Electrochemical behaviors of low-Co Mm-based alloys as MH electrodes

Abstract

A series of low-Co Mm-based alloys a ere prepared and studied for possible application in Ni/MH batteries. Alloy phase structure and electrochemical properties of MH electrodes were investigated. For comparison, the MmNi(3.75)Co(0.62)Mn(0.36)Al(0.27) alloy, having a composition close to the commercial MmNi(3.55)Co(0.75)Mn(0.4)Al(0.3) alloy, was also examined. Electrochemical measurements show that the low-Co MmNi(3.65)Co(0.22)Mn(0.36)Al(0.27)Cr(0.2)Cu(0.2)Si(0.1) alloy exhibits satisfactory cycling stability, though the initial capacity (273 mAh/g) is lower than that of the high-Co MmNi(3.75)Co(0.62)Mn(0.36)Al(0.27) alloy (314 mAh/g). After 300 cycles at 1.0C rate, the capacity decay is 25.6% for the low-Co MmNi(3.65)Co(0.22)Mn(0.36)Al(0.27)Cr(0.2)Cu(0.2)Si(0.1) alloy and 24.4% for the high-Co MmNi(3.75)Co(0.62)Mn(0.36)Al(0.27) alloy, respectively. In addition, electrochemical impedance spectroscopy (EIS) studies have also been carried out in order to understand inter-facial electrochemical reactions on MH electrodes. (C) 1998 Elsevier Science S.A.