Influence of sintering time on structure and electrochemical properties of La2MgNi9 hydrogen storage alloys

LaNi 2.3 and MgNi 1.55 intermediate alloys were used to prepare the La 2 MgNi 9 alloy by vacuum powder sintering at 800 °C, and the effects of sintering time (2 h, 4 h, 6 h and 8 h) on the phase structure and electrochemical properties of La 2 MgNi 9 hydrogen storage alloy were investigated systematically. The results show that the alloys consist of La 2 MgNi 9 phase, (La, Mg) 2 Ni 7 phase and LaNi 5 phase, and prolonging of sintering time can promote the formation of the LaNi 5 phase. It was found that appropriate sintering time can significantly enhance the maximum discharge capacity ( C max ) and improve the cycling stability( S 50 ) as well as the high-rate dischargeability ( HRD ) of the alloy. For example, the alloy sintered for 4 h exhibits the best electrochemical performance with C max =365.04 mAh/g, S 50 =73.62% and HRD 900 =88.43%. Analysis indicates that the larger cell volume, the lower pressure of the hydrogen release platform, and then the alloy sintered for 4 h showed the largest hydrogen storage in the alloy. The improvement of cycle life of the alloy was due to more homogeneous composition and higher resistance to pulverization. The electrothermal tests showed that HRD is mainly controlled by the surface charge transfer rate of the alloy electrodes.