Effect of Ball Milling on the Electrochemical Properties of La0.7(Mg0.25Ti0.05)(Ni0.85Co0.15)3.5 Hydrogen Storage Alloy

Abstract

The influence of ball milling on the structure and the electrochemical properties of La 0.7 (Mg 0.25 Ti 0.05 )(Ni 0.85 Co 0.15 ) 3.5 hydrogen storage alloy was investigated systematically. The XRD results show that the main phases of the alloy are a (LaMg)Ni 3 phase with the PuNi 3 -type rhombohedral structure and a LaNi 5 phase with the CaCu 5 -type hexagonal structure. The electrochemical studies show that the maximum discharge capacity and the high rate dischargeability decrease with the increase of milling time. Furthermore, the exchange current density first increases and then decreases with the increase of milling time from 0 (as-cast) to 120 min, consistent with the variation of the charge-transfer resistance from the electrochemical impedance spectra. However, the limiting current density first decreases from 2472.8 mA/g (as-cast) to 1719.6 mA/g (BM 30 min) and then increases to 2360.4 mA/g (BM 120 min).