A Solid-State and Flexible Supercapacitor That Operates across a Wide Temperature Range

Abstract

Electrochemical properties of most supercapacitor devices degrade quickly when the operating temperature deviates from room temperature. To exploit the potential of rGO in supercapacitors at extreme temperatures, a resilient electrolyte that is functional over a wide temperature range is also required. In this study, we have implemented a flexible, low-resistant solid-state electrolyte membrane (SSEM) into symmetric rGO electrodes to realize supercapacitor devices that operate in the temperature range −70 to 220 °C. The SSEM consists of a polycation–polybenzimidazole blend that is doped with phosphoric acid (H3PO4), and this material displays uniquely high conductivity values that range from 50 to 278 mS cm–1 in the temperature range −25 to 220 °C. The fabricated supercapacitor produced a maximum capacitance of 6.8 mF cm–2 at 100 °C. Energy and power densities ranged from 0.83 to 2.79 mW h cm–2 and 90 to 125 mW cm–2, respectively. The energy storage mechanism with a SSEM occurs by excess H3PO4 migrating from the membrane host into the electrochemical double layer in rGO electrodes. The high-temperature operation is enabled by the polycation in the SSEM anchoring phosphate type of anions preventing H3PO4 evaporation. Low-temperature operation of the supercapacitor with the SSEM is attributed to the PC–PBI matrix depressing the freezing point of H3PO4 to maintain structural proton diffusion.