快速凝固非化学计量比储氢合金LaNi4.75Mn1.25 晶体结构和电化学性能

Crystal Structure and Electrochemical Properties of Over-Stoichiometric LaNi4.75Mn1.25 Alloys Prepared by Melt Spun

摘要:

采用熔体快淬方法得到了无Co过化学计量比合金La(NiMn)6的非平衡亚稳单相CaCu5型结构,分析和研究了合金非平衡组织结构和电化学吸放氢性能.x-ray衍射分析表明,快速凝固合金组织为CaCu5型结构单相组织,与常规熔铸合金比较,快速凝固合金的晶胞参数发生了明显的各向异性变化:随着冷却速度增加,CaCu5型晶胞a轴减小,c轴及轴比c/a增大.电化学实验研究表明,当合金快凝速度≥20m/s时,过化学计量比La(NiMn)6合金MH电极的循环稳定性得到不同程度的改善,快凝速度≥30m/s时,合金电极具有良好的循环稳定性,其最大电化学容量为256mAh/g～277mAh/g,循环100次后合金MH电极容量保持率为63%～97.8%.快速凝固合金均大大提高了合金的电化学稳定性,但随着冷却速度增加其活化性能和电极容量有所下降.

Abstract:

Metastable single phase with CaCu5 type structure for Co free over-stoichiometric La(NiMn)6 alloys were obtained by non-equilibrium processing of melt spinning. The crystal structure and electrochemical properties were investigated comparatively. The XRD results show that the La(NiMn)6 alloys prepared by melt spinning, in comparison with the as-cast alloys, present a single phase with CaCu5 type. The crystal lattice constants a and c exhibit a anisotropic change. With the increase of cooling rate, the a axis decreases and c axis and ratio of c/a value increase. The electrochemical analyses show that when cooling rate increases from 20 m/s to 50 m/s, the MH electrodes discharge capacity reach 277 mAh/g~256 mAh/g and the capacity retention is 63%~97.8% after 100 cycling number. The alloys prepared by melt spinning show a good cycling stability, but a lower discharge capacity and worse activation kinetics than that of the as-cast alloys.