U.S. patent application number 09/928406 was filed with the patent office on 2003-01-02 for lithium secondary battery.
Invention is credited to Arai, Juichi, Kobayashi, Mitsuru, Yamauchi, Shuuko.
Application Number | 20030003370 09/928406 |
Document ID | / |
Family ID | 18990105 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030003370 |
Kind Code |
A1 |
Arai, Juichi ; et
al. |
January 2, 2003 |
Lithium secondary battery
Abstract
The present invention provides a lithium secondary battery
comprising a nonaqueous electrolytic solution containing a compound
which is oxidized at a voltage higher than a charge end voltage of
the lithium secondary battery and a compound which inhibits
reactions at voltages lower than said charge end voltage.
Inventors: |
Arai, Juichi;
(Higashiibaraki-gun, JP) ; Yamauchi, Shuuko;
(Hitachi, JP) ; Kobayashi, Mitsuru; (Hitachiohta,
JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
20037-1526
US
|
Family ID: |
18990105 |
Appl. No.: |
09/928406 |
Filed: |
August 14, 2001 |
Current U.S.
Class: |
429/326 ;
429/199; 429/343 |
Current CPC
Class: |
H01M 10/05 20130101;
Y02E 60/10 20130101; H01M 10/0566 20130101; Y02T 10/70 20130101;
H01M 10/0567 20130101; H01M 10/0569 20130101; H01M 10/4235
20130101; H01M 10/052 20130101; H01M 2300/0034 20130101; H01M
10/0525 20130101; H01M 6/164 20130101; H01M 6/168 20130101; Y10T
29/49108 20150115 |
Class at
Publication: |
429/326 ;
429/199; 429/343 |
International
Class: |
H01M 010/40 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2001 |
JP |
2001-144098 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. A lithium secondary battery comprising a nonaqueous electrolytic
solution containing a compound which is oxidized at a voltage
higher than a charge end voltage of the lithium secondary battery
and a compound which inhibits reactions at voltages lower than said
charge end voltage.
2. The lithium secondary battery of claim 1 wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 3(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
3. The lithium secondary battery according to claim 2 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
4. The lithium secondary battery according to claim 2 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 4(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
5. The lithium secondary battery according to claim 4 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
6. A lithium secondary battery having a nonaqueous electrolytic
solution characterized in that the lithium secondary battery has a
charge capacity of C.sub.1 when it (in discharged state) is charged
with constant current until a voltage V.sub.1 of 1.2V is reached
and the lithium secondary battery has a charge capacity of C.sub.2
when it is charged further (at a voltage higher than V.sub.1) until
it cannot be charged any longer, with the ratio (.xi.) of
C.sub.1/C.sub.2 being lower than 0.7.
7. The lithium secondary battery of claim 6 wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 5(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
8. The lithium secondary battery according to claim 7 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
9. The lithium secondary battery according to claim 7 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 6(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
10. The lithium secondary battery according to claim 9 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, to diphenylmethylsilane,
4-methylpheyltrimethylsilane, and diphenyldimethoxysilane.
11. A lithium secondary battery comprising a nonaqueous
electrolytic solution containing a compound which is oxidized at a
voltage higher than a charge end voltage of the lithium secondary
battery and a compound which inhibits reactions at voltages lower
than said charge end voltage wherein said nonaqueous electrolytic
solution is composed of a fluorinated solvent represented by the
chemical formula (1) and an aromatic compound represented by the
chemical formula (2) below. Rf.sub.1--X--Rf.sub.2 (1) (where
Rf.sub.1 denotes an entirely or partly fluorinated C.sub.2-10 alkyl
group, Rf.sub.2 denotes an entirely or partly fluorinated C.sub.1-5
alkyl group, and X denotes an ether or ester.) 7(where R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 each denotes hydrogen, fluorine,
chlorine, bromine, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, an alkyl-substituted phenyl group or
phenoxy group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
12. The lithium secondary battery according to claim 11 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
13. The lithium secondary battery according to claim 11 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 8(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
14. The lithium secondary battery according to claim 13 wherein
said phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
15. A lithium secondary battery having a nonaqueous electrolytic
solution characterized in that the lithium secondary battery has a
charge capacity of C.sub.1 when it (in discharged state) is charged
with constant current until a voltage V.sub.1 of 1.2V is reached
and the lithium secondary battery has a charge capacity of C.sub.2
when it is charged further (at a voltage higher than V.sub.1) until
it cannot be charged any longer, with the ratio (.xi.) of
C.sub.1/C.sub.2 being lower than 0.7 and wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 9(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
16. The lithium secondary battery according to claim 15 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
17. The lithium secondary battery according to claim 15 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 10(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
18. The lithium secondary battery according to claim 17 wherein
said phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
19. An electrical appliance using a lithium secondary battery as a
power source which comprises a means for protecting the lithium
secondary batteries from overcharging and overdischarging being
free from temperature and pressure detection of the batteries, a
means for detecting voltages or current of the batteries and a
means for controlling to turn on or off the batteries said lithium
secondary battery comprising a nonaqueous electrolytic solution
containing a compound which is oxidized at a voltage higher than a
charge end voltage of the lithium secondary battery and a compound
which inhibits reactions at voltages lower than said charge end
voltage.
20. The electrical appliance of claim 19 wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 11(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
21. The electrical appliance according to claim 20 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
22. The electrical appliance according to claim 20 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 12(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
23. The electrical appliance according to claim 22 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
24. The electrical appliance according to claim 19 wherein said
appliance is an electric car.
25. An electrical appliance using a lithium secondary battery as a
power source which comprises a means for protecting the lithium
secondary batteries from overcharging and overdischarging being
free from temperature and pressure detection of the batteries, a
means for detecting voltages or current of the batteries and a
means for controlling to turn on or off the said lithium secondary
battery comprising a nonaqueous electrolytic solution characterized
in that the lithium secondary battery has a charge capacity of
C.sub.1 when it (in discharged state) is charged with constant
current until a voltage V.sub.1 of 1.2V is reached and the lithium
secondary battery has a charge capacity of C.sub.2 when it is
charged further (at a voltage higher than V.sub.1) until it cannot
be charged any longer, with the ratio (.xi.) of C.sub.1/C.sub.2
being lower than 0.7.
26. The electrical appliance of claim 25 wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 13(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
27. The electrical appliance according to claim 26 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
28. The electrical appliance according to claim 26 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 14(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
29. The electrical appliance according to claim 28 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
30. The electrical appliance according to claim 25 wherein said
appliance is an electric car.
31. An electrical appliance using a lithium secondary battery as a
power source which comprises a means for protecting the lithium
secondary batteries from overcharging and overdischarging being
free from temperature and pressure detection of the batteries, a
means for detecting voltages or current of the batteries and a
means for controlling to turn on or off the batteries said lithium
secondary battery comprising a nonaqueous electrolytic solution
containing a compound which is oxidized at a voltage higher than a
charge end voltage of the lithium secondary battery and a compound
which inhibits reactions at voltages lower than said charge end
voltage wherein said nonaqueous electrolytic solution is composed
of a fluorinated solvent represented by the chemical formula (1)
and an aromatic compound represented by the chemical formula (2)
below. Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an
entirely or partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2
denotes an entirely or partly fluorinated C.sub.1-5 alkyl group,
and X denotes an ether or ester.) 15(where R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 each denotes hydrogen, fluorine, chlorine,
bromine, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, an alkyl-substituted phenyl group or phenoxy
group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
32. The electrical appliance according to claim 31 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
33. The electrical appliance according to claim 31 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 16(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
34. The electrical appliance according to claim 33 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
35. The electrical appliance according to claim 31 wherein said
appliance is an electric car.
36. An electrical appliance using a lithium secondary battery as a
power source which comprises a means for protecting the lithium
secondary batteries from overcharging and overdischarging being
free from temperature and pressure detection of the batteries, a
means for detecting voltages or current of the batteries and a
means for controlling to turn on or off the batteries said lithium
secondary battery comprising a nonaqueous electrolytic solution
characterized in that the lithium secondary battery has a charge
capacity of C.sub.1 when it (in discharged state) is charged with
constant current until a voltage V.sub.1 of 1.2V is reached and the
lithium secondary battery has a charge capacity of C.sub.2 when it
is charged further (at a voltage higher than V.sub.1) until it
cannot be charged any longer, with the ratio (4) of C.sub.1/C.sub.2
being lower than 0.7 and wherein said nonaqueous electrolytic
solution is composed of a fluorinated solvent represented by the
chemical formula (1) and an aromatic compound represented by the
chemical formula (2) below. Rf.sub.1--X--Rf.sub.2 (1) (where
Rf.sub.1 denotes an entirely or partly fluorinated C.sub.2-10 alkyl
group, Rf.sub.2 denotes an entirely or partly fluorinated C.sub.1-5
alkyl group, and X denotes an ether or ester.) 17(where R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 each denotes hydrogen, fluorine,
chlorine, bromine, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, an alkyl-substituted phenyl group or
phenoxy group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
37. The electrical appliance according to claim 36 wherein the
fluorinated solvent is methyl nanofluorobutyl ether.
38. The electrical appliance according to claim 36 wherein the
aromatic compound is a phenylsilane derivative represented by the
chemical formula (3) below. 18(where R.sub.7, R.sub.8, and R.sub.9
each denotes hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, a benzyl group, fluorine, chlorine,
bromine, or a C.sub.1-3 alkyl-substituted phenyl group, phenoxy
group, or benzyl group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13,
and R.sub.14 each denotes a C.sub.1-3 alkoxyl group, a phenyl
group, a benzyl group, or a phenyl group, phenoxy group, or benzyl
group substituted with fluorine, chlorine, or bromine.)
39. The electrical appliance according to claim 38 wherein said
phenylsilane derivative is selected from the group comprising
diphenylsilane, diphenylmethylsilane, 4-methylpheyltrimethylsilane,
and diphenyldimethoxysilane.
40. The electrical appliance according to claim 36 wherein said
appliance is an electric car.
