Study On The Development And Application Of Silica-based Composite Materials For Lithium Ion Batteries

With the continuous development of clean energy,the demand for lithium-ion batteries has increased exponentially in the past few decades.Electric vehicles and other devices that require long cycle life and high energy storage density are emerging in an endless stream,which puts forward higher requirements for the electrochemical performance of lithium-ion batteries.In the composition system of lithium-ion batteries,the negative electrode material plays an extremely important role.Silica(Si O₂)is one of the cheapest and most abundant resources on the planet.It has a high theoretical specific capacity(1965 m Ah g^-1),a lower discharge voltage platform,a higher energy density and environmental friendliness,etc.Many advantages have attracted more and more attention from researchers.However,as a negative electrode material,silicon dioxide will experience a huge(340%)volume expansion during the charge and discharge cycle,destroying the overall structure of the material,causing irreversible capacity loss and large reversible capacity degradation;on the other hand,due to Its inherent low conductivity will have a negative impact on the insertion and extraction of lithium ions between the positive and negative electrodes,reduce the electronic conductivity,and affect the long-cycle performance and rate performance of the material.At present,researchers use methods such as constructing special structures,reducing particle size,and synthesizing composite materials to cope with the challenges faced by silica as a negative electrode material for lithium-ion batteries.Based on this,this paper uses the special hollow structure of silica as the basis to explore the influence of coating type,precursor ratio and calcination temperature on carbon coated silica composite,analyzes the electrochemical performance of the system,and interprets the internal mechanism.First,we used polyacrylic acid(PAA)as the template and tetraethyl orthosilicate(TEOS)as the silicon source to prepare hollow silica nanospheres(HSi O₂).On the basis of HSi O₂,we explored the electrochemical performance of carbon-coated HSi O₂@C composites prepared by using sucrose,polyvinylpyrrolidone(PVP)and phenolic resinas as carbon sources.The experimental results show that the morphology of HSi O₂@C prepared using phenolic resin as the carbon source is smooth and dispersed.After 200 cycles of charging and discharging at a current density of 200 m A g^-1,its reversible specific capacity reaches 751 m Ah g^-1,which is better than the composite materials prepared using sucrose and PVP,and shows better cycle performance and rate performance.Then,based on the previous experiments,we continue to use PAA as template,TEOS as silicon source and phenolic resin as carbon source to prepare HSi O₂composites with the ratio of silica to phenolic resin of 1:1,1:2 and 1:3.By means of chemical characterization and electrochemical performance analysis,it is found that when the mixing ratio of 1:2 is used,the morphology of the composites is more uniform,After 200 cycles of charging and discharging at a current density of200 m A g^-1,the reversible specific capacity of the composite reaches 748.1 m Ah g^-1,and its electrochemical performance is better than that of the composite prepared with other mixing ratios.Finally,on the basis of the above work,we continue to use PAA as the template,TEOS as the silicon source,and phenolic resin as the carbon source,control the 1:2 mixing ratio of silica and phenolic resin,and prepare HSi O₂@C at different calcination temperatures,explore the calcination temperature that can make the negative electrode material show the best electrochemical performance.The results show that when the calcination temperature is maintained at 800°C,the sample has a uniformly coated and dispersed carbon layer.After 200 cycles of charging and discharging at a current density of 200 m A g^-1,its reversible specific capacity reached 903 m Ah g^-1,and the cycle performance and rate performance were greatly improved.The above experimental research results show that by constructing a unique structure,selecting appropriate precursors,mastering the ratio of precursors used,and controlling appropriate calcination temperature and other conditions when preparing composite materials,the reversible capacity,cycle performance,rate performance,charge-discharge cycle stability and cycle life of the electrode system can be significantly improved.