Quasi-solid-state gel polymer electrolyte for a wide temperature range application of acetonitrile-based supercapacitors

A quasi-solid-state gel polymer electrolyte (GPE) is designed by integrating a free-standing cross-linked film and an injectable polymer electrolyte for applications in acetonitrile-based supercapacitors (SCs) using activated carbon (AC) electrodes. The synthesized GPE exhibits a high ionic conductivity over a wide temperature range (~1.7 × 10⁻³ S cm⁻¹ at −20 °C to ~7.9 × 10⁻³ S cm⁻¹ at 60 °C) as well as thermal stability and flexibility. A quasi-solid-state SC equipped with the GPE exhibits ~13% higher specific capacitance (~56% smaller Warburg resistance) at room temperature (RT) than that of an SC containing a corresponding liquid electrolyte. The quasi-solid-state SC also exhibits excellent electrochemical characteristics over a temperature range of −20 to 60 °C with only ~23% capacitance loss at −20 °C compared to that at RT. Furthermore, the quasi-solid-state SC maintains ~93% of its initial capacitance (only ~4% increase in ESR) after 120-h storage at 85 °C (above the boiling point of acetonitrile). This capacitance is superior to an SC equipped with a film-only GPE (~73% capacitance retention and ~270% increase in ESR). The proposed strategy provides new insights into the development of GPE designs for practical applications to solid-state SCs operating over a wide temperature range.