N‐doped carbon‐coated CoSe2 nanocrystals anchored on two‐dimensional MXene nanosheets for efficient electrochemical sodium‐ and potassium‐ion storage

Summary Sodium‐ion batteries (SIBs) and potassium‐ion batteries (KIBs) have received much attention as next‐generation energy storage systems owing to the abundance. Nevertheless, they face great challenges in the design of optimum electrode materials for practical applications. Herein, we prepared a unique two‐dimensional structured composite consisting of N‐doped carbon‐coated CoSe 2 nanocrystals and MXene nanosheets (CoSe 2 @NC/MX) for efficient electrochemical Na‐ and K‐ion storage. In this strategy, a Co‐based zeolitic imidazole framework (ZIF‐67) was deposited on the surface of MXene nanosheets, and the subsequent selenization process resulted in the transformation of the ZIF‐67 into CoSe 2 @NCs. The unique structure can shorten the transport pathways for electrons/ions and provide sufficient space to accommodate the volume change of the active materials. Furthermore, the N‐doped carbon matrix and MXene can enhance the robustness of the electrode materials. Accordingly, the composites exhibited enhanced electrochemical performance in terms of cycle stability (317 mA h g −1 after 200 cycles at 0.5 A g −1 ) and rate capability (343 mA h g −1 at 7.0 A g −1 ) for SIBs. For KIBs, they exhibited a high reversible capacity of 358 mA h g −1 at 0.5 A g −1 after 100 cycles and 276 mA h g −1 at a high rate of 2.0 A g −1 .