A method to obtain a Ragone plot for evaluation of carbon nanotube supercapacitor electrodes

Abstract

Electrochemical double layer capacitors, also referred to as supercapacitors, are a promising technology in the field of energy storage. Carbon nanotube (CNT)-based supercapacitors are particularly interesting because of CNTs' high surface area and conductivity. CNT supercapacitors can potentially be used in hybrid electric vehicles due to their higher power density. Comparing energy storage systems that store energy in different ways, such as batteries, fuel cells, supercapacitors, and flywheels, requires that an appropriate set of performance data be collected. A Ragone plot is a log-log plot of a device's energy density versus power density, giving insight into its operational range. A method to obtain Ragone plots for CNT-based supercapacitors in a three-terminal electrochemical cell was adapted from a technique to test commercial capacitors for electric vehicles. Ragone plots for different types of as-grown CNT electrodes in different electrolytes are presented, along with the procedural details of this new method to obtain electrode-specific energy and power densities. Additionally, a theoretical weight calculation for a carbon nanotube film was derived and validated with a direct weight measurement of a CNT film. This weight was used in the specific energy and power densities for the Ragone plot.