrogens is replaced
with a fluorine, R.sup.15and R.sup.16, R.sup.16 and R.sup.17, or
R.sup.15 and R.sup.17 may be joined to form a ring.
15. The electrolyte composition of claim 14, wherein the organic
phosphonate is dimethylmethylphosphonate.
16. The electrolyte composition of claim 1, wherein the partial
salt of an organic phosphonate is represented by the following
formula ##STR00011## wherein R.sup.15 and R.sup.17 are each
independently linear or branched C.sub.1 to C.sub.10 alkyl or
fluoroalkyl, C.sub.3 to C.sub.10 cyclic alkyl, C.sub.2 to C.sub.10
ether, C.sub.2 to C.sub.10 ether wherein at least one of the
hydrogens is replaced with a fluorine, R.sup.15 and R.sup.17 may be
joined to form a ring, M.sup.+ is a cation selected from the group
consisting of lithium, sodium, potassium, rubidium, and cesium, and
M.sup.+2 is cation selected from the group consisting of beryllium,
magnesium, calcium, strontium, and barium.
17. The electrolyte composition of claim 1 further comprising an
additive selected from the group consisting of lithium
bis(oxalato)borate and fluoroethylene carbonate.
18. The electrolyte composition of claim 1 comprising a fluorinated
acyclic carboxylic acid ester, ethylene carbonate, an organic
phosphate or organic phosphonate additive, maleic anhydride, and
fluoroethylene carbonate.
19. An electrochemical cell comprising: (a) a housing; (b) an anode
and a cathode disposed in said housing and in ionically conductive
contact with one another; (c) the electrolyte composition of claim
1 disposed in said housing and providing an ionically conductive
pathway between said anode and said cathode; and (d) a porous
separator between said anode and said cathode.
20. The electrochemical cell of claim 19, wherein said
electrochemical cell is a lithium ion battery.
21. The electrochemical cell of claim 20, wherein the anode is
lithium titanate or graphite.
22. The electrochemical cell of claim 20, wherein the cathode
comprises a cathode active material exhibiting greater than 30
mAh/g capacity in the potential range greater than 4.6 V versus a
Li/Li.sup.+ reference electrode.
23. The electrochemical cell of claim 20, wherein the cathode
comprises a cathode active material which is charged to a potential
greater than or equal to 4.35 V versus a Li/Li.sup.+ reference
electrode.
24. The electrochemical cell of claim 20, wherein the cathode
comprises a lithium-containing manganese composite oxide having a
spinel structure as active material, the lithium-containing
manganese composite oxide being represented by the formula:
Li.sub.xNi.sub.yM.sub.zMn.sub.2-y-zO.sub.4-d wherein x is 0.03 to
1.0; x changes in accordance with release and uptake of lithium
ions and electrons during charge and discharge; y is 0.3 to 0.6; M
comprises one or more of Cr, Fe, Co, Li, Al, Ga, Nb, Mo, Ti, Zr,
Mg, Zn, V, and Cu; z is 0.01 to 0.18, and d is 0 to 0.3.
25. The electrochemical cell of claim 24, wherein y is 0.38 to
0.48, z is 0.03 to 0.12, and d is 0 to 0.1.
26. The electrochemical cell of claim 24, wherein M is one or more
of Li, Cr, Fe, Co, and Ga.
27. An electronic device comprising an electrochemical cell
according to claim 19.
Description
TECHNICAL FIELD
[0001] The disclosure herein relates to electrolyte compositions
containing a solvent, a co-solvent, certain cyclic carboxylic acid
anhydride additives, certain phosphorus-containing additives, and
an electrolyte salt, which are useful in electrochemical cells,
such as lithium ion batteries.
BACKGROUND
[0002] Carbonate compounds are currently used as electrolyte
solvents for non-aqueous batteries containing electrodes made from
alkali metals, alkaline earth metals, or compounds comprising these
metals, for example lithium ion batteries. Current lithium ion
battery electrolyte solvents typically contain one or more linear
carbonates, such as ethyl methyl carbonate, dimethyl carbonate, or
diethylcarbonate; and a cyclic carbonate, such as ethylene
carbonate. However, at cathode potentials above 4.4 V these
electrolyte solvents can decompose, which can result in a loss of
battery performance. Additionally, there are safety concerns with
the use of these electrolyte solvents because of their low boiling
point and high flammability.
[0003] Various approaches have been investigated to overcome the
limitations of commonly used non-aqueous electrolyte solvents. For
example, additives, such as cyclic carboxylic acid anhydrides, have
been used in combination with the currently used electrolyte
solvents (see, for example, Jeon et al. U.S. Patent Application
Publication No. 2010/0273064 A1).
[0004] Various fluorinated carboxylic acid ester electrolyte
solvents have also been investigated for use in lithium ion
batteries (see, for example, Nakamura et al in JP 4/328,915-B2, JP
3/444,607-B2, and U.S. Pat. No. 8,097,368). Additionally, Xu et al.
(U.S. Patent Application Publication No. 2012/0009485 A1) describes
a series of phosphorus compounds and boron compounds that can be
used as co-solvents, solutes, or additives in non-aqueous
electrolytes for use with 5 V class cathodes in lithium ion
batteries.
[0005] Despite the efforts in the art as described above, a need
remains for electrolyte compositions that will have improved
cycling performance at high temperature when used in a lithium ion
battery, particularly such a battery that operates at high voltage
(i.e. up to about 5 V).
SUMMARY
[0006] In one embodiment, there is provided herein an electrolyte
composition comprising: [0007] a) at least one solvent; [0008] b)
at least one co-solvent; [0009] c) at least one cyclic carboxylic
acid anhydride selected from the group consisting of
[0009] ##STR00001## [0010] where R.sup.7 to R.sup.14 are
independently H, F, C1 to C10 alkyl optionally substituted with
fluorine, alkoxy, and/or thioalkyl, 02 to 010 alkene, or C6 to C10
aryl; [0011] d) at least one phosphorus-containing additive
selected from the group consisting of organic phosphates, organic
phosphonates, and partial salts thereof; and [0012] e) at least one
electrolyte salt.
[0013] In another embodiment, there is provided herein an
electrochemical cell comprising: [0014] (a) a housing; [0015] (b)
an anode and a cathode disposed in said housing and in ionically
conductive contact with one another; [0016] (c) the electrolyte
composition disclosed herein, disposed in said housing and
providing an ionically conductive pathway between said anode and
said cathode; and [0017] (d) a porous separator between said anode
and said cathode.
[0018] In one embodiment, the electrochemical cell is a lithium ion
battery.
[0019] In another embodiment, there is provided herein an
electronic device comprising an electrochemical cell as disclosed
herein.
DETAILED DESCRIPTION
[0020] As used above and throughout the disclosure, the following
terms, unless otherwise indicated, shall be defined as follows:
[0021] The term "electrolyte composition" as used herein, refers to
a chemical composition suitable for use as an electrolyte in an
electrochemical cell.
