Abstract:The influences of annealing treatment on the electrochemical and structural properties of La_0.75Mg_0.25-Ni_2.8Co_0.5 hydrogen storage alloy were investigated by means of electrochemical studies and X-ray diffraction(XRD) analyses. The XRD results reveal that the peak width gets narrower with increasing annealing temperature, which can be ascribed to the structural change and more homogeneous composition after being annealed. Electrochemical studies show that the discharge capacity and the cycle stability of the alloy electrodes increase after being annealed. The maximum discharge capacity, exchange current density J₀ and limiting current density J_L of the as-cast alloy are 388mA·h/g, 340.5mA/g and 3068mA/g, respectively, and they are increased to 400mA·h/g, 372.1mA/g and 3399mA/g for the alloy annealed at 1123K for 8h, respectively. Meanwhile, as the discharge current density is 1250mA/g, the high rate dischargeability(HRD) increases from 77.4% for the as-cast alloy to 83.3% for the alloy annealed at 1123K.

Key words:  heat treatment; La_0.75Mg_0.25Ni_2.8Co_0.5 hydrogen storage alloy; electrochemical properties