AB5-type hydrogen storage alloy used as anodic materials in Ni-MH batteries

The performance of a nickel-metal hydride (Ni-MH) battery depends enormously on the characteristics of the negative electrode. The metal hydride LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 alloy powder can be used as the negative electrode material. The characteristics of the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35, including the polarization resistance, the exchange current density and the equilibrium potential were studied as functions of the number of cycles. The exchange current density of the alloy electrode increases with the increasing number of charge/discharge cycles and then remains almost constant after activation. The increase of the exchange current density is mainly attributed to the increase of the electrocatalytic activity of the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 alloy. The constant potential discharge technique was used to evaluate the diffusion coefficient of hydrogen in the compound at various states of charge (SOC). It is seen that the diffusion coefficient increases with the hydrogen content in the alloy.