DEVELOPMENT OF NICKEL-METAL HYDRIDE BATTERIES

SANYO Electric Co., Ltd. led the world by successfully marketing nickel-metal hydride betteries in 1990. Because these batteries offer the same operating voltage as nickel-cadmium batteries, and more than 1.5 times higher capacity, their use is rapidly expanding. In order to refine nickel-metal hydride batteries into a marketable product, we had to overcome a number of technical difficulties, mainly in the development of hydrogen absorbing alloys, as detailed below. We used a LaNi5-based hydrogen absorbing alloy because of its superior capabilities as an electrode catalyst. We then directed our efforts toward developing a material that offers both high capacity and excellent corrosion resistance by gradually replacing a portion of the LaNi5 with other elements. While verifying the characteristics of these new combinations through experimental electrodes and batteries, we discovered that a MmNi(3.2)Co(1.0)Al(0.2)Mn(0.6) alloy had the same characteristics, and later demonstrated that we could produce a high-capacity, long-life battery with that alloy. Moreover, we developed cadmium-free nickel electrode, and raised its performance to conventional levels. We also established structural technologies by analyzing the reaction characteristics of the nickel-metal hydride batteries. The batteries that we developed as a result of these efforts offer superior characteristics, including a 1.2-hour charge time, a 4C discharge rate, and a service life of at least 500 charge-discharge cycles. These characteristics have enabled the application of nickel-metal hydride batteries to the power supplies of high-performance equipment such as communications equipment and computers.