Regulating Lewis Acid–Base Interaction in Poly (ethylene oxide)‐Based Electrolyte to Enhance the Cycling Stability of Solid‐State Lithium Metal Batteries

Solid polymer electrolytes (SPE) offer an outstanding choice because of their lightweight, flexibility, and excellent thin‐film forming ability. However, the low ionic conductivity and poor lithium ion transfer number (t_Li⁺) restrict its application in all‐solid‐state lithium batteries (ASSLBs). Herein, UIO66‐X metal‐organic frameworks with controllable Lewis basicity, acidity, or neutrality functional groups are synthesized successfully and then incorporated into the poly (ethylene oxide) (PEO) matrix to fabricate SPE. The influence of different organic ligands on the interface interaction between PEO and LiTFSI is investigated by solid‐state nuclear magnetic resonance, Fourier transform infrared spectoscopy and Raman tests, as well as density functional theory calculations. The Lewis acidity group plays a key role in enhancing the ionic conductivity and t_Li⁺. As a result, the constructed Li–Li symmetrical cells retain stable cycling for 2300 h and the LiFePO₄‐based ASSLBs deliver outstanding electrochemical properties with 147 mAh g⁻¹ of reversible capacity after 500 cycles at 1C and 60 °C, 131 mAh g⁻¹ after 150 cycles at 0.1C and 30 °C. The fabricated SPEs are self‐standing and flexible with good mechanical stability, demonstrating the great potential for practical application. The results can guide choosing the inorganic filler to prepare high‐performance SPE.