Oxygen-Vacancy and Surface Modulation of Ultrathin Nickel Cobaltite Nanosheets as a High-Energy Cathode for Advanced Zn-Ion Batteries

The development of high-capacity, Earth-abundant, and stable cathode materials for robust aqueous Zn-ion batteries is an ongoing challenge. Herein, ultrathin nickel cobaltite (NiCo₂ O₄ ) nanosheets with enriched oxygen vacancies and surface phosphate ions (P-NiCo₂ O_4-x ) are reported as a new high-energy-density cathode material for rechargeable Zn-ion batteries. The oxygen-vacancy and surface phosphate-ion modulation are achieved by annealing the pristine NiCo₂ O₄ nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P-NiCo₂ O_4-x nanosheet electrode delivers remarkable capacity (309.2 mAh g^-1 at 6.0 A g^-1 ) and extraordinary rate performance (64% capacity retention at 60.4 A g^-1 ). Moreover, based on the P-NiCo₂ O_4-x cathode, our fabricated P-NiCo₂ O_4-x //Zn battery presents an impressive specific capacity of 361.3 mAh g^-1 at the high current density of 3.0 A g^-1 in an alkaline electrolyte. Furthermore, extremely high energy density (616.5 Wh kg^-1 ) and power density (30.2 kW kg^-1 ) are also achieved, which outperforms most of the previously reported aqueous Zn-ion batteries. This ultrafast and high-energy aqueous Zn-ion battery is promising for widespread application to electric vehicles and intelligent devices.