Synergistic Lewis Acid and Hydrogen Bonding Strategy to Enable Polymerized and Wide‐Temperature Li‐Fe‐F Conversion Solid‐State Batteries

Abstract The development of in situ polymerized electrolytes for solid‐state lithium metal batteries is hindered by poor transport kinetics, dendrite growth and limitation in operating temperature. To address these challenges, a synergistic design of Lewis acidic fluoride perovskite (KCuF 3 ) catalyst and hydrogen‐bond‐stabilized 2D layered material (CuOHF) is proposed, for the ring‐opening polymerization of 1,3‐dioxolane based electrolyte and the improvement of lithium‐ion transport and interfacial stability in a job‐sharing manner. The resulting composite electrolyte achieves the high ionic conductivity of 1.4 × 10 −4 S cm −1 and high lithium‐ion transference number of 0.7 at room temperature. The modified solid electrolyte interface enables the stable cycling of Li metal for over 5000 h and sustains an ultra‐high critical current density up to 6.4 mA cm −2 in Li‖Li symmetric cells. The cooperation of KCuF 3 and CuOHF endows the composite electrolyte with exceptional wide‐temperature operability across a range from −20 to 100 °C, enabling the stable cycling of Li‖FeF 3 cells for 200 cycles at −20 °C and with high capacity above 500 mAh g −1 (under 1 C) at 60 and 100 °C. The corresponding 10‐layer pouch‐type solid state cell based Li‐Fe‐F conversion reaction enables a highly reversible capacity as high as ≈300 mAh, which is an unprecedented level in fluoride batteries. This strategy provides a promising solution to large‐scale, high‐thermostability and interface‐stable solid polymer electrolytes for the development of high‐energy‐density and Ah‐level Li‐Fe‐F conversion batteries under extreme working temperature conditions.