U.S. patent application number 09/865608 was filed with the patent office on 2002-01-03 for non-aqueous electrolytic solution and lithium secondary battery.
This patent application is currently assigned to Ube Industries, Ltd.. Invention is credited to Abe, Koji, Hamamoto, Toshikazu, Ueki, Akira.
Application Number | 20020001756 09/865608 |
Document ID | / |
Family ID | 18659561 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001756 |
Kind Code |
A1 |
Hamamoto, Toshikazu ; et
al. |
January 3, 2002 |
Non-aqueous electrolytic solution and lithium secondary battery
Abstract
A non-aqueous electrolytic solution favorably employable for a
lithium secondary battery employs a non-aqueous electrolytic
solution which comprises a non-aqueous solvent and an electrolyte
which further contains 0.001 to 0.8 weight % of a biphenyl
derivative having the formula: 1 in which each of Y.sup.1 and
Y.sup.2 represents hydroxyl, alkoxy, hydrocarbyl, hydrogen,
acyloxy, alkoxycarbonyloxy, alkylsulfonyloxy, or halogen, and each
of p and q is an integer of 1 to 3.
Inventors: |
Hamamoto, Toshikazu;
(Yamaguchi, JP) ; Abe, Koji; (Yamaguchi, JP)
; Ueki, Akira; (Yamaguchi, JP) |
Correspondence
Address: |
REED SMITH LLP
375 PARK AVENUE
NEW YORK
NY
10152
US
|
Assignee: |
Ube Industries, Ltd.
|
Family ID: |
18659561 |
Appl. No.: |
09/865608 |
Filed: |
May 25, 2001 |
Current U.S.
Class: |
429/324 ;
429/326; 429/332; 429/338; 429/339; 429/341; 429/342 |
Current CPC
Class: |
H01M 2300/0037 20130101;
H01M 10/0567 20130101; Y02E 60/10 20130101; H01M 10/0525
20130101 |
Class at
Publication: |
429/324 ;
429/326; 429/332; 429/338; 429/339; 429/341; 429/342 |
International
Class: |
H01M 010/40 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2000 |
JP |
2000-154471 |
Claims
What is claimed is:
1. A non-aqueous electrolytic solution which comprises a
non-aqueous solvent and an electrolyte which further contains 0.001
to 0.8 weight % of a biphenyl derivative having the following
formula: 4in which each of Y.sup.1 and Y.sup.2 independently
represents a hydroxyl group, an alkoxy group, a hydrocarbyl group,
a hydrogen atom, an acyloxy group, an alkoxycarbonyloxy group, an
alkylsulfonyloxy group or a halogen atom, and each of p and q
independently is an integer of 1 to 3.
2. The non-aqueous electrolytic solution of claim 1, wherein the
biphenyl derivative has the following formula: 5in which Y
represents a hydroxyl group, an alkoxy group, a hydrocarbyl group,
a hydrogen atom, an acyloxy group, an alkoxycarbonyloxy group, or
an alkylsulfonyloxy group.
3. The non-aqueous electrolytic solution of claim 1, wherein the
amount of the biphenyl derivative is in the range of 0.01 to 0.5
weight %.
4. The non-aqueous electrolytic solution of claim 2, wherein the
amount of the biphenyl derivative is in the range of 0.01 to 0.5
weight %.
5. The non-aqueous electrolytic solution of claim 1, wherein the
non-aqueous solvent comprises a combination of a cyclic carbonate
and a linear chain carbonate.
6. The non-aqueous electrolytic solution of claim 2, wherein the
non-aqueous solvent comprises a combination of a cyclic carbonate
and a linear chain carbonate
7. The non-aqueous electrolytic solution of claim 1, wherein the
non-aqueous solvent comprises a high dielectric constant solvent
which is selected from the group consisting of ethylene carbonate,
propylene carbonate, and butylene carbonate, and a low viscosity
solvent which is selected from the group consisting of dimethyl
carbonate, methyl ethyl carbonate, diethyl carbonate,
tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-diode,
1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane,
.gamma.-butyrolactone, acetonitrile, methyl propionate, and
dimethylformamide.