[0022] The term "electrolyte salt" as used herein, refers to an
ionic salt that is at least partially soluble in the solvent of the
electrolyte composition and that at least partially dissociates
into ions in the solvent of the electrolyte composition to form a
conductive electrolyte composition.
[0023] The term "anode" refers to the electrode of an
electrochemical cell, at which oxidation occurs. In a galvanic
cell, such as a battery, the anode is the negatively charged
electrode. In a secondary (i.e. rechargeable) battery, the anode is
the electrode at which oxidation occurs during discharge and
reduction occurs during charging.
[0024] The term "cathode" refers to the electrode of an
electrochemical cell, at which reduction occurs. In a galvanic
cell, such as a battery, the cathode is the positively charged
electrode. In a secondary (i.e. rechargeable) battery, the cathode
is the electrode at which reduction occurs during discharge and
oxidation occurs during charging.
[0025] The term "lithium ion battery" refers to a type of
rechargeable battery in which lithium ions move from the anode to
the cathode during discharge, and from the cathode to the anode
during charge.
[0026] Disclosed herein are electrolyte compositions comprising at
least one solvent, at least one co-solvent, at least one cyclic
carboxylic acid anhydride additive, at least one
phosphorus-containing additive, and an electrolyte salt. The
electrolyte compositions are useful in electrochemical cells,
particularly lithium ion batteries, where they provide
significantly improved cycle life with no loss of discharge
capacity.
[0027] In the electrolyte compositions disclosed herein, the
solvent can be a fluorinated solvent, a non-fluorinated solvent, or
a mixture thereof. Suitable non-fluorinated solvents include
without limitation, ethyl methyl carbonate (EMC), dimethyl
carbonate (DMC), diethyl carbonate (DEC), propylene carbonate, and
mixtures thereof. These solvents are available commercially from
companies such as Novolyte (Independence, Ohio).
[0028] Fluorinated solvents can be selected from fluorinated
acyclic carboxylic acid esters, fluorinated acyclic carbonates, and
fluorinated acyclic ethers. Suitable fluorinated acyclic carboxylic
acid esters are represented by the formula R.sup.1--COO--R.sup.2,
where R.sup.1 and R.sup.2 independently represent an alkyl group,
the sum of carbon atoms in R.sup.1 and R.sup.2 is 2 to 7, at least
two hydrogens in R.sup.1 and/or R.sup.2 are replaced by fluorines
and neither R.sup.1 nor R.sup.2 contains a --CH.sub.2F or --CHF--
group. The presence of a monofluoroalkyl group (i.e. --CH.sub.2F or
--CHF--) in the carboxylic acid ester may cause toxicity. Examples
of suitable fluorinated acyclic carboxylic acid esters include
without limitation CH.sub.3--COO--CH.sub.2CF.sub.2H
(2,2-difluoroethyl acetate, CAS No. 1550-44-3),
CH.sub.3--COO--CH.sub.2CF.sub.3 (2,2,2-trifluoroethyl acetate, CAS
No. 406-95-1), CH.sub.3CH.sub.2--COO--CH.sub.2CF.sub.2H
(2,2-difluoroethyl propionate, CAS No. 1133129-90-4),
CH.sub.3--COO--CH.sub.2CH.sub.2CF.sub.2H (3,3-difluoropropyl
acetate), CH.sub.3CH.sub.2--COO--CH.sub.2CH.sub.2CF.sub.2H
(3,3-difluoropropyl propionate), and
HCF.sub.2--CH.sub.2--CH.sub.2--COO--CH.sub.2CH.sub.3 (ethyl
4,4-difluorobutanoate, CAS No. 1240725-43-2). In one embodiment,
the fluorinated acyclic carboxylic acid ester is 2,2-difluoroethyl
acetate (CH.sub.3--COO--CH.sub.2CF.sub.2H), or 2,2-difluoroethyl
propionate (CH.sub.3CH.sub.2--COO--CH.sub.2CF.sub.2H), or a mixture
thereof.
[0029] Suitable fluorinated acyclic carbonates are represented by
the formula R.sup.3--OCOO--R.sup.4, where R.sup.3 and R.sup.4
independently represent an alkyl group, the sum of carbon atoms in
R.sup.3 and R.sup.4 is 2 to 7, at least two hydrogens in R.sup.3
and/or R.sup.4 are replaced by fluorines and neither R.sup.3 nor
R.sup.4 contains a --CH.sub.2F or --CHF-- group. Examples of
suitable fluorinated acyclic carbonates include without limitation
CH.sub.3--OC(O)O--CH.sub.2CF.sub.2H (methyl 2,2-difluoroethyl
carbonate, CAS No. 916678-13-2),
CH.sub.3--OC(O)O--CH.sub.2CF.sub.3(methyl 2,2,2-trifluoroethyl
carbonate, CAS No. 156783-95-8),
CH.sub.3--OC(O)O--CH.sub.2CF.sub.2CF.sub.2H (methyl
2,2,3,3-tetrafluoropropyl carbonate, CAS No.156783-98-1),
HCF.sub.2CH.sub.2--OCOO--CH.sub.2CH.sub.3 (ethyl 2,2-difluoroethyl
carbonate, CAS No. 916678-14-3), and
CF.sub.3CH.sub.2--OCOO--CH.sub.2CH.sub.3 (ethyl
2,2,2-trifluoroethyl carbonate, CAS No. 156783-96-9).
[0030] Suitable fluorinated acyclic ethers are represented by the
formula: R.sup.5--O--R.sup.6, where R.sup.5 and R.sup.6
independently represent an alkyl group, the sum of carbon atoms in
R.sup.5 and R.sup.6 is 2 to 7, at least two hydrogens in R.sup.5
and/or R.sup.6 are replaced by fluorines and neither R.sup.5 nor
R.sup.6 contains a --CH.sub.2F or --CHF-- group. Examples of
suitable fluorinated acyclic ethers include without limitation
HCF.sub.2CF.sub.2CH.sub.2--O--CF.sub.2CF.sub.2H (CAS No.
16627-68-2) and HCF.sub.2CH.sub.2--O--CF.sub.2CF.sub.2H (CAS No.
50807-77-7).
