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

ABSTRACT 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, SnF ₂ and LiNO ₃ 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.