The present invention relates in general to a storage battery. More particularly, the invention relates to a metal/hydrogen alkaline storage battery having a negative electrode comprising a hydrogen-storage alloy and a positive electrode comprising a metal oxide.
Lead acid and nickel/cadmium storage batteries have been used ordinarily. Recently, a metal/hydrogen storage battery has attracted public attention, since it is light in weight and capable of exhibiting a high capacity. Some of the metal/hydrogen storage batteries have a positive electrode comprising a metal oxide such as nickel hydroxide and a negative electrode comprising a hydrogen-storage alloy capable of absorbing and desorbing hydrogen reversibly. The hydrogen-storage electrode comprising a metal hydride, i.e. hydrogen-storage alloy, has been produced generally by a process disclosed in Japanese Patent Publication No. 58-46827 wherein the hydrogen-storage alloy powder is sintered together with an electroconductive material powder to form a porous body to be used as the hydrogen-storage electrode, or a process disclosed in Japanese Patent Laid-Open No. 53-103541 wherein the hydrogen-storage alloy powder is bound with the electroconductive material powder by means of a binder.
The capacity of the thus manufactured hydrogen-storage electrode is determined by the amount of the absorbed hydrogen, i.e. active material and, therefore, the larger this amount, the better. The amount of hydrogen absorbed by the hydrogen-storage electrode depends greatly on the temperature and pressure. Generally, the higher the temperature, the higher the hydrogen-absorption pressure. However, some of the hydrogen-storage alloys used for constituting the negative electrode can not absorb hydrogen unless the pressure is elevated considerably even at a low temperature. When an open type storage battery is prepared by using a hydrogen-storage alloy having the property for constituting the negative electrode, the negative electrode cannot absorb hydrogen, since no sufficient pressure can be attained. Even when the storage battery is of the sealed type, a considerably high pressure is necessary for the battery to absorb hydrogen by the negative electrode. Such a storage battery is too dangerous to be used in general.
Further, when the charge and discharge are repeated in an alkaline electrolyte, the hydrogen-storage alloy used for the negative electrode is expanded and shrunk repeatedly due to the absorption and desorption of hydrogen and, consequently, the lattice of the alloy is deformed and the alloy is pulverized into a fine powder gradually. As a result, the fine powder falls off from the alloy to reduce the capacity and, in addition, the mechanical strength of the electrode and the conductivity are also reduced remarkably. Thus, it has been difficult to keep the capacity of the battery for a long time.