[0031] A mixture of two or more of these fluorinated acyclic
carboxylic acid ester, fluorinated acyclic carbonate, and/or
fluorinated acyclic ether solvents can also be used. In one
embodiment, the electrolyte composition comprises 2,2-difluoroethyl
acetate or 2,2-difluoroethyl propionate, or a mixture thereof,
[0032] Fluorinated acyclic carboxylic acid esters, fluorinated
acyclic carbonates, and fluorinated acyclic ethers suitable for use
herein can be prepared using known methods. For example, acetyl
chloride can be reacted with 2,2-difluoroethanol (with or without a
basic catalyst) to form 2,2-difluoroethyl acetate. Additionally,
2,2-difluoroethyl acetate and 2,2-difluoroethyl propionate can be
prepared using the method described by Wiesenhofer et al. (WO
2009/040367 A1, Example 5). Alternatively, 2,2-difluoroethyl
acetate can be prepared using the method described in the Examples
herein below. Other fluorinated acyclic carboxylic acid esters may
be prepared using the same method using different starting
carboxylate salts. Similarly, methyl chloroformate can be reacted
with 2,2-difluoroethanol to form methyl 2,2-difluoroethyl
carbonate. Synthesis of
HCF.sub.2CF.sub.2CH.sub.2--O--CF.sub.2CF.sub.2H can be done by
reacting 2,2,3,3-tetrafluoropropanol with tetrafluoroethylene in
the presence of base (e.g., NaH, etc.). Similarly, reaction of
2,2-difluoroethanol with tetrafluoroethylene yields
HCF.sub.2CH.sub.2--O--CF.sub.2CF.sub.2H. Alternatively, some of
these fluorinated solvents may be purchased from companies such as
Matrix Scientific (Columbia S.C.). For best results, it is
desirable to purify the fluorinated acyclic carboxylic esters,
fluorinated acyclic carbonates, and fluorinated acyclic ethers to a
purity level of at least about 99.9%, more particularly at least
about 99.99%. These fluorinated solvents can be purified using
methods known in the art, such as solvent extraction, column
chromatography, or distillation methods including vacuum
distillation or spinning band distillation.
[0033] In the electrolyte compositions disclosed herein, the
solvent or mixtures thereof can be used in various amounts
depending on the desired properties of the electrolyte composition.
In one embodiment, the solvent is used in an amount of about 5% to
about 95% by weight of the electrolyte composition. In another
embodiment, the solvent is used in an amount of about 10% to about
80% by weight of the electrolyte composition. In another
embodiment, the solvent is used in an amount of about 30% to about
70% by weight of the electrolyte composition. In another
embodiment, the solvent is used in an amount of about 45% to about
65% by weight of the electrolyte composition. In another
embodiment, the solvent is used in an amount of about 6% to about
30% by weight of the electrolyte composition. In another
embodiment, the solvent is used in an amount of about 61% by weight
of the electrolyte composition.
[0034] The electrolyte compositions disclosed herein also comprise
at least one co-solvent. Examples of suitable co-solvents include
without limitation one or more carbonates or sulfones. Suitable
carbonates include without limitation ethyl methyl carbonate,
dimethyl carbonate, diethyl carbonate, butylene carbonate, or
ethylene carbonate. A non-limiting example of a sulfone co-solvent
is ethyl methyl sulfone. Mixtures of two or more of these
co-solvents can also be used. In one embodiment, the co-solvent is
ethylene carbonate. It is desirable to use a co-solvent that is
battery grade or has a purity level of at least about 99.9%, and
more particularly at least about 99.99%. Many of these co-solvents
are available commercially from companies such as Novolyte,
(Independence, Ohio).
[0035] In the electrolyte compositions disclosed herein, the
co-solvent or mixtures thereof can be used in various amounts
depending on the desired properties of the electrolyte composition.
In one embodiment, the co-solvent is used in an amount of about
0.1% to about 80% by weight of the electrolyte composition. In
another embodiment, the co-solvent is used in an amount of about
0.1% to about 60% by weight of the electrolyte composition. In
another embodiment, the co-solvent is used in an amount of about
10% to about 50% by weight of the electrolyte composition. In
another embodiment, the co-solvent is used in an amount of about
20% to about 40% by weight of the electrolyte composition. In
another embodiment, the co-solvent is used in an amount of about
20% to about 30% by weight of the electrolyte composition.
[0036] In another embodiment, the co-solvent is used in an amount
of about 25% by weight of the electrolyte composition.
[0037] In one embodiment, the electrolyte composition comprises at
least one fluorinated acyclic carboxylic acid ester and ethylene
carbonate. In another embodiment, the electrolyte composition
comprises 2,2-difluoroethyl acetate or 2,2-difluoroethyl
propionate, or a mixture thereof, and ethylene carbonate.
[0038] The electrolyte compositions disclosed herein further
comprise at least one cyclic carboxylic acid anhydride. Suitable
cyclic carboxylic acid anhydrides are represented by the following
formulae:
##STR00002##
wherein R.sup.7 to R.sup.14 are independently H, F, C.sub.1 to
C.sub.10 alkyl optionally substituted with fluorine, alkoxy, and/or
thioalkyl, C.sub.2 to C.sub.10 alkene, or C.sub.6 to C.sub.1o aryl.
Examples of suitable cyclic carboxylic acid anhydrides include
without limitation maleic anhydride, succinic anhydride, glutaric
anhydride, 2,3-dimethylmaleic anhydride, citraconic anhydride,
1-cyclopentene-1,2-dicarboxylic anhydride, 2,3-diphenylmaleic
anhydride, 3,4,5,6-tetrahydrophthalic anhydride,
2,3-dihydro-1,4-dithiiono-[2,3-c] furan-5,7 dione, and phenylmaleic
anhydride. A mixture of two or more of these cyclic carboxylic acid
anhydrides can also be used. In one embodiment, the cyclic
carboxylic acid anhydride is maleic anhydride. These materials can
be obtained from a specialty chemical company such as
Sigma-Aldrich, Inc. (Milwaukee, Wis.). It is desirable to purify
the cyclic carboxylic acid anhydride to a purity level of at least
about 99.0%, more particularly at least about 99.9%. Purification
can be done using known methods, as described above.
[0039] The cyclic carboxylic acid anhydride or a mixture thereof is
generally used in the electrolyte composition in an amount of about
0.01% to about 40%, more particularly, about 0.05% to about 20%,
more particularly about 0.1% to about 30%, more particularly about
0.1% to about 20%, more particularly about 0.1% to about 10%, more
particularly about 0.5% to about 5% and more particularly about
0.7% to about 2% by weight of the total electrolyte composition. In
one embodiment, the cyclic carboxylic acid anhydride is used in the
electrolyte composition at about 1% by weight.
[0040] The electrolyte compositions disclosed herein further
comprises at least one phosphorus-containing additive selected from
organic phosphates, organic phosphonates, and partial salts
thereof.
[0041] Suitable organic phosphate additives include without
limitation organic phosphates represented by the formula:
##STR00003##
wherein R.sup.15, R.sup.16, and R.sup.17 are each independently
linear or branched C.sub.1 to C.sub.1o alkyl or fluoroalkyl,
C.sub.3 to C.sub.10 cyclic alkyl, C.sub.2 to C.sub.10 ether,
C.sub.2 to C.sub.10 ether wherein at least one of the hydrogens is
replaced with a fluorine, R.sup.15 and R.sup.16, R.sup.16 and
R.sup.17, or R.sup.15 and R.sup.17 may be joined to form a ring.
