Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-04-07
2002-09-17
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S324000
Reexamination Certificate
active
06451487
ABSTRACT:
The present invention concerns a composite electrode for electrochemical cell, an electrochemical cell comprising the composite electrode, a process for preparing the composite electrode, as well as a process for the preparation of a half-cell comprising a porous mineral composite—porous mineral separator sub-network.
More particularly, the invention concerns a composite electrode in which two solid interpenetrated electrolytes are used. The first electrolyte, of organic nature, preferably consists of a dry or gelled polymer which is made conductive by dissolving a salt or a mixture of salts preferably containing a lithium ion, and which acts as a deformable binder of the composite. The second electrolyte, of mineral nature, preferably vitreous, is a specific ion conductor, such as lithium ions, and in which the components of the first polymer electrolyte are insoluble. The solid mineral electrolyte is prepared in the form of an aqueous solution or in a mixture of water and light alcohols, which is contacted with the materials of the electrode in dispersed form so as to moisten at least in part the solid phases of the composite, i.e. the particles of the active material of the electrode, the additive of electronic conduction as well as the current collector of the electrode on which the dispersion is applied so as to form first a porous mineral sub-assembly. The organic electrolyte preferably comprising a polymer is thereafter introduced by permeation (impregnation) in the porous mineral sub-assembly so as to constitute the composite electrode of the invention.
The use of inert binders for preparing composite electrodes with liquid electrolytes has been known to one skilled in the art for a number of years. With the development of intrinsic or gelled conductive polymer electrolytes, the electrolyte has also become the binder of the composite electrode, which has made it possible to more easily adapt the variations of volume of the materials of the electrode. (Armand Europe and Bellcore). The use of appreciable amounts of mineral binders of polysilicates type in composites to mechanically bind the materials of the electrode to their current collector in a system of lithium-ion type with liquid electrolyte has also been described, and the possibility to carry out about twenty cycles has been demonstrated (Fauteux U.S. Pat. No. 5,856,045). A process of manufacturing a composite electrode including a step of preparing a porous electrode on its collector under air and a step of impregnating components of a polymer electrolyte so as to compensate for the porosity has been described in WO 97/44843, without however mentioning the preferred moistening of the phases in presence.
The treatment of active electrode materials with mineral phases to reduce the chemical aggressiveness of the active powders towards the organic electrolytes was also described for cathodes of lithium-ion systems (Tarascon).
Accessorily, the protection of current collectors such as aluminum with carbon base coatings was the object of numerous Patents which proposed the use of organic type inert binders (Fauteux U.W. U.S. Pat. No. 5,580,686).
None of these solutions meet all the criteria enabling to ensure the preservation of performances in power or cycling capacity, such as under conditions of elevated temperature, for example with polymer electrolyte lithium generators operating at temperatures between 40 and 80° C., (JPS MG) or still with lithium-ion type generators operating at room temperature but under high voltages close to 4 volts (ref. lithiumion). In particular, none of the suggested solutions propose a global solution to the problem of preserving the quality of the ionic and electronic exchanges between all the phases constituting the composite electrode, such as between the dispersed solid particles. In the cases of extreme temperature and voltage, the collectors and the interfaces between the various solid phases, or between the particles of the same phase, are strongly solicited and have a tendency to prematurely lose their properties by formation of passivation films which are prejudicial to the quality of the electrical contacts inside the generator. Under these conditions, the components of the electrolytes (solvent and salt) play an important part in the formation of passivation films at the interfaces.
An advantageous way to maintain the quality of the electrical contacts in a generator would consist in using vitreous or crystalline solid mineral electrolytes which are in addition specific conductors of lithium ions. These solid electrolytes are less kinetically or thermodynamically reactive that organic liquids or polymers and do not require the use of a mobile lithium salt which can react with the active material of the electrode or with the current collector.
On the other hand, in vitreous state and when prepared in solution, these electrolytes have wetting properties which enable them to maintain at least part of the exchange surfaces during phenomena of passivation produced by a direct contact with the components of an organic electrolyte. These electrolytes however have disadvantages in that they are poor conductors and furthermore, they are rigid and brittle, i.e. they do not easily accommodate to variations of volume taking place at the electrodes during discharge/charge cycles. It is therefore difficult to use them as the only electrolyte of a composite and it is still more difficult to use them as binder of a composite which undergoes important variations of volume of the electrodes during cycling.
It is an object of the present invention to overcome these disadvantages by associating in a same composite electrode of a generator, the use of a solid mineral electrolyte with a solid organic electrolyte, preferably a polymer electrolyte.
It is another object of the invention to use first a solid mineral electrolyte, preferably vitreous or partially vitreous, in aqueous solution, to wet and adhere to at least part of the surface of the phases in presence: current collector, active material of the electrode and to at least part of the additive of electronic conduction.
It is also an object of the invention to provide a preparation step which defines impervious contact zones between the vitreous electrolyte and each of the solid phases.
It is also an object of the invention to disperse the active material of the electrode and the additive of electronic conduction in a aqueous phase comprising the solid vitreous electrolyte in solution and to apply same on the current collector so as to constitute a porous mineral subassembly.
It is also an object of the invention to provide a process which consists in impregnating a solid organic polymer electrolyte and a lithium salt both present in the form of molten polymer, polymer solution or still in the form of polymer which will be cross-linked after formation, so as to constitute a composite electrode with two solid electrolytes, one in the form of mineral glass, the other in the form of organic elastomeric polymer.
Another object of the invention resides in the use of the vitreous solid electrolyte to wet at least part of the surface of the solid phases in presence so as to cause these contact surfaces (entirely mineral) to be inaccessible to the components of the organic solid electrolyte (polymer and lithium salt) and thus to preserve this portion of the surface from the formation of passivation films which are harmful to the quality of electrical contacts.
It is still another object of the invention to optimize the electrochemical performances of at least one composite electrode of a rechargeable lithium generator when this generator operates under difficult conditions of temperature or high voltages and for long periods of time.
It is still another object of the invention to combine into one single composite electrode the advantageous properties of a solid mineral electrolyte with the complementary properties associated with solid polymer electrolytes.
Another object of the invention is to cause the vitreous solid mineral electrolyte to wet a
Armand Michel
Belanger Andre
Besner Simon
Dupuis Elisabeth
Gauthier Michel
Hydro-Quebec
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ryan Patrick
Wills M.
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