U.S. patent application number 11/365299 was filed with the patent office on 2006-08-31 for electrolyte for a lithium battery and a lithium battery comprising the same.
Invention is credited to Cheol-Soo Jung, Yong-Beom Lee, Eui-Hwan Song, Kyoung-Han Yew.
Application Number | 20060194118 11/365299 |
Document ID | / |
Family ID | 36178165 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060194118 |
Kind Code |
A1 |
Yew; Kyoung-Han ; et
al. |
August 31, 2006 |
Electrolyte for a lithium battery and a lithium battery comprising
the same
Abstract
The present invention relates to an electrolyte for a lithium
battery and a lithium battery comprising the same. The electrolyte
includes a non-aqueous organic solvent, a lithium salt, and a first
additive capable of forming a chelating complex with a transition
metal and which is stable at voltages ranging from about 2.5 to
about 4.8 V.
Inventors: |
Yew; Kyoung-Han; (Suwon-si,
KR) ; Song; Eui-Hwan; (Suwon-si, KR) ; Jung;
Cheol-Soo; (Suwon-si, KR) ; Lee; Yong-Beom;
(Suwon-si, KR) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
36178165 |
Appl. No.: |
11/365299 |
Filed: |
February 28, 2006 |
Current U.S.
Class: |
429/326 ;
429/200; 429/330; 429/331; 429/332 |
Current CPC
Class: |
H01M 10/0525 20130101;
Y02E 60/10 20130101; H01M 10/0569 20130101; H01M 6/168 20130101;
H01M 6/164 20130101; H01M 10/052 20130101; H01M 10/0567
20130101 |
Class at
Publication: |
429/326 ;
429/330; 429/331; 429/332; 429/200 |
International
Class: |
H01M 10/40 20060101
H01M010/40 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2005 |
KR |
10-2005-0016691 |
Claims
1. An electrolyte for a lithium battery comprising: a non-aqueous
organic solvent; a lithium salt; and a first additive capable of
forming a chelating complex with a transition metal, the first
additive being stable at voltages ranging from about 2.5 to about
4.8 V.
2. The electrolyte of claim 1, wherein the first additive comprises
a compound selected from the group consisting of compounds
represented by Formulas 1 to 3 and mixtures thereof: ##STR6##
wherein n is an integer ranging from 0 to 10, n1 is an integer
ranging from 0 to 15, wherein when n1 is an odd number, a is 1 and
when n1 is an even number, a is either 1/2 or 1; and at least one
of R.sub.1 through R.sub.3 and at least one of R.sub.4 through
R.sub.6 is a compound represented by A.sub.xR', wherein A is
selected from the group consisting of N, O, P, or S, x is 0 or 1,
and R' is selected from the group consisting of CN, C.sub.1 to
C.sub.15 linear alkyls, C.sub.1 to C.sub.15 linear carboxyls,
C.sub.1 to C.sub.15 branch alkyls and C.sub.1 to C.sub.15 branch
carboxyls, and wherein the remaining R1 through R6 groups each
comprises a material selected from the group consisting of H,
halogens, C.sub.1 to C.sub.15 alkyls and C.sub.6 to C.sub.15
aryls.
3. The electrolyte of claim 2, wherein the first additive comprises
a compound selected from the group consisting of compounds
represented by Formulas 4 to 26: ##STR7## ##STR8##
4. The electrolyte of claim 1, wherein the first additive is
present in the electrolyte in an amount ranging from about 0.1 wt %
to about 10 wt % based on the total weight of electrolyte.
5. The electrolyte of claim 4, wherein the first additive is
present in the electrolyte in an amount ranging from about 1 wt %
to about 5 wt % based on the total weight of electrolyte.
6. The electrolyte of claim 4, wherein the first additive is
present in the electrolyte in an amount ranging from about 3 wt %
to about 5 wt % based on the total weight of electrolyte.
7. The electrolyte of claim 1, further comprising a second additive
capable of releasing a transition metal from a positive
electrode.
8. The electrolyte of claim 7, wherein the second additive is an
ester-based compound.
9. The electrolyte of claim 8, wherein the second additive is
selected from the group consisting of phenyl acetate, benzyl
benzoate, ethyl acetate, 1-naphthyl acetate, 2-chromanone and ethyl
propionate.
10. The electrolyte of claim 7, wherein the second additive is
present in the electrolyte in an amount ranging from about 1 to
about 10 parts by weight based on 100 parts by weight of the
electrolyte.
11. The electrolyte of claim 10, wherein the second additive is
present in the electrolyte in an amount ranging from about 1 to
about 7 parts by weight based on 100 parts by weight of the
electrolyte.
12. The electrolyte of claim 11, wherein the second additive is
present in the electrolyte in an amount ranging from about 3 to
about 5 parts by weight based on 100 parts by weight of the
electrolyte.
13. The electrolyte claim 1, wherein the lithium salt is selected
from the group consisting of LiPF.sub.6, LiBF.sub.4, LiSbF.sub.6,
LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N, LiC.sub.4F.sub.9SO.sub.3, LiAlO.sub.4,
LiAlCl.sub.4, LiCl, Lil,
LiN(C.sub.xF.sub.2x+1SO.sub.2)(C.sub.yF.sub.2y+1SO.sub.2) wherein x
and y are natural numbers and mixtures thereof.
14. The electrolyte of claim 1, wherein the lithium salt has a
concentration ranging from about 0.6 M to about 2.0 M.