8. The non-aqueous electrolytic solution of claim 2, wherein the
non-aqueous solvent comprises a high dielectric constant solvent
which is selected from the group consisting of ethylene carbonate,
propylene carbonate, and butylene carbonate, and a low viscosity
solvent which is selected from the group consisting of dimethyl
carbonate, methyl ethyl carbonate, diethyl carbonate,
tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane,
1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane,
.gamma.-butyrolactone, acetonitrile, methyl propionate, and
dimethylformamide.
9. A lithium secondary battery comprising a positive electrode, a
negative electrode, and a non-aqueous electrolytic solution which
comprises a non-aqueous solvent and an electrolyte which further
contains 0.001 to 0.8 weight % of a biphenyl derivative having the
following formula: 6in which each of Y.sup.1 and Y.sup.2
independently represents a hydroxyl group, an alkoxy group, a
hydrocarbyl group, a hydrogen atom, an acyloxy group, an
alkoxycarbonyloxy group, an alkylsulfonyloxy group or a halogen
atom, and each of p and q independently is an integer of 1 to
3.
10. The lithium secondary battery of claim 9, wherein the biphenyl
derivative in the non-aqueous electrolytic solution has the
following formula: 7in which Y represents a hydroxyl group, an
alkoxy group, a hydrocarbyl group, a hydrogen atom, an acyloxy
group, an alkoxycarbonyloxy group, or an alkylsulfonyloxy group.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a non-aqueous electrolytic
solution and a lithium secondary battery employing the non-aqueous
electrolytic solution. In particular, the invention relates to a
lithium secondary battery having improved electric capacity and
cycling performance, and a non-aqueous electrolytic solution which
is advantageously employable for preparing the lithium secondary
battery.
BACKGROUND OF THE INVENTION
[0002] At present, potable small electronic devices such as
personal computers, cellular phones, and video recorders equipped
with camera are widely used, and a small sized secondary battery
having light weight and high electric capacity is desired to
provide an electric source for driving such small electronic
devices. From the view-points of small size, light weight, and high
electric capacity, a lithium secondary battery is paid
attention.
[0003] The lithium secondary battery employs a positive active
electrode material comprising a complex oxide such as lithium
cobaltate, lithium nickelate, or lithium manganate, a negative
active electrode material comprising a carbonaceous material such
as graphite into which lithium ions are able to intercalate and
from which lithium ions are able to escape, and a non-aqueous
electrolytic solution of a lithium salt in a non-aqueous solvent
comprising a cyclic carbonate and a linear chain carbonate. The
lithium secondary battery is now studied for improving its
performances.
[0004] The lithium secondary battery employing LiCoO.sub.2,
LiOO.sub.4, or LiNiO.sub.2 as the positive electrode active
material is generally used under such condition that the electric
charge-discharge procedure is repeated in the range up to the
maximum operating voltage exceeding 4.1 V. In the procedure, the
conventional lithium secondary battery is apt to gradually lower in
its electric capacity when the charge-discharge cycle is repeated
for a long period. It is supposed that this trouble is caused by
oxidative decomposition of a portion of the non-aqueous solvent of
the electrolytic solution on the surface of the positive electrode
when the maxim operating voltage exceeds 4.1 V, and the
decomposition product disturbs the desired electrochemical reaction
in the battery. Therefore, the conventional lithium secondary
batteries are not satisfactory in their battery performances such
as the cycling performance and an electric capacity when the
batteries are operated in the charge-discharge cycles of which maxi
operating voltage exceeds 4.1 V.
[0005] U.S. Pat. No. 5,879,834 describes incorporation of an
aromatic additive such as biphenyl, 1,3-chlorothiophene, or furan
into a non-aqueous rechargeable lithium battery. The additive is
used in an amount of about 1% to 4%. The aromatic additive is
electrochemically polymerized at abnormally high voltages, thereby
increasing the internal resistance of the battery and thus
protecting it.
[0006] U.S. Pat. No. 6,074,777 describes incorporation of an
aromatic additive such as phenyl-R-phenyl compounds (R=aliphatic
hydrocarbon), fluorine-substituted biphenyl compounds, or
3-thiopheneacetonitrile into a non-aqueous rechargeable lithium
battery. The additive is preferably used in an amount of about
2.5%.
