Study On The Intercalation Reaction Of Ti₃C₂T_x, The Preparation Of Fiber Electrode Materials And Their Capacitance Properties

The development of mobile electronic devices has greatly facilitated people's live,and it has also promoted the vigorous development of wearable flexible electronic devices.Flexible fiber supercapacitors not only have small volume,good flexibility,good electrochemical stability at any bending angle,but also have the advantages of high power density,fast charge and discharge speed and long cycle life.Therefore,it has broad application prospects in the field of wearable flexible electronic devices.For flexible fiber supercapacitors with high performance,how to achieve an optimal balance between fiber electrode material flexibility and energy density is one of the main bottlenecks that need to be solved.In this thesis,at first,the intercalation reaction and exfoliation behavior of titanium carbide(Ti3C2Tx)with two-dimensional layer structure was systematically studied by using tetraalkylamine hydroxide with different sizes.Secondly,the delaminated Ti3C2Tx nanosheets with high conductivity,good hydrophilicity and large specific surface area was mixed with graphene oxide(GO)with liquid crystal phase.Ti3C2Tx/GO flexible fiber was assembled by a wet spinning technique,further it was reduced in HI solution,Ti3C2Tx/RGO flexible fiber with excellent mechanical properties was obtained.Then Ti3C2Tx/RGO flexible fiber was soaked in different KMnO4 solutions,MnO2/Ti3C2Tx/RGO composite flexible fibers with high volume specific capacitance and good flexibility were finally prepared.By using MnO2/Ti3C2Tx/RGO composite flexible fibers with high volume specific capacitance and good flexibility as positive and negative electrode,all-solid-state MnO2/Ti3C2Tx/RGO symmetrical flexible fiber supercapacitors was assembled.The obtaind electrode materials and the assembled all-solid-state symmetrical fiber supercapacitor were systematically characterized from their structure,morphology,mechanical properties and electrochemical performance.The whole thesis includes five chapters.The first chapter is the introduction.It mainly introduces the overview of all-solid-state flexible fiber supercapacitors,and the structure,preparation,classification and application of two-dimensional layered titanium carbide,graphene and manganese dioxide electrode materials,and the application and challenge as fiber electrode materials.Chapter 2 to 4 are the experimental parts and result discussion,including the intercalation and delamination behavior of Ti3C2Tx,preparation and properties of MnO2/Ti3C2Tx/RGO hybrid fiber electrode materials,and the assembly and capacitance properties of all-solid-state MnO2/Ti3C2Tx/RGO flexible fiber supercapacitors.The summary is shown in Chapter 5.The main research contents are as follows:(1)Using MAX phase Ti3AIC2 as the precursor and HF as the etchant,a multilayer Ti3C2Tx was obtained after a long time of stirring and etching.The intercalation reaction of layered Ti3C2Tx was carried out by tetraalkylammonium cations(TAA+).The relationship between the layer spacing of layered compounds and the size of intercalated ions was studied by changing the size of tetraalkylammonium cations.The different chain length tetraalkylammonium cations can be quickly intercalated into the Ti3C2Tx layer to increase the interlayer spacing.The increase of the interlayer spacing was related to the size of the intercalated alkylamine ions,but the intercalation amount was almost independent of the lamellar compound ion exchange.The basal spacing for TMA+and TEA+intercalated Ti3C2Tx products was 1.50 nm,while the basal spacing for TPA+and TBA+intercalated products was 1.73 nm and 1.86 nm,respectively.The tetraalkylammonium ion intercalated Ti3C2Tx product was further subjected to oscillating treatment,the layered Ti3C2Tx was delaminated in an aqueous medium consisted of TAA+ions,and Ti3C2Tx nanosheets with a single layer or a small layers were obtained.(2)Ti3C2Tx/RGO fibers were prepared by wet spinning and hydriodic acid reduction by using Ti3C2Tx nanosheets and liquid crystal phase GO nanosheets as basic assembly units.MnO2/Ti3C2Tx/RGO hybrid flexible fibers were prepared by in situ growth of MnO2 nanosheets on the surface of Ti3C2Tx/RGO fibers with different concentrations of KMnO4 as manganese source.The structure,morphology,mechanical properties and electrochemical properties of the prepared hybrid fibers were systematically investigated.MnO2 nanosheets were grown in situ on the surface of hybrid fibers,the volumetric capacitance of MnO2(0.03)/Ti3C2Tx/RGO composite fibers in 1 M Na2SO4 electrolyte was as high as 851 F cm-3 when the Mno2 loading amount was 29%.At the same time,the hybrid fiber had good flexibility and mechanical properties,and can be knotted and woven into the fabric without breaking.The combination of Ti3C2Tx nanosheets and RGO nanosheets can effectively inhibit the agglomeration and stacking of the sheets,it was beneficial to the transport of electrolyte ions.The in-situ growth of MnO2 nanosheets was in full contact with the electrolyte,it was beneficial for storing more charges.The synergistic effect between the highly conductive Ti3C2Tx nanosheets and the RGO nanosheets and MnO2 provides a new way to prepare Ti3C2Tx-based composite fiber electrodes with high capacity.(3)MnO2(0.03)/Ti3C2Tx/RGO composite fibers with high specific capacity and flexibility were selected as positive and negative electrodes respectively,and PVA-LiCl was used as gel electrolyte,all-solid-state MnO2(0.03)/Ti3C2Tx/RGO symmetry fiber supercapacitor was assembled by tight winding technique.The volumetric specific capacitance of the assembled MnO2(0.03)/Ti3C2Tx/RGO symmetric fiber supercapacitor at a current density of 20 mA cm-3 was 24 F cm-3,it was still 18 F cm-3 when the current density was increased to 200 mA cm-3,and its capacitance retention was 75%.At the same time,at a scanning speed of 20 mV s-1,the capacity retention of the fiber capacitor after cycling for 10000 cycles can reach 92%,showing excellent cycle stability.The assembled fiber capacitors had good power density and energy density,and the volumetric energy density can reach 2.13 mWh cm-3 when the volume power density was 8.16 mW cm-3.In addition,the capacitance retention after 90 0 continuous bending for 1000 times was 95%.The excellent mechanical properties and electrochemical stability of MnO2(0.03)/Ti3C2Tx/RGO symmetric fiber capacitors under different bending conditions showd that they have application prospects in the field of wearable energy storage devices.