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.