Towards advanced aqueous zinc battery by exploiting synergistic effects between crystalline phosphide and amorphous phosphate

High-performance aqueous zinc batteries are expected to be realized, rooting from component synergistic effects of the hierarchical composite electrode materials. Herein, hierarchical crystalline Ni–Co phosphide coated with amorphous phosphate nanoarrays (C-NiCoP@A-NiCoPO4) self-supporting on the Ni foam are constructed as cathode material of an aqueous zinc battery. In this unique core–shell structure, the hexagonal phosphide with high conductivity offers ultra-fast electronic transmission and amorphous phosphate with high stability, and open-framework provides more favorable ion diffusivity and a stable protective barrier. The synergistic effects of this intriguing core–shell structure endow the electrode material with outstanding reaction kinetics and structural stability, which is theoretically confirmed by density functional theory (DFT) calculations. As a result, the C-NiCoP@A-NiCoPO4 electrode exhibits a higher specific capacity of 350.6 mA h g−1 and excellent cyclic stability with 92.6% retention after 10 000 cycles. Moreover, the C-NiCoP@A-NiCoPO4 is coupled with Zn anode to assemble an aqueous pouch battery that delivers ultra-high energy density (626.33 W h kg−1 at 1.72 kW kg−1) with extraordinary rate performance (452.05 W h kg−1 at 33.56 kW kg−1). Moreover, the corresponding quasi-solid flexible battery with polyacrylamide hydrogel electrolyte exhibits favorable durability under frequent mechanical strains, which indicates the great promise of crystalline/amorphous hierarchical electrodes in the field of energy storage.