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

摘要

The stoichiometric alloy MlB_(5.0) and the hypo-stoichiometric alloy MlB_(4.85) 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 CaCu_5-type structure. The cell volume of the hypo-stoichiometric alloy MlB_(4.85) is slightly larger than that of the stoichiometric alloy MlB_(5.0), although its lattice constant c/a is smaller. Under 2 C discharging rate, i.e. 640 mA/g, the MlB_(4.85) has a discharge capacity of 320 mAh/g, which is higher than that of the MlB_(5.0), 312 mAh/g. Nevertheless, the capacities of the MlB_(4.85) and the MlB_(5.0) decline 24.7% and 20.2% after 400 cycles, respectively. The relationship of electrochemical performances of the alloys with their structures is discussed.