Effect of discharge cut off voltage on cycle life of MgNi-based electrode for rechargeable Ni-MH batteries

Amorphous Mg0.8Ti0.2Ni alloy was prepared by means of mechanical alloying (MA). Its cycle life as a negative electrode rechargeable alkaline Ni-MH battery has been studied with the cut off voltage varying from -0.55 to -0.75 V (versus Hg/HgO). The initial discharge capacity is increased with the depth of discharge, and at the discharge cut off voltage of -0.70 V (versus Hg/HgO) shows the best cycle life of all in 50 cycles. The results of EIS measurements show that the charge transfer resistance R-et and absorbed capacitance C-abs depended on the discharge depth, and overdischarge accelerated the capacity decay of the anodes. In contrast, the cyclic voltammogram measurement shows that in the range of -1.1 to -0.65 V, -0.70 and -0.75 V (versus Hg/HgO), a cathodic peak emerges, relevant to the electrocatalytic activity of this electrode. When the voltage is lower than -0.65 V (versus Hg/HgO), there is a partial discharge capacity associated with the oxidation of the alloy to Mg(OH)(2) and Ni(OH)(2). This can be seen from the discharge curves of the Mg0.8Ti0.2Ni electrode for a discharge cut off voltage from -0.55 to -0.75 V (versus Hg/HgO). This result assumed that the cut off voltage of MgNi-based electrode fell into the range -0.65 to -0.70 V (versus Hg/HgO). (c) 2005 Elsevier B.V. All rights reserved.