Cobalt induced multi-plateau behavior in TiNi-based Ni-MH electrodes

Nickel-metal hydride batteries Ni-MH with higher energy densities are requested while keeping good capacity retention on cycling. In this context, the structural, solid-gas and electrochemical hydrogenation properties of TiNi1-xCox (0≤x≤0.5) compounds have been investigated. Metallurgical characterizations evidence the formation of Ti(Ni,Co) pseudobinary compounds crystallizing in the cubic CsCl-type structure with lattice parameter decreasing with Co-content. Co-substitution induces a multi-plateau behavior in both solid-gas and electrochemical isotherms even at the lowest Co-content here studied (x≤0.1). Moreover, this substitution reduces the thermodynamic stability of Ti(Ni,Co) hydrides though it has little influence on discharge capacities, which are limited to 150 mAh/g at C/10 regime. Excellent capacity retention for 30 cycles is observed for low Co-contents (x≤0.3). The Co-induced multi-plateau behavior and the good capacity retention demonstrate the interest of using Co-metal as additive in TiNi-based Ni-MH electrodes for improving their cycle-life.