Sulfur modification of carbon materials as well as the redox additive of Na2S for largely improving capacitive performance of supercapacitors

Heteroatom doping is an alternative method for obtaining a supercapacitor with high specific capacitance and high energy density. Here we have designed an effective strategy. Firstly, the surface of the activated carbon is modified by sulfur powder at 700 degrees C to produce sulfur-containing groups on the surface, and it exhibits good electrochemical performance (207 F g(-1) at 1 A g(-1), and 72 Wh kg(-1)). Next, the redox additive Na2S introduced and the sulfur-containing group on the surface of the carbon material undergo a redox reaction (at the positive electrode) and form a chemical bond. As a result, the specific capacitance can still reach 643 F g(-1) when the current density is as high as 15 A g(-1) and has a high energy density of 12.6 Wh kg(-1). This improvement is attributed to the synergistic action of the sulfur-containing groups on the surface of the carbon material with S2- in the redox additive and forms a covalent bond. Therefore, our strategy (surface modification and synergy of redox additives) provides an effective means of improving the performance of carbon-based supercapacitors. (C) 2019 Elsevier B.V. All rights reserved.