Temperature effects on electrochemical performance of carbon nanotube film based flexible all-solid-state supercapacitors

The growing demand on flexible all-solid-state supercapacitors has accelerated the need for fundamental understanding of their response to extreme thermal environment. In this study, supercapacitors based on freestanding films composed of randomly oriented carbon nanotubes and H2SO4-PVA gel electrolyte were fabricated. The effect of temperature on their electrochemical behaviors was systematically investigated by using cyclic voltammogram, impedance spectroscopy and galvanostatic charge-discharge measurements at temperatures between -5 degrees C and 55 degrees C. The results indicated that the capacitance of the supercapacitor was enhanced by the increase of operating temperature while the internal resistance was reduced by virtue of the acceleration of transportation/adsorption of electrolyte ions and surface modification of the electrode. For instance, when charged with the current density of 0.2 mA cm (2), the capacitance increased by 24.3% from -5 degrees C to 25 degrees C, and by 32.6% from 25 degrees C to 55 degrees C. Operating temperatures at or below 25 degrees C were found to facilitate the charge-discharge reversibility and long-term cycle stability. It has also been concluded that supercapacitors based on H2SO4-PVA gel electrolyte were not suitable for long term use at temperatures higher than 40 degrees C due to the aging of electrolyte. (C) 2017 Elsevier Ltd. All rights reserved.