15. The electrolyte of claim 1, wherein the lithium salt has a
concentration ranging from about 0.7 M to about 1.6 M.
16. The electrolyte of claim 1, wherein the non-aqueous organic
solvent is selected from the group consisting of carbonates,
esters, ethers, ketones and mixtures thereof.
17. The electrolyte of claim 16, wherein the carbonates are
selected from the group consisting of dimethyl carbonate (DMC),
diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl
carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate
(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene
carbonate (BC) and mixtures thereof.
18. The electrolyte of claim 16, wherein the esters are selected
from the group consisting of n-methyl acetate, n-ethyl acetate,
n-propyl acetate and mixtures thereof.
19. The electrolyte of claim 16, wherein the non-aqueous organic
solvent comprises a carbonate comprising a mixture of chain
carbonates and cyclic carbonates, the volume ratio of the chain
carbonates to the cyclic carbonates ranging from about 1:1 to about
1:9.
20. The electrolyte of claim 1, wherein the non-aqueous solvent
comprises a mixture of a carbonate solvent and an aromatic
hydrocarbon solvent.
21. The electrolyte of claim 20, wherein the volume ratio of the
carbonate solvent to the aromatic hydrocarbon solvent ranges from
about 1:1 to about 30:1.
22. The electrolyte of claim 20, wherein the aromatic hydrocarbon
solvent is selected from the group consisting of solvents
represented by Formula 27: ##STR9## wherein q is an integer ranging
from 0 to 6 and R10 is selected from the group consisting of
halogens and C.sub.1 to C.sub.10 alkyls.
23. The electrolyte of claim 22, wherein the aromatic hydrocarbon
solvent is selected from the group consisting of benzene,
fluorobenzene, toluene, trifluorotoluene, chlorobenzene, xylene and
mixtures thereof.
24. The electrolyte of claim 1, further comprising a third additive
selected from the group consisting of carbonates having halogen
substituents, carbonates having cyano (CN) substituents, carbonates
having nitro (NO.sub.2) substituents, vinylene carbonate,
divinylsulfone, ethylene sulfite and mixtures thereof.
25. The electrolyte of claim 24, wherein the third additive is
selected from the group consisting of carbonates having halogen
substituents, carbonates having cyano (CN) substituents and
carbonates having nitro (NO.sub.2) substituents.
26. The electrolyte of claim 24, wherein the third additive is
selected from the group consisting of compounds represented by
Formula 28: ##STR10## wherein X1 is selected from the group
consisting of halogens, cyano (CN) groups, and nitro (NO.sub.2)
groups.
27. The electrolyte of claim 24, wherein the third additive is
fluoroethylene carbonate.
28. An electrolyte for a lithium battery comprising: a non-aqueous
organic solvent; a lithium salt; a first additive capable of
forming a chelating complex with a transition metal, the first
additive being stable at a voltage ranging from about 2.5 to about
4.8 V; a second additive capable of releasing a transition metal
from a positive electrode.
29. The electrolyte of claim 28, further comprising a third
additive selected from the group consisting of carbonates having
halogen substituents, carbonates having cyano (CN) substituents,
carbonates having nitro (NO.sub.2) substituents, vinylene
carbonate, divinylsulfone, ethylene sulfite and mixtures
thereof.
30. A lithium battery comprising: an electrolyte comprising: a
non-aqueous organic solvent, a lithium salt, and a first additive
capable of forming a chelating complex with a transition metal, the
first additive being stable at voltages ranging from about 2.5 to
about 4.8 V; a positive electrode comprising a positive active
material capable of intercalating and deintercalating lithium ions;
and a negative electrode comprising an active material selected
from the group consisting of materials capable of
intercalating/deintercalating lithium ions, lithium metals,
lithium-containing alloys, and materials capable of forming
lithium-containing compounds by reversibly reacting lithium.
31. The lithium battery of claim 30, wherein the first additive
comprises a compound selected from the group consisting of
compounds represented by Formulas (1) to (3) and mixtures thereof:
##STR11## wherein n is an integer ranging from 0 to 10, n1 is an
integer ranging from 0 to 15, wherein when n1 is an odd number, a
is 1 and when n1 is an even number, a is either 1/2 or 1; and at
least one of R.sub.1 through R.sub.3 and at least one of R.sub.4
through R.sub.6 is a compound represented by A.sub.xR', wherein A
is selected from the group consisting of N, O, P, or S, x is 0 or
1, and R' is selected from the group consisting of CN, C.sub.1 to
C.sub.15 linear alkyls, C.sub.1 to C.sub.15 linear carboxyls,
C.sub.1 to C.sub.15 branch alkyls and C.sub.1 to C.sub.15 branch
carboxyls, and wherein the remaining R1 through R6 groups each
comprises a material selected from the group consisting of H,
halogens, C.sub.1 to C.sub.15 alkyls and C.sub.6 to C.sub.15
aryls.
32. The lithium battery of claim 31, wherein the first additive
comprises a compound selected from the group consisting of
compounds represented by Formulas 4 to 26 and mixtures thereof:
##STR12## ##STR13##
33. The lithium battery of claim 30, wherein the first additive is
present in the electrolyte in an amount ranging from about 0.1 wt %
to about 10 wt % based on the total weight of electrolyte.
34. The lithium battery of claim 33, wherein the first additive is
present in the electrolyte in an amount ranging from about 1 wt %
to about 5 wt % based on the total weight of electrolyte.
