Synthesis And Mechanism Of MXenes Electrodes In Energy Storage

MXenes,a family of two-dimensional transitionmetal carbide and/or nitride materials,are supposed to be promising materials in electrochemical energy storage field because of their high electronic conductivity,hydrophilic surface and excellent mechanical properties.However,the low capacity and capacitance of MXenes limit their application in electrochemical energy storage.To solve this problem,many different methods have been tried to improve the electrochemical energy storage performance of MXene themselves in this thesis.Meanwhile,many MXene based electrode materials have been prepared,and show great performance in lithium-ion batteries and supercapacitors applications.The research contents and results are as follows:(1)Considering the high theoretical capacities of the Al element by alloying with lithium,partially etched Ti₃AlC₂ anode material is prepared in this study.The physical characterization and electrochemical test confirm that the residual Al element provides capacity contribution by alloying reaction during the discharge process.An impressive volumetric capacity of 331.6 m A h cm^–3 has been achieved with partially etched Ti₃AlC₂,and over 99%capacity retention was observed even after 1000 cycles.This performance is much better than that of the the completely etched Ti₃C₂T_x anode.This work innovatively makes use of the“A”elements which usually removed in MXene research to improve the anode performance of MXene materials,and provides a new idea to research MXene materials.(2)N-butyllithium is firstly applied to forming–O by the–F terminal groups on Ti₃C₂T_x MXene,in order to improve its electrochemical energy storage performance.The n-Bu Li-treated multi-layer Ti₃C₂T_x achieved 225 m A h g^–1 as the lithium-ion battery anode material.Moreover,in supercapacitor,the capacitance of n-Bu Li-treated multi-layer Ti₃C₂T_x and n-Bu Li-treated few layer Ti₃C₂T_x is 354,523 F g^–1,respectively.Compared with traditional alkalization treatment method,the n-Bu Li-treated Ti₃C₂T_xpossesses much more–O and limited–F terminal groups without damage on the surface structure.This study may provide a universal strategy for the modification of the MXene family.(3)We prepared completely etched V₂CT_x with HF by an improved etching process,and then treated the V₂CT_x by n-Bu Li and Na OH+Na BH₄.Electrochemical test shows that the capacitance of V₂CT_x,n-Bu Li-treated V₂CT_x and Na OH+Na BH₄ treated V₂CT_xare 304,478,302 F g^–1,respectively.Moreover,the life test shows that the capacitance retention of the n-Bu Li-treated V₂CT_x is 97.5%after 10000 cycles.This study demonstrates the great potential of V₂CT_x MXene material in electrochemical energy storage,and provides the research foundation for the preparation and modification of various MXene materials.