41. A method of fabricating a lithium secondary battery comprising
the steps of: providing an anode; providing a cathode; providing a
separator; and providing a nonaqueous electrolytic solution
containing a compound which is oxidized at a voltage higher than a
charge end voltage of the lithium secondary battery and a compound
which inhibits reactions at voltages lower than said charge end
voltage.
42. The method of claim 41 wherein said nonaqueous electrolytic
solution is composed of a fluorinated solvent represented by the
chemical formula (1) and an aromatic compound represented by the
chemical formula (2) below. Rf.sub.1--X--Rf.sub.2 (1) (where
Rf.sub.1 denotes an entirely or partly fluorinated C.sub.2-10 alkyl
group, Rf.sub.2 denotes an entirely or partly fluorinated C.sub.1-5
alkyl group, and X denotes an ether or ester.) 19(where R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 each denotes hydrogen, fluorine,
chlorine, bromine, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, an alkyl-substituted phenyl group or
phenoxy group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
43. The method according to claim 42 wherein the fluorinated
solvent is methyl nanofluorobutyl ether.
44. The method according to claim 42 wherein the aromatic compound
is a phenylsilane derivative represented by the chemical formula
(3) below. 20(where R.sub.7, R.sub.8, and R.sub.9 each denotes
hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, a benzyl group, fluorine, chlorine, bromine, or a
C.sub.1-3 alkyl-substituted phenyl group, phenoxy group, or benzyl
group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13, and R.sub.14
each denotes a C.sub.1-3 alkoxyl group, a phenyl group, a benzyl
group, or a phenyl group, phenoxy group, or benzyl group
substituted with fluorine, chlorine, or bromine.)
45. The method according to claim 44 wherein said phenylsilane
derivative is selected from the group comprising diphenylsilane,
diphenylmethylsilane, 4-methylpheyltrimethylsilane, and
diphenyldimethoxysilane.
46. A method of fabricating a lithium secondary battery comprising
the steps of: providing an anode; providing a cathode; providing a
separator; and providing a nonaqueous electrolytic solution
characterized in that the lithium secondary battery has a charge
capacity of C.sub.1 when it (in discharged state) is charged with
constant current until a voltage V.sub.1 of 1.2V is reached and the
lithium secondary battery has a charge capacity of C.sub.2 when it
is charged further (at a voltage higher than V.sub.1) until it
cannot be charged any longer, with the ratio (.xi.) of
C.sub.1/C.sub.2 being lower than 0.7.
47. The method of claim 46 wherein said nonaqueous electrolytic
solution is composed of a fluorinated solvent represented by the
chemical formula (1) and an aromatic compound represented by the
chemical formula (2) below. Rf.sub.1--X--Rf.sub.2 (1) (where
Rf.sub.1 denotes an entirely or partly fluorinated C.sub.2-10 alkyl
group, Rf.sub.2 denotes an entirely or partly fluorinated C.sub.1-5
alkyl group, and X denotes an ether or ester.) 21(where R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 each denotes hydrogen, fluorine,
chlorine, bromine, a C.sub.1-3 alkyl group or alkoxyl group, a
phenyl group, a phenoxy group, an alkyl-substituted phenyl group or
phenoxy group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
48. The method according to claim 47 wherein the fluorinated
solvent is methyl nanofluorobutyl ether.
49. The method according to claim 47 wherein the aromatic compound
is a phenylsilane derivative represented by the chemical formula
(3) below. 22(where R.sub.7, R.sub.8, and R.sub.9 each denotes
hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, a benzyl group, fluorine, chlorine, bromine, or a
C.sub.1-3 alkyl-substituted phenyl group, phenoxy group, or benzyl
group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13, and R.sub.14
each denotes a C.sub.1-3 alkoxyl group, a phenyl group, a benzyl
group, or a phenyl group, phenoxy group, or benzyl group
substituted with fluorine, chlorine, or bromine.)
50. The method according to claim 49 wherein said phenylsilane
derivative is selected from the group comprising diphenylsilane,
diphenylmethylsilane, 4-methylpheyltrimethylsilane, and
diphenyldimethoxysilane.
51. A method of fabricating a lithium secondary battery comprising
the steps of: providing an anode; providing a cathode; providing a
separator; and providing a nonaqueous electrolytic solution
containing a compound which is oxidized at a voltage higher than a
charge end voltage of the lithium secondary battery and a compound
which inhibits reactions at voltages lower than said charge end
voltage wherein said nonaqueous electrolytic solution is composed
of a fluorinated solvent represented by the chemical formula (1)
and an aromatic compound represented by the chemical formula (2)
below. Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an
entirely or partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2
denotes an entirely or partly fluorinated C.sub.1-5 alkyl group,
and X denotes an ether or ester.) 23(where R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 each denotes hydrogen, fluorine, chlorine,
bromine, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, an alkyl-substituted phenyl group or phenoxy
group, a C.sub.1-4 carboxyl group, a benzyl group, or an
alkyl-substituted or alkoxyl-substituted silyl group; and R.sub.5
and R.sub.6 each denotes hydrogen, fluorine, chlorine, bromine, or
a C.sub.1-3 alkyl group.)
52. The method according to claim 51 wherein the fluorinated
solvent is methyl nanofluorobutyl ether.
53. The method according to claim 51 wherein the aromatic compound
is a phenylsilane derivative represented by the chemical formula
(3) below. 24(where R.sub.7, R.sub.8, and R.sub.9 each denotes
hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, a benzyl group, fluorine, chlorine, bromine, or a
C.sub.1-3 alkyl-substituted phenyl group, phenoxy group, or benzyl
group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13, and R.sub.14
each denotes a C.sub.1-3 alkoxyl group, a phenyl group, a benzyl
group, or a phenyl group, phenoxy group, or benzyl group
substituted with fluorine, chlorine, or bromine.)
54. The method according to claim 53 wherein said phenylsilane
derivative is selected from the group comprising diphenylsilane,
diphenylmethylsilane, 4-methylpheyltrimethylsilane, and
diphenyldimethoxysilane.
55. A method of fabricating a lithium secondary battery comprising
the steps of: providing an anode; providing a cathode; providing a
separator; and providing a nonaqueous electrolytic solution
characterized in that the lithium secondary battery has a charge
capacity of C.sub.1 when it (in discharged state) is charged with
constant current until a voltage V.sub.1 of 1.2V is reached and the
lithium secondary battery has a charge capacity of C.sub.2 when it
is charged further (at a voltage higher than V.sub.1) until it
cannot be charged any longer, with the ratio (.xi.) of
C.sub.1/C.sub.2 being lower than 0.7 and wherein said nonaqueous
electrolytic solution is composed of a fluorinated solvent
represented by the chemical formula (1) and an aromatic compound
represented by the chemical formula (2) below.
Rf.sub.1--X--Rf.sub.2 (1) (where Rf.sub.1 denotes an entirely or
partly fluorinated C.sub.2-10 alkyl group, Rf.sub.2 denotes an
entirely or partly fluorinated C.sub.1-5 alkyl group, and X denotes
an ether or ester.) 25(where R.sub.1, R.sub.2, R.sub.3, and R.sub.4
each denotes hydrogen, fluorine, chlorine, bromine, a C.sub.1-3
alkyl group or alkoxyl group, a phenyl group, a phenoxy group, an
alkyl-substituted phenyl group or phenoxy group, a C.sub.1-4
carboxyl group, a benzyl group, or an alkyl-substituted or
alkoxyl-substituted silyl group; and R.sub.5 and R.sub.6 each
denotes hydrogen, fluorine, chlorine, bromine, or a C.sub.1-3 alkyl
group.)
56. The method according to claim 55 wherein the fluorinated
solvent is methyl nanofluorobutyl ether.
57. The method according to claim 55 wherein the aromatic compound
is a phenylsilane derivative represented by the chemical formula
(3) below. 26(where R.sub.7, R.sub.8, and R.sub.9 each denotes
hydrogen, a C.sub.1-3 alkyl group or alkoxyl group, a phenyl group,
a phenoxy group, a benzyl group, fluorine, chlorine, bromine, or a
C.sub.1-3 alkyl-substituted phenyl group, phenoxy group, or benzyl
group; and R.sub.10, R.sub.11, R.sub.12, R.sub.13, and R.sub.14
each denotes a C.sub.1-3 alkoxyl group, a phenyl group, a benzyl
group, or a phenyl group, phenoxy group, or benzyl group
substituted with fluorine, chlorine, or bromine.)
58. The method according to claim 57 wherein said phenylsilane
derivative is selected from the group comprising diphenylsilane,
diphenylmethylsilane, 4-methylpheyltrimethylsilane, and
diphenyldimethoxysilane.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a lithium secondary battery
and, more particularly, to a lithium secondary battery having
improved overcharge characteristics as well as an electrical
appliance utilizing the lithium secondary battery.
DISCUSSION OF THE RELATED ART
[0002] The rapid diffusion of portable electronic machines or
appliances has created a demand for smaller and lighter batteries
as their power source. Primary batteries that meet this demand are
lithium primary cells having an anode of lithium metal which are
small is size and light in weight and yet have a high capacity.
Unfortunately, they cannot be used repeatedly by charging and hence
they are limited in use. Secondary batteries such as lead
batteries, nickel-cadmium batteries, and nickel-hydrogen batteries
can be used repeatedly, but they are low in operating voltage
because they rely on an aqueous electrolytic solution. Therefore,
they are not suitable for use which requires high capacity, small
size, and light weight.
[0003] Demand for a secondary battery having a high capacity, small
size, and light weight has been met by the development of a
practical lithium ion battery. It has found widespread use in
portable electronic and communications machines and equipment, such
as CAM coder, digital camera, cellular phone, and notebook
computer. It has also found as a power source for hybrid cars and
pure electric cars.