35. The lithium battery of claim 34, wherein the first additive is
present in the electrolyte in an amount ranging from about 3 wt %
to about 5 wt % based on the total weight of electrolyte.
36. The lithium battery of claim 30, wherein the electrolyte
further comprises a second additive capable of releasing a
transition metal from the positive electrode.
37. The lithium battery of claim 36, wherein the second additive is
an ester-based compound.
38. The lithium battery of claim 37, wherein the second additive is
selected from the group consisting of phenyl acetate, benzyl
benzoate, ethyl acetate, 1-naphthyl acetate, 2-chromanone, and
ethyl propionate.
39. The lithium battery of claim 36, wherein the second additive is
present in the electrolyte in an amount ranging from about 1 to
about 10 parts by weight based on 100 parts by weight of the
electrolyte.
40. The lithium battery of claim 39, wherein the second additive is
present in the electrolyte in an amount ranging from about 1 to
about 7 parts by weight based on 100 parts by weight of the
electrolyte.
41. The lithium battery of claim 40, wherein the second additive is
present in the electrolyte in an amount ranging from about 3 to
about 5 parts by weight based on 100 parts by weight of the
electrolyte.
42. The lithium battery of claim 30, wherein the non-aqueous
organic solvent is selected from the group consisting of carbonate,
esters, ethers, ketones and mixtures thereof.
43. The lithium battery of claim 42, wherein the carbonates are
selected from the group consisting of dimethyl carbonate (DMC),
diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl
carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate
(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene
carbonate (BC) and mixtures thereof.
44. The lithium battery of claim 30, wherein the non-aqueous
solvent comprises a mixture of a carbonate solvent and an aromatic
hydrocarbon solvent.
45. The lithium battery of claim 44, wherein the aromatic
hydrocarbon solvent comprises a solvent represented by Formula 27:
##STR14## wherein q is an integer ranging from 0 to 6 and R10 is
selected from the group consisting of halogens and C.sub.1 to
C.sub.10 alkyls.
46. The lithium battery of claim 45, wherein the aromatic
hydrocarbon solvent is selected from the group consisting of
benzene, fluorobenzene, toluene, trifluorotoluene, chlorobenzene,
xylene and mixtures thereof.
47. The lithium battery of claim 30, wherein the electrolyte
further comprises a third additive selected from the group
consisting of carbonates having halogen substituents, carbonates
having cyano (CN) substituents, carbonates having nitro (NO.sub.2)
substituents, vinylene carbonate, divinylsulfone, ethylene sulfite
and mixtures thereof.
48. The lithium battery of claim 47, wherein the third additive is
selected from the group consisting of carbonates having halogen
substituents, carbonates having cyano (CN) substituents and
carbonates having nitro (NO.sub.2) substituents.
49. The lithium battery of claim 48, wherein the third additive is
selected from the group consisting of compounds represented by
Formula 28: ##STR15## wherein X1 is selected from the group
consisting of halogens, cyano (CN) groups, and nitro (NO.sub.2)
groups.
50. The lithium battery of claim 48, wherein the negative active
material comprises a carbonaceous material capable of
intercalating/deintercalating lithium ions.
51. A lithium battery comprising: a positive electrode comprising a
positive active material capable of intercalating and
deintercalating lithium ions; a negative electrode comprising an
active material selected from the group consisting of materials
capable of intercalating/deintercalating lithium ions, lithium
metals, lithium-containing alloys, and materials capable of forming
lithium-containing compounds by reversibly reacting lithium; and an
electrolyte comprising: a non-aqueous organic solvent, a lithium
salt, a first additive capable of forming a chelating complex with
a transition metal, the first additive being stable at voltages
ranging from about 2.5 to about 4.8 V, and a second additive
capable of releasing a transition metal from the positive
electrode.
52. The lithium battery of claim 51, wherein the electrolyte
further comprises a third additive selected from the group
consisting of carbonates having halogen substituents, carbonates
having cyano (CN) substituents, carbonates having nitro (NO.sub.2)
substituents, vinylene carbonate, divinylsulfone, ethylene sulfite
and mixtures thereof.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 110-2005-0016691 filed in the Korean
Intellectual Property Office on Feb. 28, 2005, the entire content
of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an electrolyte for a
lithium battery and a lithium battery comprising the same, and more
particularly, to an electrolyte which improves battery safety.
BACKGROUND OF THE INVENTION
[0003] Portable electronic devices are becoming smaller and lighter
due to advancements in the high-tech electronic industry. As a
result, portable electronic devices are increasingly being used.
The increased need for batteries having high energy density for use
as power sources for these portable electronic devices has led to
recent research into lithium secondary batteries.
[0004] Lithium secondary batteries have average discharge
potentials of about 4 V, and more particularly 3.7 V. These lithium
secondary batteries are essential to the digital generation because
they are indispensable energy sources for portable digital devices
such as the "3C" devices, i.e. cellular telephones, notebook
computers, and camcorders, as well as other portable electronic
devices.
[0005] Research has also been conducted on batteries to develop
effective safety characteristics such as the prevention of
overcharge. When a battery is overcharged, excess lithium ions are
deposited on the positive electrode, and excess lithium ions are
inserted into the negative electrode, making the positive and
negative electrodes thermally unstable. An explosion may occur due
to the decomposition of the electrolytic organic solvent causing
thermal runaway which can seriously decrease battery safety.
