| In this thesis, based on the review of the research and development of AB type、AB2type、 A2B type、 AB3type and AB5type hydrogen storage electrode alloys, theLa-Mg-Ni-based A5B19type alloys were selected as thestudy object of this work. The alloywas prepared by inductive melting constitument metals(purity>99%) in argon atmosphere.By means of XRD, Land and the electrochemical test methods. The influence ofcomprehensive substitution on the phase structure and electrochemical properties of A5B19type hydrogen storage alloys have been investigated systematically.According to the study of the La1-xCexMg0.25Ni4Co0.75(x=0~0.4), it is found that thehydrogen storage alloy consist of LaNi5phase、La4MgNi19phase and CeNi3phase. Withthe increase of Ce content, the cell volume of LaNi5phase becomes low gradually. When Lais substituted by Ce, Electrochemical tests show that the cycling stabilities of theLa1-xCexMg0.25Ni4Co0.75(x=0~0.4) are improved, but the activation properties and themaximum discharge capacity are lowered somewhat. The maximum discharge capacitydecreases from381.8mAh/g(x=0) to170.1mAh/g(x=0.4). It is found that the decrease inmaximum discharge capacity is mainly due to the decreases of the cell volume of LaNi5.And the decrease in the hydrogen diffusion rate in the alloy bulk is the main reason forlower high-rate dischargeability. Among the alloys studied, La0.9Ce0.1Mg0.25Ni4Co0.75has thebest overall electrochemical properties: its maximum discharge capacityCmax=372.8mAh/g, the capacity retention rate (S100) reaches57.90%, and the high-ratedischargeability HRD900=94.32%.Based on the study of La0.9Ce0.1Mg0.25Ni4Co0.75alloy, the effect of annealing on alloyphase structure and electrochemical properties were investigated. At the same time ofthermal insulation, it is found that the maximum discharge capacity and the cycling stabilityare improved with the increase of the annealing temperature, while the number of activationand the high-rate dischargeability decrease. More uniform composition and betteranti-pulverization ability lead to the improvement in cycle life. At the same annealingtemperature, the high-rate dischargeability of the alloys increases but the maximumdischarge capacity and cyclic stability showed a downward trend with the increase of the time of the thermal insulation. Among the alloys studied, the annealed alloy(1173K,16H)has the best overall electrochemical properties: Cmax=372.8mAh/g, S100=63.89%,HRD900=95.19%.Based on the study of the LaMg0.25Ni4.0-xCo0.75Alx(x=0~0.3) alloys (as-cast andannealed), Comprehensive performance of the annealed alloy is better than it of the as-castalloy. it is found that with the increase of x value, the maximum discharge capacitydecreases from385.7mAh/g(x=0) to331mAh/g(x=0.3). The cycling stability of the alloyelectrodes decreases first and then increases, when x=0.3, the cyclic life is best(S100=85.8%).The improvement in the cycling stability is due to the decrease of the degree ofpulverization. And with the increase of x value, the high-rate dischargeability of the alloyelectrodes improves somewhat. Among the alloys studied, LaMg0.25Ni3.9Co0.75Al0.1has thebest overall electrochemical properties: Cmax=372.1mAh/g, S100=79.3%, HRD900=88.34%.Based on the study of the LaMg0.25Ni3.9-xCo0.75Al0.1Mnx(x=0~0.4)alloys (as-cast andannealed), it is found that the hydrogen storage alloy consist of LaNi5phase、LaNi2phaseand La4MgNi19phase. With the increase of the Mn content, the LaNi2phase appears andincreases. And the content of the LaNi2phase increases from1.9wt%(x=0.3) to18.3wt%(x=0.4). With the increase of the Mn content, the cycling stability of the alloys isimproved, but the high-rate dischargeability and the maximum discharge capacity arelowered somewhat. Among the alloys studied, LaMg0.25Ni3.8Co0.75Al0.1Mn0.1has the bestoverall electrochemical properties: Cmax=377.3mAh/g, S100=82.36%, HRD900=87.12%. |
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