Role of sulfonamide-based covalent organic frameworks (COFs) in enhancing the electrochemical performance of PEO-based composite polymer electrolytes

Abstract

Two sulfonamide-based covalent organic frameworks (COFs), COP1 and COP2, were successfully incorporated in a poly(ethylene oxide) (PEO)–LiClO4 matrix to generate composite polymer electrolytes (CPEs). The sulfonamide COF, COP1, served as a multipurpose additive for the PEO–LiClO4 matrix by enhancing its ionic conductivity (up to 4.1 × 10–3 S/cm at room temperature and 8.7 × 10–3 S/cm at 50 °C for PEO–5% COP1–LiClO4) with an ionic transport number of 0.998, stable electrochemical window (oxidation resistance up to 1.39 V against stainless steel (SS) electrodes), and thermal and mechanical stability. The presence of strong sulfonamide groups, −SO2NH–, in the COFs enabled the dissociation of lithium ions (Li+ ions) from the lithium salt and also the assembly of the PEO for facile ionic conduction. The COF, COP2, did not result in much improvement in the conductivity of the CPEs, which may be associated with its molecular geometry. The differential scanning calorimetry (DSC) measurements confirmed the absence of any molten state of the electrolyte during the conductivity and electrochemical performance of CPEs. The performance of the supercapacitor cell synthesized using PEO–5% COP1–LiClO4 showed a specific capacitance of ∼186 F g–1 at a current density of ∼0.67 A g–1 and 3 V operating voltage. Further, the supercapacitor cell (PEO–5% COP1–LiClO4) showed a Coulombic efficiency of almost 99% at 1 V. Overall, this study highlights the promising role of sulfonamide COFs as effective additives for polymer-based solid electrolytes and their potential for developing safer and more efficient lithium-metal batteries (LMBs) in the future.