低Co与无Co型稀土-镁-镍基合金储氢的退火效应

The rapid development of Ni/MH batteries has brought an urgent need for hydrogen storage alloys with high performances as negative materials. Rare earth-Mg-Ni-based alloys have been paid more attention due to high capacity and good electrochemical characteristics. Considering that Co is not only unfriendly to the environment, but also increases the cost of the batteries, in the near future, it is devoted to develop low-Co and Co-free rare earth-Mg-Ni-based hydrogen storage alloys. In the present study, a series of as-cast and annealed low-Co and Co-free rare earth-Mg-Ni-based hydrogen storage alloys are prepared by multi-alloying coupled with annealing treatment. On one hand, the relationship between the microstructure and the hydrogen absorption/desorption capability, the effect of annealing on hydrogen storage properties of the alloys are all investigated by means of X-ray diffraction, scanning electron microscope equipped with energy dispersive spectrometer, positron annihilation, pressure-composition isotherm, thermal analysis, electrochemical measurement, and so on. On the other hand, the structural stability, the impact of electronic state, atomic bond and hydrogen potential energy on the hydrogen storage properties are discussed using the first-principle calculation, following with the annealing effect on the electrochemical behavior of the alloy electrodes. Additionally, both the alloy composition and the annealing condition are optimized to prepare low-cost and high-performance rare earth-Mg-Ni-based hydrogen storage alloys with the help of experimental measurement and theory analysis, which can be put into production in Ni/MH battery.

Ni/MH电池的快速发展急需提供高性能的储氢合金作为负极材料。稀土-镁-镍基储氢合金由于具有高容量、良好电化学性能倍受关注。鉴于Co带来的合金高成本以及Co存在环境污染隐患，未来稀土-镁-镍基合金的发展方向是开发低Co和无Co型合金。项目采用多元合金化结合退火处理制备系列铸态及退火态低Co和无Co型稀土-镁-镍基储氢合金。一方面，通过X衍射、电镜扫描-能谱分析、正电子湮没、压力-组成等温测试、热分析以及电化学测试等，研究合金微结构与吸/放氢能力的关系，明确退火对合金储氢性能提高/失效的影响作用。另一方面，通过第一性原理计算，研究合金结构的热稳定性，探索组成元素电子态、原子价键、氢输运势垒对合金储氢的作用机理，剖析合金电化学行为的退火机制。此外，综合实验测试与理论分析，实现合金成分、退火条件的优化配置，为Ni/MH电池的发展制备可实用的低成本、高性能稀土-镁-镍基储氢合金。

开发高容量、长寿命、低成本的稀土-镁-镍基合金作为Ni/MH电池的负极材料，是近年储氢合金研究的一个重要方向。本项目对稀土-镁-镍基合金的研究，以低Co、无Co型合金为主体，旨在通过实验研究、理论计算，剖析合金储氢能力与微观结构的相关性，为高性能稀土-镁-镍基合金制备提供参考，主要工作包括：（1）通过密度泛函理论的第一性原理计算，一方面，构建系列LaMg2Ni合金晶胞体系、表面体系，并计算其电子结构及表面氢吸附能，系统讨论掺杂、氢化对LaMg2Ni原子作用的影响，提出提高LaMg2Ni吸氢能力的微观机制；另一方面，构建La3-xMgxNi9（x=0-2）合金晶胞体系，并计算其单点能与电子结构，探讨Mg对合金结构稳定、原子作用以及储氢能力的调制，解读导致富Mg合金储氢容量低、但循环寿命高的微观机制；（2）采用熔炼、烧结、退火相结合实验制备RMg2Ni9（R=La、Pr、Nd）合金，并测试合金的相组成、放电容量及循环寿命，了解退火温度、时间对合金组成结构及电化学性能的影响。同时，结合RMg2Ni9（R=La、Pr、Nd）合金第一性原理理论计算，分析合金电子结构尤其是原子键特征，剖析合金组成与电化学储氢的关系。