| Energy storage is an extremely important direction of scientific development in the current era.Among the devices with high efficiency energy storage,lithium ion battery is the most widely used.Lithium-ion batteries,which have the advantages of high energy density,long cycle life,small self-discharge,no hysteresis and little impact on the environment,have been widely studied around the world and are widely used in many practical applications such as electric vehicles and portable electronic equipment.The MAX phase has a unique layered structure with excellent electrical conductivity,mechanical strength,and ductility,where M represents early transition metals(Sc,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,etc.),A represents transition metal elements,and X represents carbon and/or nitrogen.MXenes(transition metal carbides,carbonitrides and nitrides)are two-dimensional layered materials prepared by MAX precursor.They have been proved to have good conductivity and lithium ion storage performance;The electrode material of lithium ion battery with excellent performance could be prepared by combining MAX with MXene.In addition,many different carbon nanomaterials,such as carbon nanofibers and carbon nanotubes,have gradually been widely used in energy storage devices due to their advantages such as high conductivity,large specific surface area and stable energy storage performance.By combining them with the above MAX materials to prepare composite materials,lithium storage performance of these materials can be improved.Transition metal carbides,carbon nitrides,and nitrides(MXenes)are proven to possess good conductivity and lithium ion storage performance,so they are excellent electrode materials for lithium ion batteries.The general formula of MXene is Mn+1XnTx(n=1-3),where M represents an early transition metal(Sc,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,etc.),X is carbon and/or nitrogen,and Tx stands for surface terminations.The unique layered structure of the MAX phase also has excellent electrical conductivity,mechanical strength and malleability,meaning that it can fully combine the advantages of MXenes and A-site transition metal elements.In addition,many different carbon nanomaterials,such as carbon nanofibers and carbon nanotubes,are gradually being widely used in energy storage devices.In this paper,based on Ti2SnC MAX phase,three kinds of anode materials for lithium ion batteries were designed and adjusted,and their structure,morphology,battery capacity,rate performance and other electrochemical properties were studied.The main contents are as follows:(1)In view of the poor capacity of Ti2SnC MAX phase as the anode electrode of lithium ion batteries,this study successfully prepared Ti2SnC with high lithium capacity as the anode electrode material of lithium ion batteries by in-situ preparation of SnO2.The results showed that SnO2 was formed in-situ in the Ti2SnC MAX phases calcined at 800℃ and 1200℃.The morphology of SnO2 was granular with particle size ranging from 100 nm to 1 μm.After calcination at 800℃,with the formation of TiC whisker conducive to capacity improvement,the initial specific capacity reached 377.0 mAh·g-1 and 371.0 mAh·g-1 at high current density of 0.4 A·g-1 and 1.0 A·g-1,respectively.Without any treatment,the specific capacity of Ti2SnC at the same current density was 32.0 mAh·g-1 and 30.0 mAh·g-1,respectively.(2)In view of the fast capacity decay of Ti2SnC MAX phase when it is used as the anode electrode of lithium ion battery,this study successfully combined it with carbon nanofibers(CNFs)of different proportions by electrospinning,and prepared composite Ti2SnC/CNFs as the anode electrode material of lithium ion battery.The results showed that Ti2SnC/CNFs has uniform nanofiber structure.As an anode material,the material has stable lithium ion storage capacity.At high current density of 1.OA·g-1,the stable specific capacity can reach 367.5 mAh·g-1 after 500 cycles.At different current densities,the capacity retention rate reached 96.4%,and the first coulombic efficiency reached 88.6%.(3)In view of the simple structure of Ti2SnC/CNFs carbon nanofiber composite and the problems that the comprehensive electrochemical performance needs to be improved,hollow core-shell structured composite Ti3C2@Ti2SnC/CNFs(MXene@TSC/C)was successfully prepared by coaxial electrospinning as the anode material of lithium ion battery.The results showed that MXene@TSC/C has an obvious and uniform hollow core-shell carbon nanofiber structure.The composite has a specific capacity of 288.9 mAh·g-1 after 300 cycles at a current density of 0.4 A·g-1,which was attributed to the stable core-shell structure of carbon nanofibers.The addition of Ti3C2 MXene improved the capacity,and the capacity retention rate reached 105.4%in the performance test.At the scanning rate of 1.0 mV·s-1,the contribution rate of pseudocapacitance of the energy storage mechanism reached 66.4%. |
