Electrochemical cell having an electrode of silver vanadium oxide coated to a current collector

#1. Field of the Invention

#The present invention relates to the conversion of chemical energy to electrical energy and, more particularly, to a cathode of silver vanadium oxide (SVO) admixed with a combination of polymeric binders. Importantly, the silver vanadium oxide admixture is coated to a current collector for incorporation into an electrochemical cell. Prior to the present invention, SVO could only be contacted to a current collector as a pressed powder or as a free-standing sheet. The preferred binder formulation is a mixture of a halogenated polymeric binder and a polymide binder, most preferably polyvinylidene fluoride (PVDF) and a polyimide. The present electrodes built from SVO containing the mixed polymeric binders are useful in both primary and secondary cells discharged at elevated and low temperatures.

#2. Prior Art

#FIG. 1 is a schematic of an electrode active slurry being roll coated onto a current collector according to the present invention.

#FIG. 2 is a schematic of an electrode active slurry being coated onto a current collector using a doctor blade according to the present invention.

#FIG. 3 is a graph illustrating the pulse discharge characteristics of a representative Li/SVO cell according to the prior art in comparison to one according to the present invention.

#As used herein, the term “pulse” means a short burst of electrical current of a significantly greater amplitude than that of a pre-pulse current immediately prior to the pulse. A pulse train consists of at least two pulses of electrical current delivered in relatively short succession with or without open circuit rest between the pulses. An exemplary pulse train may consist of four 10 second pulses with a 15 second rest between each pulse.

#The present invention is directed to the fabrication of electrodes for use in primary and secondary electrochemical cells dischargeable at elevated temperatures, such as occur in down hole well drilling operations and in an autoclave, without diminished discharge performance in comparison to cells of a similar active chemistry discharged at or near ambient temperatures. Additionally, the present cells are dischargeable at ambient temperatures with increased discharge capability in comparison to similar conventional cells. For that purpose, the electrode active material is intimately combined with a binder mixture consisting of a first, halogenated polymeric constituent and a second, polyamic acid to form an electrode active admixture. If desired, a conductive diluent can also be added to the admixture to promote conductivity. Upon heating, the polyamic acid is converted to a polyimide. Preferably, the active mixture is coated to a conductive current collector prior to the conversion heating step.

#Halogenated polymeric materials suitable as the first binder constituent are preferably fluorinated resins, for example, polytetrafluoroethylene, modified polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, polytrifluoroethylene, ethylene-tetrafluoroethylene copolymers, fluoroethylene-hydrocarbon vinyl ether copolymers, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymers, polyvinyl fluoride, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymers, fluorinated (meth)acrylate resins, 2-fluoroacrylate resins, fluorinated epoxy resins, fluorinated epoxy (meth)acrylate resins, fluorinated polyether resins, fluorinated polyimide resins, fluorinated polyester resins, fluorinated polyamide resins, fluorinated polycarbonate resins, fluorinated polyformal resins, fluorinated polyketone resins, fluorinated polyazomethine resins, fluorinated polyazole resins, and fluorinated polyallyloxysilane resins. The first binder constituent can also be a fluorinated elastomer such as vinylidene fluoride-hexafluoropropylene fluoroelastomer, vinylidene fluoride-tetrafluoroethylene fluoroelastomer, tetrafluoroethylene-perfluoroalkyl vinyl ether fluoroelastomer, vinylidene fluoride-tetrafluoroethylenehexafluoropropylene fluoroelastomer, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluoroelastomer, tetrafluoroethylene-perfluoroalkyl vinyl ether fluoroelastomer, propylene-tetrafluoroethylene fluoroelastomer, fluorosilicone rubber, fluorinated phosphazene rubber, fluorinated thermoplastic rubbers, and flexible fluorocarbon resins. Any one of the fluorinated resins and fluorinated elastomers are suitable as the first, halogenated polymeric constituent when used alone or in mixtures thereof.