Effect of Ni content on rate capability of Mg0.9Ti0.06V0.04Nix negative electrodes for nickel/metal hydride batteries

Mg(0.9)Tio(0.06)V(0.04)Ni(x) (x = 1.0-1.3) alloys were prepared by mechanical alloying and their charge-discharge characteristics were investigated with structural characteristics. Maximum discharge capacity obtained at the 1st cycle was decreased with an increase in Ni content, while cycle performance was improved due to the suppression of surface oxidation. High-rate dischargeability (HRD) was also markedly improved with increasing Ni content. In particular, the Mg0.9Ti0.06V0.04Ni1.3 negative electrode showed HRD of 65% even at 1 A g(-1). From the results of differential chronopotentiometry and differential thermal and thermogravimetric analyses, it was suggested that hydrogen in the amorphous phase of the alloy was destabilized, leading to the accelerated hydrogen diffusion. This is likely to be a factor for the marked improvement of HRD. (C) 2004 The Electrochemical Society.