Method for making electrode of lithium secondary cells

Details Method for making electrode of lithium secondary cells Method for making electrode of lithium secondary cells

1998-01-14

2001-02-13

Weiner, Laura S (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S217000, C429S231950, C423S594120

Reexamination Certificate

active

06187476

ABSTRACT:

CLAIM FOR FOREIGN PRIORITY
This application claims priority under 35 U.S.C. § 119 from Korean Patent Application No. 1053/1997 filed on Jan. 15, 1997, which is incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for making an electrode of a secondary lithium cells and, more particularly, to a method for making a cathode of a secondary lithium cell by co-precipitating lithium and cobalt ions at a predetermined ion ratio in an alkaline solution.
2. Description of the Prior Art
A lithium secondary cell typically comprises a lithium metal or carbon for anode, a chalcogenide compound or transition metal oxide for cathode, and an organic solvent for electrolyte. The material for the cathode should exhibit chemical stability to the electrolyte, charge/discharge reversibility and high energy density. In particular, a lithium ion cell which employs carbon as an anode requires a cathode material high in unit cell voltage. For this, transition metal oxides are selected, including LiCoO
2
, LiNiO
2
, LiNi
1-y
Co
y
O
2
and LiMn
2
O
4
. Depending on the kind of materials, such as lithium and transition metal salts, and on the thermal conditions therefor, the oxides could greatly affect the properties of the cell, such as, for example, discharge capacity and cycle life span.
Most of the methods known to those skilled in the art are of solid state reaction in which the lithium salts and the transition metal salts are thermally treated at a temperature of 400-1000° C. (Japanese Pat. Laid-Open Publication No. Heisei 7-262994). The powder obtained by the solid state reaction, however, requires a temperature too high for thermal treatment and too much time for calcination in addition to being inhomogeneous in size and irregular in morphology.
In order to exhibit superior electrode properties even at high current density, the powder used as a material for lithium secondary cells should be homogeneous in size and regular in morphology. To use LiCoO
2
as an electrode material for lithium secondary cells, it is made into a powder. There has been developed no method, except for a solid state reaction technique, to make LiCoO
2
electrodes exhibiting excellent properties, thus far.
SUMMARY OF THE INVENTION
Intensive and thorough research repeated by the present inventors aiming to take advantage of solution methods in current use in other fields for the purpose of making transition metal oxide, resulted in finding that a co-precipitation method is suitable for making an LiCoO
2
electrode for secondary cells.
Therefore, it is an object of the present invention to overcome the above Problems encountered in prior arts and to provide a method for making an electrode for lithium secondary cells superior in initial discharge capacity and charge/discharge life span.
In accordance with the present invention, the above object could be accomplished by a provision of a method for making an electrode for lithium secondary cells, comprising the steps of: co-precipitating lithium ions and cobalt ions in an alkaline solution, the ratio of said lithium ions to said cobalt ions being at least 1.05:1; subjecting the co-precipitate to calcination and thermal treatment to give LiCoO
2
powder; and mixing the powder with a current collector and a binder.


REFERENCES:
patent: 4567031 (1986-01-01), Riley
patent: 5478675 (1995-12-01), Nagaura
patent: 5630993 (1997-05-01), Amatucci et al.
patent: 5686138 (1997-11-01), Fujimoto et al.
patent: 7-262994 (1995-10-01), None
patent: 8-222220 (1996-08-01), None

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