Effect of surface modification on the electrochemical performances of LaNi5 hydrogen storage alloy in Ni/MH batteries

A new surface modification method for LaNi5 hydrogen storage alloys is presented. The surface modification consists of copper coating on the alloy surface. The CuSO4 solution is used as modification reagent and HF is used as catalyst. With the help of HF, the oxide film on alloy surface is removed and copper coating is easier to deposit. The optimal amount of HF is 0.25/200 ml and the optimal copper coating amount is 3-5 wt.%. Compared with unmodified alloy, the modified alloys show improved electrochemical performance such as superior high rate discharge-ability, better charge acceptance ability, and longer cycle life. EIS results reveal decreased contact resistances and charge transfer resistances of modified alloys, which indicates the high electronic conductivity and electrochemical activity of alloy after modification. The surface modification method employed in our study has many advantages such as low cost and simple process, and points to an effective way of improving electrochemical performances for hydrogen storage alloys. (c) 2005 Elsevier B.V. All rights reserved.