Preparation Of Nitrogen And Sulfur Co-doped Silicon Oxycarbide-derived Carbon-based Composite Electrodes And Their Application In Asymmetric Supercapacitors

Supercapacitor is a new type of environmentally friendly energy storage device that can provide high power density and long service life.The electrode material is the most critical part of the supercapacitor.Carbon materials,such as activated carbon,carbon nanotubes and graphene,have the advantages of good chemical stability,good electrical conductivity and wide electrochemical working potential which attract much attention as electrode materials.As a new type of porous carbon,CDC has high specific surface area(>1800 m² g^-1),adjustable pore size,narrow size distribution,low production cost and stable cycle performance.However,ordinary CDC has low capacitance,low power density and energy density and poor surface chemical activity which limit its application in high-performance supercapacitors.In this paper,a simple and environmentally friendly hydrothermal method was used to successfully prepare nitrogen and sulfur atom-doped CDC materials(NSCDC).NSCDC was used as the matrix,which was compounded with NiO and NiCo₂O₄ respectively by controlling the porous structure,morphology and crystallinity of the composites.NiCo₂O₄ and NSCDC/NiO were compounded to obtain NSCDC/NiO/NiCo₂O₄ ternary composite electrode material with high performance.Finally,the asymmetric supercapacitor with high energy density was assembled.The specific research results are as follows:Silicone resin was cracked at high temperature to obtain SiOC.SiOC was etched with KOH to obtain CDC.CDC was co-doped with thiourea as nitrogen and sulfur sources to obtain NSCDC.By adjusting the content of the structure-directing agent sodium dodecyl sulfate(SDS),NSCDC/NiO with different morphologies and crystallinities were prepared by hydrothermal.As the content of SDS increased,the size of NiO particles on the NSCDC were smaller and then larger.When the amount of SDS was 10 g,the NSCDC/NiO was amorphous,and the distribution of NiO microspheres on the NSCDC surface was the most uniform and the size was the smallest,which was conducive to effective charge transfer on the electrolyte and electrodes.Therefore,NSCDC/NiO-10 had the best electrochemical performance.The capacitance reached804 F g^-1 at 1 A g^-1.The capacitance after 5000 cycles attenuated 26.8%(5 A g^-1).The assembled asymmetrical coin device provided high energy density(100.3 Wh kg^-1/850.2 W kg^-1).The capacitance after 5000 cycles(1 A g^-1)attenuated 16.0%.A series of NSCDC/NiCo₂O₄ composites were hydrothermally synthesized by adjusting the heat treatment temperature.As the heat treatment temperature increased,NiCo₂O₄ transitioned from nanoneedles composition to nanoparticles composition.When the heat treatment temperature was 350°C,the NiCo₂O₄ on the surface of NSCDC was composed of uniformly arranged nano-needles which was conducive to the formation of porous structure to provide more active sites.Therefore,the NSCDC/NiCo₂O₄-350 had the best electrochemical performance.The specific capacitance was 612.2 F g^-1(1 A g^-1)and 454 F g^-1(10 A g^-1).The capacitance retention after 5000 cycles attenuated 9.9%(5 A g^-1).The further assembled all-solid asymmetric device had an energy density of 58.6 Wh kg^-1 at 749.7 W kg^-1.20.1%of the capacitance was lost after 5000 charging and discharging(1 A g^-1).The light-emitting diode can be kept lit for 112 s after being charged for 60 s.The ternary composite material NSCDC/NiO/NiCo₂O₄ was obtained by compounding NSCDC with NiO and NiCo₂O₄ by two-step hydrothermal.The NiO on the surface of NSCDC was amorphous and nano-spherical,NiCo₂O₄ was nanorod-shaped.NiO and NiCo₂O₄ were tightly combined on the NSCDC.Compared with NSCDC/NiO,NSCDC/NiO/NiCo₂O₄ had better electrochemical performance.The capacitance was 1035 F g^-1 at 1 A g^-1 and 960 F g^-1 at 10 A g^-1.The capacitance retention rate after 8000 cycles was 85.8%(5 A g^-1).The further assembled all-solid asymmetric supercapacitor had an energy density of 66.9 Wh kg^-1 at 7502.8 W kg^-1.22.7%of the capacitance was lost after 5000 cycles(1 A g^-1).The supercapacitor can keep the light-emitting diode on for 179 s after being charged for 60 s.