Multirole Integrated Filler Design for Polymer-in-Salt Electrolytes Enables Long-Life, Safe Solid-State Lithium...

Although polymer-in-salt (PIS) electrolyte strategy is widely employed in solid-state lithium batteries for interface stabilization through ion transport modulation and interphase chemistry tailoring, its application remains plagued by interfacial degradation induced by residual solvent and inherent ionic conductivity-mechanics trade-off. Herein, we propose a multirole integrated filler design to simultaneously address these limitations through defect chemistry and interface engineering. CaF₂ filler, as a representative case, synergistically promotes salt dissociation and ion-conducting sites generation through fluorine vacancy defects while reinforcing the polymer matrix via hydrogen bonding interactions and high bulk modulus. This enables roll-to-roll scalable fabrication of ultra-thin (ca. 8 µm) PIS membrane with exceptional ionic conductivity of 3.32 × 10^-4 S cm^-1 at 25°C. Crucially, the in situ generated LiF/Li-Ca interphase suppresses both residual solvent decomposition and dendrite formation, achieving stable cycling in lithium symmetric cells for nearly 1600 h and high-capacity retention in full cells with LiFePO₄ or NCM811 cathodes over 1000 cycles. The outstanding thermal stability (melting point: 1418°C) of CaF₂ further boosts the inherent safety of pouch cells under mechanical and thermal abuse conditions. This single-component filler strategy effectively addresses multiple performance bottlenecks in polymer electrolytes, offering a scalable and cost-effective pathway for practical solid-state batteries.