Material Design And Energy Storage Mechanism Investigation To The Negative Electrodes For Electrochemical Capacitors

With the increasing concerns on the global energy shortage and the environmental pollution issues,human demand for clean and efficient renewable new energy and high-performance energy storage and conversion technology is increasing dramatically.Electrochemical capacitors,also known as supercapacitors,have been regarded as one of the most promising energy storage devices due to the superiority of rapid charging/discharging,long-term cycle stability and low maintenance costs.However,low energy density is still a major problem for electrochemical capacitors.To address this critical scientific problem,electrochemical capacitors need to further improve their energy density without losing their high power density and long cycling stability.The electrode material is the key to determine its performance parameters.However,cathode materials have been extensively studied and have a high capacity,while anode materials are less diverse and have lower capacity,so it is imminent to develop a novel anode material that can be matched with the anode material.At present,the anode material mainly includes carbon material and a small amount of metal compound material,but the lower capacity of the carbon material tends to result in low energy density,and the poor conductivity of most metal compounds often leads to poor power density and cycle stability.Therefore,this thesis mainly designs the anode materials with high power density,high energy density and long cycle life through the strategies of structural regulation and surface modification,and deeply explores the energy storage behavior during the electrochemical reaction process,and assembles them into high-performance electrochemical capacitors.The specific research content mainly includes four aspects.One is to improve the capacity and broaden the potential window of the carbon fiber paper electrode by constructing a porous structure and introducing a surface oxygen-containing functional group.It also exhibits excellent electrochemical performance after assembly into a symmetric electrochemical capacitor.Secondly,the?-Fe₂O₃/rGO composites were prepared by hydrothermal synthesis,and the composite was used as the negative electrode,and MnO₂ was used as the positive electrode to assemble an asymmetric electrochemical capacitor with a potential window of 2 V and excellent electrochemical performance.The third is to prepare two-dimensional ultra-thin MoO₂ nanosheets by chemical vapor deposition,and then composite with GO to prepare MoO₂/GO composites,and as the anode of pseudocapacitor,it exhibits high capacity and fast charge/discharge capability.In addition,the in-situ Raman and XRD techniques combined with density functional theory?DFT?calculations are used to investigate the structural evolution of two-dimensional MoO₂ during charge and discharge.Fourthly,nitrogen-doped carbon-coated MoO₂ composite was prepared by a simple carbon coating strategy,and its energy storage mechanism was explored by in-situ XRD.In this thesis,a high performance electrochemical capacitor anode material has been successfully constructed and its energy storage behavior has been deeply explored,which provides reference for the development of other new anode materials and has important practical significance.