The Design And Preparation Of Muti-Dimensional Carbon-Based Materials For Supercapacitor

With the depletion of oil resources and deteriorating environment,there is an urgent requirement for the clean and renewable energy and the energy conversion and storage devices.Supercapacitor is a kind of energy storage device between conventional capacitors and secondary batteries.Supercapacitors with high power density,fast charge rates and wide operating temperature range are widely applicated in electric vehicles,rail transits and flexible energy storage devices.The electrode material is the most important factor affecting its electrochemical performance.Porous carbon is the most widely used electrode material in the market because of its high specific capacitance and stable physical and chemical properties.However,porous carbon also suffers from the complex structure of pores,complicated process of preparation and low specific capacitance.To improve the electrochemical performance of conventional carbon materials,this research will improve its defects by optimizing its morphology,porous structure and introducing pseudo-capacitive materials.The main research contents and results of this dissertation are summarized as follows:?1?Synthesis and electrochemical performance of 3-dimensional porous honeycomb-like carbon materialsSodium alginate was selected as carbon precursor.Ca²⁺was introduced to get insoluble gels,followed by an one-step carbonization process to obtain the 3-dimensional porous honey-like carbon material.In this paper we also discussed the influence of the heating rate for the morphology,porous structure and electrochemical performance of the sample,and the sample with the heating rate of 6?/min was tested with an ideal architecture and the best electrochemical performance.the honeycomb-like framework was consist of numerous interconnected bubble like unites,which is an open and unimpeded structure.It could reduce the resistance of the electrolyte transferring in the carbon materials.The capacitance of the sample with the heating rate of 6?/min was 339.21 F/g at 1 A/g.It can also maintain almost 85%when the current density was 20 A/g.Moreover,the sample also exhibited a low diffusion resistance of electrolyte and excellent cycling stability.?2?Lignin-based Carbon Nanosheet Prepared by Template Method for Supercapacitor ElectrodeSodium lignosulfonate was selected as carbon sources and boron acid was selected as template to prepare lignin-based carbon nanosheet via the template method.The effect of the mass ratio of the carbon resource and the template resource on the carbon nanosheet's morphology and capacitive performance was also evaluated.The results revealed that the carbon material with the mass ratio of 1:5?SLB-5?exhibited the best capacitive performance.The capacitance of SLB-5 could reach 350.79 F/g at 1 A/g,which could also maintain almost 80%as the current density increased to 10 A/g.After 5000 cycles'endurance test at 5 A/g,its capacitance could still retain 90%.All these results proved it a promising electrode material for supercapacitor.?3?In-situ self-assembly of a 2-dimensional carbon/Fe3O4 composite as a high performance supercapacitor electrode materialSodium alginate?SA?,with a novel structure which can immobilize multivalent metal cations,was used to coordinate with Fe3+to fabricate carbon and Fe3O4 composite by an easy sol-gel method.Due to the chelation effect between SA and Fe³⁺,the carbon composite was constructed into a two-dimensional sheet-like structure,and the Fe3O4 particles were nanosize and homogenously distributed on the surface of carbon nanosheet.As electrode materials for supercapacitor,the composite electrode showed a high specific capacitance of 550 F/g at 1 A/g in the potential range from-1.1 to 0 V,and excellent cycling stability of 89%retention after 2000cycles.The enhanced electrochemical performance could be attributed to the abundant exposed active sites,producing high pseudocapacitance,to two-dimensional nanosheet structure,facilitating electrolyte transport and to strong attachment strength,empowering cycle life.This environmentally-friendly design can provide an alternative to existing method,resulting in the development of two-dimensional carbon/metal oxide composite for energy storage devices.