The term "fluoroalkyl", as used herein, refers to a linear or
branched alkyl group wherein one or more hydrogens have been
replaced with one or more fluorines. Suitable examples of organic
phosphate additives include without limitation
tris(1,1,1,3,3,3-hexafluoropropan-2yl) phosphate (CAS No.
66489-68-7), tris(2,2,2-trifluoroethyl) phosphate (CAS No.
358-63-4), tri(2,2,3,3,3-pentafluoropropyl) phosphate (CAS No.
25476-41-9), tris(2,2,3,3-tetrafluoropropyl) phosphate (CAS No.
563-10-0), triethyl phosphate (CAS No. 78-40-0), trimethyl
phosphate (CAS No. 512-56-1), tripropyl phosphate (CAS No.
513-08-6), triisopropyl phosphate (CAS No. 513-02-0),
tris(2,2,3,3,4,4,5,5,6,6-decafluorohexyl) phosphate, and
tris(2,2-difluoroethyl) phosphate (CAS No. 358-64-5).
[0042] Partial salts of organic phosphates include without
limitation compounds represented by the following formulae,
##STR00004##
wherein R.sup.15 and R.sup.16 are defined as above, R.sup.15 and
R.sup.16 may be joined to form a ring, M.sup.+ is a Group I cation
selected from lithium, sodium, potassium, rubidium, or cesium, and
M.sup.+2 is a Group II cation selected from beryllium, magnesium,
calcium, strontium, or barium. In one embodiment, M.sup.+ is
lithium, sodium, or potassium. In another embodiment, M.sup.+ is
lithium. In one embodiment, M.sup.+2 is calcium or magnesium.
[0043] Suitable organic phosphonate additives include without
limitation organic phosphonates represented by the formula:
##STR00005##
wherein R.sup.15, R.sup.16, and R.sup.17 are defined as above,
R.sup.15 and R.sup.16, R.sup.16 and R.sup.17, or R.sup.15 and
R.sup.17 may be joined to form a ring. A non-limiting example of an
organic phosphonate additive is dimethylmethylphosphonate.
[0044] Partial salts of organic phosphonates include without
limitation compounds represented by the following formulae:
##STR00006##
wherein R.sup.15 and R.sup.17 are defined as above, R.sup.15 and
R.sup.17 may be joined to form a ring, and M.sup.+ and M.sup.+2 are
defined as above.
[0045] Phosphorus-containing additives can be obtained from
commercial sources such as Sigma-Aldrich (Milwaukee, Wis.). The
phosphorus-containing additives can also be prepared using methods
known in the art. For example, organic phosphate additives can be
prepared by the method described by A. von Cresce et al. (Journal
of the Electrochemical Society, No. 158, p. A337, 2011), using the
reaction of phosphorus oxychloride with the corresponding
fluorinated alcohol in the presence of lithium hydride in diethyl
ether. Organic phosphate additives can also be prepared using the
procedure described by L. Zaharov et al., (Izvestiya Akademii Nausk
USSR, Seriya Khimicheskaya, No. 8, p.1860, 1969) and I. Kudryvtsev
et al. (Izvestiya Akademii Nausk USSR, Seriya Khimicheskaya, No.
11, pp. 2535-2540, 1982), using the reaction of phosphorus
oxychloride with the corresponding fluorinated alcohol in the
presence of LiCl catalyst in the absence of a solvent. A Lewis
acid-mediated Michaelis-Arbuzov reaction of arylmethyl halides and
alcohols with triethyl phosphite at room temperature can be used to
prepare arylmethyl and heteroarylmethyl phosphonate esters in good
yields as described by G. G. Rajeshwaran et al. (Org. Lett., 2011,
13, 1270-1273). The phosphorus-containing additives can be purified
using methods known in the art, as described above.
[0046] The phosphorus-containing additive or a mixture thereof, is
generally used in an amount of about 0.2% to about 10% by weight of
the total electrolyte composition. In another embodiment, the
phosphorus-containing additive is used in an amount of about 0.5%
to about 5% by weight of the total electrolyte composition. In
another embodiment, the phosphorus-containing additive is used in
an amount of about 0.5% to about 2% by weight of the total
electrolyte composition. In another embodiment, the
phosphorus-containing additive is used in an amount of about 0.5%
to about 1.5% by weight of the total electrolyte composition. In
another embodiment, the phosphorus-containing additive is used in
an amount of about 1% by weight of the total electrolyte
composition.
[0047] The electrolyte compositions disclosed herein may optionally
further contain additives such as lithium bis(oxalato)borate,
fluoroethylene carbonate (also referred to herein as FEC or
4-fluoro-1,3-dioxolan-2-one, CAS No. 114435-02-8), FEC derivatives,
including 4,5-difluoro -1,3-dioxolan-2-one;
4,5-difluoro-4-methyl-1,3-dioxolan-2-one;
4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one;
4,4-difluoro-1,3-dioxolan-2-one;
4,4,5-trifluoro-1,3-dioxolan-2-one, and ethylene carbonates
substituted with at least one of a saturated or unsaturated C.sub.1
to C.sub.4 fluoroalkyl group, or mixtures thereof. In one
embodiment, the additive is selected from the group consisting of
lithium bis(oxalato)borate and fluoroethylene carbonate. The
additive, if used, is generally present in the electrolyte
composition in an amount of about 0.01% to about 10%, more
particularly, about 0.05% to about 10%, more particularly about
0.1% to about 10%, more particularly about 0.1% to about 5.0%, more
particularly about 0.25% to about 5.0%, more particularly about
0.25% to about 3.0%, and more particularly about 0.25% to about
1.5% by weight of the total electrolyte composition.
[0048] In one embodiment, the electrolyte composition comprises a
nonfluorinated linear carbonate, ethylene carbonate, an organic
phosphate additive or organic phosphonate additive, maleic
anhydride, and fluoroethylene carbonate. In another embodiment, the
electrolyte composition comprises ethyl methyl carbonate, ethylene
carbonate, triethyl phosphate, maleic anhydride, and fluoroethylene
carbonate. In another embodiment, the electrolyte composition
comprises about 58% to about 65% ethyl methyl carbonate, about 23%
to about 26% ethylene carbonate, about 0.25% to about 3.0% triethyl
phosphate, about 0.25% to about 3.0% maleic anhydride, and about
0.25% to about 3.0% fluoroethylene carbonate, by weight of the
total electrolyte composition.
[0049] In another embodiment, the electrolyte composition comprises
a fluorinated acyclic carboxylic acid ester, ethylene carbonate, an
organic phosphate or organic phosphonate additive, maleic
anhydride, and fluoroethylene carbonate. In another embodiment, the
electrolyte composition comprises 2,2-difluoroethey acetate,
ethylene carbonate, triethyl phosphate, maleic anhydride, and
fluoroethylene carbonate. In another embodiment, the electrolyte
composition comprises about 58% to about 65% 2,2-difluoroethey
acetate, about 23% to about 26% ethylene carbonate, about 0.25% to
about 3.0% triethyl phosphate, about 0.25% to about 3.0% maleic
anhydride, and about 0.25% to about 3.0% fluoroethylene carbonate,
by weight of the total electrolyte composition.
