Multifunctional Epoxy-Based Solid Polymer Electrolytes for Solid-State Supercapacitors

Abstract

Solid polymer electrolytes (SPEs) have drawn attention for promising multifunctional electrolytes requiring very good mechanical properties and ionic conductivity. To develop a safe SPE for energy storage applications, mechanically robust cross-linked epoxy matrix is combined with fast ion-diffusing ionic liquid/lithium salt electrolyte (ILE) via a simple one-pot curing process. The epoxy-rich SPEs show higher Young's modulus ( E), with higher glass transition temperature ( T_g) but lower ionic conductivity (σ_dc) with a higher activation energy, compared to the ILE-rich SPEs. The incorporation of inorganic robust Al₂O₃ nanowire simultaneously provides excellent mechanical robustness ( E ≈ 1 GPa at 25 °C) and good conductivity (σ_dc ≈ 2.9 × 10^-4 S/cm at 25 °C) to the SPE. This suggests that the SPE has a bicontinuous microphase separation into ILE-rich and epoxy-rich microdomain, where ILE continuous conducting phases are intertwined with a sturdy cross-linked amorphous epoxy framework, supported by the observation of the two T_gs and low tortuosity as well as the microstructural investigation. After assembling the SPE with activated carbon electrodes, we successfully demonstrate the supercapacitor performance, exhibiting high energy and power density (75 W h/kg at 382 W/kg and 9.3 kW/kg at 44 W h/kg). This facile strategy holds tremendous potential to advance multifunctional energy storage technology for next-generation electric vehicles.

Keywords: bicontinuous composite electrolyte; energy density; ionic conductivity; power density; solid polymer electrolytes; supercapacitors.