铸态及快淬态Mm(NiCoMnAl)_5-Mg_2Ni储氢合金的微结构与电化学性能

Microstructures and Electrochemical Performances of Mm(NiCoMnAl)_5-Mg_2Ni Hydrogen Storage Alloys Prepared by Casting and Rapid Quenching

首先采用二步熔炼法制备了铸态Mm(NiCoMnAl)_5-Mg_2Ni复合储氢合金,然后在不同快淬速度下对铸态Mm(NiCoMnAl)_5-Mg_2Ni复合合金进行快淬处理,获得一系列不同快淬速度的快淬态Mm(NiCoMnAl)_5-Mg_2Ni复合储氢合金。利用X射线衍射(XRD)、扫描电镜及能谱分析(SEM/EDS)和电化学测试方法研究了所有合金的微结构和电化学性能。微结构分析表明,铸态Mm(NiCoMnAl)_5-Mg_2Ni复合合金由LaNi_5和少量的Mg_2Ni相组成。而铸态复合合金经快淬处理后,合金中少量的Mg_2Ni相消失,同时有LaNi_3和极少量的La2Ni3新相形成。快淬态合金中的Mg元素主要以固溶形式优先存在于富稀土LaNi_3相中,形成(La,Mg)Ni_3相。电化学分析表明,恰当的快淬处理能使Mm(NiCoMnAl)_5-Mg_2Ni复合合金的活化性能、最大放电容量、放电特性和循环稳定性得到改善。但快淬速度太大,上述性能均有变坏趋势。当快淬速度为15 m·s-1时,Mm(NiCoMnAl)_5-Mg_2Ni复合合金具有最大的放电容量,此时合金的最大放电容量为303.5 m Ah·g^(-1),比铸态合金的最大放电容量增大了3.3%;快淬速度为20 m·s^(-1)时,复合合金的循环稳定性最佳,80次循环后的容量保持率为98.3%,比铸态合金的容量保持率增大了11.9%。

The as- cast Mm（NiCoMnAl）5-Mg2Ni composite hydrogen storage alloys were firstly prepared by two steps melting method. Then the as- cast Mm（NiCoMnAl）5-Mg2Ni alloy was treated by rapid quenching at different quenching rates. Finally,a series of rapid quenched Mm（NiCoMnAl）5-Mg2Ni alloys at different quenching rates were obtained. The microstructures and electrochemical properties of Mm（NiCoMnAl）5-Mg2Ni composite alloys were investigated by means of X-ray diffraction（ XRD）,scanning electron microscopy with energy dispersive spectrometer（ SEM / EDS） and electrochemical measurements. Microstructure investigation showed that the as- cast Mm（NiCoMnAl）5-Mg2Ni composite alloy is composed of the La Ni5 phase and a small amount of the Mg2Ni phase. However,the quenched composite alloys consist of the La Ni5 phase and the new phases of LaNi3 and La2Ni3. Moreover,the Mg element in the quenched alloys is mainly dissolved in the rich rare earth La Ni3 phase. Finally the（La,Mg）Ni3 phase is formed. Electrochemical analysis showed that the activation performance,the maximum discharge capacity,discharge potential characteristic and cycle stability of Mm（NiCoMnAl）5-Mg2Ni composite alloys can be improved by appropriate rapid quenching technology. But the rapid quenching rate is too high,the above performances of alloys are worse. Among the alloy samples studied,the maximum discharge capacity of the quenched composite alloy at 15 m·s^-1 is the best and its value is 303. 5 m Ah·g^-1. This value increases by 3. 3 % compared to that of the as-cast alloy. Furthermore,the quenched Mm（NiCoMnAl）5-Mg2Ni alloy at the quenching rate of 20 m·s^-1 exhibits the best cycle stability. The capacity retention after 80 cycles of the composite alloy is 98. 3 % and increases by 11. 9 % compared to that of the as- cast alloy.