Temperature performance of AB5 hydrogen storage alloy for Ni-MH batteries

The substitution of manganese by molybdenum in LaNi3.6Co0.7Mn(0.4-x)Al0.3Mox (x = 0 and x = 0.1) in AB5-type alloys as anode active materials for Ni-MH batteries, was studied. We study the influence of molybdenum, on the performance of the electrode at different temperatures (10 °C, 25 °C and 45 °C). The alloys structural characterizations were performed by scanning electron microscopy concluding that manganese substitution by molybdenum generates a new segregated phase contributing in the heterogeneity of the alloy. The electrochemical properties were studied through the measurements of discharge capacity, activation process, rate capability and electrochemical P-c-T curves. The replacement of manganese by molybdenum, in the concentration tested (2% w/w) has a positive effect. Thermodynamics properties were also evaluated. Molybdenum involves a thermodynamic destabilization of the alloy hydride and the difference in the hysteresis values for AB5M0 and AB5M1 is greater for increasing values of temperature. The entropy and the enthalpy of hydriding reaction were found from a Van't Hoff plot by lineal regression for 10, 23 and 45 °C. The lower stability of molybdenum-containing hydride corresponding to higher hydrogen diffusion coefficient in the alloy, facilitates the transfer of hydrogen in the bulk and thus, increases the discharge efficiency of the alloy under high-rate current or at low temperature.