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

Abstract

LaNi_2.3 and MgNi_1.55 intermediate alloys were used to prepare the La₂MgNi₉ 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 La₂MgNi₉ hydrogen storage alloy were investigated systematically. The results show that the alloys consist of La₂MgNi₉ phase, (La, Mg)₂Ni₇ phase and LaNi₅ phase, and prolonging of sintering time can promote the formation of the LaNi₅ phase. It was found that appropriate sintering time can significantly enhance the maximum discharge capacity (C_max) and improve the cycling stability (S₅₀) 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, S₅₀ = 73.62 % and HRD₉₀₀ = 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.