Study On The Electrochemical Performance Of V₂CT_x MXene As Lithium Ion Battery Anode Materials

Lithium ion battery(LIB)is considered as the most promising electrochemical energy storage device because of its advantages of high energy density,high working voltage,no memory effect and environmental friendliness.It is widely used in all kinds of consumer electronics,hybrid and pure electric vehicles.However,the commercial LIB with graphite(theoretical capacity of 372 mAh g-1)as the anode material has been difficult to meet the current consumer demand for high-energy and high-power energy storage devices,so it is urgent to develop a new anode material with high capacity and high stability.Two dimensional(2D)layered materials are often used as anode materials for LIBs because of their large ion channels and inner space,which can provide a favorable environment for lithium-ion embedding,deblocking and storage.MXene is a 2D transition metal carbon or nitride,which has excellent conductivity and layered structure,and shows great potential as a negative material of LIB.However,the experimental capacity of MXenes as a negative material of LIB is far from theoretical capacity.Therefore,the modification of MXene materials to optimized electrochemical performance has become the focus issue of research.At present,there are two main ways to modify MXene materials.One is to control the kinds of functional groups on the surface of MXene materials to optimize the active sites.The other is to expand the inner space of MXene materials and improve the ion transport.This thesis mainly uses the method of ion pre intercalation to increase the interlayer distance of V2CTx MXene,and then expand the interlayer space of V2CTx MXene,so as to obtain more lithium storage space and faster ion transfer rate.The main research contents are as follows:(1)The multilayer V2CTx MXene with organ like morphology was synthesized by hydrothermal method,and then part of V2CTx MXene was transformed into V2O5 by heat treatment in air atmosphere.The interlayer distance of V2CTx MXene can be expanded by V2O5 junction crystal grown in 2D space,so as to improve the performance of V2CTx MXene as negative active material of LIB,and its weight ratio capacity is increased about one time.(2)By replacing the ions on the inner surface of V2CTx MXene,Ca2+was pre-intercalated into V2CTx MXene.It was found that the pre-intercalated Ca2+ can improve the inner space of V2CTx MXene,and provide a larger lithium storage space and enhance the transport capacity of electrolyte ions.During the charge/discharge process,the interlayer spacing of V2CTx MXene material will continue to increase,and more electrochemical active sites will be exposed,so that the specific capacity of LIB anode will continue to increase with the charge/discharge process.(3)Mn2+ was pre-intercalated into V2CTx MXene by alkalization and liquid-phase impregnation,and V2C-Mn was used as the active material of LIB anode to obtain higher specific capacity,more stable cycle and rate capability.It is found that the electrochemical properties of V2CTx MXene can be further improved by the above process.