Carbonyl Engineering in Covalent Organic Frameworks for Promoting Li+ Conduction.

Abstract

The rational design of covalent organic frameworks (COFs) for solid-state electrolytes (SSEs) is hindered by the precise position of polar functional groups (C ═ O) affect Li+ transport. Herein, we synthesize four COFs materials with systematically carbonyl substitution positions to elucidate their structure-property relationships. Among them, the β-ketoenamine-based COF featuring ortho-dicarbonyl groups exhibits a significantly enhanced electronegativity, which restricts anion migration and promotes selective Li+ transport. Consequently, the rich-carbonly COF SSE achieves a high ionic conductivity of 9.83 × 10-4 S/cm, a Li+ transference number of 0.8, and an electrochemical stability window exceeding 5.1 V. Symmetric cell delivers stable Li plating/stripping for over 1200 h at 0.2 mA/cm2 with a low overpotential of ∼0.1 V, and over 460 h at 0.5 mA/cm2. When coupled with a LiFePO4 cathode, the solid-state battery retains 80% capacity after 1230 cycles at 1 C and 80.2% after 700 cycles at 5 C. Theoretical calculations reveal that the ortho-dicarbonyl coordination environment lowers the Li+ migration barrier (0.376 eV) and enhances Li+-framework affinity, accelerating charge transfer. This work establishes a clear correlation from functional group positioning to pore chemistry, ion transport kinetics, and interfacial stability, offering a molecular-level design principle for high-performance COF-based solid-state electrolytes.