[0006] To overcome these problems, an aromatic compound, such as an
oxidation-reduction agent, or "redox shuttle additive," has been
added to the electrolyte. For example, U.S. Pat. No. 5,709,968 to
Shimizu discloses the use of a benzene compound, such as
2,4-difluoroanisole, in a non-aqueous lithium ion secondary battery
to prevent thermal runaway resulting from overcharge current. Also,
U.S. Pat. No. 5,879,834 to Mao discloses the use of
electrochemically polymerized aromatic compounds, such as biphenyl,
3-chlorothiophene, furan, etc., to improve battery safety by
increasing the internal resistance of the battery during unusual
overvoltage conditions.
[0007] Redox shuttle additives quickly increase the temperature
inside the battery by the heat produced by the oxidation-reduction
reaction. In addition, the additive closes the pores of the
separator by quickly and uniformly fusing the separator to inhibit
overcharge reactions. The polymerization reaction of these redox
shuttle additives consumes the overcharge current, thereby
improving battery safety.
[0008] However, the need for high capacity batteries is increasing,
and these redox shuttle additives cannot provide the high level of
safety required of such high capacity batteries. Therefore, a need
exists for an electrolyte capable of preventing overcharge and
ensuring battery safety.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the present invention, a lithium
battery electrolyte imparts improved battery safety.
[0010] In another embodiment of the present invention, a lithium
battery comprises an electrolyte which imparts improved battery
safety.
[0011] One embodiment of the electrolyte for a lithium battery
includes a non-aqueous organic solvent, a lithium salt, and an
additive which is stable at voltages ranging from about 2.5 to
about 4.8 V. The additive is capable of forming a chelating complex
with a transition metal.
[0012] In another embodiment of the present invention, a lithium
battery includes an electrolyte having a non-aqueous organic
solvent, a lithium salt, and an additive which is stable at
voltages ranging from about 2.5 to about 4.8 V. The electrolyte
additive is capable of forming a chelating complex with a
transition metal. The battery further comprises a positive
electrode and a negative electrode. The positive electrode
comprises a positive active material capable of intercalating and
deintercalating lithium ions. The negative electrode comprises an
active material selected from the group consisting of materials
capable of intercalating/deintercalating lithium ions, lithium
metals, lithium-containing alloys, and materials capable of forming
lithium-containing compounds by reversibly reacting lithium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other features and advantages of the present
invention will be better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawings, in which:
[0014] FIG. 1 is a cross-sectional view of a lithium battery
according to one embodiment of the present invention;
[0015] FIG. 2 is a graph of the voltammetry measurements of a
lithium secondary battery prepared according to Experimental
Example 1; and
[0016] FIG. 3 is a graph of the current, temperature, and voltage
characteristics, measured at 1.5 C, during overcharging of lithium
batteries prepared according to Example 2 and Comparative Example
2.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0017] Exemplary embodiments of the present invention will now be
described with reference to the accompanying drawings. However, one
of ordinary skill in the art understands that various modifications
may be made to the described embodiments, and that the invention is
not limited to the described embodiments. Rather, the embodiments
are described for illustrative purposes only.
[0018] The present invention relates to an electrolyte for a
lithium battery. FIG. 1 is a cross-sectional view of a non-aqueous
lithium secondary battery according to one embodiment of the
present invention. The battery 1 comprises an electrode assembly 8
contained within a battery case 10. The electrode assembly 8
includes a positive electrode 2, a negative electrode 4 and a
separator 6 positioned between the positive and negative electrodes
2 and 4, respectively. The positive and negative electrodes 2 and
4, respectively, comprise active materials capable of intercalating
and deintercalating lithium ions. The separator can comprise
polyethylene, polypropylene, or a combination thereof.
[0019] An electrolyte is injected into the battery case 10 and
impregnated into the positive and negative electrodes 2 and 4, and
the separator 6. The battery case 10 is sealed with a cap plate 12
and a sealing gasket 14. The cap plate 12 has a safety vent (not
shown) for releasing overpressure and comprises a lead plate 24 and
an insulating plate 26 positioned between the lead plate 24 and the
cap plate 12. A positive tab 18 is attached to the positive
electrode 2, and a negative tab 20 is attached to the negative
electrode 4. The negative terminal 22 is electrically connected to
the electrode assembly 8 through the negative tab 20. The battery
case 10 acting as a positive terminal is electrically connected to
the electrode assembly 8 through the positive tab 18.
[0020] In lithium secondary batteries, temperature increases
abruptly during overcharge due to incorrect operation or break-down
of the battery, or when short circuits occur due to a defect in
battery design. This abrupt increase in temperature results in
thermal runaway. During overcharge, excess lithium ions are
released from the positive electrode and deposited on the surface
of the negative electrode, rendering the positive and negative
electrodes unstable. As a result, exothermic reactions rapidly
increase the temperature inside the battery, causing thermal
runaway and generating fire and smoke. Such exothermic reactions
may include pyrolysis of the electrolyte, reactions between the
electrolyte and lithium, oxidation reactions of the electrolyte and
the positive electrode, reactions between the electrolyte and
oxygen gas generated from the pyrolysis of the positive active
material, etc.
[0021] In light of these problems, various additives have been
researched, including overcharge-inhibiting additives and additives
for improving battery safety when stored at high temperatures.
