Microstructures and electrochemical characteristics of La0.7Ce0.3Ni3.75−xCu0.75Mn0.35Al0.15(V0.81Fe0.19)x (x = 0–0.20) hydrogen storage alloys

Microstructures and electrochemical characteristics of La0.7Ce0.3Ni3.75−xMn0.35Al0.15Cu0.75(V0.81Fe0.19)x (x = 0–0.20) hydrogen storage alloys have been investigated. X-ray diffraction patterns and Backscatter electron images indicate that La0.7Ce0.3Ni3.75−xMn0.35Al0.15Cu0.75(V0.81Fe0.19)x alloys consist of a single phase with CaCu5-type structure. The lattice parameter a and cell volume V increase with increasing x value. Maximum discharge capacity monotonically decreases from 320 mAh/g (x = 0) to 299 mAh/g (x = 0.20). The high-rate dischargeability at the discharge current density of 1200 mA/g first increases from 52.6% (x = 0) to 55.6% (x = 0.05), and then decreases to 46.7% (x = 0.20). Cycling stability first increases with increasing x from 0 to 0.10 and then decreases when x increases to 0.20, which is resulted from the combined effect of the improvement of the pulverization resistance and the decrease of corrosion resistance.

► Commercial VFe alloy is cheaper than pure V and Ni. ► Alloys consist of a single CaCu5-type phase, and a and V increase with increasing x. ► The alloy with x = 0.05 exhibits the best high-rate dischargeability. ► The alloy with x = 0.1 exhibits the best cycling capacity retention rate. ► Substitution of VFe for Ni can improve HRD and cycling stability.