Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Patent
1996-08-16
1998-09-22
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
427 79, 427246, 4273882, H01M 214
Patent
active
058112057
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a bifunctional electrode for an electrochemical cell or a supercapacitor. It also relates to a method of producing it.
The electrodes in conventional supercapacitors and electrochemical cells are separated by a layer of porous insulating material which is impregnated with electrolyte. That separator constitutes a separate component, which is usually commercially available, which is assembled with the other components during assembly of the electrochemical element (cell or supercapacitor). It must therefore have sufficient intrinsic mechanical strength for it to be capable of being manipulated and of resisting the stresses of automated industrial production. Those components have the problem of being expensive and not specifically adapted to the type of cell in which they are used. Conventional separators limit improvements in the performance of electric cells and supercapacitors.
In order to facilitate assembly of the components, a separator supported by an electrode has been proposed. The porous sheet acting as a separator may be manufactured initially, and it is then applied to the electrode by mechanical means such as rolling or coextrusion with the metal of the electrode (European patents EP-0 219 190 and EP-0 243 653), or by a chemical method, such as using an adhesive (EP-0 195 684). The operation is difficult to perform without damaging the separator, which means a thick, mechanically strong separator must be used. Further, the adhesion obtained is imperfect and the risk of delamination is high if the dimensions of the electrode vary.
The separator can also be formed directly on the electrode which acts as a support.
As an example, one method consists of depositing, on the electrode, separator material in the form of a continuous layer which is rendered porous during a subsequent operation, normally by means of a pore-forming additive added to the material. European patent applications EP-0 143 566 and EP-0 146 246 describe a metallic lithium electrode on which a non-porous layer of a protective material is deposited, for example by rolling or extrusion. That material is then rendered porous by reaction with one of the electrode components or by the presence of an additive. That method involves several operations and the use of pore-forming additives whose choice is limited to those which are completely eliminated or to those which are compatible with the components and operating conditions of the electrochemical element.
Other methods deposit a porous layer directly onto a solid metal electrode. European patent application EP-0 143 562 describes the deposition of a porous layer on a lithium electrode from a solution which is then evaporated off. In other methods, deposition of a monomer in solution can be followed by polymerization in situ.
U.S. Pat. Nos. 4,885,007 and 4,524,509 describe a method of enveloping lead electrodes in a microporous separator. That method consists of immersing the electrodes in a coating solution containing a polymer and a filler, then drying in air. The set of operations is repeated a number of times to obtain a separator with sufficient thickness. That method requires a number of manipulations.
U.S. Pat. No. 3,023,261 describes a method of producing an electrode-separator assembly for secondary cells containing an aqueous alkaline electrolyte. The electrodes are immersed in a solution containing a synthetic resin which is insoluble in water and a polymer which swells in water, then washing with water to eliminate any traces of solvent. The polymer which swells in water is intended to give the electrolyte access to the electrode. It is advisable to use the maximum quantity of that polymer without compromising the mechanical strength of the separator. The characteristics of the separator obtained essentially depend on the choice and concentration of polymer which swells in water.
Known methods of forming the separator directly on the electrode can improve adhesion between the separator and the electrode. However, those methods include a nu
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Chemical Abstracts, vol. 118, No. 16, 19 Apr. 1993, Columbus, OH, Abstract No. 149044, Takehata, Koji et al, "Continuous microporous-containing fluropolymer membranes", XP002001519-see abstract--JP A 04 239 041 (Mitsubishi Rayon Co., Ltd., Japan).
Andrieu Xavier
Josset Laurence
Kalafut Stephen
SAFT
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