[0050] The electrolyte compositions disclosed herein also contain
at least one electrolyte salt. Suitable electrolyte salts include
without limitation
[0051] lithium hexafluorophosphate (LiPF.sub.6),
[0052] lithium tris(pentafluoroethyl)trifluorophosphate
(LiPF.sub.3(C.sub.2F.sub.5).sub.3),
[0053] lithium bis(trifluoromethanesulfonyl)imide,
[0054] lithium bis(perfluoroethanesulfonyl)imide,
[0055] lithium (fluorosulfonyl)
(nonafluorobutanesulfonyl)imide,
[0056] lithium bis(fluorosulfonyl)imide,
[0057] lithium tetrafluoroborate,
[0058] lithium perchlorate,
[0059] lithium hexafluoroarsenate,
[0060] lithium trifluoromethanesulfonate,
[0061] lithium tris(trifluoromethanesulfonyl)methide,
[0062] lithium bis(oxalato)borate,
[0063] lithium difluoro(oxalato)borate,
[0064] Li.sub.2B.sub.12F.sub.12-xH.sub.x where x is equal to 0 to
8, and
[0065] mixtures of lithium fluoride and anion receptors such as
B(OC.sub.6F.sub.5).sub.3.
[0066] Mixtures of two or more of these or comparable electrolyte
salts may also be used. In one embodiment, the electrolyte salt is
lithium hexafluorophosphate. The electrolyte salt can be used in
the electrolyte composition in an amount of about 0.2 to about 2.0
M, more particularly about 0.3 to about 1.5 M, and more
particularly about 0.5 to about 1.2 M.
[0067] In another embodiment, there is provided herein an
electrochemical cell comprising a housing, an anode and a cathode
disposed in the housing and in ionically conductive contact with
one another, an electrolyte composition, as described above,
providing an ionically conductive pathway between the anode and the
cathode, and a porous or microporous separator between the anode
and the cathode. The housing may be any suitable container to house
the electrochemical cell components. The anode and the cathode may
be comprised of any suitable conducting material depending on the
type of electrochemical cell. Suitable examples of anode materials
include without limitation lithium metal, lithium metal alloys,
lithium titanate, aluminum, platinum, palladium, graphite,
transition metal oxides, and lithiated tin oxide. Suitable examples
of cathode materials include without limitation graphite, aluminum,
platinum, palladium, electroactive transition metal oxides
comprising lithium or sodium, indium tin oxide, and conducting
polymers such as polypyrrole and polyvinylferrocene.
[0068] The porous separator serves to prevent short circuiting
between the anode and the cathode. The porous separator typically
consists of a single-ply or multi-ply sheet of a microporous
polymer such as polyethylene, polypropylene, or a combination
thereof. The pore size of the porous separator is sufficiently
large to permit transport of ions, but small enough to prevent
contact of the anode and cathode either directly or from particle
penetration or dendrites which can from on the anode and
cathode.
[0069] In another embodiment, the electrochemical cell is a lithium
ion battery. Suitable cathode materials for a lithium ion battery
include without limitation electroactive transition metal oxides
comprising lithium, such as LiCoO.sub.2, LiNiO.sub.2,
LiMn.sub.2O.sub.4, or LiV.sub.3O.sub.8; oxides of layered structure
such as LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 where x+y+z is about 1,
LiCo.sub.0.2Ni.sub.0.2O.sub.2,
Li.sub.1+zNi.sub.1-x-yCo.sub.xAl.sub.yO.sub.2 where 0<x<0.3,
0<y<0.1, and 0<z<0.06, LiFePO.sub.4, LiMnPO.sub.4,
LiCoPO.sub.4, LiNi.sub.0.5Mn.sub.1.5O.sub.4, LiVPO.sub.4F; mixed
metal oxides of cobalt, manganese, and nickel such as those
described in U.S. Pat. No. 6,964,828 (Lu) and U.S. Pat. No.
7,078,128 (Lu); nanocomposite cathode compositions such as those
described in U.S. Pat. No. 6,680,145 (Obrovac); lithium-rich
layered-layered composite cathodes such as those described in U.S.
Pat. No. 7,468,223; and cathodes such as those described in U.S.
Pat. No. 7,718,319 and the references therein.
[0070] In another embodiment, the cathode in the lithium ion
battery disclosed herein comprises a cathode active material
exhibiting greater than 30 mAh/g capacity in the potential range
greater than 4.6 V versus a Li/Li.sup.+ reference electrode. One
example of such a cathode is a stabilized manganese cathode
comprising a lithium-containing manganese composite oxide having a
spinel structure as cathode active material. The lithium-containing
manganese composite oxide in a cathode suitable for use herein
comprises oxides of the formula
Li.sub.xNi.sub.yM.sub.zMn.sub.2-y-zO.sub.4-d, wherein x is 0.03 to
1.0; x changes in accordance with release and uptake of lithium
ions and electrons during charge and discharge; y is 0.3 to 0.6; M
comprises one or more of Cr, Fe, Co, Li, Al, Ga, Nb, Mo, Ti, Zr,
Mg, Zn, V, and Cu; z is 0.01 to 0.18; and d is 0 to 0.3. In one
embodiment in the above formula, y is 0.38 to 0.48, z is 0.03 to
0.12, and d is 0 to 0.1. In one embodiment in the above formula, M
is one or more of Li, Cr, Fe, Co and Ga. Stabilized manganese
cathodes may also comprise spinel-layered composites which contain
a manganese-containing spinel component and a lithium rich layered
structure, as described in U.S. Pat. No. 7,303,840.
[0071] In another embodiment, the cathode in the lithium ion
battery disclosed herein comprises a cathode active material which
is charged to a potential greater than or equal to 4.35 V versus a
Li/Li.sup.+ reference electrode. Examples of such cathodes are
layered oxides such as LiCoO.sub.2 or
LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 where x+y+z is about 1, charged
to cathode potentials higher than the standard 4.1 to 4.25 V range
in order to access higher capacity. Other examples are
layered-layered high-capacity oxygen-release cathodes such as those
described in U.S. Pat. No. 7,468,223 charged to upper charging
voltages above 4.5 V.
[0072] A cathode active material suitable for use herein can be
prepared using methods such as the hydroxide precursor method
described by Liu et al (J. Phys. Chem. C 13:15073-15079, 2009). In
that method, hydroxide precursors are precipitated from a solution
containing the required amounts of manganese, nickel and other
desired metal(s) acetates by the addition of KOH. The resulting
precipitate is oven-dried and then fired with the required amount
of LiOH.H.sub.20 at about 800 to about 950.degree. C. in oxygen for
3 to 24 hours, as described in detail in the Examples herein.
Alternatively, the cathode active material can be prepared using a
solid phase reaction process or a sol-gel process as described in
U.S. Pat. No. 5,738,957 (Amine).
