Influence of preparation methods of non-stoichiometric hydrogen-absorbing alloys on the performance of nickel-metal hydride secondary batteries

Mm(Ni3.8Al0.2Mn0.6)((x-0.4)/4.6)Co-0.4 alloys with stoichiometry 5.0<x<5.8 were prepared through a rapid quenching process. Their microstructural and electrochemical characteristics were examined with regard to discharge capacity and durability of the negative electrode in a Ni-metal hydride (MH) battery. These multi-component alloys exhibited a high electrochemical reactivity and their discharge capacities were dominated by the stoichiometry x. The charge-discharge cycling stability was influenced by both stoichiometry and microstructure. The non-stoichiometry brought microstructural heterogeneity. However, the rapid quenching process homogenized it effectively and enhanced the cycle performance. Consequently, a capacity of 310 mA h g(-1) and a durability of up to 500 cycles were obtained in rapidly quenched Mm(Ni3.8Al0.2Mn0.6)((x-0.4)/4/6)Co-0.4 (x=5.2).