However, although these additives serve their intended objective,
they have other shortcomings. For example, overcharge-inhibiting
additives, such as phenyl acetate, decrease the safety of the
battery when stored at high temperatures. Additionally, metal
impurities, which remain after battery fabrication, cause voltage
drops.
[0022] The electrolytes according to one embodiment of the present
invention include first additives which trap the metals or metal
impurities released from the positive electrode during overcharge
or high temperate storage. These first additives are stable at
voltages ranging from about 2.5 to about 4.8 V, and are capable of
forming chelating complexes with chelating metals. The first
additive traps metals, thereby preventing voltage drops and
decreasing safety risks caused by deposition of metal on the
negative electrode, which can result in short circuits. In
particular, the first additives ensure battery safety when stored
at high temperatures.
[0023] The first additive is capable of forming a chelating complex
and comprises a compound represented by Formulas 1 to 3 and
mixtures thereof: ##STR1##
[0024] In Formulas 1 through 3, R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, and R.sub.6 may be either the same or different compounds.
However, at least one of R.sub.1 through R.sub.3 and at least one
of R.sub.4 through R.sub.6 is a compound represented by the formula
A.sub.xR', where A is selected from the group consisting of N, O, P
and S, x is 0 or 1, and R' is selected from the group consisting of
CN, C.sub.1 to C.sub.15 linear alkyls, C.sub.1 to C.sub.15 linear
carboxyls, C.sub.1 to C.sub.15 branch alkyls and C.sub.1 to
C.sub.15 branch carboxyls. The remaining R.sub.1 through R.sub.6
groups each comprise a material selected from the group consisting
of H, halogens, C.sub.1 to C.sub.15 alkyls and C.sub.6 to C.sub.15
aryls. In the Formulas 1 through 3, n is an integer ranging from 0
to 10, and n1 is an integer ranging from 0 to 15. When n1 is an odd
number, a is 1, and when n1 is an even number, a is either 1/2 or
1.
[0025] Non-limiting examples of first additives suitable for use in
the present invention include the compounds represented by the
following Formulas 4 to 26 and mixtures thereof: ##STR2##
##STR3##
[0026] In the above Formulas 4 to 26, Me is methyl and Ph is
phenyl.
[0027] In one embodiment, the first additive is present in an
amount ranging from about 0.1 to about 10 wt % based on the total
weight of the electrolyte. In another embodiment, the first
additive is present in an amount ranging from about 1 to about 5 wt
% based on the total weight of the electrolyte. In yet another
embodiment, the first additive is present in an amount ranging from
about 3 to about 5 wt % based on the total weight of the
electrolyte. When the first additive is present in an amount less
than about 0.1 wt %, the effect of the addition is negligible. When
the first additive is present in an amount more than about 10 wt %,
cycle life upon charge and discharge deteriorates.
[0028] The electrolyte may further include a second additive
capable of releasing a transition metal from the positive
electrode. The combination of the first additive, which is capable
of forming a chelating complex, with the second additive
substantially converts overcharge mode, caused by an internal short
circuit, to shut-down mode, resulting in guaranteed safety during
overcharge.
[0029] The second additive can comprise an ester-based compound.
Non-limiting examples of such an ester-based compound include
phenyl acetate, benzyl benzoate, ethyl acetate, 1-naphthyl acetate,
2-chromanone, and ethyl propionate.
[0030] In one embodiment, the second additive is present in an
amount ranging from about 1 to about 10 parts by weight based on
100 parts by weight of the electrolyte. In another embodiment, the
second additive is present in an amount ranging from about 1 to
about 7 parts by weight based on 100 parts by weight of the
electrolyte. In yet another embodiment, the second additive is
present in an amount ranging from about 3 to 5 parts by weight
based on 100 parts by weight of the electrolyte. When the second
additive is present in an amount less than about 1 part by weight,
overcharge is not substantially inhibited. When the second additive
is present in an amount more than about 10 parts by weight, cycle
life may deteriorate.
[0031] The electrolyte further includes a non-aqueous organic
solvent and a lithium salt. The lithium salt supplies the lithium
ions in the battery, making the basic operation of the lithium
battery possible. The non-aqueous organic solvent is the medium for
mobilizing the ions capable of participating in the electrochemical
reaction.
[0032] Non-limiting examples of suitable lithium salts include
LiPF.sub.6, LiBF.sub.4, LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4,
LiCF.sub.3SO.sub.3, Li(CF.sub.3SO.sub.2).sub.2N,
LiC.sub.4F.sub.9SO.sub.3, LiAlO.sub.4, LiAlCl.sub.4,
LiN(C.sub.xF.sub.2x+1SO.sub.2)(C.sub.yF.sub.2y+1SO.sub.2) wherein x
and y are natural numbers, LiCl, Lil and mixtures thereof.
[0033] In one embodiment, the concentration of the lithium salt
ranges from about 0.6 to about 2.0 M. In another embodiment, the
concentration of the lithium salt ranges from about 0.7 to about
1.6 M. When the concentration of the lithium salt is less than
about 0.6 M, electrolyte performance deteriorates due to its ionic
conductivity. When the concentration of the lithium salt is greater
than about 2.0 M, the mobility of the lithium ions decreases due to
increased electrolyte viscosity.
