Investigation on microstructures and electrochemical performances of the La0.75Mg0.25Ni2.5Cox (x = 0–1.0) hydrogen storage alloys

The La0.75Mg0.25Ni2.5Cox (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) hydrogen storage alloys were prepared by vacuum medium-frequency induction furnace under the argon atmosphere. The microstructures and electrochemical performances of the alloys were analyzed and measured. The effects of Co addition on the microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results by X-ray diffractometer (XRD) showed that alloys were composed of the (La,Mg)Ni3, the LaNi5, LaNi2 and the La2Ni7 phases. With the increase of Co content x, the LaNi2 phase decreases, the (La,Mg)Ni3, the La2Ni7 and the LaNi5 phases increase. The results by the electrochemical measurements indicated that the maximum discharge capacity of the alloys is enhanced and activation performance is improved with the incremental change of Co content. The alloy (x = 1.0) has a maximum discharge capacity of 388.7 mAh/g. The addition of Co raises the high rate discharge capacity of the alloys. The cycle stability of the alloys first increases and then decreases with the growth of Co content. When Co content is 0.4, the capacity retention rate (S100) of the alloy reaches a maximum volume of 76.9%.