Porous CoS nanosheets coated by N and S doped carbon shell on graphene foams for free-standing and flexible lithium ion battery anodes: Influence of void spaces, shell and porous nanosheet

Highlights: • Porous CoS nanosheets on flexible graphene foams were prepared by electrodeposition. • The fragile structure was maintained during coating of polydopamine by divided vortex method. • Integrated carbon coating availed the conductivity and cycling performances. • Void spaces and porous structures benefited lithium ion transfer and rate performances. • High electrode integrity offers fast Li-ion diffusion, high conductivity and flexibility. The mass production of the sixth generation flexible cell phone screen is boosting the demand for flexible lithium ion batteries with high energy density and longer lifetime. CoS with high theoretical capacity and graphene foams with excellent flexibility can be candidates. In this work, CoS nanosheets are synthesized by electrodeposition and sulfuration. For the first time, free-standing porous CoS nanosheets supported on graphene foams with N and S doped carbon shells are synthesized by carbonization and sulfuration of polydopamine, which enhances conductivity. With controllable precursors, three types of morphologies were obtained and the influences of void spaces, carbon shells and the inner pores are studied. The void space and porous structure of CoS nanosheets can benefit the lithium ion diffusion and rate capability while the void space and conformal carbon shells can improve the stability of electrodes and long cycling performances. By combining the advantages of void spaces, shells and porous nanosheet structures, a high cyclic capacity of 481.7 mA h g^-1 is delivered, evaluated by the overall weight of the electrode at 0.1C (1C = 600 mA h g^-1) after 100 cycles and good rate capability.