Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-10-02
2001-05-08
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231100, C429S231300, C029S623500
Reexamination Certificate
active
06228531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to electrodes for use in rechargeable lithium ion batteries, wherein the electrode includes an active material comprising a transition metal oxide having a surface associated with a lithium salt. The lithium salt increases compatibility of the active material with an associated electrolyte to, in turn, increase electrochemical performance of the electrode and associated electrochemical cell. The invention is also directed to a process for fabricating such a modified electrode for use in an electrochemical cell.
2. Background Art
The use of a transition metal oxide as an electrode (such as a cathode) active material between a current collecting substrate and an electrolyte in an electrochemical cell has been know in the art for several years. While such a coating improves electrical conductivity between the current collector and electrolyte, problems nevertheless have been observed with such a coating. Specifically, it is known that transition metal oxides are somewhat unstable with respect to the electrolyte (liquid, gel, plastic or polymer) during cell cycling. Accordingly, such instability results in rate and capacity loss during subsequent cycling and storage.
In an effort to combat such instability, the prior art has identified that inorganic salts, such as inorganic lithium salts, when coated on the surface of a transition metal oxide active material, will serve to stabilize the transition metal oxide relative to the associated electrolyte. Indeed, as identified in an article entitled
Phase Stability of LiAlO
2
in Molten Carbonate
, published Dec. 12, 1997, J. Electrochem. Soc., Vol. 144, No. 12, LiAlO
2
is a stable component in an associated electrolyte.
Furthermore, Japanese Kokai No. JP 09171813 (Benno, et al.) and Amatucci, U.S. Pat. No. 5,705,291, both disclose that an inorganic lithium salt can be associated with the surface of a transition metal oxide active material so as to result in a stable interface with the associated electrolyte. While stability has been addressed, none of such prior art teaches or suggests the use of an organic component associated with the lithium salt for increasing compatibility of the surface of the active material by the associated electrolyte. Such increased compatibility results in greater direct association between the surface of the active material and electrolyte which, in turn, facilitates increased ionic and electronic charge transfer therebetween.
SUMMARY OF THE INVENTION
The present invention is directed to an electrode for use in an electrochemical cell. The electrode comprises a current collector, an active material associated with the current collector, wherein the active material comprises a transition metal oxide having a surface, and means for increasing compatibility of the surface of the active material with respect to an associated electrolyte.
In a preferred embodiment, the compatibility increasing means comprises an inorganic lithium salt and organic R group associated with the inorganic lithium salt. The R group may be an aliphatic or aromatic cyclic or acyclic hydrocarbon which may comprise an aromatic ether, thioether, ester or the like (or other heteroatoms which are stable to reduction and/or oxidation and promotes electrolyte/interface interactions). The R group can attach or bond to the surface modifying inorganic lithium salt via a functional group XH where X=O, S, N(R′) (R′=H, Me Ethyl, propyl . . . ), although the O may be preferred from an oxidative stability standpoint.
In such an embodiment, the compatibility increasing means is chemically bonded to the surface of the transition metal oxide.
In another preferred embodiment, the compatibility increasing means comprises an organic lithium salt. Such an organic lithium salt is adsorbed onto the surface of the transition metal oxide.
The present invention also contemplates that the electrode comprises. a cathode for use in a rechargeable lithium ion battery.
The present invention is also directed to a process for fabricating an electrode for use in an electrochemical cell. The process comprises the steps of a) applying an active material onto a current collector, wherein the active material comprises a transition metal oxide having a surface, and wherein the surface is partially compatible by an associated electrolyte; and b) increasing the compatibility of the surface of the transition metal oxide, by an associated electrolyte, by associating a lithium salt with the surface of the transition metal oxide.
In a preferred embodiment of the process, the step of associating a lithium salt with the surface of the transition metal oxide comprises the steps of c) chemically bonding an inorganic lithium salt with the surface of the transition metal oxide; and d) associating an organic R group with the inorganic lithium salt.
In yet another preferred embodiment of the process, the step of associating a lithium salt with the surface of the transition metal oxide comprises the step of adsorbing the lithium salt onto the surface of the transition metal oxide. In such an embodiment, the step of adsorbing comprises the steps of: 1) mixing the organic lithium salt with a solvent; 2) associating the mixture with the surface of the transition metal oxide; and 3) evaporating the solvent.
The preferred process also contemplates associating the fabricated electrode with an electrolyte and another electrode so as to form an electrochemical cell, such as a rechargeable lithium ion battery.
REFERENCES:
patent: 4579792 (1986-04-01), Bruder
patent: 5705291 (1998-01-01), Amatucci et al.
patent: 5965293 (1999-10-01), Idota et al.
patent: 55-157861 (1980-12-01), None
patent: 55-163779 (1980-12-01), None
patent: 56-30264 (1981-03-01), None
patent: 56-30263 (1981-03-01), None
patent: 57-128460 (1992-08-01), None
patent: 8-111233 (1996-04-01), None
patent: 9-92280 (1997-04-01), None
patent: 09171813 (1997-06-01), None
patent: WO 96/38872 (1996-12-01), None
Hawley's Condensed Chemical Dictionary, 13th ed., p. 154, entry for “bond, chemical”, 1997.*
Article entitled Phase Stability of LiAlO2in Molten Carbonate, published Dec. 12, 1997, J. Electrochem, Soc., vol. 144, No. 12.
Fauteux Denis G.
Kolb Eric S.
Van Buren Martin
Crepeau Jonathan
Factor & Partners
Kalafut Stephen
Mitsubishi Chemical Corporation
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