High Energy Density Hybrid Supercapacitors Based On Nitrogen/Sulfur Co-Doped Carbon

Supercapacitor is a new type of energy storage device between traditional capacitors and rechargeable batteries.As an efficient and clean energy storage technology,supercapacitor has important practical and strategic significance for the utilization and development of renewable energy.Currently,compared to lithium-ion batteries,supercapacitors are difficult to be used as stand-alone energy storage sources due to their lower energy density and higher practical cost.Carbon nanomaterials,which are light and environmentally friendly,have the characteristics of high conductivity and high specific surface area,and the potential to be used as capacitive electrode materials with excellent performance.However,the low specific capacitance and narrow voltage window lead to low energy density due to the limitation of the energy storage mechanism of electric double layer capacitance and the decomposition voltage of water,which seriously restrict the practical application of carbon nanomaterials.In theory,improving the specific capacitance and expanding the voltage window are the keys to improve the energy density of supercapacitors.In view of this,two kinds of carbon nanoaerogels were prepared by polymerization-carbonization method in this paper.The specific capacitance of carbon nanoelectrodes was improved by introducing pseudocapacitance through nitrogen and sulfur co-doping.The competitive redox reactions of positive polyaniline electrode and negative bismuth oxide electrode were used to inhibit the decomposition of water,and nitrogen and sulfur co-doped carbon nanoaerogels were used as negative and positive electrode,respectively,to construct the high voltage aqueous hybrid supercapacitors.Research contents are given as follows:The first work is a hybrid supercapacitor based on positive methyl blue doped polyaniline hydrogel electrode and negative nitrogen and sulfur co-doped carbon nanoaerogel electrode.Nitrogen and sulfur co-doped carbon nanoaerogels have the characteristics of three-dimensional continuity and highly microporous structure.The highly active nitrogen doping is not only beneficial to improve the pseudocapacitance,but also to increase the spacing of carbon nanolayers and promote the diffusion of electrolyte ions.Using the redox reaction of positive methyl blue doped polyaniline hydrogel electrode in acidic electrolyte to inhibit the oxygen evolution reaction of water,the assembled hybrid supercapacitor has a voltage window of 2.0 V and an energy density of 59.7 Wh kg^-1,and provides an effective method for improving the energy density of carbon-based aqueous supercapacitors.A flexible solid-state battery-supercapacitor hybrid device based on the positive electrode of nitrogen/sulfur co-doped carbon nanoparticle aerogel and the negative electrode of Bi₂O₃nanoparticle coated by nitrogen-doped carbon.Nitrogen and sulfur co-doped carbon nanoparticle aerogels have porous structure and high active nitrogen content,and can provide the specific capacitance of 312 F g^-1at the current density of1 A g^-1.The Bi₂O₃nanosheets coated by nitrogen doped carbon,can not only improve the electrical conductivity and the rate performance,but also enhance the structural stability of Bi₂O₃in the process of charge and discharge.The low redox potential of Bi³⁺in the negative electrode of Bi₂O₃nanosheets coated by nitrogen doped carbon inhibits the hydrogen evolution reaction of water.The assembled flexible solid-state battery-supercapacitor hybrid device has a voltage window of 2.3 V and an energy density of 118 Wh kg^-1,providing a new idea for obtaining hybrid supercapacitors with high energy density.