A Single Precursor Based-one Step Synthesis Of Sulfur,nitrogen Co-doped Porous Carbon For Supercapacitors

Supercapacitors are extensively applied in the field of new energy storage system due to their fast charge-discharge,high power density,and good cycle stability.Electrode materials are a vital part of determining high-performance supercapacitors.Heteroatom-doped porous carbon materials have the advantages of high specific surface area,rich hierarchical pore structure,and high degree of hybridization,which have been attracted widespread attention in the field of electrode materials.Traditional synthesis methods usually use additional templates,activators or doping agents.Not only does it have a higher production cost,but the use of template and activator may also cause certain environmental pollution in the subsequent processing.This research proposes a simple and low-cost synthesis process.The organic alkali metal salts are used as a single precursor（carbon source,nitrogen source,sulfur source,activator and templating agent）to synthesize porous carbon co-doped with sulfur and nitrogen through a one-step pyrolysis method.The specific work contents are as follows:The saccharin sodium is used as a single precursor to prepare organic sodium-based carbon materials through a one-step pyrolysis method.The amount of heteroatom doping and pore structure are controlled by adjusting the reaction temperature.When the pyrolysis temperature is 800℃,the material shows a hierarchical pore structure composed of micropores,mesopores and macropores,with a specific surface area of445 m²g^-1 and the doped amount of high oxygen,nitrogen and sulfur（6.3 at%,3.63 at%and 1.28 at%）.In the three-electrode system,it shows a specific capacity of 223.5 Fg^-1 at 0.5 Ag^-1.The organic sodium salt-based carbon materials are used as electrode materials to be assembled into symmetrical supercapacitors through button batteries.Under the condition of 6 M KOH,it shows a specific capacity of 132.6 Fg^-1.Even at high current density(20 Ag^-1),it still has 71.2%of the initial capacitance,proving its excellent rate capability,and it can still maintain a capacitance retention rate of 96.4%after 5000 cycles,showing excellent cycle stability.At the same time,in the organic electrolyte of 1 MTEABF₄/AN,it shows an energy density of 10 Wh kg^-1.The acesulfame K is used as a single precursor to prepare organic sodium-based carbon materials through a one-step pyrolysis method.When the pyrolysis temperature is 750℃and the heating rate is 3℃/min,the material has a large amount of cheese-like macropore structure of about 1μm,high micropore/mesopore volume(0.2029 cm³g^-1 and 0.3300 cm³ g^-1),high specific surface area of 892 m² g^-1,and the synergistic effect of heteroatom doping with high oxygen（10.61 at%）,nitrogen（6.56 at%）,and sulfur（8.93 at%）.In the three-electrode system,it shows a high specific capacity of 264Fg-1(0.5 Ag^-1).By assembling into a supercapacitor,the highest specific capacity and energy density values under water system conditions are 165.2 Fg^-1 and 5.74 Wh kg^-1,respectively.At the same time,at a current density of 5 Ag^-1,the capacitance loss is only 6.5%after 5000 cycles,it shows excellent stability.In the organic system（1 MTEABF₄/AN electrolyte）,it shows a specific capacity of 144.4 Fg^-1(0.5 Ag^-1).Due to the excellent morphology and structure,the energy density can reach up to 45.13 Wh kg^-1(under the power density of 2250 W kg^-1),under the high power density of 22500W kg^-1,it can still show the energy storage capacity of 28.54 Wh kg^-1.