[0004] A lithium ion battery is characterized by its anode and
cathode active materials made of a substance capable of occluding
and releasing lithium ions. In principle, it works without
requiring electrodeposition of lithium metal. Its anode and cathode
may be made of a variety of substances capable of occluding and
releasing lithium ions. Their combination permits one to design the
battery capacity and working voltage as desired. For example, the
cathode is practically made of a carbonaceous material. It is
expected to be made of a Group IVA element or an oxide thereof, a
lithium-transition metal composite nitride, or an organic compound
such as polyacetylene. The anode is practically made of
LiMn.sub.2O.sub.4 or LiCoO.sub.2 and will be made of LiNiO.sub.2,
LiFeO.sub.2, or LiMnO.sub.2 under developmental stage. A lithium
ion battery formed from the above-mentioned anode active material
and a carbonaceous material for the cathode undergoes charging by
the following mechanism. The anode permits lithium to dissolve in
an electrolytic solution composed of an organic solvent and a
lithium salt (as en electrolyte) dissolved therein. The cathode
(which is separated from the anode by a fine porous separator)
causes the carbonaceous material to occlude (by intercalation)
lithium ions from the electrolytic solution. Discharging proceeds
in the reverse process, thereby delivering electrons to the
external circuit.
[0005] The above-mentioned lithium ion battery has a designed
battery capacity which is determined by the amount of lithium in
the anode or the capacity of the cathode occluding lithium ions,
whichever smaller. Charging in excess of this battery capacity is
referred to as overcharging. In the overcharging state, the anode
releases more lithium than it should keep, causing the active
material to disintegrate, and the cathode receives excess lithium
ions, causing lithium metal to separate out (a phenomenon called
dendrite). This results in the battery increasing in voltage and
temperature. Thus, overcharging of lithium batteries poses a
problem with battery safety.
[0006] To address this problem, there has been proposed a method of
inhibiting overcharging by causing the electrolytic solution to
consume current when overcharging occurs. See, for example,
Japanese Patent Laid-open Nos. 338347/1994, 302614/1995,
106835/1997, 17447/1994, 50822/1997, and 162512/1999. The proposed
method consists of incorporating the electrolytic solution with an
aromatic compound which has an oxidation potential which is higher
than the anode potential (usually 4.1-4.3 V) at the time of
charging. The object is achieved as the aromatic compound undergoes
oxidation reaction, thereby consuming overcharging current and
inhibiting reactions due to overcharging. This action is
attributable to the oxidation reduction reaction of the .pi.
electron conjugated system of the aromatic compound.
[0007] The above-mentioned aromatic compound produces a good effect
of inhibiting overcharging but has a disadvantage of deteriorating
the cycle characteristics and storage characteristics of the
battery.
[0008] In order to address this problem, there has been proposed a
new compound, as disclosed in Japanese Patent Laid-open Nos.
156243/2000, 58112/2000, 58113/2000, 58114/2000, 58116/2000, and
58117/2000. The proposed compound produces a good effect but has a
disadvantage because it contains many phenyl groups in the molecule
and hence has a high molecular weight. The disadvantage is that the
compound is low in solubility (and hence is limited in its amount
that can be added to the electrolytic solution) and has an extended
.pi. electron conjugated system (to inhibit overcharging), with the
result that consumption of overcharging current by each methyl
group is low and the effect per unit amount added is poor.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an
electrolyte with a compound which has a high solubility and a low
molecular weight. It is another object of the present invention to
provide a lithium battery having improved safety owing to an
electrolytic solution which effectively inhibits overcharging and
has no adverse effect on storage characteristics. Further, another
object of the present invention is to provide an electrical
appliance utilizing the lithium secondary battery of the present
invention.
[0010] According to the present invention, the above-mentioned
object is achieved by a lithium secondary battery which is
characterized in that its nonaqueous electrolytic solution contains
a compound which is oxidized at a voltage higher than the charge
end voltage of the lithium secondary battery and a compound which
inhibits reactions at voltages lower than said charge end
voltage.
[0011] The lithium secondary battery of the present invention is
characterized in that it has a charge capacity of C.sub.1 when it
(in discharged state) is charged with constant current until a
voltage V.sub.1 of 1.2V is reached and it has a charge capacity of
C.sub.2 when it is charged further (at a voltage higher than
V.sub.1) until it cannot be charged any longer, with the ratio (4)
of C.sub.1/C.sub.2 being lower than 0.7.
[0012] The lithium secondary battery of the present invention
achieves its good performance owing to the electrolytic solution
which contains a fluorinated solvent represented by the chemical
formula (1) below and an aromatic compound represented by the
chemical formula (2) as an overcharge inhibiting substance.
Rf.sub.1--X--Rf.sub.2 (1) 1
[0013] An overcharge inhibiting substance represented by the
chemical formula (3) below produces a better effect. 2
[0014] The fluorinated solvent represented by the chemical formula
(1), which is to be incorporated into the electrolytic solution, is
exemplified by the following.
[0015] 2,2,2-trifluoromethyl ethyl ether,
[0016] 2,2,2-trifluoroethyl difluoromethyl ether,
[0017] 2,2,3,3,3-pentafluoropropyl methyl ether,
[0018] 2,2,3,3,3-pentafluoropropyl difluoromethyl ether,
[0019] 2,2,3,3,3-pentafluoropropyl 1,1,2,2-tetrafluoroethyl
ether,
[0020] 1,1,2,2-tetrafluoroethyl methyl ether,
[0021] 1,1,2,2-tetrafluoroethyl ethyl ether,
[0022] 1,1,2,2-tetrafluoroethyl 1,1,2,2-trifluoroethyl ether,
[0023] 2,2,3,3,3-tetrafluoropropyl difluoromethyl ether,
[0024] 1,1,2,2-tetrafluoroethyl 2,2,3,3-trifluoroethyl ether,
[0025] Hexafluoroisopropyl methyl ether,
[0026] 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl
ether,
[0027] 1,1,2,3,3,3-hexafluoropropyl methyl ether,
[0028] 1,1,2,3,3,3-hexafluoropropyl ethyl ether,
[0029] 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether,
[0030] Methyl perfluoropropionate,
[0031] Methyl perfluorobutyrate,
[0032] Ethyl perfluorobutyrate,
[0033] Methyl perfluorooctanate,
[0034] Ethyl perfluorooctanate,
[0035] Ethyl difluoroacetate,
[0036] Ethyl 5H-octafluoropnetanoate,
[0037] Ethyl 7H-decafluoroheptanoate,
[0038] Ethyl 9H-decafluoronanoate,
[0039] Methyl 2-trifluoromethyl-3,3,3-trifluoropropionate,
[0040] Methyl nanofluorobutyl ether,
[0041] Ethyl nanofluorobutyl ether,
[0042] Propyl nanofluorobutyl ether, and
[0043] Butyl nanofluorobutyl ether.
[0044] Other solvents than fluorinated solvents include the
following.
[0045] Cyclic or chain esters (such as ethylene carbonate,
fluoropropylene carbonate, butylene carbonate, chloroethylene
carbonate, fluoroethylene carbonate, difluoroethylene carbonate,
trifluoromethylpropylene carbonate, vinylene carbonate,
dimethylvinylene carbonate, dimethyl carbonate, ethylmethyl
carbonate, diethyl carbonate, diphenyl carbonate, 1,3-propylene
carbonate, and 2,2-dimethyl-1,3-propylene carbonate); cyclic or
chain ethers (such as dimethoxy methane, 1,2-dimethoxyethane,
diglyme, triglyme, 1,3-di-oxolane, tetrahydrofuran, and
2-methylterahydrofuran); .gamma.-butyrolactone, sulfolane, methyl
propionate, ethyl propionate, ethylene sulfide, dimethylsulfoxide,
ethylmethylsulfoxide, diethylsulfoxide, methylpropylsulfoxide, and
ethylpropylsulfoxide. They may be used alone or in combination with
one another.
[0046] The electrolytic solution of the lithium battery contains a
lithium salt as the supporting electrolyte.
[0047] Examples of the supporting electrolyte include LiPF.sub.6,
LiBF.sub.4, LiClO.sub.4, LiSO.sub.3CF.sub.3, LiN(SO.sub.2CF.sub.3),
LiN(SO.sub.2CF.sub.2CF.sub.3), LiC(SO.sub.2CF.sub.2CF.sub.3).sub.3,
LiC(SO.sub.2CF.sub.3).sub.3, LiI, LiCl, LiF,
LiPF.sub.5(SO.sub.2CF.sub.3)- , and
LiPF.sub.4(SO.sub.2CF.sub.3).sub.2.
[0048] They may be used alone or in combination with one
another.
[0049] Examples of the overcharge inhibiting compound represented
by the chemical formula 2 or 3 include the following.
[0050] 4-biphneyl acetate, phehyl propionate, 4-biphenyl benzoate,
4-biphenylbenzyl carboxylate, 2-biphenyl propionate,
1,4-diphenoxybenzene, 1,3-diphenoxybenzene, diphenyl ether,
3-phenxytoluene, anisole, 2-chloroanisole, 3-chloroanisole,
4-fluoroanisole, 4-chloroanisole, 4-bromoanisole,
2,4-difluoroanisole, 3,5-difluoroanisole, 2,4-dichloroanisole,
2,4-dibromoanisole, ethoxybenzene, 2,4-difluoroethoxybenzene,
2,4-difluoropropoxybenzene, 2,5-difluoroanisole,
2,6-difluoroanisole, 3,4-difluoroanisole, 3,5-fluoroanisole,
1,2-dimethoxybenzene, 1,2-dimethoxy-4-fluorobenzne,
1,2-dimethoxy-4-chlorobenzene, 1,2-diemthoxy-4-bromobenzene,
1,3-dimethoxy-5-bromobenzene, 2,4-dichlorotoluene, 2-chloroxylene,
4-chloro-o-xylene, and 4-bromo-m-xylene. Other examples include
phenyltrimethylsilane, benzyltrimethylsilane, diphehylmethylsilane,
diphenyldimethoxysilane, diphenylsilane,
4-methoxyphenylmethylsilane, and triphenylsilane.
[0051] The cathode of the lithium secondary battery may be formed
from lithium metal, lithium-aluminum alloy, natural or artificial
graphite, amorphous carbon, a composite material of carbon with a
substance (such as silicon, germanium, and aluminum) which can be
alloyed with lithium, or silicon oxide or tin oxide or a composite
material thereof with carbon.
