高功率稀土-镁-镍系合金的相组成、结构稳定性与电极特性

This project is to reveal the effect of phase composition and structure stability on the electrochemical properties of high-power A5B19-type La–Mg–Ni-based hydrogen storage alloys. Based on the preparation of A5B19-type single phase hydrogen storage alloys, the formation condition and phase transformation mechanism of A5B19 phase, as well as the controllable preparation of A5B19-type La–Mg–Ni-based alloys having different phase compositions with A5B19 main phase and AB3, A2B7, AB4 or AB5 secondary phase are studied. The behavior of hydrogen atoms entering and leaving the alloys phases and the interrelation between A5B19 phase and other phases are thoroughly studied. Besides, the influence and mechanism of phase compositions on the electrochemical characteristics of the alloys are revealed. The effect of partial element substitution on the composition and structure stability of [A2B4] and [AB5] slabs in A5B19 phase, and the influence rule on hydrogen absorption/desorption behavior and electrochemical properties are studied. The effective methods of significant improvement on electrochemical cycling stability of A5B19-type La–Mg–Ni-based hydrogen storage alloy through increasing phase stability of A5B19 phase structure are discussed. The work provides theoretical guidance to the designation and preparation of long cycling and high power La–Mg–Ni-based negative electrode materials with good overall electrochemical properties.

为了揭示高功率A5B19型La–Mg–Ni系储氢合金的相组成和结构稳定性对电化学性能的影响，本课题拟在已获得A5B19单相合金的基础上，控制制备以A5B19相为主相，以AB3、A2B7、AB4或AB5相为辅相的A5B19型La–Mg–Ni系合金，研究A5B19相的生成条件与其它超堆垛相和非堆垛相转变机制。深入考察和分析在吸/放氢过程中，合金中A5B19相和其它相中氢原子的进出行为和不同相之间的相互作用关系，揭示合金相组成变化对合金电化学性能的影响及机理。研究元素取代对A5B19相中[A2B4]和[AB5]亚单元的组成和稳定性的影响，及其引起合金电化学性能的变化规律。探讨通过调控相组成以及提高合金结构稳定性，显著改善A5B19型La–Mg–Ni系储氢合金的循环寿命和电化学性能的有效办法，为设计制备具有良好综合电化学性能的长寿命高功率A5B19型La–Mg–Ni系储氢合金提供理论指导。

为了揭示高功率A5B19型La–Mg–Ni系储氢合金相组成和结构稳定性对电化学性能的影响，本课题在已获得A5B19单相合金基础上，研究了A5B19型相的形成条件，制备了一系列A5B19型La–Mg–Ni系储氢合金，揭示了A5B19型相与其它超堆垛相或非堆垛相相互转变机制以及合金相组成与储氢性能和电化学性能的关系。研究表明，AB3与AB5相发生固相与固相反应形成A2B7相，其与AB5相进一步发生固相反应生成A5B19相。进一步研究表明，A5B19型相结构中同素异构相3R型和2H型具有不同的热力学稳定性，在一定温度范围内，3R型相结构可逐渐转化为2H型相结构。在此基础上，研究了Ce2Ni7、LaNi5和AB4作为第二相对A5B19型合金储氢性能和电化学性能的影响及作用机制。研究了稀土元素Pr、Nd、Gd部分取代La元素对A5B19相中[AB2]和[AB5]亚单元微观结构和合金整体结构稳定性的影响，及其对合金吸/放氢行为和电化学性能的影响规律；在取得的理论研究数据基础上，进一步优化设计、筛选合金，得到了长寿命高功率A5B19型La–Mg–Ni系储氢合金，并在国内镍氢电池生产企业进行了组装电池和进行性能测试，各项指标可以满足高容量镍氢电池的市场应用化要求。本项目研究成果对推动作为高容量镍氢电池负极材料La–Mg–Ni系合金的进一步发展具有重要的理论和实际意义。