High-capacity superlattice La0.55Sm0.20Mg0.25Ni3.27Al0.01 hydrogen storage alloys with series of (A7B23)x-(A2B7)1-x (x = 0, 0.1, 0.9) structures for nickel-metal hydride batteries

Rare earth–Mg–Ni-based superlattice structure alloys are promising anode materials for nickel-metal hydride (Ni/MH) batteries. However, improvements in discharge capacity and high-rate discharge (HRD) performance are still required while maintaining a long cycle life. In this study, we introduce a series of novel A₇B₂₃-type superlattice La_0.55Sm_0.20Mg_0.25Ni_3.27Al_0.01 alloys with phase compositions of (A₇B₂₃)_x-(A₂B₇)_1-x (x = 0, 0.1, 0.9), and report their electrochemical properties and gas-solid hydrogen storage characteristics. The results show that the alloy containing ~10% A₇B₂₃ phase exhibits superior overall electrochemical performance. Specifically, the maximum discharge capacity of the alloys increases from 388.2 mAh g⁻¹ to 400.5 mAh g⁻¹ and 394.3 mAh g⁻¹, respectively, and the HRD value at a current rate of 1800 mA g⁻¹ improves from 66.4% to 72.7% and 69.2%, respectively, as x increases. Although an increased content of the A₇B₂₃-type phase leads to structural instability and a reduction in cycle life, the alloys retain over 70% capacity after 200 cycles. This study optimizes the performance of Ni/MH batteries by adjusting the phase structure and provides new insights for the development of long-life, high-rate, and high-capacity negative materials.