Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-01-27
2002-08-13
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231950, C029S623100, C029S623300, C029S623500, C427S115000
Reexamination Certificate
active
06432579
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP99/02729 which has an International filing date of May 25, 1999, which designated the United States of America.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anode for a secondary battery using, as an electrode material, a sintered material which contains silicon as an active material, a process for producing the same, and a non-aqueous secondary battery using the same.
2. Description of the Related Art
With the popularization of portable telephones and note-type personal computers, high-capacity lithium secondary batteries containing a cathode active material and an anode active material, capable of incorporating and releasing lithium ions, have attracted special interest. Among them, demands for space-saved, thin square-shaped batteries have been particularly enhanced. For the purpose of enhancing the efficiency of the battery reaction by increasing the electrode area, a cathode and an anode obtained by coating a belt-shaped metal foil with a coating composition containing an active material, a binder and a conductive material are used in a current square-shaped battery, and these electrodes are contained in a battery can after winding, together with a separator, and pressing.
This electrode is composed of about 40% by volume of an active material, 20 to 30% by volume of a binder, a conductive material and a metal foil, and 30 to 40% by volume of pores. Accordingly, there is a problem that those which do not contribute intrinsically to the capacity of the battery, such as binder, conductive material and metal foil limit the battery capacity per volume. When the wound electrodes described above are contained in the square-shaped can, it is impossible to fill corner portions of the battery and a useless space is formed. Therefore, the capacity per unit volume is further lowered.
Thus, a trial of forming the electrode of a sintered material made substantially of an active material has been made as a means for increasing the capacity per unit volume. When the electrode is formed of the sintered material, it is possible to eliminate the binder and to eliminate the conductive material or to reduce its amount, thereby making it possible to increase the filling density of the active material and to enhance the capacity per unit volume. For example, Japanese Patent Laid-Open Publication No. 5-299090 discloses an anode obtained by contact-bonding of a copper foil to a sintered material of a petroleum pitch or a carbonaceous material, while Japanese Patent Laid-Open Publication No. 8-180904 discloses a cathode formed of a sintered material of a composite oxide containing lithium and metal.
As the anode active material, carbon materials, for example, amorphous carbon such as coke (e.g. Japanese Patent Laid-Open Publication No. 62-122066 and 1-204361) and glassy carbon (e.g. Japanese Patent Laid-Open Publication No. 2-66856); and natural graphite (e.g. Japanese Patent Publication No. 62-23433) or artificial graphite (e.g. Japanese Patent Laid-Open Publication No. 4-190555) have been suggested. However, the battery capacity per unit volume is not sufficient even in case where any of amorphous and crystalline carbon materials is used and, therefore, a further improvement in performance is desired.
To increase the battery capacity per unit volume, a trial of using silicon or its compound as the anode active material to form an anode has been made. For example, Japanese Patent Laid-Open Publication No. 7-29602 discloses a process of producing an anode, which contains using Li
x
Si (0≦×≦5) as an anode active material, adding graphite as a conductive material and a binder, forming the mixture into pellets and using a conductive adhesive as a current collector. Japanese Patent Laid-Open Publication No. 5-74463 discloses a process of producing an anode, which contains using a silicon single crystal as an active material and interposing it between nickel meshes.
However, even if an anode which contains silicon as the active material is formed of a sintered material so as to increase the capacity per unit volume, the internal resistance of the battery is increased by a large contact resistance between a current collector and a sintered material, whereby the capacity is not improved necessarily at present.
In view of the requisite capacity in case of using in the portable telephone, the base area of the electrode is preferably 4 cm
2
or more because of limitation of the thickness of the battery.
However, in the anode sintered material composed mainly of silicon, those satisfying these requirements simultaneously could have not obtained by a conventionally known technique.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a process for producing an anode for a secondary battery, capable of reducing contact resistance between a current collector and a sintered material in an anode which contains silicon as an active material.
By sintering a silicon-containing coated film and a base material made of a foil or mesh of conductive material, a high capacity can be obtained. That is, the process for producing an anode for the secondary battery of the present invention comprises: (a) adding a binder and a solvent to a silicon-containing anode material to prepare a slurry; (b) coating a base material made of a foil or mesh of conductive metal with the slurry, and then removing the solvent to form a coated film; and (c) sintering the coated film in a non-oxidizing atmosphere, thereby integrating a sintered material of the coated film with the base material.
By sintering a silicon-containing coated film and a base material made of conductive metal in a non-oxidizing atmosphere, the contact area of interface between a sintered material and a current collector are increased, and the sintered material is integrated with the current collector, thereby making it possible to reduce the contact resistance between the sintered material and the current collector and to provide an anode of a thin film whose conductivity has been improved.
The anode material preferably contains a material to be carbonized by a heat treatment, or a carbon material. In that case, it is preferred to use a composite powder obtained by heat-treating silicon or its compound at a temperature within a range from 600 to 1400° C. in a non-oxidizing atmosphere in the presence of a material to be carbonized by the heat treatment, or a carbon material.
The coated film is preferably sintered at a temperature lower than the melting point of conductive metal base material, thereby making it possible to integrate the sintered material with the base material without causing thermal deformation of the base material.
By using any one metal selected from stainless steel, elements of the upper group and elements of the platinum group as the conductive metal, there can be obtained a current collector which is electrochemically stable even in a reduced state of the anode and has high conductivity.
The anode for the secondary battery according to the present invention is characterized by an anode obtained by the process of sintering a coated film which is formed on a base material made of a foil or mesh of conductive metal and comprises a silicon-containing anode material and a binder, thereby to integrate the anode sintered material with the base material.
The anode for secondary battery according to the present invention can also be obtained by peeling a coated film from a base film for coating, pressing the coated film to a base material made of a foil or mesh of it conductive metal, and sintering them, thereby integrating a sintered material of the coated film with the base material. When using the base film for coating, it also becomes possible to continuously process drying of a coated film coated with the slurry, peeling of the coated film and recovery of the coated film, using a coated film winder, thereby simplifying the production process.
The thickness of
Hirabayashi Tadashi
Nakanishi Kuniyuki
Nishimura Toru
Suzuki Atsushi
Tsuji Ryuichi
Kao Corporation
Martin Angela J
Ryan Patrick
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