Active cathode material for a lithium rechargeable cell

Details Active cathode material for a lithium rechargeable cell Active cathode material for a lithium rechargeable cell

1999-09-23

2001-08-14

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C423S594120

Reexamination Certificate

active

06274272

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an active cathode material for a lithium rechargeable cell. It also concerns a method of manufacturing the active material. It also encompasses the positive electrode and the cell containing it.
2. Description of the Prior Art
Lithium-containing oxides of transition metals have been used as active cathode materials in lithium cells, in particular LiNiO
2
and LiCoO
2
. Cobalt is a costly metal and its procurement can give rise to problems. It is therefore preferable to concentrate on improving the characteristics of the active cathode material LiNiO
2
.
On the one hand, the active material LiNiO
2
is highly unstable thermally, which represents a high risk to the safety of the user. Document EP-0 782 206 proposes one solution to the problem of stabilizing this active material and describes an active cathode material based on LiNiO
2
substituted by Al and possibly Co and/or Mn. This material has a low capacity, however.
On the other hand, the active material LiNiO
2
offers insufficient performance, especially in terms of fast discharge or discharge at high temperature. Document EP-0 744 780 proposes substituting LiNiO
2
to obtain a material whose initial capacity is in the same order of magnitude as that of LiNiO
2
but with improved performance in terms of fast discharge and discharge at high temperature. The fast cycling characteristics are improved by substituting some of the nickel by Mg, Ca, Sr or Ba and by substituting less than 10% of the Ni by Al or Cr. Improvements are also observed with a combination of Al, Mg, B and Co. However, the material has insufficient thermal stability to assure the safety of the user.
An aim of the present invention is to propose an active cathode material obtained by substituting some of the nickel of LiNiO
2
, having both a high initial capacity and good cycling stability, and which guarantees the safety of the user.
SUMMARY OF THE INVENTION
The present invention consists in an active cathode material for a lithium rechargeable cell which is in the form of lithium-containing nickel oxide substituted by three elements including at least cobalt and aluminum, wherein the material has a monoclinic crystal structure and the following general formula:
Li
L
Ni
(1−C−A−M)
Co
C
Al
A
Mg
M
O
2
where:
0.05≦L≦1.03
0.05≦C≦0.20
0.11≦A≦0.20
0.01≦M≦0.05
and C/A≧0.60
In a preferred embodiment of the present invention the active material has a general formula in which A=0.14±0.03 and C=0.15±0.05.
The X ray diffraction diagram of the active material was obtained under the following conditions:
tube voltage: 40 kV
tube current: 30 mA
scanning speed: 0.15 degrees/min
copper K&agr;
1
line: 0.154056 nm
The ratio of the intensities of the [003] and [104] lines of the X ray diffraction diagram of the active material is preferably at least equal to 1.45. For ratios lower than this the active material has a lower capacity. The ratio is even more preferably at least equal to 2.0.
The crystal structure of the active material of the invention is deformed by the substitution and differs from the LiNiO
2
structure specified by Joint Committee on Powder Diffraction reference JCPDS 9-0063. For example, for an active material of the invention of formula Li
1.00
Ni
0.72
Co
0.10
Al
0.15
Mg
0.03
O
2
, the monoclinic structure has the following lattice parameters a=0.496 nm, b=0.286 nm, c=0.502 nm and &bgr;=109.28°.
The present invention also consists in a method of manufacturing the previously defined active cathode material comprising a heat treatment step at a temperature of at least 750° C., preferably in the range from 750 to 800° C., for at least 10 hours, preferably from 15 to 25 hours, followed by slow cooling at a rate of not greater than 1° C./min and including an intermediate step at a temperature in the range from 600° C. to 700° C.
The present invention also consists in a positive electrode for a lithium rechargeable cell containing an active cathode material as previously described and further comprising a fluorinated binder and a conductive material.
The present invention further consists in a lithium rechargeable cell containing at least one negative electrode and at least one positive electrode analogous to that previously referred to in which the active anode material is a carbon-containing material into the structure of which lithium can be inserted and selected from graphite, coke, carbon black and vitreous carbon.
Other features and advantages of the present invention will become apparent in the course of the following description of embodiments which are given by way of non-limiting and illustrative example only, of course, and from the accompanying drawings.


REFERENCES:
patent: 6077496 (2000-06-01), Ito et al.
patent: 0 744 780 A1 (1996-11-01), None
patent: 0845437-A2 (1998-06-01), None
patent: 10-241691-A2 (1998-09-01), None
patent: 11-040154-A2 (1999-02-01), None

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