Alkaline storage batteries are secondary batteries that employ alkaline electrolyte solution having potassium hydroxide as the main electrolyte. Most of these battery systems use nickel oxyhydroxide (NiOOH) as the positive active material because of its superior charge-discharge cycle characteristics and long life. A nickel cadmium (Ni-Cd) system which uses cadmium as the negative active material has been the main stream of sealed alkaline storage batteries with a long charge-discharge cycle life and high reliability. Nickel-metal hydride (Ni-MH) based batteries have also been widely commercialized which use a hydrogen absorbing alloy as the negative electrode which is easier to achieve higher capacity than that with a cadmium negative electrode. Compared to other lead acid storage batteries, since the Ni-Cd battery has a higher energy density per unit weight as well as unit volume and is highly reliable in terms of cycle life, etc. as a power source for portable equipment, it has been widely applied as a power source for a variety of portable equipment. Nickel metal hydride storage batteries are secondary batteries which comprise positive electrodes mainly composed of nickel hydroxide and negative electrodes mainly composed of a hydrogen-absorbing alloy, and they have spread as secondary batteries of high capacity and high reliability. Nickel-metal hydride storage batteries practically made using hydrogen-absorbing alloys have the characteristics such as low environmental pollution and high energy density. The alkaline storage batteries presently on the market are either of the "open" type that permit gases to be exchanged with the ambient medium, or the "sealed" type having a valve and no exchange with the outside in normal operation. Sealed alkaline storage batteries typically include nickel-cadmium storage batteries and nickel-metal hydride storage batteries. Alkaline storage batteries as represented by nickel-hydrogen batteries and nickel-cadmium batteries are small, light weight and provide high output densities. Alkaline secondary batteries are widely used as power sources for various devices and apparatuses from portable devices to industrial large facilities. Alkaline storage batteries have been used as power sources for portable information equipment such as cellular phones and notebook computers, electric cars, or hybrid vehicles. An alkaline secondary battery is capable of boost charging and high-current discharging. The alkaline secondary battery is highly immune to overcharging and overdischarging. It has therefore been used for electronic products in which a large storage capacity and high charge/discharge efficiencies are required. From the points of their excellent capacity and reliability, nickel metal hydride batteries are considered to be most promising for electric power sources of electric tools and electric vehicles which require charging and discharging at high-rate.

An alkaline storage battery comprises a positive electrode configured with a nickel oxide or a nickel hydroxide, a negative electrode configured with a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen in a reversible manner, an oxide or a hydroxide of cadmium, iron or zinc or the like, and an electrolyte prepared with an alkaline aqueous solution. A separator is installed between a positive electrode and a negative electrode to separate them from each other and prevent a short-circuit. The separator can hold an electrolyte to thereby smoothly carry out an electromotive reaction. The separator is required to have an erosion resistance to an electrolyte, such as potassium hydroxide. In an alkaline storage battery, positive and negative electrode plates are spirally wound up with separators interposed respectively therebetween to provide a group of electrodes, and a set of current collectors are connected to the opposite ends of the group of electrodes to provide a cylindrical electrode assembly. A closure cap covers an opening of the external casing. A gasket usually made of nylon, is inserted between the closure cap and the external casing to seal the opening. Nickel hydroxide used as the positive electrode active material of alkaline storage batteries inherently has a very low electric conductivity, but it is converted to a trivalent nickel oxyhydroxide having a somewhat higher conductivity by charging. Negative electrode of an alkaline storage battery using hydrogen absorbing alloy repeats a cycle of electrochemically absorbing hydrogen, when charging, producing a hydride and, when discharging, desorbing hydrogen thus returning back to the initial alloy. The performance of a nickel-hydrogen battery depends on the activity of a hydrogen-absorbing alloy serving as a negative-electrode active substance. Therefore, alkaline secondary batteries employs fine powder of the hydrogen-absorbing alloy. The fine powder of the hydrogen-absorbing alloy has a large surface area for an electrochemical reaction and can be filled in an electrode substrate at a high density, thereby increasing battery capacity. The electrical conductivity of nickel hydroxide, which is the active material of the paste type positive electrode, varies with a variation in oxidation number of nickel. The oxidation of nickel hydroxide in charging process of a battery thus proceeds smoothly, but the reduction in discharging process does not proceed smoothly, due to the lowered electrical conductivity in the terminal stage of discharging process. This causes an insufficient discharge. A conductive agent, such as a cobalt compound, is added to the active material to enhance the electrical conductivity in the positive electrode and ensuring the sufficient discharge. In a sealed type alkaline storage battery, the discharge capacity of a negative electrode plate is adjusted larger than that of a positive electrode plate to restrain hydrogen gas generated from the negative electrode plate at charging and to absorb oxygen gas generated from the positive electrode plate thereby to restrain an increase of internal pressure of the battery. In order to increase internal volumetric efficiency of equipment using storage batteries, a rectangular alkaline storage battery has been developed as a replacement for a cylindrical alkaline storage battery having a group of spiral electrodes into which positive and negative electrode plates are coiled spirally with separators sandwiched therebetween.

A nickel electrode has a structure including a collector for collecting electricity and a positive-electrode active material inducing a cell reaction supported on the collector. As collectors in this case, a sintered nickel plate formed by sintering nickel powder and a punched nickel plate have been widely used. The cell capacity is determined by the volume of the active material loaded in pores in such a nickel plate, and the volume of the loaded active material depends on the porosity of the nickel plate. Nickel electrodes for alkaline storage batteries are classified into sintered electrodes and paste type electrodes. The sintered nickel electrode is formed by chemically impregnating a porous sintered substrate which is obtained by sintering with salt as an active material, and then filling nickel hydroxide as the active material into the sintered substrate. Such nickel electrode for alkaline storage battery is superior in charge/discharge characteristic at high electric current because conductivity of the sintered substrate is high and close adherence between the active material and the sintered substrate is high. The paste type positive electrode has a foamed nickel substrate having pores of approximately 500 .mu.m, where the pore is communicating each other and arranged in a three-dimensional manner. The foamed nickel substrate has a large porosity of approximately 95%. This substrate is accordingly filled with a relatively large quantity of the active material. In the pasted hydrogen-absorbing alloy electrode, electric contact among hydrogen-absorbing particles becomes defective with ease, resulting in lowering the conducting property. When the conducting property is lowered, the proportion of the hydrogen-absorbing alloy particles not involved in absorption and desorption of hydrogen is increased, which can cause decrease of the discharge capacity, degradation of the charge-discharge cycle performance and increase of the internal pressure during charge. In both paste and sintered electrodes, the positive active material utilized is nickel hydroxide, which serves as the main active component, and nickel or cobalt, which serve as an auxiliary electro-conductive component. The positive active material is contained on or in a substrate, for example, a foam nickel substrate for a paste electrode and a sintered nickel substrate for a sintered electrode.