Mechanical Process for Enhancing Metal Hydride for the Anode of a Ni-MH Secondary Battery

This study attempted tofind a simpler method for modifying hydrogen storage alloys that are used as anodes in Ni-MH batteries to prolong their cycle life. The alloy was modified by mechanical grinding with cobalt metal powder. A short grinding time yielded samples with a higher discharge capacity and longer cycle life than those of the alloy which was mixed with the cobalt powder without the mechanical treatment. However, prolonged grinding caused a decrease in the discharge capacity because of amorphization of the alloy by mechanical stress. We believed the formation of a cobalt compound on the alloy surface plus closer contact between particle nhanced the cyclic durabil ity and discharge capacity of metal hydride anodes. A load conditioner (LC), a small scale battery energy storage system for consumer use, for load-shifting can be installed in private residences for demand-side power management. The LC would be charged with low cost night time electricity for use in the daytime, leading to a shifting of the load curve. However, this system cannot, be con-structed without compact, highly efficient, and long-cycle-life secondary batteries. I Nickel-metal hydride (N i-MH) secondary batteries re-portedly have characteristics of compactness, high energy density, long cycle life, and high efficiency. 2 The N i-MH secondary battery is thus a candidate for the LC system because it has an expectancy of more than 2500 cycles, i.e., durability of about I0 years. To obtain even longer cyclic durability of the MH anode, the alloys have been modif ied by the addition of some metals, metal-coating, orplating. 3'4 Mechanical alloying (MA) has been established as a method for preparing new alloy materials? This method was used for modifying the alloys here because the mechanical treatment was expected to yield a much closer contact between the alloy powder and the added metal powder