退火处理对La1．5Mg0．5Ni7．0贮氢合金相结构和电化学性能的影响

Influence of Annealing Treatment on Structure and Electrochemical Properties of La1.5Mg0.5Ni7.0 Hydrogen Storage Alloys

摘要:

研究了退火温度对A287型La1.5Mg0.5Ni7.0合金的相结构和电化学性能的影响。结果表明：铸态合金由LaNi，相、LaMgNi4相、（La，Mg）Ni3相以及Gd2Co7型相组成，退火处理后，合金由Gd2Co7型相、Ce2Ni7型相和PuNi3型（La，Mg）Ni3相组成：随着退火温度升高，PuNi3型相的丰度减小，ce2Ni7型相的丰度增加，（La，Mg）Ni3相的a轴参数、c轴参数和晶胞体积均增大；经1073K保温24h退火后，合金电极具有最高的放电容量（391．2mAh／g），退火温度升高，合金的最大放电容量略有降低：合金电极的循环稳定性随着退火温度的升高不断提高，在1173K时合金电极经150次循环后其电极容量保持率C150／Cmax=82％；合金的高倍率放电性能（HRD）随退火温度升高略有增加，在1173K时，合金电极的HRD最好（HRD900=89．0％）；交换电流密度I0、极限电流密度I1及氢扩散系数D随着退火温度的升高而增大。

Abstract:

The influence of annealing temperature on the structure and electrochemical properties of La1.5Mg0.5Ni7.0 hydrogen storage electrode alloys was studied. XRD and SEM analyses show that the as-cast alloy consists of LaNi5 phase, LaMgNi4 phase, (La, Mg)Ni3 phase and Gd2Co7 type phase. After heat treatment, the alloys consist of Gd2Co7 type phase, Ce2Ni7 type phase and (La, Mg)Ni3 phase, and the (La, Mg)Ni3 phase content decreases and the Ce2Ni7 type phase content increases with increasing of annealing temperature. The unit cell volumes and a-axes of PuNi3 type phase increase with increasing of annealing temperature. The electrochemical studies show that the discharge capacity and cyclic stability of the alloy electrodes have been improved markedly after annealing treatment. The discharge capacity of the alloy annealed at 1073 K is the highest (391.2 mAh/g) and then decreases with increasing of annealing temperature. However, with the increase of annealing temperature, the cyclic stability of the alloy electrode increases and the cycle life of the alloy annealed at 1173 K is the longest (C150/Cmax=82%). In addition, both the as-cast and the annealed alloy electrodes have quite good HRD. The high rate dischargeability (HRD) of the alloy electrodes increases with increasing of annealing temperature and the alloy annealed at 1173 K is the best. The exchange current density (I0), the limit current density (IL) and the hydrogen diffusion coefficient (D) of the alloy electrodes are consistent with the variation of the high rate dischargeability (HRD).