Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-03-29
2001-03-20
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231900, C429S231500, C429S221000, C429S304000, C429S309000, C429S322000, C429S324000, C429S325000, C429S320000
Reexamination Certificate
active
06203947
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electrochemical cells, especially to rechargeable cells, having an anode consisting of an alkali metal or alkali metal alloy, particularly a lithium anode. The invention also relates to cathodes for use in such electrochemical cells.
BACKGROUND OF THE INVENTION
Recently, with the increased awareness of air pollution and global warming, the development of electric vehicles has gained considerable interest, thus leading to a need for improvements in the performance of secondary batteries. Of specific interest are batteries, which can be minaturized, have a high energy density and which demonstrate a long cycle life.
Non-aqueous electrolyte batteries containing anodes composed of alkali metals such as lithium are an example of known batteries that meet these criteria. Lithium batteries have recently undergone remarkable developments in terms of performance improvement and miniaturization. These developments have required improvements with respect to the material and shape of the anodes and cathodes, and also with respect to the intervening electrolyte.
For example, the thin film design of a Li/composite polymer electrolyte/pyrite (FeS
2
) battery offers low manufacture cost, high power and improved safety, as a result of the use of non-aqueous or polymer electrolytes. The Applicant' U.S. Pat. No. 5,472,808 describes a composite solid electrolyte (CSE) for use in rechargeable electrochemical cells such as lithium batteries and also relates to cells that contain such solid electrolytes. These cells, however, suffer from two main drawbacks: slow charge rate and short cycle life.
The lithiated forms of the transition metal chalcogenides, such as: TiS
2
, MoS
2
, MnO
2
, NiO
2
, MoO
3
, V
2
O
5
, V
8
O
13
are commonly used as ca active materials in high energy density lithium, rechargeable batteries.
However the cycle life and safety of these batteries, are insufficient.
One of the main reasons for the decreased reversibility of these lithium batteries is non-compatibility of the cathode active material with the non-aqueous or polymer electrolytes. This non-compatibility is more pronounced in fully charged or fully discharged batteries. The final product of fully reduced cathode material is atomic metal, usually in the form of small aggregates having a large surface area, which are excessively reactive and, therefore, highly susceptible to attack by the electrolyte components causing the electrolyte decomposition and the formation of undesirable products.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an alkali metal secondary electrochemical cell with a long cycle life and a fast charge rate. A more particular object of the invention is to provide a rechargeable lithium battery exhibiting superior cell performance as compared to such cell systems known in the art.
SUMMARY OF THE INVENTION
The above objects are achieved by the present invention, which provides a cathode for use in a secondary electrochemical cell, comprising up to about 95 volume-% of electrochemically active material, characterized in that the cathode is coated, after being assembled, by a thin, ion-permeable, electronically non-conductive protective film. The protective film of the cathode of the present invention usually has a thickness of up to about 0.1 &mgr;m.
The preferred electrochemically active materials of the cathode are LiCoO
2
, LiNiO
2
, LiMn
2
O
4
, FeS
2
, TiS
2
, V
2
O
5
or V
8
O
13
, which may be doped with up to about 10% by weight of a metal selected from Mg, Ca, Ni, Co, Al, B, Fe, Mn, or a compound of such metal.
The present invention is based on the new finding that modifing the cathode by coating it with a very thin, protective film, permeable to ions but not to electrons, provides protection against high voltage charging and overdischarging, thereby reducing the degradation of the cathode during cycling and improving the performance characteristics of the battery. This coating is preferably formed electrochernically by over-discharge of the cell, usually at the end of the fHt discharge.
The invention further relates to secondary electrochemical cells comprising a cathode as above defined, an anode which consists of an alkali metal or alkali metal alloy, preferably lithium, and a solid electrolyte. The preferred electrolytes for these cells are non-aqueous aprotic solutions, preferably containing mixtures of alkyl carbonates or polymer electrolytes, more preferably based on polyethylene oxide.
REFERENCES:
patent: 4224394 (1980-09-01), Schmidt
patent: 4298668 (1981-11-01), Schmidt et al.
patent: 5472808 (1995-12-01), Peled et al.
patent: 5552238 (1996-09-01), Carlin et al.
Peled et al., “Film forming reaction at the lithium/electrolyte interface,” Journal of Power Sources, 9, pp. 253-266, 1983.*
Peled et al., “Film Forming Reaction at the Lithium/Electrolyte Interface,” Journal of Power Sources, 9 (1983)253-266.
Peled et al., “Advanced Model for Solid Electrolyte Interphase Electrodes in Liquid and Polymer Electrolytes,” J. Electrochem, Soc., vol. 144, No. 8, Aug. 1997.
Strauss et al., “Cathode Modification for Improved Performance of Rechargeable Lithium/Composite Polymer Electrolyte-Pyrite Battery,” Electrochemical and Solid-State Letters, 2(3)115-117 (1999).
Golodnitsky Diana
Peled Emanuel
Strauss Ela
Browdy and Neimark
Chaney Carol
Martin Angela J.
Ramot University Authority for Applied Research and Industrial D
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