Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1996-06-18
1998-01-13
Nuzzolillo, M.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
H01M 462
Patent
active
057077630
DESCRIPTION:
BRIEF SUMMARY
(TECHNICAL FIELD)
The present invention relates to a binder for batteries, and electrode compositions and batteries incorporating the same.
(BACKGROUND ART)
In recent years, there is a growing demand for electric or electronic devices which are compact and suitable to carry, such as audio tape recorders, video tape recorders with a built-in camera, personal computers and cellular phones. With this trend, compactness and high performance are required of batteries, and various new batteries such as nickel-metal hydride batteries and lithium-ion batteries are commercially available in addition to conventional lead batteries and nickel/cadmium batteries. The fabrication of batteries requires binding various electrode materials including, for example, manganese dioxide (MnO.sub.2), nickel hydroxide (LiCoO.sub.2), lithium nickel dioxide (LiNiO.sub.2), lithium manganese dioxide (LiMnO.sub.2), carbon, graphite, etc. Suitable binders in wide use are fluorine-containing resin materials which have excellent chemical and thermal resistances and have binding properties.
For example, an aqueous dispersion of polytetrafluoroethylene (PTFE) is used in JP-A-236258/1988 for binding MnO.sub.2, acetylene black, graphite, etc. serving as positive electrode materials for lithium primary batteries. JP-B-10980/1994 gives an example of binding a manganese oxide, and carbon black or activated carbon with an aqueous dispersion of PTFE for an air-zinc battery. On the other hand, also known is polyvinylidene fluoride (PVDF) used as an example of binder. In regard to nickel-metal hydride batteries, JP-A-44964/1994 describes an electrode prepared by mixing a hydrogen storage alloy, carbonyl nickel powder or like conductive agent with a solution of PVDF to make the mixture into a sheet. JP-A-249860/1992 also discloses the use of PVDF as an example of binder for lithium ion secondary batteries, i.e., the use of an N-methylpyrrolidone solution of PVDF for a positive electrode comprising LiCoO.sub.2 or like lithium-containing oxide and graphite and for a negative electrode of carbonaceous material in preparing the respective mixtures and making each mixture into a sheet.
PTFE has the property of being liable to fibrillate by compressive shearing force, and therefore readily produces fibrils when mixed with other powder material and acts to interlock the particles. However, a uniform mixture is difficult to prepare because of excessive fibrillation, and PTFE is likely to impair the characteristics of electrodes if added in an amount more than is necessary. To obtain a uniform mixture, PTFE is usually frequently used in the form of a colloidal aqueous dispersion rather than a powder. The dispersion nevertheless has the problem of fibrillating excessively and encountering difficulty in forming a uniform mixture. Further the use of the aqueous dispersion eventually requires the step of removing a large amount of water and the surfactant contained therein as a stabilizer by heating, and the surfactant and water are likely to adversely affect the characteristics of some types of batteries. For example, the lithium-containing oxides for use in the positive electrode of the lithium ion secondary battery include LiNiO.sub.2 which is especially reactive with water and is not usable with the aqueous dispersion of PTFE. In the case where PVDF is used as a binder, the resin is soluble in organic solvents and can therefore be mixed in the form of a solution with electrode materials, consequently forming a uniform mixture and obviating the need for the step of removing water or surfactant unlike the PTFE aqueous dispersion. However, the property of being soluble in organic solvents renders PVDF prone to swell in organic electrolytes, such as propylene carbonate, dimethoxyethane and .gamma.-butyrolactone, for use as battery materials, and swelling is likely to impair the performance of batteries. PVDF has another drawback in being inferior to PTFE in binding properties.
An object of the present invention is to provide a binder for batteries which can b
REFERENCES:
patent: 5324785 (1994-06-01), Noda et al.
patent: 5326658 (1994-07-01), Takahashi et al.
Higashihata Yoshihide
Nakamura Takayuki
Shimizu Tetsuo
Daikin Industries Ltd.
Nuzzolillo M.
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