Microstructures and electrochemical characteristics of LaNi3.70Co0.2−xMn0.30Al0.15Cu0.65(Mo0.46Fe0.54)x hydrogen storage alloys

Abstract

Electrochemical hydrogen storage properties of LaNi3.70Co0.2Mn0.30Al0.15Cu0.65 alloy are improved by substituting Co with Mo0.46Fe0.54, rather than pure Mo and Fe. Microstructures and electrochemical properties of LaNi3.70Co0.2−xMn0.30Al0.15Cu0.65(Mo0.46Fe0.54)x (x=0–0.20) hydrogen storage alloys are investigated. X-ray diffraction and backscattered electron results indicate that the pristine alloy is LaNi5 phase with a hexagonal CaCu5-type structure, while the alloys containing Mo0.46Fe0.54 consist of LaNi5 matrix phase and Mo secondary phase. The relative abundance of Mo phase increases with the increase in x value. The lattice parameters a, c, c/a and cell volume V of LaNi5 phase increase with increasing x value. As x increases from 0 to 0.20, maximum discharge capacity of the alloy electrodes monotonically decreases from 335.4 (x=0) to 324.2mAh/g (x=0.20). The high-rate dischargeability of the alloy electrodes at the discharge current density of 1200mA/g first increases from 59.8% (x=0) to 69.6% (x=0.15), and then decreases to 64.0% (x=0.20). The cycling capacity retention rate at the 100th cycle decreases from 80.4% (x=0) to 61.9% (x=0.20), which should be ascribed to the deterioration of the corrosion resistance of alloy electrode with increasing x value.