[0073] A cathode, in which the cathode active material is
contained, suitable for use herein may be prepared by methods such
as mixing an effective amount of the cathode active material (e.g.
about 70 wt % to about 97 wt %), a polymer binder, such as
polyvinylidene difluoride, and conductive carbon in a suitable
solvent, such as N-methylpyrrolidone, to generate a paste, which is
then coated onto a current collector such as aluminum foil, and
dried to form the cathode.
[0074] A lithium ion battery as disclosed herein further contains
an anode, which comprises an anode active material that is capable
of storing and releasing lithium ions. Examples of suitable anode
active materials include without limitation lithium alloys such as
lithium-aluminum alloy, lithium-lead alloy, lithium-silicon alloy,
lithium-tin alloy and the like; carbon materials such as graphite
and mesocarbon microbeads (MCMB); phosphorus-containing materials
such as black phosphorus, MnP.sub.4 and CoP.sub.3; metal oxides
such as SnO.sub.2, SnO and TiO.sub.2; nanocomposites containing
antimony or tin, for example nanocopmposites containing antimony,
oxides of aluminum, titanium, or molybdenum, and carbon, such as
those described by Yoon et al (Chem. Mater. 21, 3898-3904, 2009);
and lithium titanates such as Li.sub.4Ti.sub.5O.sub.12 and
LiTi.sub.2O.sub.4. In one embodiment, the anode active material is
lithium titanate or graphite.
[0075] An anode can be made by a method similar to that described
above for a cathode wherein, for example, a binder such as a vinyl
fluoride-based copolymer is dissolved or dispersed in an organic
solvent or water, which is then mixed with the active, conductive
material to obtain a paste. The paste is coated onto a metal foil,
preferably aluminum or copper foil, to be used as the current
collector. The paste is dried, preferably with heat, so that the
active mass is bonded to the current collector. Suitable anode
active materials and anodes are available commercially from
companies such as Hitachi NEI Inc. (Somerset, N.J.), and Farasis
Energy Inc. (Hayward, Calif.).
[0076] A lithium ion battery as disclosed herein also contains a
porous separator between the anode and cathode. The porous
separator serves to prevent short circuiting between the anode and
the cathode. The porous separator typically consists of a
single-ply or multi-ply sheet of a microporous polymer such as
polyethylene, polypropylene, polyamide or polyimide, or a
combination thereof. The pore size of the porous separator is
sufficiently large to permit transport of ions to provide ionically
conductive contact between the anode and cathode, but small enough
to prevent contact of the anode and cathode either directly or from
particle penetration or dendrites which can from on the anode and
cathode. Examples of porous separators suitable for use herein are
disclosed in U.S. Application SN 12/963,927 (filed 9 Dec. 2010,
U.S. Patent Application Publication No. 2012/0149852, now U.S. Pat.
No. 8,518,525), which is by this reference incorporated in its
entirety as a part hereof for all purposes.
[0077] The housing of the lithium ion battery hereof may be any
suitable container to house the lithium ion battery components
described above. Such a container may be fabricated in the shape of
small or large cylinder, a prismatic case or a pouch.
[0078] The lithium ion battery disclosed herein may be used for
grid storage or as a power source in various electronically-powered
or -assisted devices ("Electronic Device") such as a transportation
device (including a motor vehicle, automobile, truck, bus or
airplane), a computer, a telecommunications device, a camera, a
radio or a power tool.
EXAMPLES
[0079] The subject matter disclosed herein is further defined in
the following examples. It should be understood that these
examples, while indicating preferred embodiments, are given by way
of illustration only, and should not be interpreted to exclude from
the scope of the appended claims, and the equivalents thereof,
subject matter that is not described in these examples.
[0080] The meaning of abbreviations used is as follows: "g" means
gram(s), "mg" means milligram(s), ".mu.g" means microgram(s), "L"
means liter(s), "mL" means milliliter(s), "mol" means mole(s),
"mmol" means millimole(s), "M" means molar concentration, "wt %"
means percent by weight, "mm" means millimeter(s), "ppm" means
parts per million, "h" means hour(s), "min" means minute(s), "A"
means amperes, "mA" mean milliampere(s), "mAh/g" mean milliamperes
hour(s) per gram, "V" means volt(s), "xC" refers to a constant
current which is the product of x and a current in A which is
numerically equal to the nominal capacity of the battery expressed
in Ah, "rpm" means revolutions per minute, "NMR" means nuclear
magnetic resonance spectroscopy, "GC/MS" means gas
chromatography/mass spectrometry.
Materials and Methods
Preparation of 2,2-Difluoroethyl Acetate
[0081] The 2,2-difluoroethyl acetate used in the following Examples
was prepared by reacting potassium acetate with
HCF.sub.2CH.sub.2Br. The following is a typical procedure used for
the preparation.
[0082] Potassium acetate (Aldrich, Milwaukee, Wis., 99%) was dried
at 100.degree. C. under a vacuum of 0.5-1 mm of Hg (66.7-133 Pa)
for 4 to 5 h. The dried material had a water content of less than 5
ppm, as determined by Karl Fischer titration. In a dry box, 212 g
(2.16 mol, 8 mol % excess) of the dried potassium acetate was
placed into a 1.0-L, 3 neck round bottom flask containing a heavy
magnetic stir bar. The flask was removed from the dry box,
transferred into a fume hood, and equipped with a thermocouple
well, a dry-ice condenser, and an additional funnel.
[0083] Sulfolane (500 mL, Aldrich, 99%, 600 ppm of water as
determined by Karl Fischer titration) was melted and added to the 3
neck round bottom flask as a liquid under a flow of nitrogen.
Agitation was started and the temperature of the reaction medium
was brought to about 100.degree. C. HCF.sub.2CH.sub.2Br (290 g, 2
mol, E.I. du Pont de Nemours and Co., 99%) was placed in the
addition funnel and was slowly added to the reaction medium. The
addition was mildly exothermic and the temperature of the reaction
medium rose to 120-130.degree. C. in 15-20 min after the start of
the addition. The addition of HCF.sub.2CH.sub.2Br was kept at a
rate which maintained the internal temperature at 125-135.degree.
C. The addition took about 2-3 h. The reaction medium was agitated
at 120-130.degree. C. for an additional 6 h (typically the
conversion of bromide at this point was about 90-95%). Then, the
reaction medium was cooled down to room temperature and was
agitated overnight. Next morning, heating was resumed for another 8
h.
