U.S. patent application number 12/888920 was filed with the patent office on 2012-03-29 for heteroaromatic-based electrolytes for lithium and lithium-ion batteries.
This patent application is currently assigned to UCHICAGO ARGONNE, LLC. Invention is credited to Daniel P. ABRAHAM, Gang CHENG.
Application Number | 20120077076 12/888920 |
Document ID | / |
Family ID | 45870983 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120077076 |
Kind Code |
A1 |
CHENG; Gang ; et
al. |
March 29, 2012 |
HETEROAROMATIC-BASED ELECTROLYTES FOR LITHIUM AND LITHIUM-ION
BATTERIES
Abstract
The present invention provides an electrolyte for lithium and/or
lithium-ion batteries comprising a lithium salt in a liquid carrier
comprising heteroaromatic compound including a five-membered or
six-membered heteroaromatic ring moiety comprising carbon atoms and
at least one heteroatom forming a neutral aromatic ring, the at
least one heteroatom being selected from a Group V element
(preferably N) and a Group VI element (preferably O or S), the
heteroaromatic ring moiety bearing least one carboxylic ester or
carboxylic anhydride substituent bound to at least one carbon atom
of the heteroaromatic ring. Preferred heteroaromatic ring moieties
include pyridine compounds, pyrazine compounds, pyrrole compounds,
furan compounds, and thiophene compounds.
Inventors: |
CHENG; Gang; (Naperville,
IL) ; ABRAHAM; Daniel P.; (Bolingbrook, IL) |
Assignee: |
UCHICAGO ARGONNE, LLC
Chicago
IL
|
Family ID: |
45870983 |
Appl. No.: |
12/888920 |
Filed: |
September 23, 2010 |
Current U.S.
Class: |
429/156 ;
429/327; 429/336; 429/337 |
Current CPC
Class: |
H01M 10/0569 20130101;
H01M 10/0567 20130101; H01M 2300/0028 20130101; H01M 10/052
20130101; H01M 10/0568 20130101; H01M 10/0525 20130101; Y02E 60/10
20130101 |
Class at
Publication: |
429/156 ;
429/336; 429/327; 429/337 |
International
Class: |
H01M 6/42 20060101
H01M006/42; H01M 6/16 20060101 H01M006/16 |
Goverment Interests
CONTRACTUAL ORIGIN OF THE INVENTION
[0001] The United States Government has rights in this invention
pursuant to Contract No. DE-AC02-06CH11357 between the United
States Government and UChicago Argonne, LLC representing Argonne
National Laboratory.
Claims
1. An electrolyte composition suitable for use in a lithium
battery, a lithium-ion battery, or both; the electrolyte
composition comprising a lithium salt in a liquid carrier
comprising a heteroaromatic compound including a five-membered or
six-membered heteroaromatic ring moiety comprising carbon atoms and
at least one heteroatom forming a neutral aromatic ring, the at
least one heteroatom being selected from a Group V element and a
Group VI element, the heteroaromatic ring moiety bearing least one
carboxylic ester or carboxylic anhydride substituent bound to at
least one carbon atom of the heteroaromatic ring.
2. The electrolyte composition of claim 1 wherein the lithium salt
comprises LiPF.sub.6, LiBF.sub.4, LiF.sub.2BC.sub.2O.sub.4,
LiB(C.sub.2O.sub.4).sub.2, LiClO.sub.4, LiAsF.sub.6,
LiN(SO.sub.2CF.sub.3).sub.2, LiC(SO.sub.2CF.sub.3).sub.3,
LiSO.sub.3CF.sub.3, LiPF.sub.3(CF.sub.2CF.sub.3).sub.3, or any
combination of two or more thereof.
3. The electrolyte composition of claim 1 wherein the lithium salt
is present at a concentration in the range of about 0.1 to about 5
M.
4. The electrolyte composition of claim 1 wherein the lithium salt
is present at a concentration in the range of about 1 to about 1.5
M.
5. The electrolyte composition of claim 1 wherein the liquid
carrier also comprises at least one additional organic solvent.
6. The electrolyte composition of claim 1 wherein the liquid
carrier also comprises at least one organic carbonate solvent
selected from the group consisting of ethylene carbonate, propylene
carbonate, dimethylcarbonate, and ethylmethylcarbonate.
7. The electrolyte composition of claim 1 wherein the
heteroaromatic compound is a material represented by the general
Formula (I): ##STR00007## wherein: each of the X atoms, X.sup.1,
X.sup.2, X.sup.3, X.sup.4, X.sup.5, and X.sup.6, independently is C
or a heteroatom selected from a Group V element and a Group VI
element, at least two of the X atoms are C atoms, and at least one
of the X atoms is a heteroatom, with the provisos that: (a) the R
substituent, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and
R.sup.6, on a C atom independently is selected from the group
consisting of H, alkyl, alkenyl, alkynyl, aryl, arylalkyl,
fluoroalkyl, fluoroalkenyl, fluoroalkynyl, fluoroaryl,
fluoroarylalkyl, a carboxylic anhydride, and a carboxylic ester
selected from the group consisting of an alkyl ester, an alkenyl
ester, an alkynyl ester, an aryl ester, an arylalkyl ester, a
fluoroalkyl ester, a fluoroalkenyl ester, a fluoroalkynyl ester, a
fluoroaryl ester, and a fluoroarylalkyl ester; (b) any R
substituent on a heteroatom independently is absent or is selected
from the group consisting H, alkyl, alkenyl, alkynyl, aryl,
arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl, fluoroaryl,
and fluoroarylalkyl; (c) the combination of X atoms and R
substituents forms a neutral aromatic ring; and (d) optionally, R
substituents on two adjacent C atoms together form a cyclic
carboxylic anhydride group; at least one R substituent on a C atom
is selected from a carboxylic ester and a carboxylic anhydride; and
n is 0 or 1; with the provisos that (i) when n is 1, then the
heteroatom is a Group V element, and (ii) when n is 0, then X.sup.1
and X.sup.5 are joined by a covalent bond.
8. The electrolyte composition of claim 7 wherein the at least one
heteroatom is selected from the group consisting of N, O, and
S.
