化学计量比对无钴AB5型贮氢合金相结构及电化学性能的影响

Effects of Stoichiometric Ratio on Phase Structure and Electrochemical Properties of Co-free AB5-Type Hydrogen Storage Alloys

用冷坩埚磁悬浮熔炼结合热处理制备了La（Ni0.87Mn0.07Al0.06）；（x=4．7-5．3）贮氢合金，采用XRD、夹片式模拟开口电池测试体系研究了合金的相结构及电化学性能。XRD分析表明，X为5．0～5．3的合金为单-CaCu5型六方结构，X为4．7-4．9的合金含有少量Ce2Ni，型和BCr型结构的杂相；随着x的增大，晶胞体积先基本保持不变，然后从89．65A3（x=4．9）减小到89．20A3（x=5．31；晶胞c／a轴比先基本保持不变，然后从0．7982（x=5．0）明显增加到0．8000（x=5．3）。电化学性能测试表明，该系列合金活化性能优异：最大放电容量Cmax从308．4mAh·g^-1（x=4．7）增加到338．5mAh·g^-1（x=5．0），然后降低到325．1mAh·g^-1（x=5．3）；循环稳定性（S100×C300）先基本保持不变，然后明显提高，与晶胞c／a轴比的变化有良好的对应关系。

The as-cast La （Ni0.87Mn0.07Al0.06）x （x=4.7-5.3） hydrogen storage alloys were prepared by cold crucible levitation melting and then were beat-treated at 1223K for 8 hours under argon gas atmosphere： Phase structure and electrochemical properties of these alloys were investigated by means of XRD and ＂sandwich open-air cell＂ testing system. XRD analysis show that the alloys with x equal to 5.0-5.3, consist of single hexagonal CaCus-type phase. The alloys with x equal to 4.7- 4.9, have slight impurity phase with hexagonal Ce=NiT-type and orthorhombic BCr-type structure, except CaCus-type main phase. With increasing stoichiometric ratio x, cell volume and c/a of CaCus-type phase keep almost constant first, then the cell volume decreases from 89.65A3 （x=4.9） to 89.20A3 （x=5.3） and c/a increases markedly from 0.7982 （x=5.0） to 0.8000 （x= 5.3）. The electrochemical results exhibit that activation property of these alloys is excellent. Maximum discharge capacity Cmax first adds form 308.4mAh·g^-1 （x=4.7） to 338.5mAh ·g^-1（x=5.0）, and after that reduces to 325.1mAh·g^-1 （x=5.3）. Cyclic stability （Sl00×C300） keeps almost constant first, and then is improved obviously, which is in perfect accordance with tendency of c/a.