A study on the characteristics of V-Ti alloy surface-modified by ball milling process

Abstract

V-Ti alloys have not been used as anode material of Ni/MH batteries because of their inability to charge/discharge in KOH electrolyte. Ni, a catalyst for hydrogen absorption/desorption in KOH electrolyte, was added to V-Ti alloy as a catalyst by the ballmilling process. The discharge capacity varied with ballmilling conditions such as ballmilling time lund Ni content. In particular, increasing ballmilling time leads to an effective alloyed surface, but a decreasing number of interstitial sites for hydrogen storage in the V-Ti alloy by structural damage of the alloy. The nickel powder alone was ballmilled causing a change in shape from spherical to Rake-type and inducing strain, as measured by X-ray diffraction. Therefore. Ni powder had a large surface area that increased the contact area of surface alloying and high activity of the surface alloying reaction. Comparing the ballmilling condition for Rake Ni with that for sphere Ni, the optimum ballmilling time was decreased so that the number of interstitial sites for hydrogen storage was nearly unchanged. Because of such a large hydrogen storage capacity to be dischargeable electrochemically, the maximum discharge capacity was 439 mAh/g. (C) 2001 The Electrochemical Society.