Preparation And Energy-Storage Properties Of Transition Metal Oxides/Nanoporous Carbon Tube Textile Composite Materials

Supercapacitors have the advantages of high power density and long life,allowing many applications in such as electric vehicles,smart grid,backup power system,and consumer electronics.With the rapid development of flexible electronics,it is particularly urgent to develop high-performance all-solid-state flexible supercapacitors.However,on the one hand,most of the reported metal matrix cannot achieve large deformations.In contrast,carbon fiber cloth has advantages in flexibility,but the common commercial carbon cloth as a flexible substrate has problems such as high price,small specific surface area,and poor binding force with grown materials.On the other hand,low-cost pseudo-capacitance transition metal oxides materials,cannot meet the requirements of long-term charge-dischage cycles when they work as small units.In this thesis,a new idea of one-step preparation is proposed.The transition metal oxide nanostructures are grown by in-situ nucleation while cotton is carbonized at high temperature,so as to construct a new composite flexible electrode material.The formation mechanism of suchcomposite structure is discussed in detail and the method is extended to other transition metal systems.The effects of material structure on electrochemical properties were analyzed,and flexible solid state devices with high performance were designed and assembled.The main contents are summarized as follows:(1)T-shirts of cotton fiber cloth as raw material,through the two step ultrasonic immersion in alkaline solution activation treatment,then in inert atmosphere next high temperature carbonization,each a piece of cotton fiber surface generated in the process of carbide many that acquired flexible nanoporous tubes fiber cloth(NPCTT),but also grow in situ Fe2O3 nanobelts arrays,Fe2O3/NPCTT composite electrode material success.By discussing the effect of reactant concentration on nanostructure and properties,the specific capacitance of the material can be improved to the greatest extent.We discussed the formation mechanism of this special structure.The new composite electrode can be bent and folded at any angle,and has high specific capacitance and good cycling stability:the area capacitance reaches 1846 mF cm-2(current density 1 mA cm-2);After charge-discharge 10,000 cycles at a high current density of 20 mA cm-2,the capacitance lost is only 4.8%.The assembled solid-state symmetric device delivers an energy density of 176 ?Wh cm-2(power density 748?W cm-2)and an 85%capacitance retention after 5,000 cycles(2)With the same experimental scheme as mentioned above,the MnO/NPCTT composite electrode materials were prepared by adjusting the concentration of Mn2+and optimizing the reaction conditions.In the optimized product,MnO was obtained in the presence of nanoparticles with a diameter of about 200 nm.The composite structure of porous NPCTT with high specific surface area and nanoparticles endowed the electrode with an areal specific capacitance of up to 933 mF cm-2(current density of 1 mA cm-2).All solid-state asymmetric devices(ASC)were assembled with the Fe2O3/NPCTT as the positive electrode and MnO/NPCTT as the negative electrode.The ASC has an energy density of 176 ?Wh cm-2(power density 750 ?W cm-2).Its capacitance retention reaches 75%after 3,000 charge-discharge cycles.