Effect of Step-wise Sintering Temperature on the Phase Structure and Electrochemical Properties of (La, Mg)2Ni7 Superlattice Hydrogen Storage Alloys

The (La, Mg) 2 Ni 7 superlattice hydrogen storage alloys were synthesized via a step-wise vacuum sintering method, and the effects of varying the final sintering temperature (825, 850, and 875 °C) on their phase composition and electrochemical performance were systematically investigated. X-ray diffraction and Rietveld refinement revealed that an optimal sintering temperature of 850 °C produces an entirely superlattice structure composed of La 1.5 Mg 0.5 Ni 7 and La 4 MgNi 19 phases, successfully eliminating the LaNi 5 -type phase. Higher temperatures exacerbate Mg volatilization, decomposing the superlattice into predominantly LaNi 5 . Electrochemical measurements demonstrate that the alloy sintered at 850 °C achieves the highest maximum discharge capacity of 360.19 mAh/g and superior cyclic stability with a capacity retention of 69.51% after 100 cycles. The homogeneous superlattice structure enables highly coordinated lattice expansion and contraction, effectively alleviating internal microstrain and inhibiting electrode pulverization during cycling. Furthermore, kinetic evaluations indicate that the fully superlattice alloy exhibits optimized surface charge-transfer efficiency and a maximized hydrogen diffusion coefficient, leading to an excellent high-rate dischargeability (87.02% at a discharge current density of 900 mA/g).