| In this paper, based on the review of the research and development of A2 B typed、AB2 type、AB3 type、AB5 type and A5B19 type hydrogen storage electrode the La-Mg-Ni-based A5B19 type alloys were selected as the study object of this work. By means of X-ray diffractometer, Land and the electrochemical test methods. The effects of the alloy preparation methods(melt-with different cooling rate: 0, 10, 15, 20, 25m/s) on the phase structure and electrochemical properties of La4MgNi17Co2 and La4MgNi17.5Mn1.5 alloys were studied systemically. And through study the influence of Al comprehensive substitution and the heat treatment on the phase structure and electrochemical properties of A5B19 type hydrogen storage alloys have been investigated systematically.According to the study of the La4MgNi17Co2 alloys(melt-with different cooling rate: 0, 10, 15, 20, 25m/s). It is found that alloys are mainly composed of LaNi5 type Ce5Co19 and Pr5Co19 type phases. With the increasing of cooling rate. The cycle stability of the alloy s show a trend of increased. The cycle stability rise from 57.20%(0m/s) to 71.27%(25m/s). Among the alloys studied, the melt-spun alloy(25m/s) has the best overall electrochemical properties: its maximum discharge capacity Cmax=345.25mAh/g, activation process need only 2 cycles, the high-rate dischargeability HRD900=83.12%, and the capacity retention rate after 100 charge-discharge cycles reaches 71.27%.According to the study of the LaMg0.25Ni4.0-xCo0.75Alx(x=0~0.3)(cooling rate: 15 m/s). It is found that alloys are mainly composed of LaNi5 type Ce5Co19 and Pr5Co19 type phases. With the increasing of Al, The maximum discharge capacity decreases from 356.00mAh/g(x=0) to 301.55mAh/g(x=0.3). but a much better cycle stability as the Al increases. the cycle life S100 increased from 59.07%(x=0) to 85.99%(x=0.3). the high-rate dischargeability HRD900 decrease after rising first. Among the alloys studied, LaMg0.25Ni3.95Co0.75Al0.05 has the best overall electrochemical properties: its maximum discharge capacity Cmax=352.24 mAh/g, activation process need only 2 cycles, the high-rate dischargeability HRD900=87.54%, and the capacity retention rate after 100 charge-discharge cycles reaches 71.15%.According to the study of the La4MgNi17.5Mn1.5 alloys(melt-with different cooling rate: 0, 10, 15, 20, 25m/s). It is found that alloys are mainly composed of LaNi5 type LaNi2 and Pr5Co19 type phases. The electrochemical tests show that La4MgNi17.5Mn1.5 alloys possess good activation performance. But a lower discharge capacity and high-rate dischargeability. Among the alloys studied, the melt-spun alloy(15m/s) has the best overall electrochemical properties: its maximum discharge capacity Cmax=314.27mAh/g, activation process need only 3 cycles, the high-rate dischargeability HRD900=86.98%, and the capacity retention rate after 100 charge-discharge cycles reaches 67.18%.Based on the study of La4MgNi17Co2 alloy(cooling rate: 15 m/s), the effect of annealing on alloy phase structure and electrochemical properties were investigated. At the same annealing temperature, It is found that alloys are mainly composed of LaNi5 type Ce5Co19 and Pr5Co19 type phases. With the increasing of time of thermal insulation. The melt-spun alloys have a lower discharge capacity and inferior high-rate dischargeability. At the same time of thermal insulation(time of thermal insulation=8h), It is found that alloys are mainly composed of LaNi5 type Ce5Co19 and Pr5Co19 type phases. With increasing of annealing temperature, the maximum discharge capacity of the alloys show a trend of rise after falling. And the high-rate dischargeability alloys show a trend of dropped after the first rise. Among the alloys studied, the alloy annealed at 1173 K shows the best overall electrochemical properties: its maximum discharge capacity Cmax=341.7mAh/g, activation process need only 3cycles, the high-rate dischargeability HRD900=85.45%, and the capacity retention rate after 100 charge-discharge cycles reaches 72.74%. |
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