[0034] The non-aqueous organic solvent may include carbonates,
esters, ethers, ketones and mixtures thereof. Non-limiting examples
of suitable carbonates include dimethyl carbonate (DMC), diethyl
carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate
(MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC),
ethylene carbonate (EC), propylene carbonate (PC), and butylene
carbonate (BC). Non-limiting examples of esters include n-methyl
acetate, n-ethyl acetate, n-propyl acetate, and the like.
[0035] In one embodiment, the organic solvent includes a mixture of
a chain carbonate and a cyclic carbonate. In this embodiment, the
volume ratio of the cyclic carbonate to the chain carbonate ranges
from about 1:1 to about 1:9. When the volume ratio of the cyclic
carbonate to the chain carbonate is within this range, and the
mixture is used as an electrolyte, electrolyte performance is
improved.
[0036] In another embodiment, the electrolyte may further comprise
a mixture of carbonate solvents and aromatic hydrocarbon solvents,
such as those represented by Formula 27: ##STR4##
[0037] In Formula 27, R10 is a compound selected from the group
consisting of halogens and C.sub.1 to C.sub.10 alkyls, and q is an
integer ranging from 0 to 6. Non-limiting examples of aromatic
hydrocarbon solvents suitable for use in the present invention
include benzene, fluorobenzene, toluene, trifluorotoluene,
chlorobenzene, and xylene.
[0038] The volume ratio of carbonate solvents to aromatic
hydrocarbon solvents ranges from about 1:1 to about 30:1. When the
volume ratio of carbonate solvents to aromatic hydrocarbon solvents
is within this range, and the mixture is used as an electrolyte,
electrolyte performance is enhanced.
[0039] The electrolyte may further include a third additive
comprising a compound selected from the group consisting of
vinylene carbonate, divinylsulfone, ethylene sulfite and carbonates
having substituents selected from the group consisting of halogens,
cyano (CN) groups, and nitro (NO.sub.2) groups. This third additive
improves the electrochemical characteristics of the battery. For
example, the third additive inhibits swelling at high temperatures
and increases capacity, cycle life, and low-temperature properties.
In one embodiment, the third additive comprises a carbonate
additive. Non-limiting examples of suitable carbonate additives
include ethylene carbonate derivatives, such as fluoroethylene
carbonate, and the compounds represented by Formula 28:
##STR5##
[0040] In Formula 28, X1 is selected from the group consisting of
halogens, cyano (CN) groups, and nitro (NO.sub.2) groups.
[0041] The electrolyte of the present invention is prepared by
adding the additives and the lithium salt to a non-aqueous organic
solvent. Alternatively, the additives may be added to a solution of
the lithium salt dissolved in the organic solvent. The order of
addition of the lithium salt and the additives is not
important.
[0042] In one embodiment of the present invention, a lithium
battery includes the inventive electrolyte. In this embodiment, the
positive active material comprises a lithiated intercalation
compound, which is capable of intercalating/deintercalating
lithium. The negative active material is selected from the group
consisting of carbonaceous materials capable of
intercalating/deintercalating lithium, lithium metals,
lithium-containing alloys and materials capable of reversibly
forming lithium-containing compounds by reacting lithium.
[0043] The lithium battery may be either a lithium primary battery
or a lithium secondary battery.
[0044] The lithium batteries of the present invention have improved
overcharge inhibition properties when compared with batteries
having conventional non-aqueous electrolytes.
[0045] The following Examples, Experimental Examples and
Comparative Examples further illustrate the present invention and
are presented for illustrative purposes only. However, the present
invention is not limited by these Examples, Experimental Examples
and Comparative Examples.
COMPARATIVE EXAMPLE 1
[0046] 94 g of LiCoO.sub.2 as a positive active material, 3 g of
Super P (acetylene black) as a conductive agent, and 3 g of
polyvinylidenefluoride (PVdF) as a binder were mixed in
N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode
slurry. The slurry was coated on aluminum foil having a width of
4.9 cm and a thickness of 147 .mu.m. The slurry coated aluminum
foil was then dried, compressed, and cut to form a positive
electrode.
[0047] 90 g of mesocarbon fiber (MCF from PETROCA company) as a
negative active material and 10 g of PVdF as a binder were mixed to
prepare a negative electrode slurry. The slurry was coated on
copper foil having a width of 5.1 cm and a thickness of 178 .mu.m.
The slurry coated copper foil was then dried, compressed and cut to
form a negative electrode.
[0048] A polyethylene film separator was positioned between the
positive and negative electrodes, and the positive and negative
electrodes and the separator were then wound to form an electrode
assembly. The electrode assembly was placed in a battery case and
an electrolyte was injected into the case under pressure, thus
completing the lithium secondary battery cell.
[0049] The electrolyte was prepared by dissolving 1 M LiPF.sub.6 in
a mixed solvent of ethylene carbonate, ethylmethyl carbonate,
dimethyl carbonate, and fluorobenzene. The volume ratio of ethylene
carbonate:ethylmethyl carbonate:dimethyl carbonate: fluorobenzene
was 3:5:1:1. Chlorotoluene was added in an amount of 10 parts by
weight based on 100 parts by weight of the prepared electrolyte,
and phenyl acetate was added in an amount of 7 parts by weight.
[0050] Three battery cells, No. 1, No. 2 and No. 3, were prepared
according to Comparative Example 1. Open Circuit Voltage (OCV),
Internal Resistance (IR), and battery thickness of each cell were
measured after standard charge and after placement at 85.degree. C.
for 4 hours. These measurements are shown in Table 1.
