Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-08-16
2002-08-20
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231800
Reexamination Certificate
active
06436573
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, a negative electrode therefor, and method of manufacturing the negative electrode.
BACKGROUND OF THE INVENTION
In recent years, non-aqueous electrolyte secondary batteries have been drawing attention as high output, high energy-density power sources and many research works are being conducted.
Among the non-aqueous electrolyte secondary batteries, lithium secondary batteries have heretofore been drawing attention and studied. Lithium secondary batteries employ as the positive active material lithiated transition metal oxides such as LiCoO
2
, LiNiO
2
and chalcogen compounds such as MoS
2
. These materials have a layer structure in which lithium ions can be reversibly inserted and detached. On the other hand, as the negative active material, metallic lithium has been employed. However, when metallic lithium is employed in the negative active material, lithium dissolution and deposition reaction is repeated with the repetition of charge and discharge, resulting in the formation of dendritic lithium on the surface of lithium. The formation of dendritic lithium causes problems of decreasing charge-discharge efficiency and a possible risk of causing short circuit by piercing the separator and getting in contact with the positive electrode.
In order to solve these problems, lithium alloy plate, metal powders, graphite or other carbon based (amorphous) materials, metal oxides, or metal sulfides, which can reversibly absorb and desorb lithium are being studied as an alternative negative electrode material to metallic lithium.
However, with the use of a lithium alloy plate, there has been a problem that charge-collecting capability of the alloy decreases with repetition of deep charge and discharge due to becomins fine of the alloy thus lowering the charge-discharge cycle life characteristic. On the other hand, when metal powders and powders of carbon materials, metal oxides or metal sulfides are employed, binders are usually added as an electrode can not be formed with these materials alone. Regarding carbon materials, for example, a method of forming an electrode by adding an elastic rubber-based polymer as the binder is disclosed in Japanese Laid-Open Patent Application No. Hei 4-255670. With metal oxides and metal sulfides, an electrically conducting material is also added to increase conductivity in addition to adding a binder.
When using a carbon material as the negative electrode, the carbon material is usually pulverized into powder and an electrode is formed by using a binder. When a highly crystalline graphite material is used as the carbon material, a battery with a higher capacity and higher voltage is obtained compared with a battery using other carbon materials. However, when a graphite material is pulverized, the powder tends to show flaky configuration. When a negative electrode is formed using this material, as the planar portions of the flaky graphite particles which are not involved in the insertion-detaching reaction of lithium are oriented in parallel to the plane of the electrode, the high-rate discharge characteristic declines. Furthermore, when a conventional rubber-based polymer material is employed as the binder, the binder covers the graphite particles thus hindering lithium insertion-detaching reaction, drastically lowering the high-rate discharge characteristic of the battery, especially the discharge characteristic at low temperatures.
Also, as the force of binding with the metallic core material is weak, it is necessary to add a large quantity of the binder, which further declines the high-rate discharge characteristic. Conversely, when the quantity of addition of the binder is reduced, problems arise such as an increase in the failure rate due to peeling of the electrode mix in the manufacturing process as the force of binding is weak, or a poor charge-discharge cycle characteristic due to low resistance to liquid electrolyte of the rubber-based polymer binder, and a sufficient characteristic has not yet been achieved.
Also, during the pressing process of an electrode, there is a problem in that the graphite particles slide in the direction of pressing thus breaking bonds of the binder and decreasing the strength of the electrode.
The present invention addresses these problems and provides batteries having a superior high-rate discharge characteristic, especially the discharge characteristic at low temperatures, and a superior charge-discharge cycle characteristic in a large quantity and with stability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a negative electrode which is strong against peeling of the negative electrode mix, superior in the ease of handling, high in reliability during mass production process, and further, superior in low-temperature discharge characteristic and cycle characteristic, and to provide a non-aqueous electrolyte secondary battery employing the negative electrode.
In accomplishing the object, in a negative electrode for a non-aqueous electrolyte secondary battery, the negative electrode comprising a carbon material which can reversibly absorb and desorb lithium and a binder, the present invention employs as the binder of the above negative electrode material at least one type of material selected from the group consisting of polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and ethylene-propylene-vinyl acetate copolymer. The present invention further provides a non-aqueous electrolyte secondary battery comprising a rechargeable positive electrode, a non-aqueous liquid electrolyte, and employing the above-described negative electrode.
Also, the present invention employs as the binder of the above negative electrode material at least one type of material selected from the group consisting of polyethylene, polypropylene, polyacrylic acid, acrylate, polymethyl acrylic acid, polymethacrylic acid, methacrylate, and polymethyl methacrylic acid. The present invention further provides a non-aqueous electrolyte secondary battery comprising a rechargeable positive electrode and a non-aqueous liquid electrolyte, and employing the above-described negative electrode.
Further, the present invention employs as the binder of the above-described negative electrode material at least one type of material selected from the group consisting of polyethylene, polypropylene, ethylene-acrylic acid copolymer, ethylene-acrylate copolymer, ethylene-methylacrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylate copolymer, and ethylene-methylmethacrylic acid copolymer. The present invention further provides a non-aqueous electrolyte secondary battery comprising a rechargeable positive electrode and a non-aqueous liquid electrolyte, and employing the above-described negative electrode.
Also, the present invention employs as the binder of the above-described negative electrode material at least one type of material selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-acrylic acid copolymer, ethylene-propylene-acrylate copolymer. ethylene-propylene-methylacrylic acid copolymer, ethylene-propylene-methacrylic acid copolymer, ethylene-propylene-methacrylate copolymer, and ethylene-propylene-methyl methacrylic acid copolymer.
The present invention further provides a non-aqueous electrolyte secondary battery comprising a rechargeable positive electrode and a non-aqueous liquid electrolyte, and employing the above-described negative electrode.
Yet further, the present invention employs as the binder of the above-described negative electrode material at least one type of material selected from the group consisting of polyethylene, polypropylene, ethylene-acrylic acid-styrene copolymer, ethylene-acrylate-styrene copolymer, ethylene-methyl acrylic acid-styrene copolymer, ethylene-methacrylic acid-styrene copolymer, ethylene-methacrylate-styrene copolymer, ethylene-methyl methacrylic acid-styrene copolymer, ethylene-propylene-acrylic a
Goto Shusaku
Inoue Kaoru
Sugimoto Toyoji
Takahashi Yui
Dove Tracy
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Ryan Patrick
LandOfFree
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