9. The electrolyte of claim 7 wherein one or two R substituents on
a C atom of the compound of Formula (I) is selected from a
carboxylic ester and a carboxylic anhydride, or two adjacent R
substituents on C atoms together form a cyclic anhydride; the
remainder of the R substituents on carbon atoms are H, and each R
substituent on a heteroatom is either absent, or selected from H
and C.sub.1 to C.sub.4 alkyl.
10. The electrolyte of claim 9 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
11. The electrolyte of claim 1 wherein the heteroaromatic compound
comprises a pyridine moiety, and is represented by general Formula
(II): ##STR00008## wherein: m is 1, 2, 3, 4, or 5; each R.sup.7 is
attached to a carbon atom of the pyridine moiety and independently
is selected from the group consisting of alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, fluoroarylalkyl, a carboxylic anhydride, and a
carboxylic ester selected from the group consisting of an alkyl
ester, an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.7 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and the compound
bears at least one R.sup.7 substituent selected from a carboxylic
anhydride and a carboxylic ester.
12. The electrolyte of claim 11 wherein m is 1 or 2 and each
R.sup.7 substituent is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.7 substituents together
form a cyclic anhydride.
13. The electrolyte of claim 12 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
14. The electrolyte of claim 1 wherein the heteroaromatic compound
comprises a pyrazine moiety, and is represented by general Formula
(III): ##STR00009## wherein p is 1, 2, 3, or 4; each R.sup.8 is
attached to a carbon atom of the pyrazine moiety and independently
is selected from the group consisting of alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, fluoroarylalkyl, a carboxylic anhydride, and a
carboxylic ester selected from the group consisting of an alkyl
ester, an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.8 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and the compound
bears at least one R.sup.8 substituent selected from a carboxylic
anhydride and a carboxylic ester.
15. The electrolyte of claim 14 wherein p is 1 or 2 and each
R.sup.8 substituent is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.8 substituents together
form a cyclic anhydride.
16. The electrolyte of claim 15 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
17. The electrolyte of claim 1 wherein the heteroaromatic compound
comprises a pyrrole moiety, and is represented by general Formula
(IV): ##STR00010## wherein x is 1, 2, 3, or 4; each R.sup.9 is
attached to a carbon atom of the pyrrole moiety and independently
is selected from the group consisting of alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, fluoroarylalkyl, a carboxylic anhydride, and a
carboxylic ester selected from the group consisting of an alkyl
ester, an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.9 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; R.sup.10 is
selected from the group consisting of H, alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, and fluoroarylalkyl; and the compound bears at least
one R.sup.9 substituent selected from a carboxylic anhydride and a
carboxylic ester.
18. The electrolyte of claim 17 wherein x is 1 or 2 and each
R.sup.9 substituent is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.9 substituents together
form a cyclic anhydride; and R.sup.10 is selected from H and
C.sub.1 to C.sub.4 alkyl.
19. The electrolyte of claim 18 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
20. The electrolyte of claim 1 wherein the heteroaromatic compound
comprises a furan moiety, and is represented by general Formula
(V): ##STR00011## wherein y is 1, 2, 3, or 4; each R.sup.11 is
attached to a carbon atom of the furan moiety and independently is
selected from the group consisting of alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, fluoroarylalkyl, a carboxylic anhydride, and a
carboxylic ester selected from the group consisting of an alkyl
ester, an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.11 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and the compound
bears at least one R.sup.11 substituent selected from a carboxylic
anhydride and a carboxylic ester.
21. The electrolyte of claim 20 wherein y is 1 or 2 and each
R.sup.11 substituent is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.11 substituents
together form a cyclic anhydride.
22. The electrolyte of claim 21 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
23. The electrolyte of claim 1 wherein the heteroaromatic compound
comprises a thiophene moiety, and is represented by general Formula
(VI): ##STR00012## wherein z is 1, 2, 3, or 4; each R.sup.12 is
attached to a carbon atom of the thiophene moiety and independently
is selected from the group consisting of alkyl, alkenyl, alkynyl,
aryl, arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl,
fluoroaryl, fluoroarylalkyl, a carboxylic anhydride, and a
carboxylic ester selected from the group consisting of an alkyl
ester, an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.12 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and the compound
bears at least one R.sup.12 substituent selected from a carboxylic
anhydride and a carboxylic ester.
24. The electrolyte of claim 23 wherein z is 1 or 2 and each
R.sup.12 substituent is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.12 substituents
together form a cyclic anhydride.
25. The electrolyte of claim 24 wherein the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl carboxylic ester.
26. An electrochemical cell comprising an anode, a cathode, and an
electrolyte of claim 1 in contact with the anode and the
cathode.
27. A battery comprising a plurality of electrochemical cells of
claim 26 arranged in series, in parallel, or both.
28. An electrochemical cell comprising an anode, a cathode, and an
electrolyte of claim 7 in contact with the anode and the
cathode.
29. A battery comprising a plurality of electrochemical cells of
claim 28 arranged in series, in parallel, or both.
Description
FIELD OF THE INVENTION
[0002] This invention relates to electrolytes for lithium and
lithium-ion batteries. More specifically this invention relates to
electrolytes comprising a heteroaromatic compound bearing a
carboxylic ester or carboxylic anhydride substituent on the
heteroaromatic moiety of the compound, which are useful in lithium
and lithium-ion batteries.
BACKGROUND OF THE INVENTION
[0003] Recent advances in cathode and anode materials have
refocused attention on electrolytes as the technological bottleneck
limiting the operation and performance of lithium-battery systems.
Attributes such as cell potential and energy density are related to
the intrinsic property of the positive and negative electrode
materials, while cell power density, calendar-life and safety are
dictated by the nature and stability of the electrolyte and the
electrode-electrolyte interfaces. A wide electrochemical window,
wide temperature stability range, non-reactivity with the other
cell components, non-toxicity, low cost, and a lithium-ion
transference number approaching unity are, in general, desirable
characteristics for lithium battery electrolytes. In addition, the
electrolyte should have excellent ionic conductivity to enable
rapid ion transport between the electrodes, and be an electronic
insulator to minimize self-discharge and prevent short-circuits
within the cell. Various carbonate solvents such as
dimethylcarbonate (DMC), ethylmethylcarbonate (EMC), ethylene
carbonate (EC), propylene carbonate (PC), and mixtures of two or
more of such carbonates, have been utilized as a solvent for
lithium salts in lithium batteries and lithium-ion batteries.
