Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-04-05
2001-08-14
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S206000, C029S002000
Reexamination Certificate
active
06274275
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a spongelike metal substrate used as an electrode substrate of an alkali storage cell and a producing method of the substrate, and further relates to an alkali storage cell employing such a substrate and a manufacturing method of the cell.
BACKGROUND ART
Electrodes for use in alkali storage cells are classified into a sintered type and a paste type. The sintered-type electrodes have excellent current collecting performance, but they require a complicated operation for being filled with active material and cannot easily achieve high energy density. In contrast, the paste-type electrodes have good workability, allowing the substrates to be directly filled with active material and achieve dense filling of active material.
As substrates for use in the paste-type electrodes, porous metal plates and spongelike metal substrates have been used. The term “spongelike” refers to a state where a multiplicity of cells are contiguous to each other and fluid such as air or paste inside these cells can travel from one cell to another. Spongelike metal substrates made of nickel or the like (foamed nickel substrates or the like) have become the mainstream, with the growing demands for cells which have higher energy density and can be manufactured at a lower cost. The reason for the popularity of the spongelike metal substrates is due to their favorable features as follows. The spongelike metal substrates contain numerous three-dimensional spaces each of which is surrounded by metallic lattices and can be filled with solid active material in paste form directly and at high density. Furthermore, contiguous numerous metallic lattices serve as a current collector, making it unnecessary to use a conductive supporter.
Generally, a spongelike nickel substrate is prepared as follows: A spongelike organic high polymer (organic polymer, organic macromolecular substance) such as foamed urethane is plated with nickel by either electroplating, electrolessplating, or vapor deposition, then the nickel-plated high polymer is baked at a high temperature. The electrode substrate thus produced is highly porous and contains numerous metallic lattices which are composed of thin metal wires. This electrode substrate can be filled with active material at high density; however, its stretching force is weak because the lattices are composed of extremely thin metal wires. As a result, the lattices are susceptible to fracture in parts during electrode pressing process or electrode coiling process after the electrode substrate has been filled with active material. The fracture of the metallic lattices leads to the deterioration of the current collecting efficiency, and as a result, there is a problem that the electrode performance cannot improve sufficiently even if the electrode substrate is filled with active material at high density.
There is another problem that cells which employ such a spongelike nickel substrate do not necessarily achieve an expected high-temperature consecutive charge characteristic, whose cause has been unknown.
DISCLOSURE OF THE INVENTION
The present invention has been achieved to solve the above-described problems. The invention has the following construction.
(1) The first invention relates to a spongelike porous metal substrate having a multiplicity of cells connected with each other three-dimensionally for use in an alkali storage cell, which is produced by making an organic high polymer with a porous sponge structure retain a metal and baking the metal-retained organic polymer, and which contains 0.5% by weight or low of carbon.
In this construction, there is no fear that remaining carbon has a harmful influence on the electrochemical characteristic of a cell which employs the spongelike porous metal substrate. Consequently, a paste-type alkali storage cell employing this spongelike porous metal substrate can have excellent high-temperature consecutive charge characteristic.
It is preferable that the spongelike porous metal substrate whose carbon content is 0.5% by weight or low contain a multiplicity of three-dimensional spaces each of which is surrounded by lattices each having a longer length and a shorter length, that the segments of the longer lengths of the lattices which are approximately parallel to the substrate surface be directed approximately in the same direction, and that a ratio of the segments of the longer lengths of the lattices to the segments of the shorter lengths which cross the segments of the longer lengths at approximately right angles (the segments of the longer length/the segment of shorter length) be 1.7 or below.
This spongelike porous metal substrate can be filled with active material at high density, and have good current-collecting rate against active material. Consequently, an alkali storage cell employing this spongelike porous metal substrate can have excellent high-temperature consecutive charge characteristic.
(2) The second invention relates to a method of producing a spongelike porous metal substrate having a multiplicity of cells connected with each other three-dimensionally for use in an alkali storage cell by putting a metal into a multiplicity of three-dimensional voids in a belt-shaped organic polymer sheet having a porous sponge structure where the a multiplicity three-dimensional voids and approximately spindle-shaped organic polymer units, are arranged alternately burning the metal-retained organic polymer units so as to eliminate the spindle-shaped organic polymer units, and sintering the metal. The method is characterized by comprising the following processes: a longer length/shorter length ratio adjustment process for directing the longer lengths of the organic polymer units to the longitudinal direction of the organic polymer sheet, and setting the ratio of the segments of the longer lengths to the segments of the shorter lengths which cross the segments of the longer lengths at approximately right angles at 1.7 or below by adjusting applying a stretching force both in the longitudinal direction of the organic polymer sheet and in the direction which crosses the longitudinal direction at right angles; a metal retention process for putting a metal into the a multiplicity of three-dimensional voids of the organic polymer sheet in which the longer length/shorter length ratio has been adjusted; a burning process for burning the metal-retained organic polymer sheet until the amount of remaining carbon becomes 0.5% by weight or below; and a sintering process for sintering the burnt metal in a reducing atmosphere.
In this construction, it is secured to produce the spongelike metal substrate of the first invention which contains 0.5% by weight or less of carbon and also contains lattices having a longer length/shorter length ratio of 1.7 or less.
In the second invention, in order to make the substrate retain a metal, it is preferable that the belt-shaped organic high polymer sheet having lattices whose longer length/shorter length ratio has been adjusted be subjected to metal plating or metal-containing slurry impregnating. With these processes, the belt-shaped organic high polymer sheet can retain the metal easily and without fail. It is possible to evaporate a metal as an alternative method for making the substrate retain a metal.
Furthermore, in the second invention it is preferable to employ foamed urethane as the spongelike organic high polymer. The reason for this is as follows. Foamed urethane contains numerous three-dimensional contiguous voids, and urethane constituent units surrounded by these voids can be easily transformed by applying a stretching force in the longitudinal or lateral direction. Therefore, the longer length/shorter length ratio of the foamed urethane constituent units is set at 1.7 or less with ease by balancing the stretching forces in the longitudinal direction and the direction crossing the longitudinal direction at right angles. After making the voids having this ratio retain a metal, the foamed urethane is baked (which includes being burned and sintered) to remove th
Tadokoro Motoo
Yamawaki Akifumi
Chaney Carol
Foley & Lardner
Sanyo Electric Company Ltd.
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