Pr替代La对La-Mg-Ni系A_2B_7型电极合金微观结构及循环稳定性的影响

Influences of substituting La with Pr on structures and electrochemical cycle stability of La-Mg-Ni-based A_2B_7-type electrode alloys

为了改善La-Mg-Ni系A2B7型电极合金的电化学循环稳定性,用Pr部分替代合金中的La,并用熔体快淬技术制备了La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1(x=0、0.1、0.2、0.3、0.4)电极合金。用XRD、SEM、TEM分析了铸态及快淬态合金的微观结构,测试了铸态及快淬态合金的电化学循环稳定性,研究了Pr替代La对合金微观结构及循环稳定性的影响,探讨了合金电极在电化学循环过程中的失效机理。结果表明,铸态及快淬态合金均具有多相结构,包括2个主相(La,Mg)Ni3及LaNi5和一个残余相LaNi2。Pr替代La使(La,Mg)Ni3明显增加而LaNi5减少。电化学测试的结果表明,合金的循环稳定性随Pr替代量的增加而增加。导致合金电极失效的主要原因是电极表面被电解液剧烈腐蚀以及合金电极在电化学循环过程中的粉化。

In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys,La in the alloy is partially substituted by Pr and the melt-spinning technology was used for preparing La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1（x=0,0.1,0.2,0.3,0.4） electrode alloys.The microstructures of the as-cast and spun alloys were analyzed by XRD,SEM and TEM.The electrochemical cycle stability of the alloys was measured.Influences of substituting La with Pr on structures and electrochemical cycle stability of the alloys were investigated systemically,and the mechanism of lose efficacy of the alloy electrodes was researched.The results obtained show that the as-cast and spun alloys have a multiphase structure which consists of two main phases（La,Mg）Ni3 and LaNi5 as well as a residual phase LaNi2.The substitution of Pr for La leads to an obvious increase of the（La,Mg）Ni3 phase and a decrease of the LaNi5 phase in the alloys.The results of the electrochemical measurement indicate that the cycle stability of the alloy monotonously rises with increasing Pr content.The radical reasons of which cause lose efficacy of the alloy electrodes are that the surface of the alloy electrodes is severely corroded by electrolyte and that the alloy electrodes are pulverized in process of the electrochemical charge-discharge cycle.