NICKEL METAL HYDRIDE BATTERY

Metal Hydride electrodes which utilize MmNi5-wAlxCoyFez (w = x+y+z,w = 1.0 approximately 1.5, x = 0.1 approximately 0.6, y = 0.1 approximately 0.9, z = 0.1 approximately 0.6) have a long cycle life and show excellent performance. On the surface of the alloy after cycling, a transition metal layer was observed. It was considered that the layer was made up of Ni, Co and Fe arising from the reduction the corrosion products in the alloy, and this layer is effective to provide the superior characteristics to the electrodes. Meanwhile, in order to raise the energy density of nickel-metal hydride batteries, we have employed a pasted nickel electrode using nickel hydroxide powder with a higher density than usual, as a new material. Formerly it was necessary to add a small amount of Cd as a solid solution to the nickel hydroxide, but replacing this with Zn allowed a Cd-free battery that is not harmful to the environment. Additionally, improvement in the charge acceptance of the positive electrode at high temperatures through the addition of Co as a solid solution made it possible to preclude one of the problems of this battery, namely, reduced capacity at high temperatures.