Structure and electrochemical properties of hypo-stoichiometric hydro-gen storage alloys prepared by twin-roller rapid quenching process

摘要

The stoichiometric alloy MlB5.0 and the hypo-stoichiometric alloy MlB4.85 were prepared by twin-roller rapid quenching process, and their structure and electrochemical properties were studied. The results of XRD show that both of the alloys have a typical single-phase hexagonal CaCu5-type structure. The cell volume of the hypo-stoichiometric alloy MlB4.85 is slightly larger than that of the stoichiometric alloy MlB5.0, although its lattice constant c/a is smaller. Under 2 C discharging rate, i.e. 640 mA/g, the MlB4.85 has a discharge capacity of 320 mAh/g, which is higher than that of the MlB5.0, 312 mAh/g. Nevertheless, the capacities of the MlB4.85 and the MlB5.0 decline 24.7% and 20.2% after 400 cycles, respec- tively. The relationship of electrochemical performances of the alloys with their structures is discussed.