RE-Mg-Ni系纳米晶A2B7型储氢合金成相机制及其吸放氢过程中相结构的原位转变研究

RE-Mg-Ni (RE: rare-earth elements) superlattice hydrogen storage alloys have received considerable interest due to their large hydrogen storage capacity, security and other advantages in the field of power battery, but poor cycle stability of hydrogen absorption-desorption limit their application. RE-Mg-Ni superlattice alloys, consisting of the CaCu5 unit and Laves unit ordered stacking, have a complex mechanism of the phase transformation, and a strong sensitivity of the composition and heat treatment conditions. The reaction mechanism of the hydrides formation and decomposition remains to be deeply studied. In the present work, nanocrystalline RE-Mg-Ni alloys will be prepared by rapid solidification (RS) technology. From the determination and thermodynamic calculation of the phases, the mechanism of phase transformation of RE-Mg-Ni alloys will be studied by the mean of the CALPHAD technology, and the composition is further optimized. It will be studied on the position of alternative elements in the lattice, and its effect on phase lattice parameter, hydrogen absorption-desorption capacity as well as cycle stability. Combined with in-situ X-ray diffraction (XRD) and in-situ synchrotron radiation X-ray diffraction (SR-XRD), a transformation process of the alloys during hydrogen absorption-desorption as well as the nucleation, growth and decomposition reaction mechanism of the hydrides will be studied. The relationship between the microstructure and cycle stability of hydrogen absorption-desorption will be established and theoretically explained. The stable A2B7-type nanocrystalline RE-Mg-Ni superlattice alloys will be developed, which the initial capacity is higher than 380mAh/g, and the capacity retention rate is above 60% after 500 cycles.

超晶格RE-Mg-Ni（RE为稀土元素）储氢合金因储氢量大、安全性好等优点在动力电池领域倍受青睐，但吸放氢循环稳定性差限制了其应用。由CaCu5和Laves单元有序堆垛组合形成超晶格合金的成相规律较复杂，与成分和热处理条件有较强的敏感性，氢化物形成和分解反应机理尚有待深入研究。本项目采用快速凝固（RS）技术制备纳米晶合金；利用CALPHAD技术，从合金相关系测定及热力学计算出发，研究合金的成相规律，并指导成分设计；研究替代元素在晶格中的位置及其对相晶格参数、合金吸放氢容量和循环稳定性的影响；结合原位X射线衍射(XRD) 和原位同步辐射X 射线衍射(SR-XRD)技术研究合金吸放氢转变过程，揭示氢化物形核长大和分解机理，建立微观组织与吸放氢循环稳定性之间的模型并进行理论解释；指导物相稳定的A2B7型纳米晶合金的开发，使其初始容量大于380mAh/g，循环500次容量保持率为60%以上。

目前，储氢合金作为镍氢动力电池用负极材料仍然是一个研究热点，超晶格RE-Mg-Ni（RE为稀土元素）储氢合金因储氢量大、安全性好等优点在混合动力电动车(HEV)领域倍受青睐，但吸放氢循环稳定性差限制了其应用。针对RE-Mg-Ni超晶格储氢合金在动力电池领域应用所存在的吸放氢循环稳定性差和成相规律复杂问题，本项目以A2B7型RE-Mg-Ni超晶格储氢合金为主要研究体系，开展了以下工作：（a）采用RS技术和适当的热处理工艺成功制备了纳米晶RE-Mg-Ni超晶格储氢合金；（b）利用晶体学理论及Rietveld晶体结构解析方法，揭示了合金物相转变机制、替代元素对成相内在规律、a/c轴变化的影响，进一步优化了合金成分；（c）开发了物相稳定的A2B7型纳米晶RE-Mg-Ni超晶格储氢合金，使其初始放电容量381mAh/g、循环500次容量保持率为62%。本项目的研究成果为A2B7型超晶格储氢合金在超低温下的应用打下了研究基础。对于促进储氢合金在HEV领域应用具有重要的理论和实际意义。