[0052] The anode of the lithium secondary battery may be formed
from any of the following materials. A composite oxide of lithium
with cobalt, nickel, or iron; a material incorporated with
transition metal, silicon, germanium, aluminum, manganese, or
magnesium; lithium manganate or a mixture thereof with lithium,
transition metal, silicon, germanium, aluminum, manganese, or
magnesium; or a material whose crystal is partly replaced by any of
the above-mentioned materials.
[0053] The separator of the lithium secondary battery may be formed
from a fine porous film of polymeric material such as polyethylene,
polypropylene, vinylene copolymer, and polybutylene. The porous
film may be used in the form of double-layered or triple-layered
laminate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] The above advantages and features of the invention will be
more clearly understood from the following detailed description
which is provided in connection with the accompanying drawings.
[0055] FIG. 1 is a sectional view of the cylindrical lithium
secondary battery in one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0056] Exemplary embodiment of the present invention will be
described below in connection with the drawings. Other embodiments
may be utilized and structural or logical changes may be made
without departing from the spirit or scope of the present
invention. Like items are referred to by like reference numerals
throughout the drawings. The invention will be described in more
detail with reference to the following examples which are not
intended to restrict the scope thereof.
COMPARATIVE EXAMPLE 1
[0057] This comparative example is designed to evaluate the
overcharging characteristics and storage characteristics. A
cylindrical lithium secondary battery constructed as shown in FIG.
1 was produced in the following manner. For the cathode active
material, a mixture was prepared from artificial graphite
(mesophase microbeads) and PVDF as a binder in a ratio of 91:9 by
weight. The mixture was dissolved in N-methylpyrrolidone (NMP for
short) as a solvent to give a paste. This paste was applied to both
sides of copper foil as a cathode current collector 1. The coating
was dried, pressed with heating, and vacuum-dried. In this way the
cathode layer 2 was formed on both sides of the cathode current
collector 1. Thus there was obtained the cathode. For the anode
active material, a mixture was prepared from lithium cobaltite,
graphite as a conducting material, and PVDF as a binder in a ratio
of 85:7:8 by weight. The mixture was dissolved in NMP as a solvent
to give a paste. This paste was applied to both sides of aluminum
foil as an anode current collector 3. The coating was dried,
pressed with heating, and vacuum-dried. In this way the anode layer
4 was formed on both sides of the anode current collector 3. Thus
there was obtained the anode. A cathode lead 5 and an anode lead 6
(both made of nickel foil) were attached by electric welding
respectively to the uncoated parts of the cathode and anode. The
cathode and anode, with a separator 7 interposed between them, were
wound up. The outermost separator was fixed with a tape. The thus
obtained electrode group was inserted into a battery can 10 of
stainless steel, in such a way that the cathode lead 5 comes into
contact with the bottom of the can, with a polypropylene insulator
8 interposed between them. The cathode lead 5 was connected by
electric welding to the battery can 10 so as to form the cathode
circuit. The anode lead 6 was connected by electric welding to the
anode cap 12, with an anode insulator 9 interposed between them.
For the electrolytic solution, a mixed solvent was prepared from
ethylene carbonate (EC) and dimethyl carbonate (DMC) in a ratio of
1:2 by volume. In this solvent was dissolved 1M (mol/dm.sup.-3) of
LiPF.sub.6. (The composition of the electrolytic solution will be
described as "1M LiPF.sub.6 EC/DMC (1/2 by volume)" hereinafter.)
The thus obtained electrolytic solution (about 4 ml) was poured
into the battery can 10 through its opening. The cathode can 10 was
mechanically crimped with an anode cap 12 (with a gasket 11). Thus
there was obtained the cylindrical lithium secondary battery
(cobalt-based battery) for Comparative Example 1. Incidentally, the
anode cap 12 is equipped with a safety device which is a pressure
switch CID (Current Interrupt Device, which opens the circuit at
about 100 kPa) consisting of heat-sensitive resistance element PTC
(Positive Temperature Coefficient, resistance trip temperature at
about 80.degree. C.) and aluminum foil circuit.
[0058] The thus obtained battery was charged at a constant current
of 1 A and a constant voltage of 4.2 V, with the charge end current
being 20 mA. Then the battery was discharged at a discharge current
of 1 A, with the discharge end voltage being 3 V. In other words,
V.sub.1 was 4.2 V and the discharge voltage was 3 V. The
charging-discharging cycle was repeated twice. Then the battery was
charged until 4.2 V at a current of 1 A. The battery was charged
further (for overcharging) at 1 A until charging was interrupted by
the action of the safety device. It was found that the battery has
a charging capacity C.sub.1 of 1380 mAh when charged to 4.2 V and
the battery has an overcharging capacity C.sub.2 of 1300 mAh when
overcharged until charging was interrupted by the safety device. It
follows therefore that the safety effect (.xi.) of the battery
defined in the formula (4) below is 0.94.
Safety effect (.xi.)=(Overcharging effect C.sub.2)/(Initial
discharge capacity C.sub.1) (4)
[0059] The smaller value of safety effect means that the battery is
safe with a remote possibility of overcharging.
[0060] For evaluation of the initial discharge capacity S.sub.1,
the battery prepared in the same way as above was charged at 1 A up
to 4.2 V and then discharged at room temperature under the same
conditions as mentioned above. The battery was charged again under
the same conditions. The charged battery was allowed to stand at
60.degree. C. for 10 days. After cooling to room temperature, the
battery was discharged at 1 A. The battery was charged and
discharged again and the recovered capacity was measured. The
capacity after storage is designated as S.sub.2. The storage
characteristic was evaluated according to the formula (5)
below.
Storage characteristic (%)=(Recovered discharge capacity after
storage S.sub.2)/(Initial discharge capacity S.sub.1).times.100
(5)
[0061] The battery in Comparative Example 1 has a storage
characteristic of 93%. The larger is this value, the better is the
storage characteristic of the battery.
COMPARATIVE EXAMPLE 2
[0062] A cobalt-based battery was produced in the same way as in
Comparative Example 1 except that the electrolytic solution (1M
LiPF.sub.6 EC/DMC (1/2 by volume)) contains 0.1 M of anisole (An
for short hereinafter) dissolved therein. The resulting battery had
an overcharging capacity of 1120 mAh and a safety effect (.xi.) of
0.81. However, it had a storage characteristic of 72%, which is
lower than that of the battery in Comparative Example 1.
EXAMPLE 1
[0063] An electrolytic solution was prepared from 1M LiPF.sub.6
EC/DMC (1/2 by volume), 5 vol % of methyl perfluorobutyrate (HFE1
for short hereinafter) as a fluorinated solvent, and 0.1 M of An.
This electrolytic solution was used to produce the same
cobalt-based battery as in Comparative Example 1. The resulting
battery had a charging capacity (up to 4.2 V) of 1395 mAh, but it
had an overcharging capacity of 870 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.62. This result indicates that
the battery containing a specific fluorinated solvent (HFE1) in the
electrolytic solution decreases in overcharge current capacity much
more than that in Comparative Examples 1 and 2 even though An as an
overcharge inhibiting agent is used in common. Moreover, the
battery in this example had a storage characteristic of 82%, which
is higher by 10% than that in Comparative Example 2.
EXAMPLE 2
[0064] An electrolytic solution was prepared from 1M LiPF.sub.6
EC/DMC (1/2 by volume), 5 vol % of 2,2,3,3,3-tetrafluoropropyl
difluoromethyl ether (HFE2 for short hereinafter) as a fluorinated
solvent, and 0.1 M of An. This electrolytic solution was used to
produce the same cobalt-based battery as in Comparative Example 1.
The resulting battery had a charging capacity (up to 4.2 V) of 1410
mAh, but it had an overcharging capacity of 820 mAh. Therefore, the
safety effect (.xi.) of the battery was 0.58 (which is better than
that in Example 1). This result indicates that the fluorinated
solvent of ether structure added to the electrolytic solution
improves further the effect of inhibiting overcharging. Moreover,
the battery in this example had a storage characteristic of 86%,
which is higher by 4% than that in Example 1. This suggests that
the fluorinated solvent of ether structure also contributes to the
storage characteristics.
EXAMPLE 3
[0065] An electrolytic solution was prepared from 1M LiPF.sub.6
EC/DMC (1/2 by volume), 5 vol % of nanofluorobutyl methyl ether
(HFE3 for short hereinafter) as a fluorinated solvent, and 0.1 M of
An. This electrolytic solution was used to produce the same
cobalt-based battery as in Comparative Example 1. The resulting
battery had a charging capacity (up to 4.2 V) of 1390 mAh, but it
had an overcharging capacity of 810 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.58. This result indicates that
the fluorinated solvent of ether structure produces the effect of
inhibiting overcharging. Moreover, the battery in this example had
a storage characteristic of 88%, which is higher by 2% than that in
Example 1. This suggests that the nanofluorobutyl methyl ether
greatly improves the storage characteristics.
COMPARATIVE EXAMPLE 3
[0066] A manganese-based battery was prepared in the same way as in
Comparative Example 1 except that the anode active material was
lithium manganate and the cathode active material was amorphous
carbon (PIC from Kureha Chemical Industry Co., Ltd.), with the
electrolytic solution remaining unchanged from 1M LiPF.sub.6 EC/DMC
(1/2 by volume). The resulting battery was measured for capacity by
charging under the same condition (V.sub.1=4.2 V) as in Comparative
Example 1. The battery was found to have a charging capacity of 920
mAh and an overcharging capacity of 850 mAh at 4.2 V and above.
Therefore, the safety effect (.xi.) of the battery was 0.94, and
the storage characteristic of the battery was 94%.
COMPARATIVE EXAMPLE 4
[0067] A manganese-based battery was prepared in the same way as in
Comparative Example 3 except that the electrolytic solution was
replaced by the one consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume) and 0.1M of An dissolved therein. The resulting battery was
found to have a charging capacity of 910 mAh (up to 4.2 V) and an
overcharging capacity of 720 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.79, which means that the battery has
better safety than that in Comparative Example 3. However, the
storage characteristic of the battery was 67%, which is lower than
that of the battery in Comparative Example 3.
