Multifunctional Covalent Organic Framework Electrolyte with Bidirectional Interfacial Engineering for PEO‐Based Solid‐State Batteries

The application of polyethylene oxide (PEO)-based solid-state electrolytes is constrained by their low ambient-temperature ionic conductivity and poor electrode/electrolyte interfacial stability. Here, we propose a multi-level synergistic strategy that enhances both bulk ion transport and stabilizes the electrode/electrolyte interfaces. This is achieved by designing a composite electrolyte incorporating a covalent organic framework (COF) functionalized with oligomeric ethylene oxide chains (TPB-BMTP-COF). The ordered porous structure and abundant ether oxygen sites of COF promote lithium salt dissociation and create fast ion-conduction pathways, boosting the ionic conductivity to 1.5 × 10^-4 S cm^-1 at 30°C. To achieve bidirectional interfacial stability, SnF₂ and LiNO₃ are introduced to promote a robust, inorganic-rich solid electrolyte interphase (SEI), while lithium difluoro(oxalato)borate (LiDFOB) is introduced to construct a hybrid organic-inorganic cathode electrolyte interphase (CEI). Thus, Li symmetric cells maintain stable polarization over 1200 h, and Li//LFP full cells achieve a capacity retention of nearly 100% after 180 cycles at 30°C. Moreover, Li//NCM811 cells demonstrate a capacity retention exceeding 80% after 100 cycles at both 45°C and 60°C. This work provides a synergistic electrolyte design strategy that integrates molecular-level architecture with dual-interface engineering, offering new insights into practical high-performance all-solid-state batteries.