Development of AB[sub 2]-Type Zr-Ti-Mn-V-Ni-M Hydride Electrode for Ni-MH Secondary Battery

Abstract

A series of multicomponent (M = Fe, Co, Cu, Mo, and Al) alloys are prepared and their crystal structure and pressure-composition-temperature curves are examined. The electrochemical properties of these alloys such as discharge capacity, cycling performance, and rate capability are also investigated. (M = Fe, Co, Cu, Mo, and Al) alloys have predominantly C14 Laves phases multiple phase structure. The alloys with M = Co and Fe have relatively larger hydrogen storage capacities. The discharge capacities just after activation are relatively large in the case of the alloys with M = Co and Fe. They are 226 and 225 mAh/g, respectively, at the current density 60 mA/g. The alloy is the best one with a relatively large discharge capacity and good cycling performance. The gradual increases in the discharge capacities of the alloys with the increase in the current density (from 60 to 250 mA/g) are considered to result from the spontaneous hydrogen evolution due to an insufficient hydrogen overvoltage. During activation Ni-rich and Fe-rich regions form on the surface of the alloy. They may act as active sites for the electrochemical reaction. With the increase in the number of charge/discharge cycles for the alloy, the quantities of the zirconium and iron dissolved in the solution increase. © 2001 The Electrochemical Society. All rights reserved.