[0084] At this point the starting bromide was not detectable by NMR
and the crude reaction medium contained 0.2-0.5% of
1,1-difluoroethanol. The dry-ice condenser on the reaction flask
was replaced by a hose adapter with a Teflon.RTM. valve and the
flask was connected to a mechanical vacuum pump through a cold trap
(-78.degree. C., dry-ice/acetone). The reaction product was
transferred into the cold trap at 40-50.degree. C. under a vacuum
of 1-2 mm Hg (133 to 266 Pa). The transfer took about 4-5 h and
resulted in 220-240 g of crude HCF.sub.2CH.sub.2OC(O)CH.sub.3 of
about 98-98.5% purity, which was contaminated by a small amount of
HCF.sub.2CH.sub.2Br (about 0.1-0.2%), HCF.sub.2CH.sub.2OH
(0.2-0.8%), sulfolane (about 0.3-0.5%) and water (600-800 ppm).
Further purification of the crude product was carried out using
spinning band distillation at atmospheric pressure. The fraction
having a boiling point between 106.5-106.7.degree. C. was collected
and the impurity profile was monitored using GC/MS (capillary
column HP5MS, phenyl-methyl siloxane, Agilent19091S-433, 30.m, 250
.mu.m, 0.25 .mu.m; carrier gas--He, flow rate 1 mL/min; temperature
program: 40.degree. C., 4 min, temp. ramp 30.degree. C/min,
230.degree. C., 20 min). Typically, the distillation of 240 g of
crude product gave about 120 g of HCF.sub.2CH.sub.2OC(O)CH.sub.3 of
99.89% purity, (250-300 ppm H.sub.2O) and 80 g of material of
99.91% purity (containing about 280 ppm of water). Water was
removed from the distilled product by treatment with 3A molecular
sieves, until water was not detectable by Karl Fischer titration
(i.e., <1 ppm).
Preparation of LiMn.sub.1.5Ni.sub.0.45Fe.sub.0.05O.sub.4 Cathode
Active Material
[0085] The following is a typical procedure used to prepare
LiMn.sub.1.5Ni.sub.0.45Fe.sub.0.05O.sub.4 cathode active material.
For the preparation, 401 g manganese (II) acetate tetrahydrate
(Aldrich, Milwaukee Wis., Product No. 63537), 125 g nickel (II)
acetate tetrahydrate (Aldrich, Product No. 72225) and 10 g iron
(II) acetate anhydrous (Alfa Aesar, Ward Hill, Mass., Product No.
31140) were weighed into bottles on a balance, then dissolved in
5.0 L of deionized water. KOH pellets were dissolved in 10 L of
deionized water to produce a 3.0 M solution inside a 30 L reactor.
The solution containing the metal acetates was transferred to an
addition funnel and dripped into the rapidly stirred reactor to
precipitate the mixed hydroxide material. Once all 5.0 L of the
metal acetate solution was added to the reactor, stirring was
continued for 1 h. Then, stirring was stopped and the precipitate
was allowed to settle overnight. After settling, the liquid was
removed from the reactor and 15 L of fresh deionized water was
added. The contents of the reactor were stirred, allowed to settle
again, and the liquid was removed. This rinse process was repeated.
Then, the precipitate was transferred to two (split evenly) coarse
glass frit filtration funnels covered with Dacron.RTM. paper. The
solids were rinsed with deionized water until the filtrate pH
reached 6.0 (pH of deionized rinse water), and a further 20 L of
deionized water was added to each filter cake. Finally, the cakes
were dried in a vacuum oven at 120.degree. C. overnight. The yield
at this point was typically 80-90%.
[0086] The hydroxide precipitate was ground and mixed with lithium
carbonate. This step was done in 50 g batches using a Pulverisette
automated mortar and pestle (FRITSCH, Germany). For each batch the
hydroxide precipitate was weighed, then ground alone for 5 min in
the Pulveresette. Then, a stoichiometric amount with small excess
of lithium carbonate was added to the system. For 50 g of hydroxide
precipitate, 10.5 g of lithium carbonate was added. Grinding was
continued for a total of 60 min with stops every 10-15 min to
scrape the material off the surfaces of the mortar and pestle with
a sharp metal spatula. If humidity caused the material to form
clumps, it was sieved through a 40 mesh screen once during
grinding, then again following grinding.
[0087] The ground material was fired in an air box furnace inside
shallow rectangular alumina trays. The trays were 158 mm by 69 mm
in size, and each held about 60 g of material. The firing procedure
consisted of ramping from room temperature to 900.degree. C. in 15
h, holding at 900.degree. C. for 12 h, then cooling to room
temperature in 15 h.
[0088] After firing, the powder was ball-milled to reduce particle
size. Then, 54 g of powder was mixed with 54 g of isopropyl alcohol
and 160 g of 5 mm diameter zirconia beads inside a polyethylene
jar. The jar was then rotated on a pair of rollers for 6 h to mill.
The slurry was separated by centrifugation, and the powder was
dried at 120.degree. C. to remove moisture.
Cathode Preparation
[0089] The following is a typical procedure used to prepare
cathodes. The binder was obtained as a 12% solution of
polyvinylidene fluoride in NMP (N-methylpyrrolidone, KFL No. 1120,
Kureha America Corp. New York, N.Y.). The following materials were
used to make an electrode paste: 4.16 g
LiMn.sub.1.5Ni.sub.0.45Fe.sub.0.05O.sub.4 cathode active powder as
prepared above; 0.52 g carbon black (Denka uncompressed, DENKA
Corp., Japan); 4.32 g PVDF (polyvinylidene difluoride) solution;
and 7.76 g+1.40 g NMP (Sigma Aldrich). The materials were combined
in a ratio of 80:10:10, cathode active powder:PVDF:carbon black, as
described below. The final paste contained 28.6% solids.
[0090] The carbon black, the first portion of NMP, and the PVDF
solution were first combined in a plastic vial and centrifugally
mixed (ARE-310, Thinky USA, Inc., Laguna Hills, Calif.) two times,
for 60 s at 2000 rpm each time. The cathode active powder and the
2.sup.nd portion of NMP were added and the paste was centrifugally
mixed two times (2.times.1 min at 2000 rpm). The vial was placed in
an ice bath and the rotor-stator shaft of a homogenizer (model PT
10-35 GT, 7.5 mm diameter stator, Kinematicia, Bohemia, N.Y.) was
inserted into the vial. The gap between the vial top and the stator
was wrapped with aluminum foil to minimize water ingress into the
vial. The resulting paste was homogenized for two times for 15 min
each at 6500 rpm and then twice more for 15 min at 9500 rpm.
Between each of the four homogenization periods, the homogenizer
was moved to another position in the paste vial.
[0091] The paste was cast using doctor blades with a 0.41-0.51 mm
gate height onto aluminum foil (25 .mu.m thick, 1145-0, Allfoils,
Brooklyn Heights, Ohio) using an automatic coater (AFA-II, MTI
Corp., Richmond, Calif.). The electrodes were dried for 30 min at
95.degree. C. in a mechanical convection oven (model FDL-115,
Binder Inc., Great River, N.Y.). The resulting 51-mm wide cathodes
were placed between 125 .mu.m thick brass sheets and passed through
a calender three times using 100 mm diameter steel rolls at ambient
temperature with nip forces increasing in each of the passes,
starting at 260 kg with the final pass at 770 kg. Loadings of
cathode active material were 9 to 12 mg/cm.sup.2.
