Sustained‐Release PVDF‐Based Electrolyte Producing LiF‐Li ₂ O Layered Interphases for High‐Rate Solid‐State Lithium Metal Batteries

Abstract Sustained release refers to a formulation designed to gradually and consistently release active ingredients over an extended period. In liquid electrolytes, sudden release of active components leads to thick and porous solid‐electrolyte interphases (SEIs), which increase polarization voltage and degrade cycling stability. Herein, a sustained‐release polyvinylidene difluoride (SR‐PVDF) solid polymer electrolyte is presented, using dimethylformamide (DMF) and high‐boiling‐point fluoroethylene carbonate (FEC) as co‐solvents during the electrolyte preparation process. The slow evaporation of salt‐soluble FEC induces a dense bulk configuration with a β‐phase‐rich structure and promotes the formation of a sub‐micron, salt‐rich surface with sustained release characteristics. This salt‐rich surface, with a confined FEC solvate structure primarily consisting of contact ion pairs and aggregates, controls the release of TFSI− anions and FEC, producing a highly oriented LiF‐Li ₂ O bi‐layer SEI during a prolonged cycling life. The SR‐PVDF shows a high ambient ionic conductivity of 0.59 mS cm ⁻¹ and a high critical current density of 10 mA cm ⁻² in Li||Li symmetric cells. Tested in Li||LiFePO ₄ full cells, it achieves a high‐rate capability of 97.9 mAh g ⁻¹ at 20C and long‐term cyclability with over 12000 cycles at 10C. The stable cycling of the LiNi _0.8 Mn _0.1 Co _0.1 O ₂ cathode further demonstrates its compatibility in high‐energy solid‐state batteries.