[0007] It is an object of the invention to provide a non-aqueous
electrolytic solution which is favorably employable for a lithium
secondary battery and which shows high battery performances such as
high electric capacity and high cycling performance, particularly,
under the conditions that the maximum operating voltage exceeds 4.1
V and/or the battery is used at high temperatures such as
40.degree. C. or higher.
[0008] It is another object of the invention to provide a lithium
secondary battery which shows high battery performances such as
high electric capacity and high cycling performance, particularly,
under the conditions that the maximum operating voltage exceeds 4.1
V and/or the battery is used at high temperatures such as
40.degree. C. or higher.
SUMMARY OF THE INVENTION
[0009] The present invention resides in a non-aqueous electrolytic
solution which comprises a non-aqueous solvent and an electrolyte
which further contains 0.001 to 0.8 weight % of a biphenyl
derivative having the formula (I): 2
[0010] in which each of Y.sup.1 and Y.sup.2 independently
represents a hydroxyl group, an alkoxy group, a hydrocarbyl group,
a hydrogen atom, an acyloxy group, an alkoxycarbonyloxy group, an
alkylsulfonyloxy group or a halogen atom, and each of p and q
independently is an integer of 1 to 3.
[0011] More preferably, the biphenyl derivative has the following
formula (II): 3
[0012] in which Y represents a hydroxyl group, an alkoxy group, a
hydrocarbyl group, a hydrogen atom, an acyloxy group, an
alkoxycarbonyloxy group, or an alkylsulfonyloxy group
[0013] In the formulas (I) and (II), the alkoxy group preferably
has a formula of --OR.sup.1 in which R.sup.1 is a hydrocarbyl group
having 1 to 12 carbon atoms; the hydrocarbyl group preferably has a
formula of -R.sup.2 in which R.sup.2 has 1 to 12 carbon atoms; the
acyloxy group preferably has a formula of --O--C(.dbd.O)-R.sup.3 in
which R.sup.3 is a hydrocarbyl group having 1 to 12 carbon atoms;
the alkoxycarbonyl group preferably has a formula of
--O--C(.dbd.O)--O-R.sup.4 in which R.sup.4 is a hydrocarbyl group
having 1 to 12 carbon atoms; the alkylsulfonyloxy group preferably
has a formula of --O--S(.dbd.O).sub.2-R.sup.5 in which R.sup.5 is a
hydrocarbyl group having 1 to 12 carbon atoms; and a halogen atom
can be F, Cl, Br or I.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The non-aqueous electrolytic solution of the invention
contains the biphenyl derivative of the formula (I) or the formula
(II) in a very small amount such as 0.001 to 0.8 wt. %, preferably
0.01 to 0.5 wt. %, more preferably 0.03 to 0.3 wt. %. If the amount
of the biphenyl derivative exceeds the upper limit, the
incorporation of the biphenyl derivative does not give satisfactory
improvements of the battery performances such as high electric
capacity and high cycling performance. If the amount of the
biphenyl derivative is less than 0.001 wt %., no noticeable
improvement is observed.
[0015] It is supposed that the appropriate amount of the biphenyl
derivative forms an appropriately thin film on the positive
electrode upon its decomposition thereon to improve the battery
performances, particularly, the cycling performance. If the amount
of the additive, i.e., the biphenyl derivative, is too larger, a
thick film is produced on the positive electrode, and the thick
film disturbs the cycling performance of the battery.