EXAMPLE 4
[0068] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of An, and 5 vol % of HFE1. The resulting battery was
found to have a charging capacity of 920 mAh (up to 4.2 V) and an
overcharging capacity of 640 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.70, which means that the battery has
better safety than that in Comparative Example 4. Moreover, the
storage characteristic of the battery was 72%, which is better than
that of the battery in Comparative Example 4. This result suggests
that the fluorinated solvent prevents the overcharging inhibiting
agent (An) from lowering the storage characteristics even in the
case of manganese-based battery.
EXAMPLE 5
[0069] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of An, and 5 vol % of HFE2. The resulting battery was
found to have a charging capacity of 930 mAh (up to 4.2 V) and an
overcharging capacity of 590 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.63, which means that the battery has
better safety than that in Example 4. Moreover, the storage
characteristic of the battery was 81%, which is better than that of
the battery in Example 4. This result suggests that the fluorinated
solvent of ether structure prevents the overcharging inhibiting
agent from lowering the storage characteristics even in the case of
manganese-based battery.
EXAMPLE 6
[0070] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 4-biphenyl benzoate (Bph for short hereinafter),
and 5 vol % of HFE2. The resulting battery was found to have a
charging capacity of 910 mAh (up to 4.2 V) and an overcharging
capacity of 550 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.60, which means that the battery has better safety
than that in Example 4. In addition, the storage characteristic of
the battery was 83%. This result suggests that the Bph does not
greatly decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 7
[0071] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 1,2-dimethoxybenzene (VL for short hereinafter),
and 5 vol % of HFE2. The resulting battery was found to have a
charging capacity of 910 mAh (up to 4.2 V) and an overcharging
capacity of 580 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.64, which means that the battery has better safety
than that in Example 4. In addition, the storage characteristic of
the battery was 81%. This result suggests that the VL does not
greatly decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 8
[0072] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 4-fluoroanisole (FAn for short hereinafter), and 5
vol % of HFE2. The resulting battery was found to have a charging
capacity of 920 mAh (up to 4.2 V) and an overcharging capacity of
530 mAh. Therefore, the safety effect (.xi.) of the battery was
0.58, which means that the battery has better safety than that in
Example 4. In addition, the storage characteristic of the battery
was 83%. This result suggests that the FAn does not greatly
decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 9
[0073] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 2,5-diphenylanisole (DFAn for short hereinafter),
and 5 vol % of HFE2. The resulting battery was found to have a
charging capacity of 910 mAh (up to 4.2 V) and an overcharging
capacity of 510 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.56, which means that the battery has better safety
than that in Example 4. In addition, the storage characteristic of
the battery was 81%. This result suggests that the DFAn does not
greatly decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 10
[0074] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 4-biphenylacetate (BphA for short hereinafter),
and 5 vol % of HFE2. The resulting battery was found to have a
charging capacity of 900 mAh (up to 4.2 V) and an overcharging
capacity of 510 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.57, which means that the battery has better safety
than that in Example 4. In addition, the storage characteristic of
the battery was 83%. This result suggests that the BphA does not
greatly decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 11
[0075] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of phenyl propionate (PhP for short hereinafter), and
5 vol % of HFE2. The resulting battery was found to have a charging
capacity of 900 mAh (up to 4.2 V) and an overcharging capacity of
520 mAh. Therefore, the safety effect (.xi.) of the battery was
0.58, which means that the battery has better safety than that in
Example 4. In addition, the storage characteristic of the battery
was 82%. This result suggests that the PhP does not greatly
decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 12
[0076] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of ethoxybenzene (EtOB for short hereinafter), and 5
vol % of HFE2. The resulting battery was found to have a charging
capacity of 910 mAh (up to 4.2 V) and an overcharging capacity of
570 mAh. Therefore, the safety effect (.xi.) of the battery was
0.63, which means that the battery has better safety than that in
Example 4. In addition, the storage characteristic of the battery
was 81%. This result suggests that the EtOB does not greatly
decrease the storage characteristics unlike the battery in
Comparative Example 4.
EXAMPLE 13
[0077] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 4-bromoanisole (BrAn for short hereinafter), and 5
vol % of HFE2. The resulting battery was found to have a charging
capacity of 920 mAh (up to 4.2 V) and an overcharging capacity of
560 mAh. Therefore, the safety effect (.xi.) of the battery was
0.61, which means that the battery has better safety than that in
Example 4. In addition, the storage characteristic of the battery
was 81%. This result suggests that the BrAn does not greatly
decrease the storage characteristics unlike the battery in
Comparative Example 4.
[0078] The above-mentioned results are summarized in Table 1. As
mentioned above, the combination of an aromatic compound and a
fluorinated solvent produces the effect of inhibiting overcharging
for both the cobalt/graphite carbon battery and the
manganese/amorphous carbon battery and gives rise to batteries
which decrease in capacity only a little during storage. In
addition, it was found that the aromatic compound known as an
overcharge inhibiting agent has its effect enhanced when used in
combination with a fluorinated solvent. Of several fluorinated
solvents, that of ether structure is most effective.
1 TABLE 1 Over- Charging charging Safety Storage Battery type
capacity capacity effect character- Example No. Electrolytic
solution (mAh) (mAh) (.xi.) istic (%) LiCoO.sub.2/ graphite carbon
Comparative 1 M LiPF.sub.6 EC/DMC = 1/2 1380 1300 0.94 93 Example 1
Comparative 1 M LiPF.sub.6 EC/DMC = 1/2, An = 0.1 M 1390 1120 0.81
72 Example 2 Example 1 1 M LiPF.sub.6 EC/DMC = 1/2, HFE1 = 5% + An
= 0.1 M 1395 870 0.62 82 Example 2 1 M LiPF.sub.6 EC/DMC = 1/2,
HFE2 = 5% + An = 0.1 M 1410 820 0.58 86 Example 3 1 M LiPF.sub.6
EC/DMC = 1/2, HFE3 = 5% + An = 0.1 M 1390 810 0.58 88
LiMn.sub.2O.sub.4/ amorphous carbon Comparative 1 M LiPF.sub.6
EC/DMC = 1/2 920 850 0.92 94 Example 3 Comparative 1 M LiPF.sub.6
EC/DMC = 1/2, An = 0.1 M 910 720 0.79 67 Example 4 Example 4 1 M
LiPF.sub.6 EC/DMC = 1/2, HFE1 = 5% + An = 0.1 M 920 640 0.70 72
Example 5 1 M LiPF.sub.6 EC/DMC = 1/2, HFE2 = 5% + An = 0.1 M 930
590 0.63 81 Example 6 1 M LiPF.sub.6 EC/DMC = 1/2, HFE2 = 5% + Bph
= 0.1 M 910 550 0.60 83 Example 7 1 M LiPF.sub.6 EC/DMC = 1/2, HFE2
= 5% + VL = 0.1 M 910 580 0.64 81 Example 8 1 M LiPF.sub.6 EC/DMC =
1/2, HFE2 = 5% + FAn = 0.1 M 920 530 0.58 83 Example 9 1 M
LiPF.sub.6 EC/DMC = 1/2, HFE2 = 5% + DFAn = 0.1 M 910 510 0.56 81
Example 10 1 M LiPF.sub.6 EC/DMC = 1/2, HFE2 = 5% + BphA = 0.1 M
900 510 0.57 83 Example 11 1 M LiPF.sub.6 EC/DMC = 1/2, HFE2 = 5% +
PhP = 0.1 M 900 520 0.58 82 Example 12 1 M LiPF.sub.6 EC/DMC = 1/2,
HFE2 = 5% + EtOB = 0.1 M 910 570 0.63 81 Example 13 1 M LiPF.sub.6
EC/DMC = 1/2, HFE2 = 5% + BrAn = 0.1 M 920 560 0.61 81
EXAMPLE 14
[0079] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of An, and 5 vol % of HFE3. The resulting battery was
found to have a charging capacity of 920 mAh (up to 4.2 V) and an
overcharging capacity of 560 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.61, which means that owing to HFE3 as a
fluorinated solvent the battery has better safety than that in
Examples 4 and 5 which employs HFE1 or HFE2 as a fluorinated
solvent. In addition, the storage characteristic of the battery was
85%. Thus the battery in this example is greatly improved over that
in Example 4 or 5. This result suggests that an adequate selection
of fluorinated solvents contributes to improvement in safety and
storage properties.
EXAMPLE 15
[0080] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of PhP, and 5 vol % of HFE3. The resulting battery
was found to have a charging capacity of 900 mAh (up to 4.2 V) and
an overcharging capacity of 520 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.58. This result suggests that PhP as an
overcharge inhibiting agent contributes more to the battery safety
when used in combination with HFE3 as a fluorinated solvent than
when used in combination with HFE2 as a fluorinate solvent, as in
Example 12. In addition, the storage characteristic of the battery
in this example is 85%, which is much better than that in Example
11. Thus it was confirmed in this example that HFE3 produces its
good effect even though the kind of the overcharge inhibiting agent
is changed.
EXAMPLE 16
[0081] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of EtOB, and 5 vol % of HFE3. The resulting battery
was found to have a charging capacity of 910 mAh (up to 4.2 V) and
an overcharging capacity of 570 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.63. This result suggests that EtOB as
an overcharge inhibiting agent contributes more to the battery
safety when used in combination with HFE3 as a fluorinated solvent
than when used in combination with HFE2 as a fluorinate solvent, as
in Example 12. In addition, the storage characteristic of the
battery in this example is 86%, which is much better than that in
Example 12. Thus it was confirmed in this example that HFE3
produces its good effect even though the kind of the overcharge
inhibiting agent is changed.
[0082] The following examples demonstrate how the battery safety
and storage characteristics vary depending on the main solvent of
the electrolytic solution and the kind of the electrolyte.
EXAMPLE 17
[0083] In this example, DMC was replaced by ethyl methyl carbonate
(EMC for short hereinafter). A manganese-based battery was prepared
which contains an electrolytic solution consisting of 1M LiPF.sub.6
EC/EMC (1/2 by volume), 0.1M of An, and 5 vol % of HFE3. The
resulting battery was found to have a charging capacity of 920 mAh
(up to 4.2 V) and an overcharging capacity of 560 mAh. Therefore,
the safety effect (.xi.) of the battery was 0.60, which is equal to
that of the battery in Example 14 which employs DMC as the solvent.
