Electrochemical performance of CoSe with mixed phases decorated with N-doped rGO in potassium-ion batteries.

Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs). Nevertheless, they still face great challenges in the design of the best electrode materials for applications. Herein, we have successfully synthesized nano-sized CoSe encapsulated by N-doped reduced graphene oxide (denoted as CoSe@N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe phases. The CoSe@N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g at 0.05 A g in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g after 100 cycles at 0.2 A g. Density functional theory (DFT) calculations show that CoSe with N-doped carbon can greatly accelerate electron transfer and enhance the rate performance. In addition, the intrinsic causes of the higher electrochemical performance of orthorhombic CoSe than that of cubic CoSe are also discussed.