Research on electrolytes and on functional electrolyte additives to
improve cell life, thermal abuse behavior and low-temperature
(e.g., <0.degree. C.) performance of lithium-ion cells is
ongoing. Consequently, there is a need for new electrolyte solvents
for use in lithium and lithium ion batteries. The compositions of
the present invention address this need.
SUMMARY OF THE INVENTION
[0004] The present invention provides an electrolyte composition
for lithium and/or lithium-ion batteries comprising a lithium salt
in a liquid carrier comprising heteroaromatic compound including a
five-membered or six-membered heteroaromatic ring moiety comprising
carbon atoms and at least one heteroatom forming a neutral aromatic
ring, the at least one heteroatom being selected from a Group V
element (preferably N) and a Group VI element (preferably O or S),
the heteroaromatic ring moiety bearing at least one carboxylic
ester or carboxylic anhydride substituent bound to at least one
carbon atom of the heteroaromatic ring. Preferred heteroaromatic
ring moieties include pyridine compounds, pyrazine compounds,
pyrrole compounds, furan compounds, and thiophene compounds.
[0005] Preferred carboxylic ester substituents include methyl,
ethyl propyl, isopropyl, and butyl esters. Suitable anhydride
substituents include internal anhydrides in which the two carbonyl
groups of the anhydride are bound to adjacent carbon atoms of the
heteroaromatic moiety, or mixed anhydrides in which one carbonyl of
the anhydride is bound to the heteroaromatic moiety and the other
carbonyl is bound to an alkyl group such as a methyl, ethyl,
propyl, or butyl group, an alkenyl group, an alkynyl group, an
aromatic hydrocarbon group, or a fluorinated derivative
thereof.
[0006] The composition can include one heteroaromatic compound or
more than one. The heteroaromatic compound can be the exclusive
organic solvent component of the electrolyte, or can be included in
any proportion with one or more other solvent suitable for use in
lithium and/or lithium-ion batteries, such as ethylene carbonate,
propylene carbonate, and the like. Preferred heteroaromatic
compounds for use in the electrolyte compositions of the present
invention are liquids at ambient room temperature, and are stable
over a wide temperature range that may be encountered in lithium
and lithium-ion batteries (e.g., -30 to +50.degree. C.). The
preferred heteroaromatic components typically have a wide range of
electrochemical stability (e.g., 0 V to 5V), and exhibit excellent
ionic conductivity. Many of the heteroaromatic components also are
low cost, have relatively low toxicity, and relatively low
flammability compared to many conventional electrolyte
solvents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 provides non-limiting examples of heteroaromatic
compounds useful in the electrolyte compositions of the present
invention.
[0008] FIG. 2 provides non-limiting examples of heteroaromatic
compounds useful in the electrolyte compositions of the present
invention.
[0009] FIG. 3 provides non-limiting examples of heteroaromatic
compounds useful in the electrolyte compositions of the present
invention.
[0010] FIG. 4 provides non-limiting examples of heteroaromatic
compounds useful in the electrolyte compositions of the present
invention.
[0011] FIG. 5 provides non-limiting examples of heteroaromatic
compounds useful in the electrolyte compositions of the present
invention.
[0012] FIG. 6 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of either methyl picolinate or ethyl
picolinate, compared to a control electrolyte without any
heteroaromatic compound present.
[0013] FIG. 7 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 3 wt % of either methyl picolinate or ethyl
picolinate, compared to a control electrolyte without any
heteroaromatic compound present.
[0014] FIG. 8 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of various pyridine heteroaromatic
compounds, compared to a control electrolyte without any
heteroaromatic compound present.
[0015] FIG. 9 is a plot of dQ/dV over a voltage range of about 1.8
to about 4.2 volts for cells utilizing electrolytes of the
invention containing about 0.3 wt % of various pyridine
heteroaromatic compounds, compared to a control electrolyte without
any heteroaromatic compound present.
[0016] FIG. 10 is a plot of AC impedance data for electrochemical
cells utilizing an electrolyte of the invention including about 0.3
wt % of various pyridine heteroaromatic compounds, compared to a
control electrolyte without any heteroaromatic compound
present.
[0017] FIG. 11 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of methyl picolinate in which the
formation cycle was conducted at either 30.degree. C. or 55.degree.
C., compared to a control electrolyte without any heteroaromatic
compound present.
[0018] FIG. 12 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.1 to about 1 wt % of methyl isonicotinate,
compared to a control electrolyte without any heteroaromatic
compound present.
[0019] FIG. 13 is a plot of AC impedance data for electrochemical
cells utilizing an electrolyte of the invention comprising about
0.1 to about 1 wt % of methyl isonicotinate, compared to a control
electrolyte without any heteroaromatic compound present.
[0020] FIG. 14 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of methyl isonicotinate, compared to a
control electrolyte without any heteroaromatic compound present,
over 250 cycles.
[0021] FIG. 15 is a plot of AC impedance data for electrochemical
cells utilizing an electrolyte of the invention comprising about
0.3 wt % of methyl isonicotinate, compared to a control electrolyte
without any heteroaromatic compound present, over 50, 100, and 200
cycles.
[0022] FIG. 16 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of various pyridine, pyrazine, and
pyrrole heteroaromatic compounds, compared to a control electrolyte
without any heteroaromatic compound present.
[0023] FIG. 17 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of various pyridine and pyrazine
heteroaromatic compounds, compared to a control electrolyte without
any heteroaromatic compound present, over 100 cycles.
[0024] FIG. 18 is a plot of capacity versus cycle number for
electrochemical cells utilizing an electrolyte of the invention
comprising about 0.3 wt % of various furan and thiophene
heteroaromatic compounds, compared to a control electrolyte without
any heteroaromatic compound present.
[0025] FIG. 19 is a plot of dQ/dV over a voltage range of about 1.8
to about 4.2 volts for electrolytes of the invention containing
about 0.3 wt % of various furan and thiophene heteroaromatic
compounds, compared to a control electrolyte without any
heteroaromatic compound present.
