Investigation of Capacitance Degradation in Activated Carbon Supercapacitors Subjected to Cryogenic Conditions

This study examined the electrochemical performance of 18650 cylindrical supercapacitors subjected to a cryogenic temperature at −196 °C. Cylindrical supercapacitor cells, utilizing 1 M tetraethylammonium tetrafluoroborate (TEABF 4 ) in acetonitrile as the electrolyte, were immersed in liquid nitrogen. Results indicated a 6.4% decrease in capacitance following exposure. To identify the cause of this reduction, we analyzed the surface chemistry of the electrodes and electrolyte degradation using X-ray photoelectron spectroscopy and proton nuclear magnetic resonance (¹H NMR), respectively. No significant changes were detected in either the surface chemistry or electrolyte. Instead, the capacitance reduction was linked to the higher activation energy required for electric double-layer adsorption/desorption, as described by the Arrhenius equation. This effect is attributed to the deformation of the styrene-butadiene rubber (SBR) binder because −196 °C is much lower than its glass transition temperature of −50 °C. At −196 °C, the SBR transitions from a flexible, rubbery state to a brittle, glassy state can cause the SBR to crack or shatter, thereby reducing the adhesive contact between the current collector and the active materials. These findings highlight the importance of polymer binders in ensuring long-term stability, especially for supercapacitors intended for low-temperature environments.