Fe0.8CoSe2 nanosphere coated by N-doped carbon for ultra-high rate potassium selenium battery

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 selenide 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 K 2 Se. The unique design in this work may provide certain directions on researching for high power density K-storage materials.