Mutsumi Yano

Effect of additives in zinc alloy powder on suppressing hydrogen evolution

Abstract The addition of 0.025 wt.% bismuth and 0.025 wt.% lead to zinc particles modified with 0.10 wt.% indium by a dry-coating process, or a conventional wet-coating process is examined to clarify the effect on suppressing hydrogen gas evolution due to the self-discharging reactions of zinc in alkaline manganese batteries. The dry-coating process of indium metal modifies the zinc alloy powder, such that oxidation of the powder is less, and hydrogen-gas evolution is suppressed more effectively than in the case of the conventional wet-coating process. In the dry-coating process, the bismuth diffuses into the surface to be alloyed with the indium. As a result, zinc alloy powder containing 0.025 wt.% bismuth modified with 0.10 wt.% indium (Zn–In–Bi) by the dry-coating process suppresses hydrogen gas evolution on a competitive level with zinc powder containing 0.15 wt.% mercury (Zn–Hg).

Storage characteristics of mercury-free alkaline manganese batteries

The amount and distribution of additive species in zinc alloy particles containing 0.025wt% bismuth modified with 0.10wt% indium for mercury-free alkaline manganese batteries were examined after storage at various discharging levels at 60°C. The amount of hydrogen gas evolution due to the self-discharging reactions of zinc and the internal cell impedance were also evaluated. The amount of additive species in the zinc alloy particles was found to increase with increasing depth of discharge. Indium was homogeneously distributed on the surface even after partial discharge and also after storage for 1200h at 60°C. This behaviour is considered to contribute to the suppression of hydrogen gas evolution and increase in the internal cell impedance to the same level as when mercury is employed. As a result, mercury-free alkaline manganese batteries showed the same storage characteristics as conventional batteries containing mercury.