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 Rct and absorbed capacitance Cabs 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).