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[Display omitted] • Insoluble Mn 3 (PO 4) 2 coating layer is electrodeposited on the amorphous MnO 2 surface. • Long-range disordered MnO 2 can release strain and provide plenty structural defects. • Mn 3 (PO 4) 2 layer can be transferred to compact coating via electrochemical activation. • Mn 3 (PO 4) 2 can prevent the dissolution of amorphous MnO 2 to enhance the stability. • The composite reveals excellent energy storage performance as the ZIBs cathode. 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 Mn 3 (PO 4) 2 coating layer is tightly encapsulated on soluble amorphous MnO 2 nanosheets (AMO@A-MP/CC). The long-range disordered atomic arrangements of amorphous MnO 2 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 Mn 3 (PO 4) 2 coating layer can inhibit the gradual diffusion of Mn2+ into electrolyte and enhance structural stability of amorphous MnO 2. 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. [ABSTRACT FROM AUTHOR]