Electrode characteristics of C14-type Zr-based laves phase alloys

The thermodynamic and electrochemical properties of ZrCr_0.8M_0.2NiMm_0.05 (M V, Mn, Fe, Co; Mm, misch metal) and Zr_1−χTi_χCrNiMm_0.05 (χ = 0, 0.1, 0.2) are investigated by measuring the pressure—composition isotherms using a Sieverts-type apparatus and the electrode characteristics of the Ni—metal hydride (MH) battery. From the results it is found that the substituted alloying elements Fe, Co and Ti are effective in modifying the hydrogen desorption pressure. When Mn or V is substituted for Cr, although it does not have a significant influence on these properties, the dischargeability at low temperatures and the rate capability are greatly improved. This improvement may be due to the increase in the surface area of the metal hydride alloy in the electrode, which is caused by the decrease in particle size or the dissolution of V into the KOH solution. On the basis of the effects of the alloying elements on the thermodynamic and electrochemical properties of ZrCrNiMm_0.05, the alloy Zr----Ti----Cr----Mn----V----Fe(or CO)----NiMm_0.05 is found to be suitable for the anode material in Ni----MH batteries. This alloy, which has the C14 hexagonal structure, shows high discharge capacities (300–370 mA h g⁻¹), good dischargeabilities at low temperatures and good rate capabilities.