Determination of internal cell pressures in sealed Ni-MH rechargeable batteries using Zr0.9Ti0.1(Mn0.7V0.5Ni1.2)0.92 hydrogen-storage alloys

Extensive and systematic work has been carried out to investigate the internal pressure characteristics of a sealed Ni-MH battery in which Zr0.9Ti0.1(Mn0.7V0.5Ni1.2)(0.92) alloys are used in the anode. The pressure of this type of Ni-MH battery increases more rapidly during charge/discharge cycling than that of other Ni-MH batteries with commercial AB(5)-type alloys. The pressure increase with the above Zr-Ti-Mn-V-Ni alloy is mainly due to the accumulation of oxygen gas during charge/discharge cycling. The accumulation of oxygen is a result of the low rate of oxygen recombination reaction on the MH electrode surface. The difference in oxygen recombination reaction rate between the AB(5)-type and the Zr-Ti-Mn-V-Ni alloy electrode is caused by the difference in the reaction surface areas resulting from the different particle sizes after their activation and the difference in surface catalytic activity for the oxygen recombination reaction. From electrical impedance spectroscopy analysis, it was found that the surface catalytic activity has a greater effect on the oxygen recombination reaction than does the reaction surface area. In order to suppress the internal pressure of a Ni-MH battery with Zr-Ti-Mn-V-Ni alloy anode, it is suggested that the surface catalytic activity for the oxygen recombination reaction should be improved.