La 0.75 Mg 0.25 Ni 3.5 Si 0.10 hydrogen storage alloy was prepared by vacuum induction melting furnace and subsequently heated treatment at 940°C for 8 h and cooled to room temperature in the oven. The electrochemical properties of La 0.75 Mg 0.25 Ni 3.5 Si 0.10 compound were measured by LAND CT2001A battery test system. The morphologies of the samples were characterized by scanning electron microscopy (SEM). The surface state of samples was analyzed by X-ray photoelectron spectroscopy (XPS). It was found that the charge–discharge rate plays the key impact on the cycling stability of the alloy. During the cycle test, the prepared La 0.75 Mg 0.25 Ni 3.5 Si 0.10 compound presented an excellent capacity retention at the charge–discharge of 1 C while the capacity of sample declined rapidly at 0.2 C. The excellent cycling stability performance of La 0.75 Mg 0.25 Ni 3.5 Si 0.10 electrode at 1 C could be attributed to the less powder and less oxidation of surface effective active elements. The pulverization inevitably leads to the separation of the part of the cracking alloy and the electrode, resulting in reduction of the effective active substance and increasing attenuation of the capacity per cycle. In addition, on the analysis of the different cut-off potential effects on the electrode, it was found that the La 0.75 Mg 0.25 Ni 3.5 Si 0.10 electrode shows good comprehensive electrochemical properties at 1 C cut-off 0.6–0.7 V. During charging, heavy overcharge will not be conducive to cycling stability performance during the charging test.
Effect of the discharge rate on the electrochemical properties of LaY2Ni9 hydrogen storage alloy
