Enhancing potassium‐ion storage of Bi₂S₃ through external–internal dual synergism: Ti₃C₂T_x compositing and Cu²⁺ doping

Abstract Potassium‐ion batteries (PIBs) offer a cost‐effective and resource‐abundant solution for large‐scale energy storage. However, the progress of PIBs is impeded by the lack of high‐capacity, long‐life, and fast‐kinetics anode electrode materials. Here, we propose a dual synergic optimization strategy to enhance the K⁺ storage stability and reaction kinetics of Bi₂S₃ through two‐dimensional compositing and cation doping. Externally, Bi₂S₃ nanoparticles are loaded onto the surface of three‐dimensional interconnected Ti₃C₂T_x nanosheets to stabilize the electrode structure. Internally, Cu²⁺ doping acts as active sites to accelerate K⁺ storage kinetics. Various theoretical simulations and ex situ techniques are used to elucidate the external–internal dual synergism. During discharge, Ti₃C₂T_x and Cu²⁺ collaboratively facilitate K⁺ intercalation. Subsequently, Cu²⁺ doping primarily promotes the fracture of Bi₂S₃ bonds, facilitating a conversion reaction. Throughout cycling, the Ti₃C₂T_x composite structure and Cu²⁺ doping sustain functionality. The resulting Cu²⁺‐doped Bi₂S₃ anchored on Ti₃C₂T_x (C‐BT) shows excellent rate capability (600 mAh g^–1 at 0.1 A g^–1; 105 mAh g^–1 at 5.0 A g^–1) and cycling performance (91 mAh g^–1 at 5.0 A g^–1 after 1000 cycles) in half cells and a high energy density (179 Wh kg^–1) in full cells.