Facile Synthesis of Copper Sulfide Nanosheet@Graphene Oxide for the Anode of Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are promising to expedite future energy storage progress because of the low price and high energy density of potassium. Copper sulfide (CuS), a plentiful, low-priced, and nontoxic transition metal sulfide, is going to be a promising anode material with high capacity and excellent rate performance for energy storage. Herein, thioacetamide is chosen as the sulfur source to prepare CuS nanosheets uniformly anchored on graphene oxide (CuS@GO) using a simple one-step method. The prepared CuS@GO increases the active sites and GO effectively alleviates the polymerization of CuS during the cycling. When CuS@GO is utilized as an anode material for PIBs, it exhibits a preeminent specific capacity of 410 mAh g(-1) (at a current density of 100 mA g(-1)) and outstanding rate capability (even achieving a higher capacity of 196.5 mAh g(-1) at a current density of 1000 mA g(-1)). In this study, the phase evolution of CuS during the potassium-ion insertion and extraction process is further explored by in situ X-ray diffraction studies, which is significant to clearly understand the energy storage mechanism of CuS. A novel perspective in potassium storage mechanism for transition metal sulfides is provided.