Electrochemical performance of CoSe 2 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 2 encapsulated by N-doped reduced graphene oxide (denoted as CoSe 2 @N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe 2 phases. The CoSe 2 @N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g -1 at 0.05 A g -1 in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g -1 after 100 cycles at 0.2 A g -1 . Density functional theory (DFT) calculations show that CoSe 2 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 2 than that of cubic CoSe 2 are also discussed.