Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-10-26
2001-05-01
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S233000
Reexamination Certificate
active
06225003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to electrode materials, and more particularly, to electrode material clusters having an elastomer binder which increases, among other things, electrical conductivity and adhesion of the electrode material clusters to the current collector, as well as enhances mechanical properties. The present invention is further directed to an electrochemical process and a process for fabricating an electrode having such components.
2. Background Art
Lithium ion electrochemical cells have been known in the art for several years. Furthermore, lithium ion batteries having electrode active materials which are mixed with binders are likewise well known. Such binders have been used to deter a phenomenon known as “falling out” of active material. “Falling out” of active material commonly results in a loss of particle-to-particle contact between active material particles which, in turn, adversely affects the electrochemical performance of the cell. At least one contributing factor which hastens the “falling out” of active material is the physical characteristics of the binder materials. In particular, prior art electrodes utilize binders which are rigid, or non-malleable after curing. Binders having such rigidity remain especially problematic for secondary cells designed for extensive cycling—where ions intercalate and deintercalate repeatedly.
In an attempt to remedy the above-identified problems, the prior art introduced additional quantities of binder into the electrochemical cell. Unfortunately, when additional binder is introduced into the cell a considerable rise in internal resistivity is observed which adversely affects the cell's capacity and electrochemical performance.
SUMMARY OF THE INVENTION
The present invention is directed to an electrode for use in an electrochemical cell comprising a current collecting substrate, an electrode active material cluster having at least one particle wherein the particle includes at least one inclusion, an elastomer binder surrounding at least a portion of the at least one particle and means associated with the elastomer binder for precluding mechanical degradation of the electrode active material cluster and, in turn, loss of electrical continuity between the at least one particle therein.
In a preferred embodiment the degradation preclusion means comprises the at least one particle having a volumetric variation which is less than the maximum elasticity of the associated elastomer binder. In this embodiment, the elastomer binder comprises a non-fluorinated compound having non-conjugated double bonds and a cross linking agent. In particular, the elastomer binder is preferably selected from at least one of the group of polymers and copolymers of ethylene, butylene, butadiene, isoprene, styrene, chloroprene, siloxane, and nitrite rubbers and the cross-linking agent is preferably butadiene sulfone.
In another embodiment of the invention the concentration of the butadiene sulfone ranges from about 1 wt. % to about 10 wt. % of the overall elastomer binder.
The present invention is further directed to an electrochemical cell generally comprising an electrolyte, a first electrode, and a second electrode wherein at least one of the first and second electrodes includes a current collecting substrate, an electrode active material cluster having at least one particle wherein the particle includes at least one inclusion, an elastomer binder surrounding at least a portion of the at least one particle and means associated with the elastomer binder for precluding mechanical degradation of the electrode active material cluster and, in turn, loss of electrical continuity between the at least one particle therein.
In this preferred embodiment, the degradation preclusion means comprises the at least one particle having a volumetric variation which is less than the maximum elasticity of the associated elastomer binder. In this embodiment the elastomer binder comprises a non-fluorinated compound having non-conjugated double bonds and a cross linking agent.
The present invention is also directed to a process for fabricating an electrochemical cell comprising the steps of: a) synthesizing a first electrode active material cluster having at least one particle wherein the particle includes at least one inclusion; b) synthesizing an elastomer binder; c) mixing the electrode active material cluster with the elastomer binder to, in turn, create a first electrode paste; d) applying the first electrode paste to a current collecting substrate; e) curing the first electrode paste; f) associating an electrolyte with the first electrode paste; and g) associating a second electrode adjacent the electrolyte.
In another preferred embodiment of the process, the step of synthesizing the elastomer binder includes the step of preparing the binder to have a maximum elasticity greater than the volumetric variation of the at least one particle. In this process the step of preparing the elastomer binder includes the step of mixing a non-fluorinated polymer having non-conjugated double bonds with a cross linking agent.
In other embodiments of the invention the process further includes the steps of drying the solvent/coating fluid of the electrode paste before the step of curing the electrode paste as well as the step of compressing the electrode paste after the step of curing the electrode paste.
In yet another preferred embodiment, the step of curing the electrode paste includes heating the electrode pate in at least one atmosphere selected from the group of argon, nitrogen, oxygen, carbon dioxide, ammonia, and mixtures thereof.
The present invention is also directed to an electrochemical process associated with an electrochemical cell comprising the steps of: a) applying an electrical charge to an electrochemical cell having an anode, a cathode, and an electrolyte wherein the anode includes an active material cluster having particles with at least one inclusion and an elastomer binder surrounding at least a portion of each of the particles, wherein each of the particles has at least a portion in contact with the associated clastomer binder, and each of the particles are conductively associated with another particle; b) intercalating metal ions into the inclusions within the associated particles; and c) maintaining continuity between the elastomer binder and the associated particles during and after the step of intercalating.
In a preferred embodiment of the invention, the process further includes the steps of: a) deintercalating the previously intercalated ions out of the inclusions; and b) maintaining continuity between the clastomer binder and the associated particles during and after the step of deintercalating.
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Fauteux Denis G.
Krawiec Wlodek T.
Van Buren Martin
Factor & Partners
Mitsubishi Chemical Corporation
Weiner Laura
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