The storage characteristic of the battery was 85%, which is equal
to that of the battery which employs DMC as the solvent. This
result suggests that EMC is as effective as DMC in safety and
storage characteristics.
EXAMPLE 18
[0084] In this example, DMC was replaced by diethyl carbonate (DEC
for short hereinafter). A manganese-based battery was prepared
which contains an electrolytic solution consisting of 1M LiPF.sub.6
EC/DEC (1/2 by volume), 0.1M of An, and 5 vol % of HFE3. The
resulting battery was found to have a charging capacity of 900 mAh
(up to 4.2 V) and an overcharging capacity of 520 mAh. Therefore,
the safety effect (.xi.) of the battery was 0.58, which is equal to
that of the battery in Example 17 which employs EMC as the solvent.
The storage characteristic of the battery was 84%, which is
slightly inferior to that of the battery which employs DMC or EMC
as the solvent but is superior to that of the battery in Example 5.
This result suggests that the performance of the battery depends
little on the solvent of the electrolytic solution.
EXAMPLE 19
[0085] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 PC (propylene
carbonate), 0.1M of An, and 0.5 vol % of HFE3. The resulting
battery was found to have a charging capacity of 890 mAh (up to 4.2
V) and an overcharging capacity of 490 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.55. This result suggests that PC
used alone for the electrolytic solution produces a better result
than 1M LiPF.sub.6 EC/DMC (1/2 by volume) used in Example 14. The
storage characteristic of the battery was 86%, which is better than
that of the battery in Example 14.
EXAMPLE 20
[0086] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 GBL
(?-butyrolactone), 0.1M of An, and 0.5 vol % of HFE3. The resulting
battery was found to have a charging capacity of 870 mAh (up to 4.2
V) and an overcharging capacity of 490 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.55. This result suggests that
the battery in this example which employs GBL alone for the
electrolytic solution is superior to that in Example 14. The
storage characteristic of the battery was 88%, which is better than
that of the battery in Example 14.
EXAMPLE 21
[0087] In this example, the lithium salt was replaced by
LiBF.sub.4. A manganese-based battery was prepared which contains
an electrolytic solution consisting of 1M LiBF.sub.4 PC, 0.1M of
An, and 0.5 vol % of HFE3. The resulting battery was found to have
a charging capacity of 890 mAh (up to 4.2 V) and an overcharging
capacity of 480 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.54, which is better than that of the battery in
Example 19. The storage characteristic of the battery was 87%,
which is better than that of the battery in Example 19. This result
suggests that in the case of a solvent consisting of PC alone, the
electrolytic solution containing LiBF.sub.4 is superior to that
containing LiPF.sub.6.
EXAMPLE 22
[0088] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 GBL, 0.1M of An,
and 0.5 vol % of HFE3. The resulting battery was found to have a
charging capacity of 890 mAh (up to 4.2 V) and an overcharging
capacity of 480 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.54, which is better than that of the battery in
Example 19. The storage characteristic of the battery was 87%,
which is better than that of the battery in Example 19. This result
suggests that in the case of a solvent consisting of PC alone, the
electrolytic solution containing LiBF.sub.4 is superior to that
containing LiPF.sub.6.
EXAMPLE 23
[0089] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 EC/GBL/PC (1/1/1
by volume), 0.1M of An, and 0.5 vol % of HFE3. The resulting
battery was found to have a charging capacity of 910 mAh (up to 4.2
V) and an overcharging capacity of 480 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.53, which is better than that of
the battery in Example 22. The storage characteristic of the
battery was 89%, which is better than that of the battery in
Example 22. This result suggests that the three-component solvent
for the electrolytic solution also improves the safety and storage
characteristics.
EXAMPLE 24
[0090] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 0.8M
LiN(SO.sub.2CF.sub.2CF.sub.3) (LiBETI for short hereinafter) and
0.2M LiBF.sub.4 dissolved in BGL, 0.1M of An, and 0.5 vol % of
HFE3. The resulting battery was found to have a charging capacity
of 930 mAh (up to 4.2 V) and an overcharging capacity of 490 mAh.
Therefore, the safety effect (.xi.) of the battery was 0.53, which
is better than that of the battery in Example 23. The storage
characteristic of the battery was 87%.
EXAMPLE 25
[0091] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 0.2M LiPF.sub.6 and 0.8M
LiBF.sub.4 dissolved in BGL, 0.1M of An, and 0.5 vol % of HFE3. The
resulting battery was found to have a charging capacity of 940 mAh
(up to 4.2 V) and an overcharging capacity of 490 mAh. Therefore,
the safety effect (4) of the battery was 0.52, which is better than
that of the battery in Example 23. The storage characteristic of
the battery was 88%. This result suggests that a mixture of lithium
salts tends to increase the charging capacity although its effect
of improving the safety and storage characteristics remains almost
unchanged.
[0092] The above-mentioned results are summarized in Table 2. As
mentioned above, HFE3 as a fluorinated solvent improves the battery
safety and storage characteristics more than HFE1 and HFE2. This
holds true even when the composition of the electrolytic solution
was changed.
2 TABLE 2 Over- Charging charging Safety Storage Battery type
capacity capacity effect character- Example No. Electrolytic
solution (mAh) (mAh) (.xi.) istic (%) LiMn.sub.2O.sub.4/ amorphous
carbon Example 14 1 M LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + An = 0.1
M 900 520 0.58 85 Example 15 1 M LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5%
+ PhP = 0.1 M 910 570 0.63 86 Example 16 1 M LiPF.sub.6 EC/DMC =
1/2, HFE3 = 5% + EtOB = 0.1 M 920 560 0.61 85 Example 17 1 M
LiPF.sub.6 EC/EMC = 1/2, HFE3 = 5% + An = 0.1 M 920 550 0.60 86
Example 18 1 M LiPF.sub.6 EC/DEC = 1/2, HFE3 = 5% + An = 0.1 M 900
520 0.58 84 Example 19 1 M LiPF.sub.6 PC, HFE3 = 0.5% + An = 0.1 M
890 490 0.55 86 Example 20 1 M LiPF.sub.6 GBL, HFE3 = 0.5% + An =
0.1 M 870 490 0.56 88 Example 21 1 M LiBF.sub.4 PC, HFE3 = 0.5% +
An = 0.1 M 890 480 0.54 87 Example 22 1 M LiBF.sub.4 GBL, HFE3 =
0.5% + An = 0.1 M 880 470 0.53 88 Example 23 1 M LiBF.sub.4
EC/GBL/PC = 1/5/1, HFE3 = 0.5% + An = 910 480 0.53 89 0.1 M Example
24 0.8 M LiBF.sub.4 0.2 M LiBETI GBL, HFE3 = 0.5% + An = 930 490
0.53 87 0.1 M Example 25 0.8 M LiBF.sub.4 0.2 M LiPF.sub.6 GBL,
HFE3 = 0.5% + An = 940 490 0.52 88 0.1 M
EXAMPLE 26
[0093] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of phenyltrimethylsilane (PS1 for short hereinafter),
and 5 vol % of HFE3. The resulting battery was found to have a
charging capacity of 900 mAh (up to 4.2 V) and an overcharging
capacity of 450 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.50, which is best among all the batteries obtained in
the foregoing Examples. The storage characteristic of the battery
was 91%, which is best among all the batteries obtained in the
foregoing Examples. This result suggests that the silicon compound
(with a silyl group) used as the overcharge inhibiting agent
greatly improves the battery safety and storage
characteristics.
EXAMPLE 27
[0094] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of diphenylmethylsilane (PS2 for short hereinafter),
and 5 vol % of HFE3. The resulting battery was found to have a
charging capacity of 910 mAh (up to 4.2 V) and an overcharging
capacity of 430 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.47, which is best among all the batteries obtained in
the foregoing Examples. The storage characteristic of the battery
was 92%, which is best among all the batteries obtained in the
foregoing Examples.
EXAMPLE 28
[0095] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of diphenylsilane (PS3 for short hereinafter), and 5
vol % of HFE3. The resulting battery was found to have a charging
capacity of 920 mAh (up to 4.2 V) and an overcharging capacity of
430 mAh. Therefore, the safety effect (.xi.) of the battery was
0.47, which is equal to that of the battery in Example 27. The
battery in this Example has an improved charge capacity. The
storage characteristic of the battery was 93%, which is best among
all the batteries obtained in the foregoing Examples.
EXAMPLE 29
[0096] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of diphenyldimethoxysilane (PS4 for short
hereinafter), and 5 vol % of HFE3. The resulting battery was found
to have a charging capacity of 920 mAh (up to 4.2 V) and an
overcharging capacity of 420 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.46, which is best among all the
batteries obtained in the foregoing Examples. The storage
characteristic of the battery was 93%, which is equal to that of
the battery in Example 28.
EXAMPLE 30
[0097] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1M of 4-methoxyphenyltrimethylsilane (PS5 for short
hereinafter), and 5 vol % of HFE3. The resulting battery was found
to have a charging capacity of 920 mAh (up to 4.2 V) and an
overcharging capacity of 410 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.465, which is best among all the
batteries obtained in the foregoing Examples. The storage
characteristic of the battery was 93%, which is equal to that of
the batteries in Examples 28 and 29.
EXAMPLE 31
[0098] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 EC/DMC (1/2 by
volume), 0.1M of PS5, and 5 vol % of HFE3. The resulting battery
was found to have a charging capacity of 910 mAh (up to 4.2 V) and
an overcharging capacity of 390 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.43, which is best among all the
batteries obtained in the foregoing Examples. The storage
characteristic of the battery was 93%, which is equal to that of
the batteries in Examples 28 to 30. The result remained unchanged
even though the lithium salt was replaced by LiBF.sub.4.
