合金化元素的选择及其对(La, Mg)5Ni19 A5B19型相稳定性和电化学储氢性能的影响

La-Mg-Ni-based A5B19-type alloys have attracted much attention due to high theoretical capacity, good corrosion resistance and low lattice strains in hydrogen absorption/desorption. However, the overall electrochemical hydrogen storage properties are not satisfying. La-Mg-Ni A5B19-type alloys have attracted extensive attentions due to their high theoretical capacity, low lattice strains during hydrogen absorption/desorption and good corrosion resistance. However, the overall electrochemical hydrogen storage properties are yet not satisfying. In fact, selection of alloying elements plays a critical role in improving the overall electrochemical hydrogen storage properties with excellent cycling stability. Proper chosen of alloying element is believed to benefit the phase stability and the matching ability between [A2B4] and [AB5], and can also lower the lattice strains during the hydrogen absorption/desorption. This project aims to take La4MgNi19 A5B19-type phase as research system, study the site occupancy and preference of alloying elements, and clarify their influences on matching ability between [A2B4] and [AB5] and the stability of A5B19-type alloys by both experimental and theoretical methods. At the same time, the microstructures and hydrogen storage performances of the alloyed A5B19-type alloys would be investigated to reveal the law of the effect of alloying elements on the lattice strains during the hydrogen absorption/desorption as well as on the cycling stability. Based on the above results, alloying elements would be selected to optimize the microstructures and hydrogen storage performances of La4MgNi19 alloy and prepare La-Mg-Ni-based A5B19-type alloys with high specific capacity, low self-discharge and also good cycling stability.

镧-镁-镍A5B19型合金因理论比容量高、吸/放氢晶格应力低和耐腐蚀性好而受到广泛关注，但其综合电化学储氢性能有待进一步提高。在保持良好循环稳定性的同时，优化合金电化学储氢性能的关键在于合理选择合金化元素，所选元素应有利于提高A5B19型相稳定性和[A2B4]/[AB5]子单元的匹配性，并降低吸/放氢过程中晶格应力。本项目拟选择La4MgNi19 A5B19型相合金作为基体，采用理论计算与实验研究相结合的方法，明确合金化元素在A5B19型相中的占位及合金化对[A2B4]/[AB5]子单元匹配性和相稳定性的影响；研究合金化后A5B19型相合金的微观结构和储氢性能，揭示合金化对吸/放氢过程中晶格应力和循环稳定性的影响规律；结合相稳定性和循环稳定性，合理选择合金化元素，多元优化La4MgNi19合金的微观结构和储氢性能，以期得到高比容量、低自放电、长寿命的镧-镁-镍基A5B19型相储氢合金。

镧-镁-镍A5B19型合金因理论比容量高、吸/放氢晶格应力低和耐腐蚀性好而受到广泛关注，但其综合电化学储氢性能有待进一步提高。本项目以La-Mg-Ni基A5B19相合金为研究对象，深入解析了合金化元素和化学计量比对合金中A5B19相稳定性和合金电极循环稳定性的影响。采用真空感应熔炼方法制备了La4MgNi19、La3RMgNi19（R = La、Pr、Nd、Sm、Gd和Y）、La4MgNi18M（M = Ni、Al、Co和Cu）和La4MgNix（x = 16–19）系列合金的样品，并研究了热处理温度对合金微观结构和电化学性能的影响，结果表明，Gd、Sm和Y元素有利于A5B19相的生成，而Nd和Pr元素取代则有利于A2B7相的生成，且Pr、Nd、Sm、Gd和Y元素取代均一定程度的提高了合金电极的循环稳定性能，但Gd、Sm和Y在提高电化学循环稳定方面更加突出。Al元素的部分取代有利于A5B19相的生成，而Cu和Co元素取代则有利于A2B7相的生成。Al、Cu和Co均促进电化学循环稳定性的改善。增加La4MgNix合金的化学计量比，A2B7和LaNi5的相丰度逐渐减小，A5B19相丰度逐渐增加，这表明化学计量比的增加有利于A5B19相的生成。在此基础上，通过组成优化，制备了综合电化学性能良好的A5B19相（主相）/A2B7相（第二相）的La-Sm-Nd-Mg-Ni-Al的合金。项目完成期间，共发表SCI收录论文6篇，申请发明专利5项，培养硕士研究生4名。