[0026] FIG. 20 is a plot of AC impedance data for electrochemical
cells utilizing an electrolyte of the invention comprising about
0.3 wt % of various furan and thiophene heterocyclic compounds,
compared to a control electrolyte without any heteroaromatic
compound present.
[0027] FIG. 21 is a plot of voltage versus capacity for a graphite
electrode in an electrolyte of the invention containing 1.2 M
LiPF.sub.6 in a 1:8 (w/w) mixture of ethyl picolinate and DMC.
[0028] FIG. 22 is a plot of dQ/dV over a voltage range of about 0.2
to about 1.7 volts for a graphite electrode in an electrolyte an
electrolyte of the invention containing 1.2 M LiPF.sub.6 in a 1:8
(w/w) mixture of ethyl picolinate and DMC, showing solid
electrolyte interphase (SEI) formation.
[0029] FIG. 23 is a plot of dQ/dV over a voltage range of about 0
to about 0.3 volts for a graphite electrode in an electrolyte of
the invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
ethyl picolinate and DMC, showing lithiation and delithiation.
[0030] FIG. 24 is a plot of voltage versus capacity over three
charge/discharge cycles for an oxide electrode in an electrolyte of
the invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
ethyl picolinate and DMC, over three charge/discharge cycles.
[0031] FIG. 25 is a plot of dQ/dV over a voltage range of about 2
to about 4.4 volts for an oxide electrode in an electrolyte of the
invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
ethyl picolinate and DMC, over three charge/discharge cycles.
[0032] FIG. 26 is a plot of voltage versus capacity for a
graphite/oxide cell utilizing an electrolyte of the invention
containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of ethyl
picolinate and DMC, over 20 charge/discharge cycles.
[0033] FIG. 27 is a plot of voltage versus capacity for a graphite
electrode in an electrolyte of the invention containing 1.2 M
LiPF.sub.6 in a 1:8 (w/w) mixture of 3-ethyl furoate and DMC.
[0034] FIG. 28 is a plot of dQ/dV over a voltage range of about 0.2
to about 1.7 volts for a graphite electrode in an electrolyte of
the invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
3-ethyl furoate and DMC, showing SEI formation.
[0035] FIG. 29 is a plot of dQ/dV over a voltage range of about 0
to about 0.3 volts for a graphite electrode in an electrolyte of
the invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
3-ethyl furoate and DMC, showing lithiation and delithiation.
[0036] FIG. 30 is a plot of voltage versus capacity for an oxide
electrode in an electrolyte of the invention containing 1.2 M
LiPF.sub.6 in a 1:8 (w/w) mixture of 3-ethyl furoate and DMC, over
10 charge/discharge cycles.
[0037] FIG. 31 is a plot of dQ/dV over a voltage range of about 3
to about 4.3 volts for an oxide electrode in an electrolyte of the
invention containing 1.2 M LiPF.sub.6 in a 1:8 (w/w) mixture of
3-ethyl furoate and DMC, over 10 charge/discharge cycles.
[0038] FIG. 32 depicts a schematic representation of an
electrochemical cell.
[0039] FIG. 33 depicts a schematic representation of a battery
consisting of a plurality of cells connected electrically in series
and in parallel.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0040] The present invention provides novel electrolyte
compositions for use in lithium and lithium ion batteries. The
compositions comprise a lithium salt in a liquid carrier containing
a heteroaromatic compound bearing a carboxylic acid or carboxylic
anhydride substituent.
[0041] The heteroaromatic component of the electrolytes of the
present invention comprises a five-membered or six-membered
heteroaromatic ring moiety comprising carbon atoms and at least one
heteroatom forming a neutral aromatic ring, the at least one
heteroatom being selected from a Group V element and a Group VI
element, the heteroaromatic ring moiety bearing least one
carboxylic ester or carboxylic anhydride substituent bound to at
least one carbon atom of the heteroaromatic ring. Preferred
heteroatoms include, without limitation, N, O, and S. In some
preferred embodiments, the heteroaromatic component can be a
5-membered or 6-membered ring heteroaromatic compound of the
general Formula (I):
##STR00001##
[0042] wherein:
[0043] each of the X atoms, X.sup.1, X.sup.2, X.sup.3, X.sup.4,
X.sup.5, and X.sup.6, independently is C or a heteroatom selected
from a Group V element (preferably N) and a Group VI element
(preferably O or S), at least two of the X atoms are C atoms, and
at least one of the X atoms is a heteroatom, with the provisos
that: (a) the R substituent, R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5, and R.sup.6, on a C atom independently is selected from
the group consisting of H, alkyl (preferably C.sub.1 to C.sub.4
alkyl), alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl,
fluoroalkenyl, fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a
carboxylic anhydride, and a carboxylic ester selected from the
group consisting of an alkyl ester (preferably C.sub.1 to C.sub.4
alkyl), an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; (b) any R substituent on a heteroatom independently is
absent or is selected from the group consisting H, alkyl
(preferably C.sub.1 to C.sub.4 alkyl), alkenyl, alkynyl, aryl,
arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl, fluoroaryl,
and fluoroarylalkyl; (c) the combination of X atoms and R
substituents forms a neutral aromatic ring; and (d) optionally, R
substituents on two adjacent C atoms together form a cyclic
carboxylic anhydride group;
[0044] at least one R substituent on a C atom is selected from a
carboxylic ester and a carboxylic anhydride; and
[0045] n is 0 or 1; with the provisos that (i) when n is 1, then
the heteroatom is a Group V element, and (ii) when n is 0, then
X.sup.1 and X.sup.5 are joined by a covalent bond.
[0046] In a preferred embodiment, one or two R substituents on a C
atom of the compound of Formula (I) is selected from a carboxylic
ester and a carboxylic anhydride, or two adjacent R substituents on
C atoms together form a cyclic anhydride, the remainder of the R
substituents on carbon atoms are H, and R substituents on
heteroatoms are either absent, or are selected from H, and C.sub.1
to C.sub.4 alkyl.
[0047] Non-limiting examples of some heteroaromatic compounds of
Formula (I) include pyridine, pyrazine, triazine, pyrrole, furan,
and thiophene compounds. Non-limiting examples of some preferred
heteroaromatic compounds are set forth in general Formulas (II),
(III), (IV), (V), and (VI). Non-limiting examples of some specific
heteroaromatic compounds useful in the electrolytes of the present
invention are shown in FIGS. 1 to 5, including specific compounds
of Formulas (I), (II), (III), (IV), (V), and (VI).