Anode Preparation
[0092] The following is a typical procedure used to prepare anodes.
An anode paste was prepared from the following materials: 5.00 g
graphite (CPreme.RTM. G5, Conoco-Philips, Huston, Tex.); 0.2743 g
carbon black (Super
[0093] C65, Timcal, Westlake, Ohio); 3.06 g PVDF (13% in NMP. KFL
#9130, Kureha America Corp.); 11.00 g 1-methyl-2-pyrrolidinone
(NMP); and 0.0097 g oxalic acid. The materials were combined in a
ratio of 88 : 0.17 : 7 : 4.83, graphite:oxalic acid:PVDF:carbon
black, as described below. The final paste contained 29.4%
solids.
[0094] Oxalic acid, carbon black, NMP, and PVDF solution were
combined in a plastic vial. The materials were mixed for 60 s at
2000 rpm using a planetary centrifugal mixer. The mixing was
repeated a second time. The graphite was then added. The resulting
paste was centrifugally mixed two times. The vial was mounted in an
ice bath and homogenized twice using a rotor-stator for 15 min each
time at 6500 rpm and then twice more for 15 min at 9500 rpm. The
point where the stator shaft entered the vial was wrapped with
aluminum foil to minimize water vapor ingress to the vial. Between
each of the four homogenization periods, the homogenizer was moved
to another position in the paste vial. The paste was then
centrifugally mixed three times.
[0095] The paste was cast using a doctor blade with a 230 .mu.m
gate height on to copper foil (CF-LBX-10, Fukuda, Kyoto, Japan)
using the automatic coater. The electrodes were dried for 30 min at
95.degree. C. in the mechanical convection oven. The resulting
51-mm wide anodes were placed between 125 .mu.m thick brass sheets
and passed through a calender three times using 100 mm diameter
steel rolls at ambient temperature with nip forces increasing in
each of the passes, starting at 260 kg with the final pass at 770
kg.
Coin Cells
[0096] Circular anodes 14.3 mm diameter and cathodes 12.7 mm
diameter were punched out from the electrode sheets described
above, placed in a heater in the antechamber of a glove box (Vacuum
Atmospheres, Hawthorne, Calif., with HE-493 purifier), further
dried under vacuum overnight at 90.degree. C., and brought into an
argon-filled glove box. Nonaqueous electrolyte lithium-ion CR2032
coin cells were prepared for electrochemical evaluation. The coin
cell parts (case, spacers, wave spring, gasket, and lid) and coin
cell crimper were obtained from Hohsen Corp (Osaka, Japan). The
separator was a polyimide nanofiber (Energain.RTM., E.I. du Pont de
Nemours and Company, Wilmington, Del.). The nonaqueous electrolytes
used in the preparation of the coin cells are described in the
following Examples.
Examples 1-2 and Comparative Examples 1-4
High Temperature Performance of Coin Cells
[0097] The coin cells were cycled twice for formation using a
commercial battery tester (Series 4000, Maccor, Tulsa, Okla.) at
ambient temperature using constant current charging and discharging
between voltage limits of 3.4-4.9 V at a current of 12 mA per gram
of cathode active material, which is approximately a 0.1 C rate.
The coin cells were placed in an oven at 55.degree. C. and cycled
using constant current charging and discharging between voltage
limits of 3.4-4.9 V at a current of 240 mA per gram of cathode
active material, which is approximately a 2 C rate.
[0098] The results are summarized in the Table, which provides the
solvents and additives used; the coulombic efficiency (CE) measured
in the first cycle of formation, where CE=(discharge
capacity)/(charge capacity); the discharge capacity in the first
cycle at 55.degree. C. per gram of cathode active material; the CE
in the 10th cycle; and the cycle life at 55.degree. C. (which is
the number of cycles completed at 55.degree. C.). The column
labelled "N" indicates the number of cells for each Example or
Comparative Example for which data was averaged to provide the
numerical values in the corresponding row. The cycle life was
measured as the number of cycles required to reduce the discharge
capacity to 80% of the capacity measured in the 2nd cycle of
cycling at 55.degree. C.
[0099] In Example 1, the electrolyte was a mixture of 25.0 wt %
ethylene carbonate (EC), 60.5 wt % 2,2-difluoroethyl acetate
(DFEA), 1.0% maleic anhydride (MA), 1.0% fluoroethylene carbonate
(FEC), 1.0% TEP (triethyl phosphate, obained from Sigma-Aldrich and
distilled), and 11.5 wt % LiPF.sub.6.
[0100] In Example 2, the electrolyte was a mixture of 25.0 wt % EC,
60.5% EMC, 1.0% MA, 1.0% FEC, 1.0%TEP, and 11.5% LiPF.sub.6.
[0101] In Comparative Example 1, the electrolyte was a mixture of
26.5 wt % EC, 62.0% EMC, and 11.5 wt % LiPF.sub.6.
[0102] In Comparative Example 2, the electrolyte was a mixture of
26.5 wt % EC, 62.0% DFEA, and 11.5 wt % LiPF.sub.6.
[0103] In Comparative Example 3, the electrolyte was a mixture of
26.0 wt % EC, 61.5% EMC, 1.0% TEP, and 11.5 wt % LiPF.sub.6.
[0104] In Comparative Example 4, the electrolyte was a mixture of
26.0 wt % EC, 61.5% DFEA, 1.0% TEP, and 11.5 wt % LiPF.sub.6.
[0105] The results shown in the Table demonstrate that the
electrolytes containing a cyclic carboxylic acid anhydride (i.e.,
MA), a cyclic carbonate (i.e. fluoroethylene carbonate) and a
trialkylphosphate (i.e. triethylphosphate), as disclosed herein
(Examples 1 and 2) gave a significantly longer cycle life, and
comparable or better discharge capacity and first and tenth cycle
coulombic efficiency than the electrolyte either containing no
additional additives (Comparative Examples 1 and 2) or a
trialkylphosphate additive alone (Comparative Examples 3 and
4).
TABLE-US-00001 TABLE High Temperature Performance of Coin Cells CE
1st Discharge Cycle Cycle Capacity 1st CE 10th Life Formation cycle
55.degree. C. Cycle 55.degree. C. Example Solvents Additive(s) (%)
(mAh/g) (%) (cycles) N 1 EC/DFEA 1% MA + 79.37 113 98.88 81 2 1%
FEC + 1% TEP 2 EC/EMC 1% MA + 77.02 111 98.18 103 3 1% FEC + 1% TEP
Comp. EC/DFEA none 65.30 104 95.67 16 3 Ex. 1 Comp. EC/EMC none
78.90 115 98.52 51 3 Ex. 2 Comp. EC/DFEA 1% TEP 60.93 99 95.03 12 3
Ex. 3 Comp. EC/EMC 1% TEP 77.40 107 98.04 51 3 Ex. 4
* * * * *