Superior electrochemical performance of the substituted A2B7-type multiphase La/Y–Mg–Ni/Co/Al alloy electrodes

This paper presents the effect of elemental substitution (La → Y, Ni → Co, and Ni → Al) in La–Mg–Ni alloys on their electrochemical properties. The studied alloys were obtained by sintering and annealing of pressed powder precursor alloys with magnesium. The samples were characterized by X-ray diffraction and energy-dispersive analysis. The synthesized alloys exhibited a multiphase nature, which included intergrowth structures with CaCu₅ and MgSnCu₄ slabs. Electrodes based on La₃MgNi₁₂Co₂, La₃MgNi₁₁Co₃ and La_2.5Y_0.5MgNi₁₁Co₃ alloys demonstrated the highest discharge capacity of over 400 mAh/g, and electrodes of the La_2.5Y_0.5MgNi_13.5-xCo_xAl_0.5 (x = 0–3) series showed the best cyclic stability of over 90 % after 50 cycles for all operating charge-discharge modes. Furthermore, electrodes based on La₃MgNi_14-xCo_x and La_2.5Y_0.5MgNi_14-xCo_x exhibited high values of high-rate dischargeability (over 90 % at a current density of 1000 mA/g). The ability to fast charge at a current of 1000 mA/g was found in all electrodes. In addition to the above characteristics, Tafel curves, cyclic voltammetric measurements, and calculations of the hydrogen diffusion coefficient were performed and used to analyze additional electrode parameters.