[0048] Some preferred heteroaromatic compounds comprising a
pyridine heteroaromatic moiety are represented by general Formula
(II):
##STR00002##
[0049] wherein:
[0050] m is 1, 2, 3, 4, or 5; each R.sup.7 is attached to a carbon
atom of the pyridine moiety and independently is selected from the
group consisting of alkyl (preferably C.sub.1 to C.sub.4 alkyl),
alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl, fluoroalkenyl,
fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a carboxylic anhydride,
and a carboxylic ester selected from the group consisting of an
alkyl ester (preferably C.sub.1 to C.sub.4 alkyl), an alkenyl
ester, an alkynyl ester, an aryl ester, an arylalkyl ester, a
fluoroalkyl ester, a fluoroalkenyl ester, a fluoroalkynyl ester, a
fluoroaryl ester, and a fluoroarylalkyl ester; optionally R.sup.7
substituents on two adjacent C atoms together form a cyclic
carboxylic anhydride group; and the compound bears at least one
R.sup.7 substituent selected from carboxylic anhydride and a
carboxylic ester. In a preferred embodiment, m is 1, 2 or 3, and
each R.sup.7 substituent of the compound of Formula (II) is
selected from a carboxylic ester and a carboxylic anhydride, or two
adjacent R.sup.7 substituents together form a cyclic anhydride.
Preferably, the carboxylic ester is a C.sub.1 to C.sub.4 alkyl
ester.
[0051] Some preferred heteroaromatic compounds comprising a
pyrazine heteroaromatic moiety are represented by general Formula
(III):
##STR00003##
[0052] wherein p is 1, 2, 3, or 4; each R.sup.8 is attached to a
carbon atom of the pyrazine moiety and independently is selected
from the group consisting of alkyl (preferably C.sub.1 to C.sub.4
alkyl), alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl,
fluoroalkenyl, fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a
carboxylic anhydride, and a carboxylic ester selected from the
group consisting of an alkyl ester (preferably C.sub.1 to C.sub.4
alkyl), an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.8 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and
[0053] the compound bears at least one R.sup.8 substituent selected
from a carboxylic anhydride and a carboxylic ester. In a preferred
embodiment, p is 1 or 2, and each R.sup.8 substituent of the
compound of Formula (III) is selected from a carboxylic ester and a
carboxylic anhydride, or two adjacent R.sup.8 substituents together
form a cyclic anhydride. Preferably, the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl ester.
[0054] Preferred heteroaromatic compounds comprising a pyrrole
heteroaromatic moiety are represented by general Formula (IV):
##STR00004##
[0055] wherein x is 1, 2, 3, or 4; each R.sup.9 is attached to a
carbon atom of the pyrrole moiety and independently is selected
from the group consisting of alkyl (preferably C.sub.1 to C.sub.4
alkyl), alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl,
fluoroalkenyl, fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a
carboxylic anhydride, and a carboxylic ester selected from the
group consisting of an alkyl ester (preferably C.sub.1 to C.sub.4
alkyl), an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.9 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group;
[0056] R.sup.10 is selected from the group consisting of H, alkyl
(preferably C.sub.1 to C.sub.4 alkyl), alkenyl, alkynyl, aryl,
arylalkyl, fluoroalkyl, fluoroalkenyl, fluoroalkynyl, fluoroaryl,
and fluoroarylalkyl; and
[0057] and the compound bears at least one R.sup.9 substituent
selected from a carboxylic anhydride and a carboxylic ester. In a
preferred embodiment, x is 1 or 2, and each R.sup.9 substituent of
the compound of Formula (IV) is selected from a carboxylic ester
and a carboxylic anhydride, or two adjacent R.sup.9 substituents
together form a cyclic anhydride, and R.sup.10 is either H or
C.sub.1 to C.sub.4 alkyl. Preferably, the carboxylic ester is a
C.sub.1 to C.sub.4 alkyl ester.
[0058] Some preferred heteroaromatic compounds comprising a furan
heteroaromatic moiety are represented by general Formula (V):
##STR00005##
[0059] wherein y is 1, 2, 3, or 4; each R.sup.11 is attached to a
carbon atom of the furan moiety and independently is selected from
the group consisting of alkyl (preferably C.sub.1 to C.sub.4
alkyl), alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl,
fluoroalkenyl, fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a
carboxylic anhydride, and a carboxylic ester selected from the
group consisting of an alkyl ester (preferably C.sub.1 to C.sub.4
alkyl), an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.11 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and the compound
bears at least one R.sup.11 substituent selected from a carboxylic
anhydride and a carboxylic ester. In a preferred embodiment, y is 1
or 2, and each R.sup.11 substituent of the compound of Formula (V)
is selected from a carboxylic ester and a carboxylic anhydride, or
two adjacent R.sup.8 substituents together form a cyclic anhydride.
Preferably, the carboxylic ester is a C.sub.1 to C.sub.4 alkyl
ester.
[0060] Some preferred heteroaromatic compounds comprising a
thiophene moiety heteroaromatic are represented by general Formula
(VI):
##STR00006##
[0061] wherein z is 1, 2, 3, or 4; each R.sup.12 is attached to a
carbon atom of the thiophene moiety and independently is selected
from the group consisting of alkyl (preferably C.sub.1 to C.sub.4
alkyl), alkenyl, alkynyl, aryl, arylalkyl, fluoroalkyl,
fluoroalkenyl, fluoroalkynyl, fluoroaryl, fluoroarylalkyl, a
carboxylic anhydride, and a carboxylic ester selected from the
group consisting of an alkyl ester (preferably C.sub.1 to C.sub.4
alkyl), an alkenyl ester, an alkynyl ester, an aryl ester, an
arylalkyl ester, a fluoroalkyl ester, a fluoroalkenyl ester, a
fluoroalkynyl ester, a fluoroaryl ester, and a fluoroarylalkyl
ester; optionally R.sup.12 substituents on two adjacent C atoms
together form a cyclic carboxylic anhydride group; and
[0062] the compound bears at least one R.sup.12 substituent
selected from a carboxylic ester and a carboxylic anhydride. In a
preferred embodiment, z is 1 or 2, and each R.sup.12 substituent of
the compound of Formula (VI) is selected from a carboxylic ester
and a carboxylic anhydride, or two adjacent R.sup.12 substituents
together form a cyclic anhydride. Preferably, the carboxylic ester
is a C.sub.1 to C.sub.4 alkyl ester.
