Potassium-selenium(K-Se)batteries are a promising electrical energy storage candidate because of the cost-effectiveness and material sustainability,yet they suffer from shuttle effect,volume expansion and low powder density.The development of Se-based cathode is an effective way to overcome the above issues.Here we designed a hollow nano-spherical Co-Fe bi-metallic sele-nide coated with N-doped carbon(denoted as CFS@N-C)as cathode for K-Se batteries.Bimetallic selenide is benefit to improve the conductivity of composite materials;N-doped carbon layer encapsulation effectively inhibits the dissolution of poly-selenides and relieves the volume expansion.The as-prepared K-Se battery exhibits excellent rate performance(300 mAh·g-1 at 1000 mA·g-1)and slow-charge/ultrafast-discharge capability(discharge at 5000 mA·g-1 and charge at 100 mA·g-1 with ultrahigh capacity of 227 mAh·g-1)with Coulombic efficiency nearly 100％.In addition,the ex-situ high-resolution transmission electron microscopy(HRTEM)images reveal that the charge-discharge mechanism of CFS@N-C is K+replaces the bimetal and forms K2Se.The unique design in this work may provide certain directions on researching for high power density K-storage materials.