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 (NiCo2O4) nanosheets with enriched oxygen vacancies and surface phosphate ions (P-NiCo2O4-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 NiCo2O4 nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P-NiCo2O4-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-NiCo2O4-x cathode, our fabricated P-NiCo2O4-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.