[0063] As used herein, the term "alkyl" refers to a saturated
hydrocarbon group, preferably comprising 1 to about 22 carbon atoms
(more preferably 1 to 4 carbon atoms), which can be in a linear
chain or branched. The term "alkenyl", as used herein refers to
hydrocarbon group, preferably comprising 2 to about 22 carbon atoms
(more preferably 2 to 4 carbon atoms), which can be in a linear
chain or branched, and which includes at least one carbon-carbon
double bond. The term "alkynyl", as used herein refers to
hydrocarbon group, preferably comprising 2 to about 22 carbon atoms
(more preferably 2 to 4 carbon atoms), which can be in a linear
chain or branched, and which includes at least one carbon-carbon
triple bond. As used herein, the term "aryl" refers to an aromatic
hydrocarbon group, preferably comprising a phenyl or naphthyl
group, which optionally can be substituted with one or more alkyl
groups. The term "arylalkyl", as used herein, refers to an alkyl
group substituted with an aryl group. The prefix "fluoro" as
applied to an alkyl, alkenynl, alkynyl, aryl, or alkylaryl group,
indicates that one or more hydrogen atoms of the specified group is
replace by a fluorine atom.
[0064] Non-limiting, specific examples of nitrogen heteroaromatic
compounds useful in the electrolytes and electrochemical cells of
the present invention are illustrated in FIG. 1: methyl picolinate
(MP), ethyl picolinate (EP), ethyl nicotinate (EN), methyl
isonicotinate (MIN), 3,4-diethyl pyridinecarboxylate (3,4-DEPC),
3,4-diethyl pyridinecarboxylic anhydride (3,4-PyDCA),
2,3-pyridinecarboxylic anhydride (2,3-PyDCA),
2,3-pyrazinecarboxylic anhydride (2,3-PzDCA),
methyl-2-pyrazinecarboxylate (2-MPzC), and
methyl-1-methylpyrrole-2-carboxylate (MMPC). FIG. 2 illustrates
some furan and thiophene heteroaromatic compounds of use in the
electrolytes and electrochemical cells of the invention: 2-ethyl
furoate (2-EF), 3-ethyl furoate (3EF), and 2-ethyl
thiophenecarboxylate (2-ETC). Various pyridine heteroaromatic
compounds of use in the electrolytes and electrochemical cells of
the invention are shown generically in FIG. 3. FIG. 4 generically
illustrates various pyrazine and pyrrole heteroaromatic compounds
of use in the electrolytes and electrochemical cells of the
invention. FIG. 5 generically illustrates various nitrogen, sulfur,
oxygen, and phosphorus heteroaromatic compounds of use in the
electrolytes and electrochemical cells of the invention.
[0065] Lithium salts suitable for use in the present invention
include any lithium salt or combination of salts that can be used
in a lithium or lithium ion battery cell. Non-limiting examples of
some suitable lithium salts include LiPF.sub.6, LiBF.sub.4,
LiF.sub.2BC.sub.2O.sub.4, LiB(C.sub.2O.sub.4).sub.2, LiClO.sub.4,
LiAsF.sub.6, LiN(SO.sub.2CF.sub.3).sub.2,
LiC(SO.sub.2CF.sub.3).sub.3, LiSO.sub.3CF.sub.3, and
LiPF.sub.3(CF.sub.2CF.sub.3).sub.3. The concentration of lithium
salt in the electrolyte composition can be any concentration
suitable for used as an electrolyte in a lithium or lithium ion
cell. Preferably, the concentration of lithium salt in the carrier
is in the range of about 0.1 molar (M) to about 5 molar, more
preferably about 1M to about 1.5 M (e.g., about 1.2 M).
[0066] In addition to the heteroaromatic compound, the liquid
carrier can include one or more other solvents suitable for use in
lithium and lithium ion cell electrolyte compositions. Non-limiting
examples of such addition solvents include ethylene carbonate,
propylene carbonate, dimethylcarbonate, and ethylmethylcarbonate,
as well as combinations of two or more such carbonates.
Non-limiting examples of other solvents that have been utilized in
lithium ion batteries, and which can be incorporated in the
electrolytes of the present invention, include esters (e.g.,
gamma-butyrolactone, methyl formate, methyl acetate), ethers (e.g.,
diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxane), nitriles (e.g., acetonitrile), sulfolanes, and the
like. In some preferred embodiments, the liquid carrier comprises
the heteroaromatic compound and at least one additional organic
solvent, preferably an organic carbonate solvent, wherein the
weight ratio of heteroaromatic compound-to-the at least one
additional solvent is in the range of about 1:100 to about 100:1.
In other preferred embodiments, the liquid carrier comprises the
heteroaromatic compound and at least additional solvent wherein the
weight ratio of heteroaromatic compound-to-the at least one
additional solvent is in the range of about 1:10 to about 10:1.
[0067] The electrolyte compositions of the present invention are
particularly useful in an electrochemical cell in combination with
an anode and a cathode. Any anode or cathode suitable for use in
lithium and/or lithium ion electrochemical cells can be utilized in
the cells of the present invention. A preferred anode comprises
carbon (e.g., graphite particles, carbon nanoparticles, carbon
nanotubes, or a combination thereof), a metal oxide compound, or a
combination thereof. A preferred cathode comprises lithium or a
lithium compound (e.g., a lithium-bearing layered oxide compound
such as LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2). A battery of
the present invention comprises a plurality of such electrochemical
cells arranged in series, in parallel, or both. Typically, the
anode and cathode compartments of the cells are separated by an
electrolyte-permeable membrane, as is well known in the art. The
cathodes and anodes also typically include metallic current
collectors (e.g., aluminum and copper) on which the cathode and
anode active components are coated, also as is well known in the
art. The electrolyte can include one or more other organic solvents
suitable for use in a lithium or lithium ion electrochemical
cell.
