The Structure Design And Performance Research Of Silicon Based Anode Material Of Li-ion Battery

With the development and application of electric vehicles and portable electronic devices,the demand for energy storage battery has grown rapidly.The electrochemical energy storage technology represented by lithium-ion batteries has been widely used.The graphite anode materials can no longer meet the current requirements because of its low capacity and poor rate performance,while silicon has become one of the most promising anode materials for lithium-ion batteries due to its high theoretical capacity,low voltage platform and abundant reserves.However,the conductivity of silicon is poor,and the volume expansion during lithiation/delithiation is more than 300%,resulting in poor electrochemical stability.In order to overcome the problems above,silicon was composited with other materials to increase the conductivity and alleviate the volume expansion of the silicon-based material,thus improving the electrochemical performance.Firstly,a new synthetic process was studied for the preparation of Si@TiN@NC double-coated structure.Titanium dioxide layer and carbon layer were coated on the surface of micron silicon by liquid phase method.After heat treatment,Si@TiN@NC was obtained.In order to improve its processing performance,the compounds are formed into thick film by a tape casting method before heat treatment,so as to achieve the goal of easy grinding to powder.The effects of different thickness of titanium dioxide layer and carbonization temperature on the cycling and rate performance of Si@TiN@NC were studied to optimize the processing conditions.At the same time,the effects of different carbon contents on the electrochemical properties of Si@TiN@NC materials were investigated to obtain optimized components.The experimental results show that the Si@TiN@NC anode material demonstrates the best electrochemical performance when the TBOT content is 4 ml,the carbonization temperature is 1100?and the carbon content is 29.9%.The reversible capacity and capacity retention remain as high as 1420.1 mAh g^-11 and 86.8%after 200 cycles at a current density of 0.4 A g^-1,respectively.Even at 8A g^-1,the reversible capacity is still as high as 1080 mAh g^-1.when cycled at 4 A g^-1,the capacity can maintain 1024.2 mAh g^-11 after 550 cycles.The drastically enhanced cycling performance and rate capability of Si@TiN@NC can be ascribed to the good conductivity of TiN and the buffering effect of NC.A Si/C composite with the"Pitaya"structure was prepared by the combination of hydrothermal method and magnesiothermic reduction method.The effects of fructose content on the morphology,structure and electrochemical properties of Si/C were systematically studied to obtain the optimum Si/C composite.The experimental results show that the structure of Si/C particles prepared by TEOS and fructose at the molar ratio of 3:2 is similar to that of"pitaya pulp",and its electrochemical performance is the best.The capacity can remain as high as 84.8%after 300 cycles at a current density of 0.4 A g^-1.Furthermore,the reversible capacity can maintain 730.3 mAh g^-11 after 1000 cycles at a current density of 4 A g^-1.The excellent electrochemical performance of Si/C composite can be attributed to its unique structure with the tiny silicon nanoparticles uniformly embedded in the porous carbon matrix,which can improve the conductivity and alleviate the volume change during cycling.The results of this thesis show that the composite anode material with Si and high conductive materials such as TiN and C has the characteristics of stable structure and low cost,and this strategy can effectively enhance the conductivity of the silicon-based anode and alleviate its volume expansion,thus improving the electrochemical stability and kinetic performance.It is expected that this strategy can promote the application of Si anode in Li-ion battery.