N-doped carbon/ultrathin 2D metallic cobalt selenide core/sheath flexible framework bridged by chemical bonds for high-performance potassium storage

Potassium-ion batteries (KIBs) have been considered as a promising alternative to lithium-ion batteries (LIBs) due to the diffusely distributed and low-cost potassium resources and high operating voltage. However, achieving satisfactory battery performance is still a main challenge for KIBs development. Here, ultrathin metallic cobalt selenide (CoSe₂) nanosheets are successfully assembled onto three-dimensional nitrogen doped carbon foam (CSNS/NCF) bridged by Co-C and Co-N-C bonds as a flexible core/sheath framework for potassium storage. The CSNS/NCF not only features with large surface area for sufficient contact with electrolyte with fast electrons and K ions diffusion but also provides a robust network with strong chemical bonds for stable potassium storage. Density functional theory (DFT) calculations show that the barrier for K atom migration in ultrathin CoSe₂ nanosheets is lower than that in bulk CoSe₂. Benefiting from the above advantages, the optimized CSNS/NCF displays a high specific capacity of 335 mAh g⁻¹ after 200 cycles at 50 mA g⁻¹. This work provides a practical approach to construct advanced anode materials for KIBs systems.