[0068] The following non-limiting examples are provided to better
illustrate certain aspects of the present invention.
Example 1
[0069] An electrolyte composition designated as Gen2 was prepared,
comprising 1.2 M LiPF.sub.6 in a 3:7 (w/w) mixture of ethylene
carbonate (EC) and ethyl methyl carbonate (EMC) Electrolytes of the
invention were prepared by adding about 0.3 wt % of either methyl
picolinate (MP) or ethyl picolinate (EP) to the Gen2 electrolyte.
The electrolytes were then evaluated in an electrochemical cell
including a cathode comprising a 35 micron thick coating of
Li.sub.0.08Co.sub.0.15Al.sub.0.05O.sub.2 on an aluminum collector
plate, an anode comprising a 35 micron thick coating of 5 micron
graphite particles on a copper collector plate, and a 25 micron
CELGARD.RTM. 3501 separator membrane.
[0070] FIG. 6 is a plot of discharge capacity versus cycle number
for electrochemical cells at 30.degree. C. over a 3 to 4.1V range
for the electrolytes containing 0.3 wt % of MP or EP compared to
the Gen2 control. The 1st and seconds cycles were run at a C/12
rate, and the next 50 cycles were run at a C/4 rate. The results in
FIG. 6 demonstrate that small amounts of MP or EP added to the Gen2
electrolyte improves capacity retention over the long term (at
least up to 50 charge/discharge cycles).
[0071] FIG. 7 is a plot of discharge capacity versus cycle number
for electrochemical cells utilizing about 3 wt % of either MP or
EP, compared to a control the Gen2 control. The results in FIG. 7
indicate that larger amounts of MP and EP (i.e., 3 wt % versus 0.3
wt %) resulted in lower capacity and poorer capacity retention.
Example 2
[0072] Electrolytes containing about 0.3 wt % of either MP, EP,
methyl isonicotinate (MIN), or ethyl nicotinate (EN) added to the
Gen2 electrolyte of Example 1 were evaluated in a cell of the same
design as described in Example 1. FIG. 8 is a plot of discharge
capacity versus cycle number for the electrochemical cells, which
shows that addition of 0.3 wt % of the heteroaromatic additives to
the Gen2 electrolyte improved the retention capacity relative to
the Gen2 electrolyte. MIN provided the least initial capacity
loss.
[0073] FIG. 9 is a plot of dQ/dV over a voltage range of about 1.8
to about 4.2 volts the cells, which shows that addition of 0.3 wt %
of the heteroaromatic compounds to the Gen2 electrolyte induced
significant changes between 1.8 V and 3V, indicating that reactions
with graphite occurred.
[0074] FIG. 10 is a plot of AC impedance data for the
electrochemical cells, which shows that addition of 0.3 wt % of the
heteroaromatic compounds to the Gen 2 electrolyte did not
significantly alter cell impedance. The electrolytes with added
heteroaromatic compounds exhibited either similar or lower
impedance.
Example 3
[0075] Electrolytes containing about 0.3 wt % of MP added to the
Gen2 electrolyte of Example 1 were evaluated in a cell of the same
design as described in Example 1 with the formation cycle being run
at about 30.degree. C. or 55.degree. C. FIG. 11 is a plot of
discharge capacity versus cycle number for the electrochemical
cells compared to the control Gen2 electrolyte. The results in FIG.
11 indicate that the initial capacity of the cell that included MP
in the electrolyte increased when the formation cycle was performed
at the higher temperature. Capacity improvement is indicative of
improved electrode "wetting" by the electrolyte.
Example 4
[0076] Electrolytes containing about 0.1 to about 1 wt % of methyl
isonicotinate (MIN) added to the Gen2 electrolyte of Example 1 were
evaluated in a cell of the same design as described in Example 1.
FIG. 12 is a plot of discharge capacity versus cycle number for
electrochemical cells compared to the control Gen2 electrolyte,
which demonstrates that addition of about 0.1 to about 0.6 wt % MIN
to the Gen2 electrolyte improves cell capacity retention over 50
charge/discharge cycles. FIG. 13 is a plot of AC impedance data for
electrochemical cells. The results in FIG. 13 indicate that
impedance is smallest for cells with 0.1 to 0.6 wt % MIN. Higher
levels of MIN increased the impedance slightly.
Example 5
[0077] An electrolyte containing about 0.3 wt % of MIN added to the
Gen2 electrolyte of Example 1 was evaluated in a cell of the same
design as described in Example 1. FIG. 14 is a plot of discharge
capacity versus cycle number for electrochemical cells utilizing
the MIN-containing electrolyte compared to the control Gen2
electrolyte. Cycles were run at C/4 rate, 1C rate, and C/12 rate.
The results in FIG. 14 indicate that cell capacity retention was
about 90% over 200 cycles at 1C rate, and over 95% when measured at
a C/12 rate; that is, the true capacity loss was relatively small
for the long-term cycling. FIG. 15 is a plot of AC impedance data
for electrochemical cells over 50 cycles at C/4 rate, 100 cycles at
1C rate, and 200 cycles at 1C rate. The cells containing 0.3 wt %
MIN exhibited minimal impedance increase after 200 cycles at 1C
rate.
Example 6
[0078] Electrolytes containing about 0.3 wt % of 3,4-diethyl
pyridinecarboxylate (3,4-DEPC), 3,4-diethyl pyridinecarboxylic
anhydride (3,4-PyDCA), 2,3-pyridinecarboxylic anhydride
(2,3-PyDCA), 2,3-pyrazinecarboxylic anhydride (2,3-PzDCA),
methyl-2-pyrazinecarboxylate (2-MPzC), or
methyl-1-methylpyrrole-2-carboxylate (MMPC) added to the Gen2
electrolyte of Example 1 were evaluated in a cell of the same
design as described in Example 1. FIG. 16 is a plot of discharge
capacity versus cycle number for the electrochemical cells,
compared to the control Gen2 electrolyte, which demonstrates that
0.3 wt % of the added heteroaromatic compounds 3,4-DEPC, 2,3-PzDCA,
3,4-PyDCA, 2-MPzC and MMPC improved the capacity retention.
