Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1993-02-09
1994-11-22
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
429232, H01M 462
Patent
active
053668316
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a nickel electrode for use in an alkaline battery such as a nickel-cadmium battery, a nickel-metal hydride battery etc.
BACKGROUND ART
As a nickel electrode made up by directly loading a nickel hydroxide powder forming an active material, there are a paste-type electrode in which the nickel hydroxide powder is formed into a paste and loaded in a porous substrate comprising a nickel, and a button-type electrode and a pocket-type electrode in which the nickel hydroxide powder is wrapped by a current collector. The porous substrate comprising an alkaline-proof metal forming the current corrector is comparatively expensive in the paste-type electrode, so that a study has been made on an electrode utilizing a core metal as its current collector.
On the other hand, with a recent tendency to minimize a size and weight of portable electric equipment, a demand for enhancing an energy density is increasing against batteries serving as portable power sources. In order to meet this demand, a nickel-cadmium battery, a nickel-metal hydride battery and a nickel-zinc battery etc., which utilize a paste-type nickel electrode, have been developed and put to practical use.
The paste-type nickel electrode is made up by forming the nickel hydroxide powder into a paste and directly loading it in a porous substrate comprising a nickel. Therefore, in order to obtain a paste-type nickel electrode having a high energy density, it is enough to increase a porosity of the electrode substrate and a density of the nickel hydroxide powder forming the active material.
A nickel fibrous porous body and a foamed nickel porous body etc. which have a porosity of about 95% which is approximately a manufacture limit of porosity have been put in practical use for the electrode substrate. A nickel hydroxide powder an inner pore volume of which is controlled to under 0.1 ml/g incl. has been developed for the active material. Since the nickel hydroxide powder has a bulk density as high as about 2 g/ml, it becomes possible to load the powder by about 20% more than conventional one. By using the high-porous electrode substrate and the high-density nickel hydroxide powder, it becomes possible to make up a paste-type nickel electrode having 550 mAh/ml or larger so that the electrode is applied to a battery system having a high energy density.
On the other hand, the nickel hydroxide powder the inner pore volume of which is controlled to under 0.1 ml/g incl. has a feature that it is obtained in a spherical shape caused by its manufacturing process. For this reason, clearances are produced between powder particles under a loaded state as illustrated by FIG. 7, and this point has been a negative primary factor to increase the energy density.
DISCLOSURE OF INVENTION
In the conventional paste-type nickel electrode having a high energy density, there have been serious problems of (1) a swelling of electrode due to a decrease in density of the active material caused by repeated charging and discharging and (2) a low charging efficiency at a high temperature. In order to solve the above problem (1), it has so far been known that adding a small quantity of cadmium to the active material in a solid solution state has been effective. Further, in order to solve the above problem (2), a method of adding hydroxide lithium to potassium hydroxide solution used as an electrolyte has been used generally.
However, the use of cadmium which is hazardous heavy metal becomes unpreferable in connection with the recent environmental problem, so that a development of new additional element is desired earnestly in place of cadmium. In addition, in the above method to solve the problem (2), there have been demerits of a lowering of discharge voltage and a decrease in discharge capacity at a low temperature.
While, from the stand point of increasing the energy density, it is desired to minimize clearances between powder particles produced when loading the nickel hydroxide powder.
An object of a first invention of this application is t
REFERENCES:
patent: 4016091 (1977-04-01), Jackovitz et al.
patent: 4844999 (1989-07-01), Oshitani et al.
Onishi Masuhiro
Oshitani Masahiko
Watada Masaharu
Kalafut Stephen
Yuasa Corporation
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