La-Mg-Ni-Co-Al-Ti合金电极的失效研究

Investigation on failure of La_(0.75)Mg_(0.25)Ni_(3.41)Co_(0.2)Al_(0.03)Ti_(0.06) hydrogen storage alloy electrode

采用中频感应炉真空熔炼制备La0.75Mg0.25Ni3.41Co0.2Al0.03Ti0.06合金,通过电化学和气态循环、电化学阻抗、颗粒形貌以及表面成分测试,分析了合金电极的失效原因。实验结果表明,合金的容量保持率在循环过程中分为快速和缓慢衰减阶段,合金颗粒表面上的裂纹随循环次数的增加而逐渐增多。随循环次数增多,合金电极的电化学接触电阻和电荷传递电阻先降低后提高;经气态吸放氢循环后合金颗粒裂纹开裂程度增大;循环前期合金颗粒粉化严重,循环后期粉化减弱。循环过程中合金中主要元素La和Mg的氧化腐蚀是导致合金电极失效的主要原因,合金颗粒粉化加剧了La和Mg的氧化,进一步恶化合金电极性能。

La0.75Mg0.25Ni3.41Co0.2Al0.03Ti0.06 alloy was prepared by induction melting under vacuum. Mechanisms of the efficacy loss of the electrode alloy were investigated by electrochemical and gaseous cycling tests, electrochemical impedance, SEM and XPS. The results show that the capacity retention rate is characterized by rapid decay and slow decay during the gaseous cycling, the number of cracks increase and the cracking is more serious on surface of the alloy particles with increasing number of cycles. With rising cycling number, the electrochemical contact resistance and charge transfer resistance first decreases and then increases on the surface of alloy particles. For gaseous cycling, the serious pulverization of the alloy particles is observed from 1 to 15 cycles and the pulverization is weakened from 15 to 30 cycles. The main reason of the capacity decay of the alloy electrode is the oxidation and corrosion of La and Mg, the pulverization accelerates the corrosion of La and Mg, and further deteriorates the cycling performance of the alloy electrode.