Fe-Doped CoP Flower-Like Microstructure on Carbon Membrane as Integrated Electrode with Enhanced Sodium Ion Storage

Poor cyclability and rate performance always impede the development of transition metal phosphide-based anode materials. Many strategies have been used to address the above problems, such as the designing of hierarchical structures, combination with carbon materials, and doping with other metal elements. Considering those strategies, a flower-like Fe-doped CoP material is designed. The synthesis consists of microsheets grown on a carbon membrane (CM, leaves as precursor) through a hydrothermal method and in situ phosphorization. The Fe doping and carbon membrane synergistically induce the formation of a flower-like hierarchical microstructure during the crystal-growing process. The unique hierarchical microstructure increases the contact area between electrode and electrolyte, and accommodates the volume expansion during cycling. The hierarchical Fe-doped CoP grown directly on the carbon membrane increases the active sites for intercalation of sodium species and further promotes the internal electron conduction in the Fe-doped CoP/CM electrode. Thereby, the Fe-doped CoP/CM as the anode electrode for sodium ion batteries exhibits a high specific capacity of 515 mA h g^-1 at 100 mA g^-1 after 100 cycles. Even if the current density rises to 500 mA g^-1 , the specific capacity is still maintained at 324 mA h g^-1 after 500 cycles, showing superior rate performances and cyclability.