Preparation Of Carbon-based Composites And Their Application In Supercapacitors

Supercapacitor is a new type of clean energy storage device with high power density,good rate performance,long cycle life,fast and stable for high current charge and discharge,and safety.It can be completed the charged and discharged of energy storage device in a very short time,but the energy density of supercapacitor are much lower than lithium ion battery and fuel cell.Therefore,the development of high energy density supercapacitors is one of the hotspots in the field of new energy research.Carbon materials are the most commonly used electrode materials for supercapacitors due to their abundant structures,excellent conductivities and chemical stability.However,the lower specific capacitance and lower energy density still limit its application in some fields.The research content of this thesis is mainly based on carbon materials.First,pseudocapacitor material were grown on carbon material to increase the specific capacitance of the composite material through hydrothermal method.And then,heteroatom doped carbon nanosheets with optimized porous structure,enhanced wettability with electrolyte,high conductivity,and cycle stability were fabricated through template method.Thereby,the as-prepared carbon nanosheets exhibit improved capacitance,high energy density and power density.The specific content of this thesis is as follows:1.A self-standing electrode with NiCo₂S₄ nanosheets aligned on double capillary carbon nanofiber?NiCo₂S₄@DCCNF?is fabricated by using combination of coaxial electrospinning technology with hydrothermal process.Such unique 1D hollow nanofiber-2D nanosheet-shaped hierarchical structure is capable of increasing the accessible surface area for active sites,shortening the ion diffusion length,and decreasing the ion diffusion resistance for high-performance supercapacitors.The all-solid-state supercapacitors based on NiCo₂S₄@DCCNF achieved a high capacitance of 166 F g^-1 and outstanding cycling stability.Our simple method to prepare hierarchical core/shell structure electrode with prominent electrochemical properties may have great potential in various energy storage technologies.2.A facile and industrially scalable approach was developed to produce nitrogen-doped porous carbon nanosheets?PNDC-4?with excellent pore size distribution,large specific surface area(>1200 m² g^-1),high conductivity(>700 S m^-1),and superb wettability either in aqueous or organic electrolyte.Particularly,PNDC-4 shows high capacitance of 387 F g^-1 in a three-electrode configuration and80 F g^-1(at 1 A g^-1)in a symmetric two-electrode system with EMIMBF₄ as the electrolyte.The device exhibits an ultrahigh energy density of 81 Wh kg^-1 at a power density of 1.3 kW kg^-1,which can still maintain 60.8 Wh kg^-1 when the power density increased to as high as 266.6 kW kg^-1.Moreover,the devices show unprecedentedly high capacitance retention of 94%after 100,000 cycles at a high current density of 20A g^-1.