Positive active material for rechargeable lithium battery

Details Positive active material for rechargeable lithium battery Positive active material for rechargeable lithium battery

1999-12-09

2001-09-18

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231300, C429S223000, C429S231900

Reexamination Certificate

active

06291103

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based on application No. 98-54089 filed in the Korean Industrial Property Office on Dec. 10, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a positive active material for a rechargeable lithium battery and, more particularly, to a positive active material for a rechargeable lithium battery which exhibits high capacity and good cycle life characteristics.
(b) Description of the Related Art
Rechargeable lithium batteries are generally used in cellular phones, camcorders or notebook personal computers. The cycle life characteristics are critical for the rechargeable lithium batteries, which depend on capacity of the batteries. Because the capacity of the batteries depends on positive active materials, there have been attempted to development of positive active materials exhibiting high capacity.
Manganese-based active material such as LiMn
2
O
4
or LiMnO
2
, or cobalt-based active materials have introduced as a positive active material exhibiting high capacity for the early. The active materials, however, exhibit low capacity such as 120 mAh/g or 160 mAh/g at 4.3 V charge and discharge, respectively. Recently, an attempt has been to develop nickel-based positive active materials with 20% higher discharge capacity than the manganese- or cobalt-based positive active materials.
LiNiO
2
which is employed for the nickel-based positive active material, exhibits high capacity, about 203mAh/g of initial discharge capacity at 0.1 C discharge based on 4.3 V charge and about 180 mAh/g thereof at 1 C. LiNiO
2
, however, shows undesirable cycle life characteristics due to the change from monoclinic structure to hexagonal structure. This problem is addressed by adding cobalt to LiNiO
2
, but the amount of cobalt should be more than 30 mole % of total transition metal, which causes the capacity loss.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a positive active material for a rechargeable lithium battery which has a stable structure and exhibits good cycle life characteristics and high capacity.
These and other objects may be achieved by a positive active material for a rechargeable lithium battery represented by the formula 1 or 2.
Li
a
N
1−(x+y+z)
Co
x
M
y
N
z
O
b
  (1)
(where 0.95≦a≦1.05, 0.01≦x+y≦0.5, 0<y≦0.1, 0≦z≦0.05, 1.7≦b≦2.3, M is at least one metal selected from La or Ce, and N is at least one metal selected from Mg or Sr.)
Li
a
N
b
Ni
1−(x+y)
Co
x
M
y
O
z
  (2)
(where 0.95≦a+b≦1.05, 0≦b≦0.05, 0.01≦x+y≦0.5, 0<y≦0.1, 1.7≦z≦2.3, M is at least one metal selected from La or Ce, and N is Mg.)


REFERENCES:
patent: 5626635 (1997-05-01), Yamaura et al.
patent: 6007947 (1999-12-01), Mayer
patent: 6017654 (2000-01-01), Kumta et al.
patent: 10-64549 (1998-03-01), None

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