Non-sintered type thin electrode for battery, battery using same and process for same

Abstract

An electrode substrate is formed by mechanically processing a nickel foil so as to be made three dimensional through the creation of concave and convex parts, and then, this substrate is filled with active material or the like so that an electrode is manufactured, wherein the above described concave and convex parts are rolling pressed so as to incline in one direction. Furthermore, an electrode for secondary battery is formed by using the above described method.

Description

FIELD OF INVENTION [0001] The present invention relates to a paste type thin electrode for a battery, in which the cost is reduced and the high rate discharge characteristics and the cycle life are improved, and to a secondary battery using this electrode. BACKGROUND OF THE INVENTION [0002] At present electrodes for batteries, used commercially for secondary batteries, are broadly categorized as sintered type electrodes and non-sintered type electrodes. In the sintered type electrodes, active material is filled into a highly porous three dimensional substrate where metal powder is sintered to have a large porosity on both sides of a two dimensional metal substrate. In the non-sintered type electrodes, the active material powder with a binder is coated on a two dimensional metal substrate or grid, or filled into a three dimensional substrate, such as foamed nickel, metal bag or tube, without employing a sintered substrate. [0003] In general, the former exhibits excellent characterist...

AI Technical Summary

Benefits of technology

[0026] (d) Preventing the peeling of the active material powders layer from the substrate through the spirally winding process of the electrode and also the shedding of active material powders that formed the electrode through the repetitive charging and discharging afterwards, by bending the walls of the concave and convex hollow parts into one direction specifically in the vicinity of the edge, just as to wrap the space between the concave and the next concave or the convex and the next convex in order to prevent the shedding of the active material powders.

[0028] Though the present invention is not particularly limited to a nickel positive electrode, in the case of application for a nickel positive electrode, in particular, a thinner nickel positive electrode is provided in which the thickness is 500 μm or less for alkaline storage batteries, and the electrode uses an inexpensive, light weight and conductive metal substrate that can be formed only through mechanical operations on a metal foil or only through electrolytic metal deposition on the same pattern, without sintering or plating, resulting in excellent characteristics in charge and discharge characteristics, restraining the shedding of active material powder and light weight. Therefore, an inexpensive, light weight sealed cylindrical or prismatic nickel-metal hydride battery (Ni / MH battery) that shows excellent characteristics of high-rate charge / discharge and long cycle-life is achieved.

Problems solved by technology

In general, the former exhibits excellent characteristics in electronic conductivity (high-rate charge and discharge characteristics) due to a large amount of metal used in the sintered plaque and has a long cycle-life with excellent mechanical strength and stability in the shedding of active material, while it has the defect that the electrode is heavy and has a small volumetric energy density due to a small amount of active material impregnated therein because of a large volume of the electrode substrate.

On the contrary, a representative and simple non-sintered type electrode is inexpensive and light weight, and has a large volumetric energy density because of using an inexpensive substrate of a small volumetric amount in the electrode, which is easy to manufacture, through the coating or direct filling process of active material powder, while it entails the problem that the entire electrode is inferior in current collection ability as a whole, in the mechanical strength and in the holding of the active material.

These are significant problems in secondary batteries where charging and discharging is repeated and, therefore, a variety of ideas are incorporated into respective battery systems.

However, though these types of electrodes have a high capacity and a high reliability and are easily made to have higher capacity and to be lighter weight compared with the sintered type, due to a small amount of metal employed in the substrate, they have the technical problems that the mechanical strength is low and the electronic conduction of the entire electrode is inferior due to a large pore diameter within the substrate and, in addition, have the technical problem that the cost of the substrate is high.

As for the structure of this nickel positive electrode for a mass-production level, the non-sintered type was limited only to the pocket type, due to the electrode mechanical stability.

Though a light weight nickel positive electrode with a high capacity is realized by using this foamed nickel as a substrate, it has the problems that the high power drain of the entire active material is not sufficient due to the large diameter of the internal spherical space, which is approximately 450 μm in the case of even the smallest diameter, and it is expensive.

However, the following shortcomings of the sintered type electrodes for those applications have been increasing, as problems in practical use, while applications are expanding, and, therefore, the introduction of the paste type electrodes are desirable.

The structures or the substrates in the above described (1) to (4), however, have not solved all of the problems.

In (1), there still remains the problem of the active mass shedding of each thin electrode due to the swelling of the active material during charge and discharge cycles, which essentially cannot be prevented.

In (2), the thickness of the paste layer lacks uniformity due to the low binding strength between the metal fiber in bristle or whisker, or due to the non-uniformity of the holes of the substrate itself with respect to its characteristics and, additionally, it costs more than the conventional substrates.

In (3), the structure is basically not three dimensional and, therefore, it has problems in the shedding of the active material powders following a decay in charge and discharge characteristics.

In (4), though the above described problems have been improved to some extent and low cost can be expected, there still remains the problem that a desired three dimensional substrate shape is difficult to maintain.

Because, the substrate of the corrugated form is easily expanded in the direction of the wave form during the electrode press work, which leads to the problem that the active material is easily peeled off from the substrate when it is wound into an electrode of a spiral form or when charging and discharging are repeated.

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