Synthesis And Lithium Storage Performance Of 2d Materials(V_x,Ti_1-x)₂C

As a host of new two-dimentional materials,MXenes have become promising candidates for energy storage applications such as LIBs for their superior properties of good hydrophilia,chemical stabilities,tunable chemical composition,high specific surface area and low Li+diffusion energy barrier characteristics.Nevertheless,the high energy density and power density LIBs is becoming more and more meaningful with the rapid development of electronic information industry and electric vehicle industry,the enhancement of electrochemical performance in MXenes-based electrodes is still needed.MXenes5 rich chemical tunability also provides an effective way of optimizing their performance.In this paper,chemical exfoliation of MAX(Vx,Ti1-x)2AlC(x=1,0.7,0.5,0.3,0)phases is employed to synthesize solid solution MXene(Vx,Ti1-x)2C,on which oxidation and composite methods are carried out to enhance MXenes' electrochemical properties.Both the exfoliated MXene and their derivatives are used as the anodes for LIBs.Firstly,raw materials including vanadium(V),titanium(Ti),aluminum(Al)and carbon(C)are used to sinter solid solution(Vx,Ti1-x)2AlC precursors.LiF+HCl is used as the etchant to selectly etch Al layers and prepare corresponding MXene(Vx,Ti1-x)2C layered materials.The resulted(Vx,Ti1-x)2C is measured by XRD and SEM,showing that the etching time of(Vx,Ti1-x)2C with different ingredients becomes shorter because of the more content of Ti in MXene.Secondly,the obtained(Vx,Ti1-x)2C are tested as anode materials for LIB s by galvanostatic charge-discharge(GCV),electrochemical impedance spectroscopy(EIS)and cyclic voltammetry(CV).From which,we find that compared to the end members V2C and Ti2C,solid solution(Vx,Til_X)2C exhibit better electrochemical performance with more stable and more tunable layered structure under the synergy of two kinds of metal elements V and Ti.And the electrochemical performance is optimized for the compound of(V0.5,Tio.5)2C which possesses the highest reversible capacity of 204.9 mAh g-1 and a coulombic efficiency of nearly 100%at 1 A g-1.The heteroatoms in M site of MXene are responsible for the enhanced lithium storage performance.Finally,Two methods for improving the electrochemical performance are described by taking(V0.5,Ti0.5)2C as an example.On the one hand,the surface modification treatment of(V0.5,Ti0.5)2C is carried out by microwave-induced oxidation.It' s found that the surface of the(V0.5,Ti0.5)2C is covered with vanadium/titanium oxides,which results in an increasing interlayer spacing with the original two-dimensional morphology remains.And the cycling stability and rate performance are significantly improved:the resulting product has a reversible capacity of 291.9 mAh g"1 after 200 cycles at 1 A g"1,stable coulomb efficiency is also close to 100%.On the other hand,Sn02-(V0.5,Ti0.5)2C nano-composite was synthesized by hydrothermally combining SnO2 with(V0.5,TiO.5)2C.Since SnO2 can alleviate the re-stacking of(V0.5,Ti0.5)2C sheets,which is beneficial to the intercalation-deintercalation of Li+,and the(V0.5,TiO.5)2C matrix can reduce the agglomeration of SnO2 nanoparticles,so does its volume expansion inhibiton.The composite owns a higher lithium storage capacity.The results show that the first discharge capacitiy of SnO2-(V0.5,TiO.5)2C reach up to 1137.0 mAh g-1,and its reversible capacity remains at 200.3 mAh g-1 after 100 cycles,hinting that the electrochemical performance of SnO2-(V0.5,TiO.5)2C nanocomposites is better than that of the previous(V0.5,TiO.5)2C.