Effect of temperature on the capacitance of carbon nanotube supercapacitors

Abstract

The effect of temperature on the kinetics and the diffusion mechanism of the ions in a supercapacitor assembled with single-walled carbon nanotube (SWNT) film electrodes and an organic electrolyte were thoroughly investigated. An improved room temperature performance of the supercapacitor was observed due to the combined effects of an increase in the conductivity of the SWNT films and surface modifications on the SWNT films by repeatedly heating and cooling the supercapacitor between the temperatures of 25 and 100 °C. Modified Randles equivalent circuit was employed to carry out an extensive analysis of the Nyquist spectra measured at different temperatures between 25 and 100 °C in order to understand the fundamentals of the capacitive and resistive variations in the supercapacitor. The experimental results and their thorough analysis will have significant impact not only on the fundamental understanding of the temperature-dependent electrode/electrolyte interfacial properties but also on supercapacitor design with appropriate electrode materials for numerous industrial and consumer applications. The supercapacitor with SWNT film electrodes was capable of withstanding current densities as high as 100 A/g, yielding eminent specific power density values of about 55 kW/kg. Ultralong galvanostatic charge-discharge cycling over 200 000 cycles with a constant current density of 20 A/g at 25 and 100 °C, respectively, showed excellent stability in capacitance with more than 80% efficiency. The usage of such a supercapacitor potentially enables far-reaching advances in backup energy storage and high pulse power applications. © 2009 American Chemical Society.