Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1997-10-01
2000-12-05
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
429215, 429217, 429223, H01M 4607
Patent
active
061564532
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a water-repelling agent for batteries and a battery produced by using the water-repelling agent.
BACKGROUND ART
Recently demand for precise electric and electronic apparatuses which are small-sized and portable, such as audio tape recorder, camera built-up video tape recorder, personal computer and portable phone has been increasing more and more. As a result of such an increased demand, there has come to be required so-called secondary battery which is light and rechargeable, provides power source for driving those apparatuses and has high energy density. New secondary batteries of nickel-metal hydride type and lithium type have been commercialized by turns in addition to conventional lead storage batteries and nickel-cadmium secondary batteries.
A factor which greatly influences performance of those batteries is an active material for a battery (hereinafter referred to simply as "active material") among materials for positive and negative electrodes of a battery. Examples of the active material for positive electrode are, for instance, manganese dioxide (MnO.sub.2), nickel hydroxide (Ni(OH).sub.2), lithium cobalt dioxide (LiCoO.sub.2), lithium nickel dioxide (LiNiO.sub.2), vanadium pentoxide (V.sub.2 O.sub.5), niobium pentoxide (Nb.sub.2 O.sub.5), lithium manganese dioxide (LiMnO.sub.2) and the like, and examples of the active material for negative electrode are, for instance, cadmium hydroxide (Cd(OH).sub.2), hydrogen storage alloy (M--H), carbonaceous materials (natural graphite, artificial graphite, coke, etc.) and the like.
When producing a battery, those active materials are bound to electroconductive carbonaceous materials, for example, carbon blacks such as acetylene black and Ketjen black and graphites to produce an electrode. In such a case, fluorine-containing resins being excellent in chemical resistance and heat resistance and having binding property have been used widely as a suitable binder.
Among the above-mentioned fluorine-containing resins, as an example of use of polytetrafluoroethylene as a binder, for instance, JP-A-63-236258 discloses use of a dispersion of high molecular weight polytetrafluoroethylene (PTFE)(homopolymer) for binding MnO.sub.2 which is the active material for positive electrode of lithium primary battery with an electroconductive carbonaceous material such as acetylene black or graphite. JP-B-6-10980 discloses use of a dispersion of high molecular weight PTFE (homopolymer) for binding manganese oxide which is the active material for positive electrode of air-zinc battery with carbon black and activated carbon which are electroconductive carbonaceous materials.
On the other hand, there is known a disclosure of use of poly(vinylidene fluoride) (PVDF) as a binder. For example, JP-A-6-44964 discloses an electrode of a nickel-metal hydride secondary battery which is produced by mixing hydrogen storage alloy and carbonyl-nickel powder which are the active materials with a PVDF solution and molding the mixture into a sheet.
As a property for evaluating performance of such secondary batteries, there is used a cycle life. In secondary batteries employing nickel compound as the active material for positive electrode, particularly a nickel-metal hydride secondary battery, at the time of over-charging or rapid charging by large current, oxygen gas is generated from the positive electrode and an internal pressure of the battery increases. This is the main cause for shortening the cycle life. Namely, when the internal pressure of the battery increases over a certain level and a safety valve mounted is actuated, an aqueous solution of electrolyte and oxygen gas are released outside the battery to lower discharge capacity and cause leakage of the solution, which results in a problem of shortening of battery life.
To solve the mentioned problem, there is a method to diffuse the generated gas quickly and accelerate a reaction for converting the generated gas to water, an oxide or a hydroxide. As means therefor, there have been alre
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Higashihata Yoshihide
Nakamura Takayuki
Shimizu Tetsuo
Daikin Industries Ltd.
Martin Angela J.
Nuzzolillo Maria
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