Preparation And Electrochemical Performance Of V₂C-MXene-based Anode Materials For Lithium-ion Batteries

With the continuous increase of social energy demand,lithium-ion batteries(LIBs)have become one of the most important energy storage devices due to their high energy density,and the anode material is one of the key factors to affect the performance of LIBs.Traditional graphite anode materials have some defects such as low theoretical specific capacity and poor structural stability.Therefore,it is significant to develop the new anode materials.MXene is a new kind of two-dimensional material,which has a good application prospect in the field of lithium-ion battery anode materials due to its good conductivity and low lithium-ion transport barrier.However,the complex preparation process and low specific capacity of MXene have impeded its practical application.Based on the above analysis,this thesis studied the optimum conditions for preparing V2C-MXene and compound modification and some other methods were adopted to further improve the electrochemical performance of the V2C-MXene material.The specific research results are as follow:(1)V2C-MXene was prepared by a hydrothermal etching method using commercial V2AlC as precusor,and HCl and NaF as etchants.The optimal etching condition was determined through controlling different reaction times.The results showed that the product by etching 72h(V2C-72)exhibited the optimal layered structure and electrochemical performance.The electrochemical test showed that V2C-72 can still maintain a reversible specific capacity of 275.1 mA·g-1 after 50 cycles at 50mA·g-1,and the coulombic efficiency was above 95%,In addition,it also exhibited a reversible specific capacity of 83.7 mAh·g-1 at the high current density of 1A·g-1.(2)The in-situ growth of MoS2 nanosheets on the V2C surface was achieved by hydrothermal reaction and subsequent annealing treatment.The structural characterization of the product showed that some petal-like MoS2 nanosheets were uniformly loaded on the surface of V2C with high crystallinity.The electrochemical test results showed that the V2C@MoS2 composite material exhibits excellent electrochemical performance.At a current density of 50mA·g-1,it can still maintain a reversible specific capacity of 524.4 mA·g-1 after 50 cycles,and at a high current density of 1A·g-1,it also showed a reversible specific capacity of 258.1 mAh·g-1.(3)The V2C@CoNi-LDH composite material was synthesized by one-step hydrothermal process using V2C as the basic material,and nickel nitrate and cobalt nitrate as the nickel source and cobalt source,respectively.The structural characterization of the product showed that a large number of CoNi-LDH nanosheets had grown on the surface of V2C.The electrochemical test results showed that the composite material exhibited a higher reversible specific capacity at the first few cycles.However,after a few cycles,the specific capacity was gradually reduced,and it only delivered a reversible specific capacity of 232.1 mA·g-1 after 50 cycles.The above study shows that the V2C-MXene material exhibits excellent electrical conductivity and lithium storage performance.In addition,V2C-MXene can also compound with other materials as conductive substrastes to improve overall conductivity and stability.Therefore,V2C-MXene is an attractive potential anode material for lithium-ion batteries due to their high research and application value.