TABLE-US-00001 TABLE 1 After standard After placement charge at
85.degree. C. for 4 hours Cell IR Thickness IR Thickness No. OCV(V)
(mohm) (mm) OCV(V) (mohm) (mm) No. 1 4.15 51.3 5.65 1.00 430.0 8.00
No. 2 4.14 52.7 5.57 0.80 457.4 7.50 No. 3 4.14 51.8 5.59 1.10
347.5 7.80
[0051] As shown in Table 1, when only phenyl acetate is used as an
additive, after placement of the cells at high temperature, the OCV
of each cell decreased significantly and battery thickness
increased remarkably. This indicates that gas was generated inside
the battery, causing serious swelling.
COMPARATIVE EXAMPLE 2
[0052] A lithium secondary battery was prepared as in Comparative
Example 1, except that phenyl acetate was not used.
EXPERIMENTAL EXAMPLE 1
[0053] A working electrode was prepared using glassy carbon, and a
reference electrode and counter electrode was prepared using
lithium metal. Cyclic voltammetry of succino nitrile was then
measured three times at a scanning rate of 0.5 mV/second. The
results are shown in FIG. 2. As shown in FIG. 2, succino nitrile
did not show an oxidation-reduction peak between 2.5 and 4.8 V,
indicating that this compound is stable in this voltage range.
EXPERIMENTAL EXAMPLE 2
[0054] A positive electrode was prepared as in Comparative Example
1 and subjected to the standard charge conditions. The positive
electrode was then dipped in an electrolyte solution. Subsequently,
phenyl acetate and a first additive capable of forming a chelating
complex were added to the positive electrode, and the positive
electrode was then stored at 85.degree. C. for four hours. Table 2
lists the first additive used and the color of the electrolyte
solution. TABLE-US-00002 TABLE 2 Color after storage at Initial
color 85.degree. C. for 4 hours Example 1 Transparent Deep orange
Succino nitrile Transparent pale yellow Aceto nitrile Transparent
Light pink Valero nitrile Transparent Light pink
3-ethoxy-propionitrile Transparent Light pink Ethylene glycol
diacrylate Transparent Pink 1,2- Pale yellow Yellow
bis(diphenylphosphino)ethane 1,2-dibromoethane Transparent Pale
orange Ethylenediamine Yellow Deep brown Tetraethylenediamine
Yellow Deep brown
[0055] Table 2 shows that after cobalt was released a complex was
formed resulting in a change of color. From the results shown in
Table 2, amine-based compounds are expected to react with the
electrolyte solution to cause the color to change to deep
brown.
EXAMPLE 1
[0056] A lithium secondary battery was fabricated as in Comparative
Example 1, except that the electrolyte was prepared by adding
succino nitrile to a solution of 1 M LiPF.sub.6 dissolved in a
mixed solvent of ethylene carbonate, ethylmethyl carbonate,
dimethyl carbonate and fluorobenzene. The volume ratio of ethylene
carbonate: ethylmethyl carbonate:dimethyl carbonate:fluorobenzene
was 3:5:5:1. The succino nitrile was added in an amount of 5 wt %
based on the total weight of electrolyte.
EXAMPLE 2
[0057] A lithium secondary battery was fabricated as in Example 1,
except that the electrolyte was prepared by adding succino nitrile
and phenyl acetate to a solution of 1 M LiPF.sub.6 dissolved in a
mixed solvent of ethylene carbonate, ethylmethyl carbonate,
dimethyl carbonate and fluorobenzene. The volume ratio of ethylene
carbonate: ethylmethyl carbonate:dimethyl carbonate:fluorobenzene
was 3:5:5:1. The succino nitrile was added in an amount of 5 wt %
based on the total weight of electrolyte, and the phenyl acetate
was added in an amount of 3 parts by weight based on 100 parts by
weight of the electrolyte.
EXAMPLE 3
[0058] A lithium secondary battery was fabricated as in Example 1,
except that 3-ethoxy-propionitrile (EPN) was used instead of
succino nitrile. The 3-epoxy-propionitrile was added in an amount
of 5 wt % based on the total weight of electrolyte.
EXAMPLE 4
[0059] A lithium secondary battery was fabricated as in Example 1,
except that ethylene glycol diacrylate (EGDA) was used instead of
succino nitrile. The ethylene glycol diacrylate was added in an
amount of 5 wt % based on the total weight of electrolyte.
EXAMPLE 5
[0060] A lithium secondary battery was fabricated as in Example 1,
except that 1,2-bis(diphenylphosphino)ethane (DPPE) was used
instead of succino nitrile. The 1,2-bis(diphenylphosphino)ethane
was added in an amount of 5 wt % based on the total weight of
electrolyte.
EXAMPLE 6
[0061] A lithium secondary battery was fabricated as in Example 1,
except that 1,2-dibromoethane (DBE) was used instead of succino
nitrile. The 1,2-dibromoethane was added in an amount of 5 wt %
based on the total weight of electrolyte.
[0062] The lithium battery cells prepared according to Example 2
and Comparative Example 1 were overcharged at 1.5 C, and voltage
and temperature were measured according to operating time. These
measurements are shown in FIG. 3. As shown in FIG. 3, the lithium
battery cell prepared according to Comparative Example 1, using
only phenyl acetate as an additive, exhibited unstable voltage
according to operating time, and the battery temperature was very
high indicating poor battery safety. On the contrary, the lithium
battery cell prepared according to Example 2, using phenyl acetate
and succino nitrile, exhibited uniform operating voltage and the
battery temperature was lower than that of Comparative Example 1,
indicating improved battery safety.
