Electrode characteristics of non-stoichiometric Ml(NiMnAlFe)x alloys
(1. Department of Materials Science and Engineering,
Zhejiang University, Hangzhou 310027, P.R.China;
2. Central Laboratory, Zhejiang University, Hangzhou 310028, P.R.China)
Zhejiang University, Hangzhou 310027, P.R.China;
2. Central Laboratory, Zhejiang University, Hangzhou 310028, P.R.China)
Abstract: The phase structure and electrochemical properties of Co-free Ml(Ni0.82Mn0.07Al0.06Fe0.05)x alloys with stoichiometry 4.6≤x ≤5.6 were investigated. The results revealed that most of the as-cast non-stoichiometric alloys have the main CaCu5 type structure with a small amount of La2Ni7 and LaNi or AlNi secondary phase, the alloys all have typical dendrite structure, the lattice parameter of the alloys increases with the decrease of stoichiometry. Electrochemical measurements showed that the stoichiometric alloy AB5.0 (the Ml(Ni0.82Mn0.07Al0.06Fe0.05 )x alloy with x =5.0) has the highest discharge capacity (310 mAh·g-1), and the over-stoichiometric alloys have relatively higher cycling stability and high-rate dischargeability than others although their maximum discharge capacities are relatively lower compared with the AB5.0 alloy.
Key words: hydrogen storage alloys; non-stoichiometry; phase structure; electrochemical properties