3,4-PyDCA provided the best performance in terms of initial
capacity loss.
Example 7
[0079] Electrolytes containing about 0.3 wt % of 3,4-DEPC,
3,4-PyDCA, or 2-MPzC added to the Gen2 electrolyte of Example 1
were evaluated in a cell of the same design as described in Example
1. FIG. 17 is a plot of discharge capacity versus cycle number for
electrochemical cells compared to the control Gen2 electrolyte over
100 cycles, which indicates that 0.3 wt % of 3,4-DEPC or 3,4-PyDCA
added to Gen2 electrolyte provided more than 95% capacity retention
a 1C rate over 100 cycles. The cell including 2-MPzC did not
perform as well at 1C rate.
Example 8
[0080] Electrolytes containing about 0.3 wt % of 2-ethyl furoate
(2-EF), 3-ethyl furoate (3-EF), or 2-ethyl thiophenecarboxylate
(2-ETC) added to the Gen2 electrolyte of Example 1 were evaluated
in a cell of the same design as described in Example 1. FIG. 18 is
a plot of capacity versus cycle number for the electrochemical
cells compared to the control Gen2 electrolyte. The results in FIG.
18 show that addition of about 0.3 wt % of these furan and
thiophene heteroaromatic compounds to the Gen2 electrolyte improved
capacity retention. Evaluations of electrolytes containing about 2
wt % added heteroaromatic compound provided similar results.
[0081] FIG. 19 is a plot of dQ/dV over a voltage range of about 1.8
to about 4.2 volts for the electrolytes compared to the control
Gen2 electrolyte, which demonstrates that the added heteroaromatic
compounds induced significant changes in the dQ/dV data between 2.4
and 3 V, which is indicative of reactions at graphite. FIG. 20 is a
plot of AC impedance data for electrochemical cells compared to the
control Gen2 electrolyte. The results in FIG. 20 show that 0.3 wt %
of the heteroaromatic compounds added to Gen2 electrolyte did not
significantly alter the cell impedance. The cells containing the
heteroaromatic compounds exhibited similar or lower impedance that
the cells utilizing the Gen2 electrolyte.
Example 9
[0082] Electrolytes containing about 1.2 M LiPF.sub.6 in a 1:8
mixture of ethyl picolinate (EP) and dimethyl carbonate (DMC) were
evaluated in a cell comprising a graphite electrode and a Li metal
counter electrode. FIG. 21 is a plot of voltage versus capacity for
cycles 1, 2, 5, and 20. The results in FIG. 21 indicate that
graphite electrodes can be cycled in EP-based electrolytes in the
absence of ethylene carbonate. FIG. 22 is a plot of dQ/dV over a
voltage range of about 0.2 to about 1.7 volts, showing solid
electrolyte interphase (SEI) formation. FIG. 23 is a plot of dQ/dV
over a voltage range of about 0 to about 0.3 volts, showing
lithiation and delithiation. Electrolyte reduction peaks were only
observed during the first lithiation cycle. The observed increased
capacity with cycling may be due to improved electrode wetting.
[0083] The same electrolyte was evaluated in a cell with an oxide
electrode (LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2) and a Li
metal counter electrode. FIG. 24 is a plot of voltage versus
capacity over three charge/discharge cycles for the oxide electrode
over three charge/discharge cycles. FIG. 25 is a plot of dQ/dV over
a voltage range of about 2 to about 4.3 volts over three
charge/discharge cycles. The results demonstrate that the oxide
electrodes can be cycled in EP-based electrolytes, albeit with some
Li consumption during the first cycle. After 10 cycles, the
electrochemical efficiency was about 86%, which may be due to a
slow electrolyte oxidation during cycling.
[0084] FIG. 26 is a plot of voltage versus capacity for an
oxide/graphite cell utilizing the same electrolyte, over 20
charge/discharge cycles. The data in FIG. 26 indicate that Li
consumption during EP decompositions may deplete the lithium
inventory in a full cell during the first cycle. Although low, the
capacity remained stable during subsequent cycles.
Example 10
[0085] Electrolytes containing about 1.2 M LiPF.sub.6 in a 1:8
mixture of 3-ethyl furoate (3-EF) and dimethyl carbonate (DMC) were
evaluated in a cell comprising a graphite electrode. FIG. 27 is a
plot of voltage versus capacity. FIG. 28 is a plot of dQ/dV over a
voltage range of about 0.2 to about 1.7 volts, showing SEI
formation. FIG. 29 is a plot of dQ/dV over a voltage range of about
0 to about 0.3 volts, showing lithiation and delithiation. These
results indicate that graphite electrodes can be cycled in
3-EF-based electrolytes that are free from ethylene carbonate.
Electrolyte reduction was only observed during the first lithiation
cycle. After 5 cycles, the capacity values stabilized.
[0086] FIG. 30 is a plot of voltage versus capacity for an oxide
electrode (LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2) in the same
electrolyte over 10 charge/discharge cycles. The results in FIG. 30
show that oxide electrodes can be cycled in a 3-EF-based
electrolyte. Some lithium consumption was observed during the first
cycle. Coulombic efficiency was greater than 98%. FIG. 31 is a plot
of dQ/dV over a voltage range of about 3 to about 4.3 volts for the
oxide electrode over 10 charge/discharge cycles. No unusual peaks
were observed in the dQ/dV data, indicating that little if any
oxidation of the electrolyte occurred.
Electrochemical Cells and Batteries.
[0087] Electrochemical cells and batteries comprising the
electrolytes of this invention are schematically illustrated in
FIG. 32 and FIG. 33. FIG. 32 illustrates an electrochemical cell 10
having a negative electrode 12 separated from a positive electrode
16 by an electrolyte of the invention 14, all contained in an
insulating housing 18 with suitable terminals (not shown) being
provided in electronic contact with the negative electrode 12 and
the positive electrode 16. Binders and other materials normally
associated with both the electrolyte and the negative and positive
electrodes are well known in the art and are not described herein,
but are included as is understood by those of ordinary skill in
this art. FIG. 33 shows a schematic illustration of one example of
a battery in which two strings of electrochemical lithium cells 10,
described above, are arranged in parallel, each string comprising
three cells arranged in series.
[0088] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0089] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0090] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *