Compact and insoluble Mn3(PO4)2 coating layer confined amorphous MnO2 as cathode for aqueous zinc ion batteries

Manganese-based composites are considered as valid cathodes for aqueous zinc-ion batteries (ZIBs). However, the gradually dissolute and structural collapse of the Mn species are still restricting the practical application. Herein, an electrochemical activated insoluble Mn3(PO4)2 coating layer is tightly encapsulated on soluble amorphous MnO2 nanosheets (AMO@A-MP/CC). The long-range disordered atomic arrangements of amorphous MnO2 can release the strain due to volume changes, while the abundant structural defects can act as ion storage sites with high reversibility, thus effectively enhance the intrinsic capacity and reduce the capacity degradation. Moreover, the compact and insoluble Mn3(PO4)2 coating layer can inhibit the gradual diffusion of Mn2+ into electrolyte and enhance structural stability of amorphous MnO2. Therefore, AMO@A-MP/CC composite delivers ultra-high specific capacity (420.0 mAh g−1 at 0.3 A g−1), remarkable cyclic stability (97.5 % capacity retention after 1000 cycles) and excellent rate capability (224.2 mAh g−1 at 3.0 A g−1). Significantly, the energy-density of 225.0 Wh kg−1 for single electrode and bendable ability can be achieved in the flexible Zn/AMO@A-MP battery, demonstrating the synergistic effect of amorphous structure and surface coating for future ZIBs development.