[0016] In the biphenyl derivatives of the formula (I) or the
formula (II), the substituent such as Y.sup.1, Y.sup.2 or Y.sup.3
preferably is a hydrogen atom, a hydroxyl group, a linear chain
alkoxy group such as methoxy, ethoxy, propoxy, or butoxy, a
branched chain alkoxy group such as isopropoxy or isobutoxy, a
cycloalkoxy group such as cyclopropoxy or cyclohexyloxy, an aryloxy
group such as phenoxy, p-tolyloxy, or biphenylyloxy, a linear chain
alkyl group such as methyl, ethyl, propyl, or butyl, a branched
chain alkyl group such as isopropyl or isobutyl, a cycloalkyl group
such as cyclopropyl or cyclohexyl, an aryl group such as phenyl,
p-tolyl, or biphenylyl, an acyloxy group such as acetyloxy,
propionylox, acryloyloxy, or benzoyloxy, an alkoxycarbonyloxy group
such as methoxycarbonyloxy, ethoxycarbonyloxy, phenoxycarbonyloxy,
or benzyloxycarbonyloxy, or an alkylsulfonyloxy group such as
methanesulfonyloxy, ethanesulfonyloxy, or benzensulfonyloxy.
[0017] Preferred are biphenyl derivatives of the formula (II).
Examples of the biphenyl derivatives of the formula (II) include
2-hydroxybiphenyl, 3-hydroxybiphenyl, 4-hydroxybiphenyl,
2-methoxybiphenyl, 3-methoxybiphenyl, 4-methoxybiphenyl,
p-diphenylylphenyl ether, 4-biphenylyl, p-tolyl ether 4-biphenylyl
ether, 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl,
4-ethylbiphenyl, 4-propylbiphenyl, 4-isopropylbiphenyl,
4-butylbiphenyl, 4-t-butylbiphenyl, 4-cyclohexylbiphenyl,
o-terphenyl (Y=phenyl), m-terphenyl, p-terphenyl,
2-methyl-o-terphenyl (Y=tosyl), o-qarterphenyl (Y=biphenylyl),
biphenyl, 4-biphenylyl acetate (Y=acetyloxy), 4-biphenylyl benzoate
(Y=benzyloxy), 4-biphenylyl benzylcarboxylate
(Y=benzylcarbonyloxy), 2-biphenylyl propionate, 2-biphenylyl
methylcarbonate (Y=methoxycarbonyloxy), 4-biphenylyl
methylcarbonate, 4-biphenylyl butylcarbonate (Y=butoxycarbonyloxy),
4-methanesulfonyloxybiphenyl, 4ethanesulfonyloxybiphenyl, and
4-benzenesulfonyloxybiphenyl.
[0018] The non-aqueous electrolytic solution of the invention
comprises a non-aqueous solvent which preferably comprises a
combination of a cyclic carbonate and a linear chain carbonate. The
non-aqueous solvent is also preferred to comprise a high dielectric
constant solvent such as ethylene carbonate, propylene carbonate,
or butylene carbonate, and a low viscosity solvent such as dimethyl
carbonate, methyl ethyl carbonate, diethyl carbonate,
tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane,
1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane,
.gamma.-butyrolactone, acetonitrile, methyl propionate, or
dimethylformamide. The high dielectric constant solvent and the low
viscosity solvent are preferably employed in a volume ratio of 1:9
to 4:1, preferably, 1:4 to 7:3 (former:latter).
[0019] The non-aqueous solvent may contain a phosphate ester such
as triethyl phosphate, tributyl phosphate, or trioctyl phosphate,
vinylene carbonate, and 1,3-propanesultone.
[0020] Examples of the electrolytes include LiPFG, LiPF.sub.4,
LiClO.sub.4, LiN(SO.sub.2CF.sub.3).sub.2,
LiN(SO.sub.2CF.sub.3).sub.3, LiC(SO.sub.2CF.sub.3).sub.3, LiPF,
(CF.sub.3).sub.3, LiPF.sub.3 (C.sub.2F.sub.5).sub.3 LiPF.sub.4
C.sub.2F.sub.5).sub.2, LiPF.sub.3 (iso-C.sub.3F.sub.7).sub.3, and
LiPF.sub.5(iso-CF.sub.7) The electrolytes can be employed singly or
in combination. Generally, the electrolyte can be dissolved in the
non-aqueous solvent in such an amount to give an electrolytic
solution of 0.1 M to 3 M, preferably 0.5 M to 1.5 M.
[0021] The non-aqueous electrolytic solution of the invention is
prepared, for instance, by dissolving the electrolyte in a mixture
of a cyclic carbonate and a linear chain carbonate.
[0022] The non-aqueous electrolytic solution of the invention is
preferably employed for manufacturing a lithium secondary battery.
