Preparation Of High Energy Density Electrode Materials And Their Electrochemical Properties

With the rapid development of the global economy,the shortage of fossil fuels and deteriorating environmental pollution have become a threat to humanity.Therefore,the vigorous development of new green energy?such as solar energy,wind energy,geothermal energy,tidal energy,etc.?and its utilization technology have been widely concerned.It will also be an important measure to reduce environmental pollution and achieve sustainable development.However,intermittent nature of these renewable energy and low storage efficiency make the development of efficient energy storage technology urgent.Among various electrochemical energy storage devices,rechargeable batteries are an indispensable part of modern society and can provide electricity on demand in a variety of applications.In particular,lithium-ion batteries have been a huge commercial success in portable electronic devices and begun to enter the electric car and hybrid car market.However,their safety deficiencies and low power density impose restrictions on their large-scale application in the automotive industry.Supercapacitors with high power density property can make up for the disadvantages of batteries according to the requirements of different electronic equipment.According to charge storage mechanisms,electrochemical capacitors can be divided into:?1?Electrical double layer capacitors?EDLCs??2?Faradic pseudo-capacitors.With the rapid development of electrochemical technology,hybrid supercapacitorhasemerged.Electrochemical performances of supercapacitors are closely related to the properties of electrode materials,Therefore,researchers have been focusing on developping the electrode materials for supercapacitors to obtain high energy density on the premise of high power density.This work mainly investigates the preparation,for supercapacitor,and research their characterization and electrochemical performance of electrode materials for hybrid supercapacitor in detail,the main work follow as:?1?Two-dimensional surface-modified Ti₂CT_x material was prepared as a cathode material,which possessed a large specific surface area of 41.92 m² g^-1 after urea treatment.The specific capacitance is 267.2 F g^-1 that is higher than 119 F g^-1 of pure Ti₂CT_x at the current density of 1 A g^-1 after 10000 cycles.The assembled AC//N-doped TiO₂ nanoparticles@Ti₂CT_x nanohybrid hybrid supercapacitor can deliver a high energy density of 27.61 Wh kg^-1.Besides,it behaves a good cycling stability and reversibility during the charge-discharge cycling.The excellent electrochemical properties imply that surface-modified Ti₂CT_x may be a promising material for supercapacitors.?2?Ti₂CT_x,Mg-MnO₂ and Ti₂CT_x/Mg-MnO₂ materials were synthesized by solution method.The Ti₂CT_x/Mg-MnO₂ electrode demonstrates excellent electrochemical stabilities with less than 14.8%capacity loss over 1000 cycles at 1 A g^-1.Moreover,AC//Ti₂CT_x/Mg-MnO₂ asymmetric supercapacitor can offer a maximum energy density of 20.68 Wh kg^-1 at power density of 339.95 W kg^-1.It shows the certain application value of Ti₂CT_x/Mg-MnO₂ composite in high performance and long lifetime energy storage devices.?3?Demand for high-performance energy storage materials has motivated researchers to develop new energy materials that benefit from both high-rate and high-capacitance materials.Herein,NiMnO₃,NiMnO₃/Mn₂O₃/NiO and NiMn₂O₄/MnNi₂O₄ have been synthesized through a moderate method and their electrochemical properties have been evaluated as electrode materials.The NiMnO₃sample exhibited a high specific capacitance of 232.08 F g^-1 at a current density of 1A g^-1,which is much higher than other samples(120 F g^-1 for NiMnO₃/Mn₂O₃/NiO and 54.79 F g^-1 for NiMn₂O₄/MnNi₂O₄).Moreover,NiMnO₃ has shown excellent cycle stability with 92.39%capacitance retention over 10000 cycles at 1 A g^-1.Furthermore,aqueous hybrid supercapacitor with NiMnO₃ as a positive electrode and activated carbon?AC?as the negative electrode was assembled in an aqueous hybrid energy storage device.This system displayed a high energy density of 28.71Wh kg^-1.