[0063] The battery cells of Examples 1 to 6 and Comparative
Examples 1 and 2 were stored at 85.degree. C. for 4 hours. The
battery cells of Examples 1 to 6 and Comparative Examples 1 and 2
were each separately overcharged. Overcharge was performed fully
charging each cell to 4.2 V. Lead wires were prepared by
resistant-welding a nickel tab to respective terminals. The lead
wires were connected to charge-discharge equipment, and the battery
cell was overcharged to 1.5 C (1.6 A)/12 V under constant
current/constant voltage. After reaching 12 V, current was applied
for 2.5 hours. During overcharge, the firing and explosion of cells
were measured. These measurements are shown in Table 3. In Table 3,
safety at overcharge is reported as follows:
[0064] L0: good, L1: leakage, L2: flash, L2: flame, L3: smoke, L4:
ignition, L5: explosion. TABLE-US-00003 TABLE 3 Additive Amount of
capable of phenyl forming acetate Standard Placement chelating
Amount (parts by capacity at high complex (%) weight) (mAh)
temperature Overcharge Com. Ex. 2 -- -- 0 1083 OK L5 Com. Ex. 1 --
-- 7 1060 NG L0 Ex. 1 succino 5 0 1070 OK L3 nitrile Ex. 2 succino
5 3 1060 OK L0 nitrile Ex. 3 EPN 5 0 1088 OK L4 Ex. 4 EGDA 5 0 1051
OK L3 Ex. 5 DPPE 5 0 1048 OK L4 Ex. 6 DBE 5 0 1062 OK L5
[0065] As shown in Table 3, Example 2, in which succino nitrile and
phenyl acetate were used exhibited good characteristics after high
temperature storage and exhibited safety at overcharge. Examples 3
to 6, in which no phenyl acetate was used, exhibited satisfactory
characteristics after high temperature storage and exhibited
improved safety properties compared to Comparative Example 2, in
which no additive was used. However, Examples 3 to 6 did not
exhibit safety levels near L0.
[0066] Comparative Example 2, in which no additive was used,
satisfied requirements for high temperature storage, but showed
poor safety during overcharge. Comparative Example 1, in which only
phenyl acetate was used as an additive, showed good safety at
overcharge but poor performance after high temperature storage.
[0067] The battery cells according to Example 2 and Comparative
Example 2 were subjected to standard charge, after which the OCV,
IR, and battery thickness were measured. The battery cells were
then stored at 85.degree. C. for 4 hours, after which the OCV, IR,
and battery thickness (t) were measured again. The battery
thickness (t) was measured at 85.degree. C. and at room
temperature. These measurements are reported in Table 4.
[0068] Table 4 also reports the capacity of each cell after
standard charge-discharge (STD_DC). In addition, Table 4 reports
the discharge capacity of each cell measured after storage at high
temperature and immediately cooling (ret(DC)). Finally, Table 4
reports the capacity of each cell measured after storage at high
temperature, discharging, and then charging-discharging (rec(DC)).
In Table 4, ret(DC) indicates charge capacity maintenance and
rec(DC) indicates capacity maintenance after storage at high
temperature. TABLE-US-00004 TABLE 4 After placing at 85.degree. C.
After standard for 4 hours charge t (mm, STD OCV IR t OCV IR t (mm,
Room DC ret(DC) rec(DC) (V) (mohm) (mm) (V) (mohm) 85.degree. C.)
temp.) (mAh) (mAh) (mAh) Ex. 2 4.15 48.6 5.67 4.11 59.8 6.13 5.85
1053.4 944.2 959.2 (No. 1) Ex. 2 4.15 48.1 5.69 4.12 58.1 6.27 5.88
1063.5 975.3 991.9 (No. 2) Ex. 2 4.18 48.8 5.72 4.12 59.8 6.12 5.91
1061.2 959.0 966.2 (No. 3) Ex. 2 4.18 50.0 5.63 4.12 69.8 6.01 5.76
1039.2 920.6 922.4 (No. 4) Ex. 2 4.18 47.9 5.66 4.13 58.4 6.23 5.86
1066.9 956.5 965.5 (No. 5) Average 4.17 48.7 5.67 4.12 61.2 6.15
5.85 1056.8 951.1 961.0 Com. 4.16 44.7 5.47 4.14 48.8 5.79 5.70
1085.6 1022.1 1019.6 Ex. 2 (No. 1) Com. 4.16 45.9 5.45 4.14 50.1
5.82 5.66 1082.9 1011.8 1009.3 Ex. 2 (No. 2) Average 4.16 45.3 5.46
4.14 49.5 5.81 5.68 1084.3 1017.0 1014.5
[0069] The measurements reported in Table 4 show that the battery
cell prepared according to Example 2 and the battery cell prepared
according to Comparative Example 2 perform similarly. As shown in
Tables 3 and 4, the combination of succino nitrile and phenyl
acetate maintains battery performance, improves battery stability
at high temperatures, and ensures battery safety during
overcharge.
[0070] The present invention has been described with reference to
exemplary embodiments. However, those skilled in the art will
appreciate that various modifications and substitutions can be made
without departing from the spirit and scope of the present
invention as set forth in the appended claims.
* * * * *