Electrochemical, Structural, and Thermogravimetric Studies of Activated Supercapacitor Electrodes Based on Carbonized Cellulose Cloth

Abstract

The high–temperature reagentless activation of carbonized cellulose cloth is used to manufacture supercapacitor (SC) electrodes with different fast times of activation t. It is established by means of the standard contact porosimetry that an increase in t raises both the degree of electrode hydrophilicity and the specific surface area. Thermogravimetry shows that the mass–temperature curves have two steps in the temperature ranges of 25 to 100 and 500 to 650°C, and a plateau in the range of 200 to 400°C. For symmetric supercapacitors (SCs), the potentiodynamic approach provides the voltage–capacity curves characteristic of double–layer SCs. An increase in t raises the electrode capacity from 130 to 170 F/g in 30% KOH solution, due probably to the growing influence of surface groups. It is found that the self–discharge current grows upon an increase in t. The maximum energy density for pulse SCs can be obtained at a charging voltage of 1.4 V. Life cycle tests are performed for a pulse symmetrical SC based on activated carbon electrodes with t = 60 s. It is shown that such SCs can withstand long–term cycling (at least several thousands of cycles) with no noticeable degradation and a negligible reduction in capacity.