Study On Preparation And Electrochemical Performances Of Silica Aerogel

Silica aerogel is made of nanometer level of polyethylene structyre of ultrafine particles into nanometer porous three-dimensional network structure.The material has a large specific surface,large porosity,causing lots of researchers concern.Silica aerogel has been applied to thermal insulation material,catalyst and catalyst carrier,integrated circuit,thermal insulating carrier,detector,etc.however,its potential of applications in lithium ion batteries material were not caused lots of concern.The main purpose of this paper is using the sol-gel method to prepare nano silica aerogel,and used for anode material of lithium ion battery,then explore its electrochemical performance.Surface coating modification and depth reduction are used in order to develop its electrochemical performance.The main content of research is as follows:1.Using the sol-gel method and atmospHeric pressure drying method to prepare nano porous silica aerogel,its particle size is about 50¹50 nm,forming a pore nanomaterial of arrangement by the spHerical particles.The surface of spHerical particles are smooth and flat,also the particles size distribution is concentrated.pH has an obvious effect on the preparation of silica aerogel,and when the pH is 3.2,the performance of silica aerogel is optimal.When it used for anode material of lithium ion battery,the discharge capacity of 2,3,5,10,100,500 cycle is 401、398、394、383、338、310 mAh·g-1 respectively if the current density is 0.1C,and the efficiency of change and discharge is 95%,95.7%,97.7%,97.7%,98.2%,98.1% respectively,delivering a superior efficiency of change and discharge.The second cycle capacity of charge and discharge are 422 mAh·g-1 and 401 m Ah·g-1,coulombic efficiency is 95%.The capacity of charge and discharge are 316 mAh·g-1and 311 mAh·g-1after 499 cycles,coulombic efficiency is 98.4%.The retention rate of charge and discharge during whole cycles is 74.9% and 77.6%,and coulombic efficiency is about95%¹00%,showing the extremely coulombic efficiency and excellent reversibility of charge and discharge.In addition,the rate performance is also excellent.Through the research,the single silica aerogel has low capacity,poor stability when used as anode material of lithium ion battery.2.In an attempt to improve the electrochemical stability,carbon coated on the surface of silica aerogel can improve its stability and avoid the collapse of the structure.Different carbon source and carbon content in the coating process will affectthe electrochemical properties of the composites,when carbon source was sucrose,the carbon content was 10%,electrochemical performance is best.the cycle performance of material life is wonderful,coulombic efficiency distribute in the range of 95% ¹00%.The capacity remain at 98.6% after 399 cycles,delivering a very excellent electrochemical performance.Carbon coating can also singnificantly reduce impedance of electrode.3.Silica aerogel was reduced by magnesium thermal reduction process to obtain nano silicon.XRD analysis shows that the reduction process is very sufficient.electrochemical performance tests shows that the material are activated before the first20 cycles,the second cycle discharge capacity is 698 mAh·g-1 and persistently improved.Discharge capacity increased to 812 mAh·g-1at 20 th cycle.From 32 th cycle,capacity gradually slow down,discharge capacity remains at about 52% after 200 cycles,showing excellent cycle life and cycle stability.In the process of circulation,coulomb efficiency is between 95% 100%.When the density of current increased from 420 to 840,2100,4200,2100 mA·g-1 and then return to 420 m A·g-1,after 125 cycles,the charge and discharge capacitycan retain at 664 and 662 mAh·g-1.Compared to the initial charge and discharge capacity of 710 and 698 mAh·g-1at 420mA·g-1,charge and discharge capacity remains 93.5% and 94.8% respectively,showing an excellent rate performance.In addition,the impedance of electrode is singnificantly reduced compared to the silica aerogel and SiO₂/C compound.