Materials other than the electrolytic solution are known for the
manufacture lithium secondary battery, and the known materials can
be employed without specific limitations.
[0023] For instance, the positive electrode active material can be
a complex metal oxide comprising lithium and at least one metal
element selected from the group consisting of cobalt, nickel,
manganese, chromium, vanadium and iron. Examples of the complex
metal oxides include LiCoO.sub.2, LiMn.sub.2O.sub.4, and
LiNiO.sub.2.
[0024] The positive electrode can be prepared by kneading a mixture
of the above-mentioned positive electrode active material, an
electro-conductive agent such as acetylene black or carbon black, a
binder such as poly(vinylidene fluoride) (PVDF) or
polytetrafluoroethylene (PIEs), and an 1-methyl-2-pyrrolidone
solvent to produce a positive electrode composition, coating the
positive electrode composition on a metal plate such as aluminum
foil or stainless sheet, drying the coated composition, molding the
dry film under pressure, and then heating the molded film under
reduced pressure at 50 to 250.degree. C. for 2 hours The negative
electrode preferably comprises a natural or artificial graphite
having a lattice spacing (or lattice distance, in terms of 402) of
0.335 to 0.340 nm. Other known negative electrode materials such as
thermally decomposed carbonaceous articles, cokes, thermally fired
polymer articles, and carbon fibers can be employed.
[0025] The negative electrode can be prepared by kneading a mixture
of the above-mentioned graphite, a binder such as PVDF, PTFE or
ethylene-propylene diene terpolymer (EPDM), and an
1-methyl-2-pyrrolidone solvent to produce a negative electrode
composition, coating the negative electrode composition on a metal
plate such as aluminum foil or stainless sheet, drying the coated
composition at 50 to 250.degree..
[0026] There are no specific limitations with respect to the
structure of the lithium secondary battery of the invention. For
instance, the lithium secondary battery can be a battery of coin
type comprising a positive electrode, a negative electrode, plural
separators, and the electrolytic solution, or a cylindrical,
prismatic or laminate battery.
[0027] The lithium secondary battery of the invention is preferably
employed in the operating voltage range having the maximum
operating voltage exceeding 4.1 V, more preferably 4.2 V, most
preferably 4.3 V. The cut-off voltage preferably is higher than 2.0
V, more preferably is higher than 2.5 V. The battery is generally
operated at a constant current discharge of 0.1 to 2 C. The
charge-discharge cycles are preferably operated at temperatures of
20 to 100.degree. C., more preferably 40 to 80.degree. C.
EXAMPLE 1
[0028] 1) Preparation of electrolytic solution
[0029] A non-aqueous solvent, i.e., a mixture (1:2, volume ratio)
of propylene carbonate (PC) and diethyl carbonate (DEC), was
prepared. Subsequently, LiPF.sub.6 was dissolved in the non-aqueous
solvent to give a 1M concentration solution. Further, biphenyl was
added to give a 0.1 wt. % solution. Thus, an electrolytic solution
was prepared.
[0030] 2) Preparation of lithium secondary battery and measurement
of battery performances
[0031] LiCoO.sub.2 (positive electrode active material, 80 wt %),
acetylene black (electro-conductive material, 10 wt %), and
poly(vinylidene fluoride) (binder, 10 wt. %) were mixed. The
resulting mixture was diluted with 1-methyl-2-pyrrolidone. Thus
produced positive electrode composition was coated on aluminum
foil, dried, molded under pressure, and heated to give a positive
electrode.
[0032] Natural graphite (d.sub.002=0.3354, 90 wt. %) and
poly(vinylidene fluoride) (binder, 10 wt. %) were mixed. The
mixture was then diluted with 1-methyl-2-pyrrolidone. Thus produced
negative electrode composition was coated on copper foil, dried,
molded under pressure, and heated, to give a negative
electrode.
[0033] The positive and negative electrodes, a micro-porous
polypropylene film separator, and the electrolytic solution were
combined to give a coin-type battery (diameter: 20 mm, thickness:
3.2 mm).
