Effect of Al content on structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys

The structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys have been investigated by XRD and simulated battery test, including maximum capacity, cyclic stability, self-discharge, high-rate dischargeability (HRD). Samples A, B, C and D were used to represent alloys LaNi4.4Co0.3Mn0.3Al, LaNi4.3Co0.3Mn0.3Al0.1, LaNi4.2Co0.3Mn0.3Al0.2 and LaNi4.1Co0.3Mn0.3Al0.3 respectively. The results indicated that as-prepared LaNi4.4 − xCo0.3Mn0.3Alx alloys are all single-phase alloys with hexagonal CaCu5 type structure. The maximum discharge capacity is 330.4 mAh g−1 (Alloy C). With the increase of Al content from A to D, cycle life of alloy electrode has been improved. Higher capacity retention of 89.29% (after 50 charge/discharge cycles) has been observed for electrode D, while with a smaller capacity loss of 12.5% in its self-discharge test. Better high-rate charge/discharge behaviors have been observed in electrode B, and the maximum data is 54.7% at charge current of 900 mA/g) and 68.54% at discharge current of 1800 mA/g). Furthermore, the electrochemical impedance spectroscopy (EIS) analysis shown that the reaction of alloy electrode is controlled by charge-transfer step. The addition of Al results in the formation of protective layer of aluminum oxides on the surface of the alloy electrode, which is good for the improvement of electrode properties in alkaline solution and is detrimental for the charge-transfer process. Therefore, a suitable addition of Al is needed to improve its electrode properties.