Preparation And Electrochemical Performance Of Silicon-based Two-dimensional Ti₃C₂T_x Composites

With ultra-high theoretical specific capacity(4200 m A h g^-1),lower working potential(?0.4 V vs.Li⁺/Li)and higher abundance,silicon is the most likely candidate to replace graphite anode.However,the poor conductivity and the huge volume change during the cycle limit the practical application of silicon.At present,nanostructured and composite strategies have been proposed to design various silicon-based composite materials to achieve a significant improvement in electrochemical performance.But for silicon materials,what factors are related to the recombination of these materials,and how effective are they?This thesis focused on silicon-based electrodes.First,three most studied materials were selected to construct different silicon-based composites to discuss the improvement of silicon anodes by different matrix materials;Then the optimal matrix material was modified by introducing an amorphous contact interface to solve the problem of poor electrolyte contact interface of the silicon electrode;Finally,a three-dimensional hierarchical interpenetrating conductive network structure was constructed through the matrix electrostatic attraction of carbon nanotubes(CNTs)to solve the problems of poor conductivity and volume expansion of silicon electrode.The main research contents of this paper are as follows:(1)In first part of this paper,silicon-based carbon nanofibers were constructed by electrostatic spinning method and the influences of the addition of MXene,graphene and CNTs on silicon-based electrodes were discussed.The prepared electrodes all showed significantly improved electrochemical performance and different advantages in all aspects of electrochemical performance.The addition of MXene can improve the cycling stability of the electrode,thus achieving a high-capacity retention rate.CNTs are beneficial to the rate performance of the electrode.The addition of graphene oxide can increase the reversible capacity of the electrode.(2)After selecting the MXene matrix material with the best stability,the second part of this paper further constructed porous silicon/MXene composite with an amorphous interface coating by combining the sol-gel and the magnesium thermal reduction method.This design has several advantages:First,Ti₃C₂ can acts as a supporting nanosheet loaded with porous silicon and Si Ox to provide high conductivity for the electrode;Secondly,the combination of Si/Si Ox intermediate layer provides high capacity for the electrode and can alleviate the volume expansion of silicon.Finally,the amorphous Ti O₂ outer layer as a protective layer not only prevents the porous silicon from contacting the electrolyte,thereby depositing a stable solid electrolyte interface film on the surface of the electrode,but also provides low diffusion resistance and fast lithium-ion transport capability.Therefore,Ti₃C₂@Si/Si O_X@Ti O₂ composite with sandwich structure not only showed stable cycle performance(a reversible capacity of 939 m A h g^-1 after 100 cycles),but also obtained improvements in the lithium-ion diffusion coefficient and the capacity retention rate of the first ten cycles compared with Ti₃C₂@Si/Si O_X electrode.(3)In the third part of this paper,one-dimensional CNTs are introduced to construct MXene@Si/CNTs(HIEN-MSC)composites with hierarchical interpenetrating conductive network by electrostatic self-assembly method.The influence of the position of CNTs in the composite on the electrode performance was investigated by modifying different charges in CNTs and changing the addition sequence of materials.The design of the three-dimensional conductive frame can not only promote the rapid transmission of lithium ions,but also ensure the stability of the electrode structure.Therefore,the HIEN-MSC electrode showed excellent rate performance(high reversible capacity of 280 m A h g^-1 at 10 A g^-1)and cyclic stability(reversible capacity of 547 m A h g^-1 after200 cycles at 1 A g^-1).In summary,we summarize the whole paper and point out the shortcomings of this paper.