EXAMPLE 32
[0099] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 0.8M LiPF.sub.6 0.2M LiBETI
EC/DMC (1/2 by volume), 0.1 M of PS5, and 5 vol % of HFE3. The
resulting battery was found to have a charging capacity of 920 mAh
(up to 4.2 V) and an overcharging capacity of 410 mAh. Therefore,
the safety effect (.xi.) of the battery was 0.45, which is equal to
that of the battery employing a compound having a silyl group. The
storage characteristic of the battery was 94%, which is equal to
that of the battery in Comparative Example 3.
EXAMPLE 33
[0100] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 0.8M LiBF.sub.4 0.2M LiBETI
EC/DMC (1/2 by volume), 0.1M of PS5, and 5 vol % of HFE3. The
resulting battery was found to have a charging capacity of 930 mAh
(up to 4.2 V) and an overcharging capacity of 420 mAh. Therefore,
the safety effect (.xi.) of the battery was 0.45, which is equal to
that of the battery in Example 32 which employs a mixture of
lithium salts.
EXAMPLE 34
[0101] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 PC, 0.1M of PS5,
and 0.5 vol % of HFE3. The resulting battery was found to have a
charging capacity of 900 mAh (up to 4.2 V) and an overcharging
capacity of 430 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.48 and the storage characteristic was 92%. This
result suggests that even a single solvent greatly improves the
battery safety and storage characteristics compared with the
battery in Example 21.
EXAMPLE 35
[0102] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 GBL, 0.1M of PS5,
and 0.5 vol % of HFE3. The resulting battery was found to have a
charging capacity of 910 mAh (up to 4.2 V) and an overcharging
capacity of 420 mAh. Therefore, the safety effect (.xi.) of the
battery was 0.46 and the storage characteristic was 92%. The
battery in this example is much better in safety and storage
characteristic than the battery in Example 22.
EXAMPLE 36
[0103] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 EC/PC (1/2 by
volume), 0.1M of PS5, and 0.5 vol % of HFE3. The resulting battery
was found to have a charging capacity of 910 mAh (up to 4.2 V) and
an overcharging capacity of 400 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.44, which is best among all the
batteries obtained in the foregoing Examples. The storage
characteristic of the battery was as high as 93%.
EXAMPLE 37
[0104] A manganese-based battery was prepared which contains an
electrolytic solution consisting of 1M LiBF.sub.4 EC/GBL/PC (1/1/1
by volume), 0.1M of PS5, and 0.5 vol % of HFE3. The resulting
battery was found to have a charging capacity of 920 mAh (up to 4.2
V) and an overcharging capacity of 390 mAh. Therefore, the safety
effect (.xi.) of the battery was 0.42, which is best among all the
batteries obtained in the foregoing Examples. The storage
characteristic of the battery was 93%, which also best among all
the batteries obtained in the foregoing Examples.
[0105] The above-mentioned results are summarized in Table 3. As
mentioned above, the phenylsilane compound as an overcharge
inhibiting agent and HFE3 as a fluorinated solvent improve the
safety and storage characteristics for lithium secondary batteries
varying in the composition of the electrolytic solution.
3 TABLE 3 Over- Charging charging Safety Storage Battery type
capacity capacity effect character- Example No. Electrolytic
solution (mAh) (mAh) (.xi.) istic (%) LiMn.sub.2O.sub.4/ amorphous
carbon Example 26 1 M LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + PS1 =
0.1 M 900 450 0.50 91 Example 27 1 M LiPF.sub.6 EC/DMC = 1/2, HFE3
= 5% + PS2 = 0.1 M 910 430 0.47 92 Example 28 1 M LiPF.sub.6 EC/DMC
= 1/2, HFE3 = 5% + PS3 = 0.1 M 920 430 0.47 93 Example 29 1 M
LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + PS4 = 0.1 M 920 420 0.46 93
Example 30 1 M LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + PS5 = 0.1 M 920
410 0.45 93 Example 31 1 M LiBF.sub.4 EC/DMC = 1/2, HFE3 = 5% + PS5
= 0.1 M 910 390 0.43 93 Example 32 0.8 M LiPF.sub.6 0.2 M LiBETI
EC/EMC = 1/2, HFE3 = 5% 920 410 0.45 94 + PS5 = 0.1 M Example 33
0.8 M LiBF.sub.4 0.2 M LiBETI EC/EMC = 1/2, HFE3 = 5% 930 420 0.45
94 + PS5 = 0.1 M Example 34 1 M LiBF.sub.4 PC, HFE3 = 0.5% + PS5 =
0.1 M 900 430 0.48 92 Example 35 1 M LiBF.sub.4 GBL, HFE3 = 0.5% +
PS5 = 0.1 M 910 420 0.46 94 Example 36 1 M LiBF.sub.4 EC/PC = 1/2,
HFE3 = 0.5% + PS5 = 0.1 M 910 400 0.44 93 Example 37 1 M LiBF.sub.4
EC/GBL/PC = 1/5/1, HFE3 = 0.5% + PS5 = 920 390 0.42 94 0.1 M
COMPARATIVE EXAMPLE 5
[0106] A battery of the same shape as in Comparative Example 4 was
prepared in which the anode active material is
LiNi.sub.0.5Mn.sub.1.5O.su- b.4 and the cathode active material is
graphite carbon and the electrolytic solution is 1M LiPF.sub.6
EC/DMC (1/2 by volume). This battery will be referred to as
"5V-class Mn-graphite battery" hereinafter. This battery was
charged under the condition of constant current and constant
voltage (V.sub.1) of 4.9 V. The charging voltage was set at 4.9 V
because this battery has a high average discharge voltage. The
current at the end of charging was 20 mA. The battery was
discharged at a constant current of 1 A until the voltage decreased
to 3.7 V. This charging and discharging cycle was repeated twice,
and the charging capacity (C.sub.1) and the overcharging capacity
(C.sub.2) were measured. It was found that the charging capacity
(C.sub.1) is 1100 mAh and the overcharging capacity (C.sub.2) is
870 mAh and the safety effect (.xi.) is 0.79. The storage
characteristic is 89% (evaluated under the same condition as in
Comparative Example 4).
EXAMPLE 38
[0107] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiBF.sub.4 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE1. When evaluated under the
same condition as in Comparative Example 5, the resulting battery
was found to have a charging capacity of 1110 mAh and an
overcharging capacity of 660 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.6, which is lower by 0.19 than that of
the battery in Comparative Example 5. The storage characteristic of
the battery was 82%.
EXAMPLE 39
[0108] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE2. When evaluated under the
same condition as in Comparative Example 5, the resulting battery
was found to have a charging capacity of 1110 mAh and an
overcharging capacity of 650 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.59, which is lower by 0.01 than that of
the battery in Example 38. The storage characteristic of the
battery was 83%, which is 1% higher than that of the battery in
Example 38.
EXAMPLE 40
[0109] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE3. When evaluated under the
same condition as in Comparative Example 5, the resulting battery
was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 630 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.57, which is lower by 0.02 than that of
the battery in Example 39. The storage characteristic of the
battery was 85%, which is 2% higher than that of the battery in
Example 39.
[0110] As mentioned above, the combined use of fluorinated solvent
and overcharge inhibiting agent improves the safety effect and
prevents the storage characteristics from decreasing also in the
case of 5V-class Mn-graphite battery. In addition, ether-type
fluorinated solvents are more effective than ester-type ones also
in the case of 5V-class Mn-graphite battery.
EXAMPLE 41
[0111] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of An, and 1 vol % of HFE3. When evaluated under the
same condition as in Comparative Example 5, the resulting battery
was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 580 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.52, which is lower by 0.05 than that of
the battery in Example 40. The storage characteristic of the
battery was 86%, which is 1% higher than that of the battery in
Example 40. This result suggests that the battery is improved in
safety effect and storage characteristic when the solvent for
electrolytic solution is switched from DMC to GBL.
EXAMPLE 42
[0112] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of PS1, and 1 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 5, the resulting
battery was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 550 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.49, which is lower by 0.03 than that of
the battery in Example 41. The storage characteristic of the
battery was 87%, which is 1% higher than that of the battery in
Example 41. This result suggests that PS1 (phenyltrimethylsilane)
as the overcharge inhibiting agent contributes to safety and
storage characteristic also in the case of 5V-class Mn-graphite
battery.
EXAMPLE 43
[0113] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of PS2, and 1 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 5, the resulting
battery was found to have a charging capacity of 1110 mAh and an
overcharging capacity of 510 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.45, which is lower by 0.03 than that of
the battery in Example 42. The storage characteristic of the
battery was 88%, which is 1% higher than that of the battery in
Example 42.
EXAMPLE 44
[0114] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of PS3, and 1 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 5, the resulting
battery was found to have a charging capacity of 1110 mAh and an
overcharging capacity of 460 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.41, which is lower by 0.05 than that of
the battery in Example 43. The storage characteristic of the
battery was 89%, which is equal to that of the battery in
Comparative Example 5.
EXAMPLE 45
[0115] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of PS4, and 1 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 5, the resulting
battery was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 450 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.40, which is lower by 0.01 than that of
the battery in Example 44. The storage characteristic of the
battery was 89%, which is equal to that of the battery in
Comparative Example 5.
EXAMPLE 46
[0116] A 5V-class Mn-graphite battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/GBL (1/2 by
volume), 0.1 M of PS5, and 1 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 5, the resulting
battery was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 420 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.38, which is lower by 0.02 than that of
the battery in Example 45. The storage characteristic of the
battery was 89%, which is equal to that of the battery in
Comparative Example 5.
[0117] It is apparent from the foregoing results that the 5V-class
Mn-graphite battery improves in safety and storage characteristic
when PS1 (as the overcharge inhibiting agent) is replaced by any of
PS2 (diphenylmethylsilane), PS3 (diphenylsilane), PS4
(diphenyldimethoxysilan- e), and PS5
(4-methoxyphenyltrimethylsilane).
