Electorchemical Performance Of V₂CT_x And Its Composite Material

Energy storage device has been widely applied in daily life.The advantages of lithium ion batteries and supercapacitors in energy density and power density make them into widely attention.Electrode material is an important part of the energy storage devices,because of the increasingly demand for energy storage devices.The development of new electrode materials becomes the focus of attention.Two-dimensional materials cause the attention of people due to the unique electrical,optical and mechanical properties.Among them,MXene materials are the most promising anode materials for LIBs due to their good conductivity and excellent layered structure.The research of this paper mainly focus on the preparation of MXene V₂CT_x material and its composite.Through studying the layered effect of etching time and the influence of layer spacing on the electrochemical properties,specific results are as follows:Commercially vanadium powder,aluminum powder and graphite powder mixture were used to synthesize the MAX phase V2 Al C,by adjusting the sintering temperature we have synthesized high purity MAX phase V2 Al C.The V2 Al C powder was etched by hydrofluoric acid,and we determine the best V₂CT_x layered structure through adjusting the different etching time.XRD,SEM,TEM,FTIR,XPS were used to study the morphology,structure and chemical composition of materials,respectively.And we combine the analysis above with GCPL,CV and EIS to test the materials as anode materials for lithium ion batteries to uncover the relationship between the etching time and electrochemical properties.Results show that the materials of etching time for 20 h exhibit the best layered structure and highest specific capacity,whose capacity is 320 m Ahg^-1 at the current density of 200 m Ag^-1,after 200 cycles.When the current density increased to 2000 m Ag^-1 the capacity still maintains 80 m Ahg^-1.In addition,V₂CT_x showed excellent long cycle performance.Expanding the interlayer spacing of MXene is advantageous to the ion storage.To provide a new way of expanding layer spacing of V₂CT_x material,we create composite material of V₂CT_x mixed with different proportion of Sn O₂ by hydrothermal method.The proportion of compound Sn O₂ were 2 %,5 %,10 %,20 %,30 % and 40 %.The more proportion of Sn O₂,the more obvious characteristics peaks of Sn O₂ showed in the XRD.According to the SEM,V₂CT_x materials were completely wrapped by Sn O₂ and the layered structure disappeared.Combining with GCPL,CV and EIS,the proportion of 10 % demonstrates the best specific capacity which is 560 m Ahg^-1 at 1 Ag^-1.The results show that the synergistic effect between V₂CT_x and Sn O₂ materials not only inhibited the volume expansion of Sn O₂ but also increased interlayer spacing of V₂CT_x.V₂CT_x and Mn O₂ were mixed to create composite materials by microwave hydrothermal way.The proportion of compound Mn O₂ are 10 % and 20 % respectively.XRD,SEM and FTIR were used to analysis the morphology and structure of the material which showed that V₂CT_x/Mn O₂ composite was synthesized successfully.Using CV,GCPL,PEIS,We found that the 10 % materials showed more excellent performance of capacitance in three-electrode system,at sweep speed of 2 m Vs^-1,whose capacitance is 179 Fg^-1.And even at a hihg sweep speed of 50 m Vs^-1,the capacitance is 61 Fg^-1.