Fe _0.8 CoSe ₂ nanosphere coated by N‐doped carbon for ultra‐high rate potassium selenium battery

Abstract

Abstract 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.