Building K–C Anode with Ultrahigh Self‐Diffusion Coefficient for Solid State Potassium Metal Batteries Operating at −20 to 120 °C

Abstract Solid state potassium (K) metal batteries are intriguing in grid‐scale energy storage, benefiting from the low cost, safety, and high energy density. However, their practical applications are impeded by poor K/solid electrolyte (SE) interfacial contact and limited capacity caused by the low K self‐diffusion coefficient, dendrite growth, and intrinsically low melting point/soft features of metallic K. Herein, a fused‐modeling strategy using potassiophilic carbon allotropes molted with K is demonstrated that can enhance the electrochemical performance/stability of the system via promoting K diffusion kinetics (2.37 × 10 −8 cm 2 s −1 ), creating a low interfacial resistance (≈1.3 Ω cm 2 ), suppressing dendrite growth, and maintaining mechanical/thermal stability at 200 °C. A homogeneous/stable K stripping/plating is consequently implemented with a high current density of 2.8 mA cm −2 (at 25 °C) and a record‐high areal capacity of 11.86 mAh cm −2 (at 0.2 mA cm −2 ). The enhanced K diffusion kinetics contribute to sustaining intimate interfacial contact, stabilizing the stripping/plating at high current densities. Full cells coupling ultrathin K–C composite anodes (≈50 µm) with Prussian blue cathodes and β/β″‐Al 2 O 3 SEs deliver a high energy density of 389 Wh kg −1 with a retention of 94.4% after 150 cycles and fantastic performances at −20 to 120 °C.