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

Abstract 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 (NiCo 2 O 4 ) nanosheets with enriched oxygen vacancies and surface phosphate ions (P–NiCo 2 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 NiCo 2 O 4 nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P–NiCo 2 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–NiCo 2 O 4‐ x cathode, our fabricated P–NiCo 2 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.