Engineering oxygen vacancies and surface chemical reconstruction of MOF-derived hierarchical CoO/Ni₂P-Co₂P nanosheet arrays for advanced aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (ZIBs) are emerging as promising alternatives among various energy storage devices. However, the lack of research on cathode materials with both high capacity and electrochemical stability restricts widespread applications of ZIBs. Herein, surface chemical reconstruction and partial phosphorization strategies are employed to synthesize MOF-derived hierarchical CoO/Ni₂P-Co₂P nanosheet arrays on Ni foam substrates as cathodes for ZIBs. The unique hierarchical nanostructure and multiple components with exposed surfaces and rich oxygen vacancies accelerate charge transfer and ion diffusion, expose more active sites, and promote the accessibility between the active materials and electrolyte. The oxide/phosphide composites obtained by novel partial phosphorization achieve a common improvement of performance and stability. As expected, the CoO/Ni₂P-Co₂P electrode delivers a high specific capacity (370.4 mA h g^-1 at 3 A g^-1) and excellent rate performance (63.3% retention after a six-fold increase in the current density). Moreover, when employed as the cathode of the CoO/Ni₂P-Co₂P-30//Zn battery, the assembled battery exhibits a superior specific capacity (322.8 mA h g^-1 at 2 A g^-1), a long cycle life (104.9% retention after 6000 cycles), a favorable energy density (547.5 W h kg^-1) and power density (9.7 kW kg^-1). Therefore, this study provides a suitable candidate which meets the requirements of high-performance cathode materials for ZIBs.