4 TABLE 4 Over- Charging charging Safety Storage Battery type
capacity capacity effect character- Example No. Electrolytic
solution (mAh) (mAh) (.xi.) istic (%) LiNi.sub.0.5Mn.sub.15
O.sub.4/graphte carbon Comparative 1 M LiPF.sub.6 EC/DMC = 1/2 1100
870 0.79 89 Example 5 Example 38 1 M LiPF.sub.6 EC/DMC = 1/2, HFE1
= 5% + An = 0.1 M 1110 660 0.60 82 Example 39 1 M LiPF.sub.6 EC/DMC
= 1/2, HFE2 = 5% + An = 0.1 M 1110 650 0.59 83 Example 40 1 M
LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + An = 0.1 M 1120 630 0.57 85
Example 41 1 M LiPF.sub.6 EC/GBL = 1/2, HFE3 = 1% + An = 0.1 M 1120
580 0.52 86 Example 42 1 M LiPF.sub.6 EC/GBL = 1/2, HFE3 = 1% + PS1
= 0.1 M 1120 550 0.49 87 Example 43 1 M LiPF.sub.6 EC/GBL = 1/2,
HFE3 = 1% + PS2 = 0.1 M 1110 510 0.46 88 Example 44 1 M LiPF.sub.6
EC/GBL = 1/2, HFE3 = 1% + PS3 = 0.1 M 1100 460 0.41 89 Example 45 1
M LiPF.sub.6 EC/GBL = 1/2, HFE3 = 1% + PS4 = 0.1 M 1120 450 0.40 89
Example 46 1 M LiPF.sub.6 EC/GBL = 1/2, HFE3 = 1% + PS5 = 0.1 M
1120 420 0.38 89
COMPARATIVE EXAMPLE 6
[0118] A battery of the same shape as in Comparative Example 4 was
prepared in which the anode active material is
LiNi.sub.0.5Mn.sub.1.5O.su- b.4 and the cathode active material is
amorphous carbon and the electrolytic solution is 1M LiPF.sub.6
EC/DMC (1/2 by volume). This battery will be referred to as
"5V-class Mn-amorphous battery" hereinafter. This battery was
charged under the condition of constant current and constant
voltage (V.sub.1) of 4.9 V. The charging voltage was set at 4.9 V
because this battery has a high average discharge voltage. The
current at the end of charging was 20 mA. The battery was
discharged at a constant current of 1 A until the voltage decreased
to 3.7 V. This charging and discharging cycle was repeated twice,
and the charging capacity (C.sub.1) and the overcharging capacity
(C.sub.2) were measured. It was found that the charging capacity
(C.sub.1) is 940 mAh and the overcharging capacity (C.sub.2) is 890
mAh and the safety effect (.xi.) is 0.95. The storage
characteristic is 87% (evaluated under the same condition as in
Comparative Example 5).
EXAMPLE 47
[0119] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE1. When evaluated under the
same condition as in Comparative Example 6, the resulting battery
was found to have a charging capacity of 950 mAh and an
overcharging capacity of 660 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.69, which is lower by 0.26 than that of
the battery in Comparative Example 6. The storage characteristic of
the battery was 81%.
EXAMPLE 48
[0120] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE2. When evaluated under the
same condition as in Comparative Example 6, the resulting battery
was found to have a charging capacity of 960 mAh and an
overcharging capacity of 650 mAh. Therefore, the safety effect (4)
of the battery was 0.67, which is lower by 0.02 than that of the
battery in Example 47. The storage characteristic of the battery
was 82%, which is higher by 1% than that of the battery in Example
47.
EXAMPLE 49
[0121] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/DMC (1/2 by
volume), 0.1 M of An, and 5 vol % of HFE3. When evaluated under the
same condition as in Comparative Example 6, the resulting battery
was found to have a charging capacity of 960 mAh and an
overcharging capacity of 630 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.66, which is lower by 0.01 than that of
the battery in Example 48. The storage characteristic of the
battery was 84%, which is higher by 2% than that of the battery in
Example 48.
[0122] As mentioned above, the combined use of fluorinated solvent
and overcharge inhibiting agent improves the safety effect and
prevents the storage characteristics from decreasing also in the
case of 5V-class Mn-amorphous battery. In addition, ether-type
fluorinated solvents are more effective than ester-type ones also
in the case of 5V-class Mn-amorphous battery.
EXAMPLE 50
[0123] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of An, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 940 mAh and an
overcharging capacity of 560 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.60, which is lower by 0.06 than that of
the battery in Example 49. The storage characteristic of the
battery was 85%, which is higher by 1% than that of the battery in
Example 49. This result suggests that the battery improves in
safety and storage characteristic when the solvent for electrolytic
solution is switched from DMC to PC.
EXAMPLE 51
[0124] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of PS1, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 950 mAh and an
overcharging capacity of 520 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.55, which is lower by 0.05 than that of
the battery in Example 50. The storage characteristic of the
battery was 87%, which is higher by 2% than that of the battery in
Example 50. This result suggests that the battery improves in
safety and storage characteristic when phenylsilane is used as the
overcharge inhibiting agent.
EXAMPLE 52
[0125] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of PS2, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 950 mAh and an
overcharging capacity of 490 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.52, which is lower by 0.03 than that of
the battery in Example 51. The storage characteristic of the
battery was 88%, which is higher by 1% than that of the battery in
Example 51.
EXAMPLE 53
[0126] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of PS3, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 940 mAh and an
overcharging capacity of 470 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.50, which is lower by 0.02 than that of
the battery in Example 52. The storage characteristic of the
battery was 88%.
EXAMPLE 54
[0127] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of PS4, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 950 mAh and an
overcharging capacity of 430 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.45, which is lower by 0.05 than that of
the battery in Example 53. The storage characteristic of the
battery was 88%.
EXAMPLE 55
[0128] A 5V-class Mn-amorphous battery was prepared which contains
an electrolytic solution consisting of 1M LiPF.sub.6 EC/PC (1/2 by
volume), 0.1 M of PS5, and 0.5 vol % of HFE3. When evaluated under
the same condition as in Comparative Example 6, the resulting
battery was found to have a charging capacity of 1120 mAh and an
overcharging capacity of 420 mAh. Therefore, the safety effect
(.xi.) of the battery was 0.44, which is lower by 0.01 than that of
the battery in Example 54. The storage characteristic of the
battery was 88%.
[0129] It is apparent from the foregoing results that the 5V-class
Mn-amorphous battery improves in safety and storage characteristic
when PS1 (as the overcharge inhibiting agent) is replaced by any of
PS2 (diphenylmethylsilane), PS3 (diphenylsilane), PS4
(diphenyldimethoxysilan- e), and PS5
(4-methoxyphenyltrimethylsilane).
5 TABLE 5 Over- Charging charging Safety Storage Battery type
capacity capacity effect character- Example No. Electrolytic
solution (mAh) (mAh) (.xi.) istic (%) LiNi.sub.0.5Mn.sub.15
O.sub.4/ amorphous carbon Comparative 1 M LiPF.sub.6 EC/DMC = 1/2
940 890 0.95 87 Example 6 Example 47 1 M LiPF.sub.6 EC/DMC = 1/2,
HFE1 = 5% + An = 0.1 M 950 660 0.69 81 Example 48 1 M LiPF.sub.6
EC/DMC = 1/2, HFE2 = 5% + An = 0.1 M 960 650 0.67 82 Example 49 1 M
LiPF.sub.6 EC/DMC = 1/2, HFE3 = 5% + An = 0.1 M 930 630 0.68 84
Example 50 1 M LiPF.sub.6 EC/PC = 1/2, HFE3 = 0.5% + An = 0.1 M 940
560 0.60 85 Example 51 1 M LiPF.sub.6 EC/PC = 1/2, HFE3 = 0.5% +
PS1 = 0.1 M 950 520 0.55 87 Example 52 1 M LiPF.sub.6 EC/PC = 1/2,
HFE3 = 0.5% + PS2 = 0.1 M 950 490 0.52 88 Example 53 1 M LiPF.sub.6
EC/PC = 1/2, HFE3 = 0.5% + PS3 = 0.1 M 940 470 0.50 88 Example 54 1
M LiPF.sub.6 EC/PC = 1/2, HFE3 = 0.5% + PS4 = 0.1 M 950 430 0.45 88
Example 55 1 M LiPF.sub.6 EC/PC = 1/2, HFE3 = 0.5% + PS5 = 0.1 M
940 410 0.44 88
[0130] It has been demonstrated by Examples in the foregoing that
the combined use of an overcharge inhibiting agent and a
fluorinated solvent protects the lithium secondary battery from
overcharging. (The fluorinated solvent enhances the action of the
overcharge inhibiting agent and prevents the adverse effect of the
fluorinated solvent on the storage characteristics.) The lithium
secondary battery according to the present invention has a lower
overcharge current than the conventional one by more than 20%.
Therefore, it can be increased in capacity with safety. The first
commercialized lithium secondary battery had a capacity of 1000
mAh; the capacity has increased to 2000 mAh since then. The
increase in capacity is accompanied by danger. Assuming a safety
effect of 0.9, the battery with a capacity of 1000 mAh has an
energy of 17.1 kJ if overcharged up to 5V, whereas the battery with
a capacity of 2000 mAh has an energy of 34.2 kJ if overcharged up
to 5V. In other words, the latter battery has twice as much energy
as the former battery. By contrast, the battery according to the
present invention has a safety effect of, say, 0.6 and hence it has
an energy of 28.8 kJ in its overcharged state even though it has a
capacity of 2000 mAh. The magnitude of this energy is 1.68 times
that of the battery with a capacity of 1000 mAh. In other words, if
the safety effect is set at 0.6, the battery with an overcharge
capacity of 2400 mAh will have the same energy of the conventional
battery with an overcharge capacity of 2000 mAh which has a safety
effect of 0.9. Thus according to the present invention, it is
possible to increase the capacity of lithium batteries without
impairing safety. Also, the present invention can be utilized in
any electrical appliance as well. Note, an electrical appliance is
defined to include any electrical object capable of utilizing a
lithium secondary battery.
[0131] Although the invention has been described above in
connection with exemplary embodiments, it is apparent that many
modifications and substitutions can be made without departing from
the spirit or scope of the invention. Accordingly, the invention is
not to be considered as limited by the foregoing description, but
is only limited by the scope of the appended claims.
* * * * *