Synergistic Dissociation‐and‐Trapping Effect to Promote Li‐Ion Conduction in Polymer Electrolytes via Oxygen Vacancies

Abstract Despite their promised safety and mechanical flexibility, solvent‐free polymer electrolytes suffer from low Li‐ion conductivities due to poor dissociation of conducting salts and low Li⁺‐transference numbers due to Li⁺‐trapping by ether‐linkages. In this work, the authors found that oxygen vacancies carried by nanosized Al₂O₃ fillers preferentially promotes Li⁺‐conduction in poly(ethylene oxide) (PEO). These vacancies and free electrons therein, whose concentration can be tuned, effectively break up the ion pairs by weakening the Coulombic attraction within them, while simultaneously interacting with the anions, thus preferentially constraining the movement of anions. This synergistic dissociation‐and‐trapping effect leads to the significant and selective improvement in Li‐ion conductivity. Solid state batteries built on such PEO‐based electrolytes exhibits superior performance at high current density. This discovery reveals a molecular‐level rationale for the long‐observed phenomenon that certain inorganic nano‐fillers improve ion conduction in PEO, and provides a universal approach to tailor superior polymer‐based electrolytes for the next generation solid‐state batteries.