Nanostructured Mg 2Ni materials prepared by cold rolling and used as negative electrode for Ni–MH batteries

Abstract

In the present work, cold rolling has been investigated as a new means of producing Mg-based metal hydrides for nickel–metal hydride (Ni–MH) batteries. Structure and electrochemical evolution of 2Mg–Ni cold-rolled samples were investigated as a function of the number of rolling passes as well as heat treatment. It was found that nanocrystalline Mg 2Ni alloy can be obtained by an appropriate three step process involving rolling, heat treatment and rolling again. It was shown that the number of primary and secondary rolling passes must be carefully optimized in order to favour the complete formation of Mg 2Ni alloy having a nanocrystalline structure (∼10 nm in crystallite size) without excessive sample oxidation. Actually, the best result was obtained by first rolling 90 times, followed by a heat treatment at 400 °C for 4 h and roll again 20 times. The resulting material displayed an initial discharge capacity of 205 mAh g −1, which is quite similar to that obtained with ball-milled Mg 2Ni alloy.