A Comprehensive Study on the Interactive Effects of Carbon Crystallinity and Electrochemical Activation for KOH-Modified Soft Carbons and Their High-Voltage Supercapacitor Application

Abstract

The interactive influences between carbon crystallinity and electrochemical activation (EA) on the capacitive behavior for a series of soft carbons (SCs) modified with KOH have been systematically examined for the high-voltage (≥ 4.0 V) super-capacitors in the conventional liquid electrolyte of 1 M tetraethylammonium tetra-fluoroborate/propylene carbonate (TEABF4/PC). The energy storage behavior of SCs without and with the KOH modification as well as before and after the EA treatment in various potential regions are investigated by galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) tests. Characterizations including scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption/desorption isotherms are employed to probe possible changes in carbon structure after the KOH and EA treatments. The results show that the specific capacitance of SCs can be significantly promoted by the KOH modification through crystallinity reducing and the EA via the irreversible insertion of either BF4 − or TEA+. The EA process is found to be more effective for KOH-modified SCs with relatively low crystallinity. After the optimization of both positive and negative electrodes, a 4 V full cell with the specific energy of 71.2 and 54.9 Wh kg−1 at the specific power of 0.9 and 6.1 kW kg−1 can be obtained. This 4 V supercapacitor also delivers the superior energy density of 37.7 Wh l−1 at 0.5 kW l−1 and 29.1 Wh l−1 at 3.2 kW l−1. For the stability, the 4 V supercapacitor exhibits about 85% capacitance retention after 10000 GCD cycles. The results have demonstrated the application potential of KOH-modified SCs as promising electrode materials for the high-voltage supercapacitors.