AbstractThe development of high‐performance anode materials for potassium‐based energy storage devices with long‐term cyclability requires combined innovations from rational material design to electrolyte optimization. A three‐dimensional K⁺‐pre‐intercalated Ti₃C₂T_x MXene with enlarged interlayer distance was constructed for efficient electrochemical potassium‐ion storage. We found that the optimized solvation structure of the concentrated ether‐based electrolyte leads to the formation of a thin and inorganic‐rich solid electrolyte interphase (SEI) on the K⁺‐pre‐intercalated Ti₃C₂T_x electrode, which is beneficial for interfacial stability and reaction kinetics. As a proof of concept, 3D K⁺‐Ti₃C₂T_x//activated carbon (AC) potassium‐ion hybrid capacitors (PIHCs) were assembled, which exhibited promising electrochemical performances. These results highlight the significant roles of both rational structure design and electrolyte optimization for highly reactive MXene‐based anode materials in energy storage devices.