[0034] The coin-type battery was charged for 6 hours at a high
temperature (40.degree. C.) with a constant electric current (0.8
mA) to reach 4.3 V and then the charging was continued under a
constant voltage of 4.3 V. Subsequently, the battery was discharged
to give a constant electric current (0.8 mA). The discharge was
continued to give a terminal voltage of 2.7 V. The charge-discharge
cycle was repeated 100 times.
[0035] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0036] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.5% of the initial discharge capacity. The
low temperature characteristics were satisfactory.
COMPARISON EXAMPLE 1
[0037] A secondary battery was prepared in the same manner as in
Example 1, except for adding no biphenyl to the solvent.
[0038] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0039] After the 100 cycle charge-discharge procedure, the
discharge capacity was 63.8% of the initial discharge capacity.
COMPARISON EXAMPLE 2
[0040] A secondary battery was prepared in the same manner as in
Comparison Example 1.
[0041] Thus prepared battery was charged in the same manner as in
Example 1, except that the charging procedure was performed to
reach 4.1 V and then the charging was continued under a constant
voltage of 4.1 V.
[0042] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0043] The initial discharge capacity was 0.90 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0044] After the 100 cycle charge-discharge procedure, the
discharge capacity was 75.3% of the initial discharge capacity.
COMPARISON EXAMPLE 3
[0045] A secondary battery was prepared in the same manner as in
Example 1, except that biphenyl was added to the solvent in an
amount of 2.5 wt. %.
[0046] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0047] The initial discharge capacity was 1.00 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0048] After the 100 cycle charge-discharge procedure, the
discharge capacity was 20.7% of the initial discharge capacity.
COMPARISON EXAMPLE 4
[0049] A secondary battery was prepared in the same manner as in
Example 1, except that biphenyl was added to the solvent in an
amount of 2.5 wt. %.
[0050] Thus prepared battery was charged in the same manner as in
Example 1, except that the charging procedure was performed at
20.degree. C. (ambient temperature).
[0051] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0052] The initial discharge capacity was 1.00 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0053] After the 100 cycle charge-discharge procedure, the
discharge capacity was 62.20% of the initial discharge
capacity.
COMPARISON EXAMPLE 5
[0054] A secondary battery was prepared in the same manner as in
Example 1, except that biphenyl was added to the solvent in an
amount of 2.5 wt. %.
[0055] Thus prepared battery was charged in the same manner as in
Example 1, except that the charging procedure was performed to
reach 4.1 V and then the charging was continued under a constant
voltage of 4.1 V.
[0056] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0057] The initial discharge capacity was 0.90 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0058] After the 100 cycle charge-discharge procedure, the
discharge capacity was 73.7%. of the initial discharge
capacity.
COMPARISON EXAMPLE 6
[0059] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt % of biphenyl was replaced with 2.5
wt. % of 2,2-diphenylpropane.
[0060] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0061] The initial discharge capacity was 1.00 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0062] After the 100 cycle charge-discharge procedure, the
discharge capacity was 58.8% of the initial discharge capacity.
EXAMPLE 2
[0063] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.05
wt. % of 4-methoxybiphenyl.
[0064] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0065] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0066] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.8% of the initial discharge capacity.
EXAMPLE 3
[0067] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt. % of 4-methoxybiphenyl.
[0068] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0069] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0070] After the 100 cycle charge-discharge procedure, the
discharge capacity was 92.4% of the initial discharge capacity.
EXAMPLE 4
[0071] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.3
wt. % of 4-methoxybiphenyl.
[0072] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0073] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0074] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.7% of the initial discharge capacity.
EXAMPLE 5
[0075] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.5
wt. % of 4-methoxybiphenyl.
[0076] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0077] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0078] After the 100 cycle charge-discharge procedure, the
discharge capacity was 88.8% of the initial discharge capacity.
EXAMPLE 6
[0079] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt. % of 4-hydroxybiphenyl.
[0080] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0081] The initial discharge capacity was 1.00 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0082] After the 100 cycle charge-discharge procedure, the
discharge capacity was 91.4% of the initial discharge capacity.
EXAMPLE 7
[0083] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt. % of o-terphenyl.
