Modulating selective interaction of NiOOH with Mg ions for high-performance aqueous batteries

Aqueous Mg-ion batteries (AMIBs) featuring advantages of good safety, low cost, and high specific energy have been recognized as a promising energy-storage technology. However, the performance of AMIBs is consistently limited by sluggish diffusion kinetics and structural degradation of cathode materials arising from the strong electrostatic interactions between high-charge-density Mg2+ and host materials. Here, layered-structured NiOOH, as traditional cathodes for alkaline batteries, is initially demonstrated to realize proton-assisted Mg-(de)intercalation chemistry with a high discharge platform (0.57 V) in neutral aqueous electrolytes. Benefiting from the unique core/shell structure, the resulting NiOOH/CNT cathodes achieve a high capacity of 122.5 mAh g−1 and long cycle stability. Further theoretical calculations reveal that the binding energy of hydrated Mg2+ is higher than that of Mg2+ with NiOOH, resulting in that Mg2+ is easily intercalated/de-intercalated into/from NiOOH. Benefiting from the freestanding design, the assembled fiber-shaped "rocking-chair" NaTi2(PO4)3//NiOOH AMIB shows a high energy density and satisfactory mechanical flexibility, which could be woven into a commercial fabric and power for fiber-shaped photoelectric sensors.