Room‐Temperature Single Li ⁺ Ion Conducting Organic Solid‐State Electrolyte with 10 ⁻⁴ S cm ⁻¹ Conductivity for Lithium‐Metal Batteries

Abstract Covalent organic frameworks (COFs) are promising solid‐state electrolytes (SSEs) for lithium (Li)‐metal batteries due to their tunable structures, ordered nanochannels, and suppressed segmental motion, which support Li⁺ ion transport at ambient temperatures. However, pellet‐type COF‐based SSEs have exhibited low ionic conductivity, attributed to suboptimal ion transport pathways, limited crystallinity, and extensive grain boundary formation. Here, a 20 µm‐thick disulfonate‐functionalized COF (COF _ds ) film is presented that achieves an ionic conductivity of 1.0 × 10 ^‒4 S cm ^‒1 at 25 °C. The integration of immobile disulfonate anions and carbonyl groups enables inter‐subchannel Li⁺ hopping with minimal spatial separation. Molecular dynamics (MD) simulations under applied fields confirm that the molecular design facilitates optimized Li⁺ conduction pathways. Solution‐phase synthesis enabled COF _ds films with high crystallinity, uniform morphology, and smooth surfaces, which enhanced electrochemical performance. As a result, symmetric Li cells with the COF _ds film showed stable cycling for over 1300 h at 25 °C, while full cells with LiFePO ₄ cathodes retained ≈95% capacity and 99.999% Coulombic efficiency over 300 cycles at 0.2 C. This study highlights the importance of integrating molecular and structural engineering for developing COF‐based SSEs in Li‐metal batteries.