[0084] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure-
[0085] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0086] After the 100 cycle charge-discharge procedure, the
discharge capacity was 91.2% of the initial discharge capacity.
EXAMPLE 8
[0087] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt % of 4-biphenylyl acetate.
[0088] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0089] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0090] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.1% of the initial discharge capacity.
EXAMPLE 9
[0091] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt. % of 4-biphenylyl methylcarbonate.
[0092] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0093] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0094] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.7% of the initial discharge capacity.
EXAMPLE 10
[0095] A secondary battery was prepared in the same manner as in
Example 1, except that 0.1 wt. % of biphenyl was replaced with 0.1
wt. % of 4-methanesulfonyloxybiphenyl.
[0096] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0097] The initial discharge capacity was 1.03 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0098] After the 100 cycle charge-discharge procedure, the
discharge capacity was 90.3% of the initial discharge capacity
EXAMPLE 11
[0099] A secondary battery was prepared in the same manner as in
Example 1, except that the natural graphite was replaced with
artificial graphite.
[0100] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure
[0101] The initial discharge capacity was 1.06 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0102] After the 100 cycle charge-discharge procedure, the
discharge capacity was 93.2% of the initial discharge capacity.
EXAMPLE 12
[0103] A secondary battery was prepared in the same manner as in
Example 11, except that LiCo% of the positive electrode material
was replaced with LiMn.sub.2O.sub.4.
[0104] The prepared secondary battery was subjected to the 100
cycle charge-discharge procedure.
[0105] The initial discharge capacity was 0.85 (relative value
based on 1 for that measured in a battery of Comparison Example 1
which contained no biphenyl in the electrolytic solution).
[0106] After the 100 cycle charge-discharge procedure, the
discharge capacity was 93.0% of the initial discharge capacity.
[0107] The preparations and evaluations of the batteries of
Examples 1 to 12 and Comparison Examples 1 to 6 are summarized in
Table 1. In Table 1, the standard conditions are as follows:
[0108] Positive electrode: LiCoO.sub.2
[0109] Negative electrode: natural graphite
[0110] Terminal voltage for charging: 4.3 V
[0111] Cycle temperature: 40.degree. C.
[0112] Electrolytic solution: 1M LiPF.sub.6 in EC/DEC=1/2
1TABLE 1 Additive Initial discharge 100 Cycle Example (wt. %)
capacity (relative) retention Ex. 1 biphenyl (0.1) 1.03 90.5% Com.1
none 1 63.8% Com.2* none 0.90 75.3% Com.3 biphenyl (2.5) 1.00 20.7%
Com.4* biphenyl (2.5) 1.00 62.2% Com.5* biphenyl (2.5) 0.90 73.7%
Com.6 2,2-diphenyl- 1.00 58.8% propane (2.5) Ex. 2 4-methoxy- 1.03
90.8% biphenyl (0.05) Ex. 3 4-methoxy- 1.03 92.4% biphenyl (0.1)
Ex. 4 4-methoxy- 1.03 90.7% biphenyl (0.3) Ex. 5 4-methoxy- 1.03
88.8% biphenyl (0.5) Ex. 6 4-hydroxy- 1.00 91.4% biphenyl (0.1) Ex.
7 o-terphenyl (0.1) 1.03 91.2% Ex. 8 4-biphenylyl 1.03 90.1%
acetate (0.1) Ex. 9 4-biphenylyl methyl- 1.03 90.7% carbonate (0.1)
Ex. 10 4-methanesulfonyloxy- 1.03 90.3% biphenyl (0.1) Ex. 11*
biphenyl (0.1) 1.06 93.2% Ex. 12* biphenyl (0.1) 0.85 93.0%
[0113] Remarks:
[0114] Com. Ex 2 (Terminal voltage for charging: 4.1 V)
[0115] Com. Ex. 4 (Cycle temperature: 20.degree. C.)
[0116] Com. Ex. 5 (Terminal voltage for charging: 4.1 V)
[0117] Example 11 (Negative electrode: artificial graphite)
[0118] Example 12 (Negative electrode: artificial graphite,
[0119] Positive electrode: LiMn.sub.2O.sub.4)
* * * * *