Dual ions intercalation drives high-performance aqueous Zn-ion storage on birnessite-type manganese oxides cathode

Rechargeable aqueous zinc-ion batteries (ZIBs) emerge as promising candidates for grid-scale storage due to the low cost of zinc and high safety. However, aqueous ZIBs still remain the grand challenges in the poor Zn2+ transport kinetics and the structural instability of the cathode materials during Zn2+ intercalation/deintercalation. In this work, we rationally introduce Mg ion and K ion into birnessite-type manganese oxide (K0.16Mg0.06Mn2O4·1.4H2O) by one-step hydrothermal method. The intercalation of dual ions guarantees accelerated Zn2+ diffusion and excellent structural stability. Such an elegant structure delivers an ultrahigh reversible capacity of 400 mAh g-1 at 0.1 A g-1 and outstanding cycling stability (capacity retention of 94% after 1000 cycles at 500 mA g-1). With the aid of ex-situ XRD, SEM and XPS, the zinc-ion storage mechanism is explored to uncover the origin of superior electrochemical performance. This study opens up the possibilities for designing high-power ZIBs and makes a step forward to the practical application of Zn-MnO2 batteries.