Electrochemical properties of the CaNi_5−xMn_x electrodes synthesized by mechanical alloying

In this article, we exhaustively examined the effects of Mn substitution for Ni on the structures and electrochemical characterization of the CaNi_5−xMn_x (x = 0.2, 0.3, 0.5, 1) alloys prepared by mechanical synthesis for 40 hours at ball to powder weight ratio of 8:1. The characterization of electrodes was examined by X-ray diffraction, scanning electron microscope and electrochemical tests. In this context, the structural properties for each alloy have two major phases Ni, Ca₂Ni₇; Ni, CaNi₃; Ni, CaNi₅; Ni, CaNi₃ where x = 0.2, 0.3, 0.5 and 1 respectively. The powder micrograph shows the existence of agglomerates has average particle size between 22 and 35 μm. In addition, the quantification by energy dispersive spectroscopy has been indicated the chemical composition of the all produced alloys is near their nominal composition. All electrodes are activated during the first cycle, independent of the Mn substitution rate. The highest values of discharge capacity and reversibility are obtained for x = 0.3 (125 mAh g⁻¹, 0.17 V) and x = 0.5 (119 mAh g⁻¹, 0.19 V) despite their low cycle stability. The evolution of D_H/a² ratio and the I₀ exchange current density for the different Mn substitution rates is in accordance with that of the evolution of discharge capacities. The better kinetic properties is observed for x = 0.5 during electrochemical cycling.