The effect of annealing on the electrochemical properties of Zr0.5Ti0.5Mn0.5V0.3Co0.2Ni1.1 alloy electrodes

The annealing treatment was found to result in the improvement in the cyclic stability but the degradation of discharge capacity, activation and high-rate dischargeability for Zr0.5Ti0.5Mn0.5V0.3Co0.2Ni1.1 alloy electrode. A lower discharge potential in the annealed alloy electrode was found owing to a more homogeneous alloy, which is consistent with the pressure–composition isotherms (P–C–T) measurement. We found that the annealed alloy also had lower and flatter pressure plateaus, and larger pressure hysteresis. At high discharge rates, the hydrogen diffusion in the bulk of the alloy was the rate-determining step. The diffusion coefficients for hydrogen in the annealed and as-cast alloys were calculated to be 1.4×10−12 cm2 s−1 and 4.3×10−12 cm2 s−1, respectively. The lowering of high-rate discharge capacity can be ascribed to the reason that the hydrogen diffusion coefficient is lower due to homogeneous microstructure in the annealed alloy.