Lithium secondary battery

Details Lithium secondary battery Lithium secondary battery

1999-03-19

2001-12-25

Griffin, Steven P. (Department: 1754)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S218100, C429S219000, C429S222000, C429S223000, C429S224000, C429S231600, C429S231300

Reexamination Certificate

active

06333128

ABSTRACT:

BACKGROUND OF THE INVENTION
This application claims the priority of Japanese Patent Application No. 10-92734 fled on Mar. 19, 1998, which is incorporated herein by reference.
The present invention relates to a lithium secondary battery, and more particularly, it relates to improvement of a positive electrode active material used therein for the purpose of providing a lithium secondary battery with an excellent charge-discharge cycle characteristic.
A lithium secondary battery can be improved in its voltage and capacity by appropriately selecting a positive electrode material because there is no need to consider a water decomposition voltage. Therefore, in accordance with recent development of portable and/or cordless electronic equipment, lithium secondary batteries have been regarded as a promising driving power supply for such electronic equipment.
Lithium cobaltite (LiCoO
2
) has already been practically used as a positive electrode active material in a lithium secondary battery, and the use results in a battery with a high energy density and a high discharge voltage of the 4-V class. Cobalt, that is, a raw material of lithium cobaltite, is, however, a scarce resource and expensive, and hence, use of lithium nickelate (LiNiO
2
) in place of lithium cobaltite is now under examination.
Lithium nickelate has, however, a disadvantage that the capacity of a battery including this material is largely degraded through charge-discharge cycles because its crystal structure is less stable than that of lithium cobaltite.
As a positive electrode active material usable for overcoming this problem, a composite oxide obtained by substituting part of nickel atoms included in lithium nickelate with cobalt atoms and manganese atoms is reported (see Japanese Laid-Open Patent Publication No. 8-37007/1996). However, the stability, during charge-discharge cycles, of the crystal structure of this composite oxide is still not sufficient to be used in place of lithium cobaltite.
SUMMARY OF THE INVENTION
In consideration of the aforementioned conventional disadvantages, an object of the invention is providing a lithium secondary battery having an excellent charge-discharge characteristic. This object can be achieved by utilizing a specific positive electrode active material as follows:
The lithium secondary battery of this invention comprises, as a positive electrode active material, a composite oxide powder having a median diameter of 3.0 through 20.0 &mgr;m and a content of particles with a grain size of 1 &mgr;m or less of 10% by volume or less and being represented by a composition formula, Li
a
Co
b
M
c
Ni
1-b-c
O
2
, in which M is at least one element selected from the group consisting of B, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Y, Nb, Mo, Ru, Rh, Pd,Ag, Cd,InandSn; 0≦a≦1.2; 0.01≦b≦0.4; 0.01≦c≦0.4; and 0.02≦b+c≦0.5.
Alternatively, the lithium secondary battery of this invention comprises, as a positive electrode active material, a composite oxide powder having a median diameter of 6.0 through 15.0 &mgr;m and a content of particles with a grain size of 1 &mgr;m or less of 10% by volume or less and being represented by a composition formula, Li
a
Co
b
M
c
Ni
1-b-c
O
2
in which M is at least one element selected from the group consisting of B, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Y, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In and Sn; 0≦a≦1.2; 0.01≦b≦0.4; 0.01≦c≦0.4; and 0.02≦b+c≦0.5.
Alternatively, the lithium secondary battery of this invention comprises, as a positive electrode active material, a composite oxide powder having a median diameter of 3.0 through 20.0 &mgr;m and a content of particles with a grain size of 1 &mgr;m or less of 10% by volume or less and being represented by a composition formula, Li
a
Co
b
M
c
Ni
1-b-c
O
2
, in which M is at least one element selected from the group consisting of B, Mg, Al, Ca, Ti, V, Mn, Fe, Cu, Zn and Ga; 0≦a≦1.2; 0.01≦b≦0.4; 0.01≦c≦0.4; and 0.02≦b+c≦0.5.
Alternatively, the lithium secondary battery of this invention comprises, as a positive electrode active material, a composite oxide powder having a median diameter of 6.0 through 15.0 &mgr;m and a content of particles with a grain size of 1 &mgr;m or less of 10% by volume or less and being represented by a composition formula, Li
a
Co
b
M
c
Ni
1-b-c
O
2
, in which M is at least one element selected from the group consisting of B, Mg, Al, Ca, Ti, V, Mn, Fe, Cu, Zn and Ga; 0≦a≦1.2; 0.01≦b≦0.4; 0.01≦c≦0.4; and 0.02≦b+c≦0.5.
Owing to these features of the composite oxide powder according to the invention, a lithium secondary battery having an excellent charge-discharge cycle characteristic can be obtained.


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