MH/Ni电池电极材料在过充电条件下的失效分析

采用SEM,XRD,TEM以及EIS等检测方法,研究不同过充循环前后MH/Ni电池性能与正负极材料形貌及表面元素的变化.实验结果表明,经正常充放电循环70周后,正极活性物质表面保持良好的球形形貌,而经持续过充电循环相同次数后,因晶格的不可逆膨胀而呈不同程度破裂,储氢合金颗粒并无明显粉化现象,但其表面却覆盖许多绒状或针状物,经能谱检测,该绒状物主要成分为稀土金属的氢氧化物或氧化物.EIS阻抗谱分析表明,电池的欧姆电阻(Rs)、反应电阻(Rt)和Warburg阻抗(Zw)均有不同程度的增加,而界面电容(Ci)则呈逐渐降低趋势,这些均是最终导致电池电化学性能衰减的原因.

Degradation Behavior of Electrodes in MH/Ni Batteries Under Conditions of Overcharge

Effects of overcharging on the electrode material performance of MH/Ni batteries were investigated using SEM, XRD, TEM and EIS methods. The results indicated that the positive materials remained in their original spherical morphology after 70 cycles under normal charge/discharge processes. However, the spherical particles were cracked with the irreversible expansion of crystal lattice under overcharge conditions. Hydrogen storage alloy particles were covered with lots of needle-like corrosive products but without obvious pulverization after cycling. The main components of the needle-like corrosive products were detected to be rare earth hydroxide or oxide by means of EDAX. It was found from EIS analysis that R_s, R_t and Z_w increased to some extent, while C_i decreased. These changes during the overcharge cycling resulted in the degradation behavior of MH/Ni batteries.