Surface treatment of rare earth-magnesium-nickel based hydrogen storage alloy with lithium hydroxide aqueous solution

The alkaline treatments of rare earth-magnesium-nickel based hydrogen storage alloy with lithium hydroxide (LiOH) aqueous solutions of various concentrations (1 M, 2 M, 4 M, 5 M, and 6 M) were investigated. The morphology and composition of the alloy surface and the electrochemical characters of the electrode were tested. The discharge capacity and cycle life of the alloy electrode were effectively improved after the treatment with LiOH solution of 5 M or higher. The samples treated in 5 M LiOH for 1 h and 6 M LiOH for 10 min showed better electrochemical properties than the other samples. The passive oxide and hydroxide layer formed in LiOH solution increased the charge retention rate and decreased the high rate dischargeability of the alloy electrode. The high concentration LiOH solution diminished the formation of oxygen containing species on the alloy surface during the treatment. The LiOH solution can remove the Mg element on the alloy surface effectively.