Preparation And Performance Optimization Of Nanostructured Tin Dioxide And Silicon Carbon Composite Anode Materials

Since the 21st century,due to the continuous increase in the global population and the rapid development of society,energy demand has shown rapid growth every year.Therefore,it is urgent to find a new type of renewable energy.Lithium-ion battery stands out due to its high energy density and low cost.Therefore,it is very important to find lithium-ion battery with high specific capacity and long cycle life.Because of its high specific capacity,abundant resources of tin and silicon on the earth,low cost of development and utilization,and environmental friendliness,it has been widely studied.However,SnO₂ and Si materials still face several thorny issues:(1)The surface adsorption of nano-structured SnO₂ and Si is strong,and it is very easy to agglomerate during the cycle,which leads to the rapid decrease of capacity;(2)The formation of SEI film during the first cycle leads to excessive loss of initial irreversible capacity;(3)Pure SnO₂ or Si material undergoes huge volume expansion during charging and discharging process,which causes the material to be crushed and separated from the current collector,resulting in a decrease with cycle stability.In order to solve these problems,the volume expansion effect of SnO₂ composite material and the silicon/carbon composite material with a special structure coated by carbon matrix can be effectively suppressed,and the cycle performance and rate performance can be improved.SnCl₂·2H₂O,sodium citrate dihydrate and glucose as raw materials,a one-dimensional junction structure SnO₂/C composite material was successfully obtained through complexation reaction,one-step hydrothermal method and heat treatment as the anode material of lithium ion battery.Compared with pure SnO synthesized without introducing glucose,both the cycle stability and the rate performance were greatly improved.When the mass percentage of SnO₂ reached 35%,it showed the most ideal electrochemical performance.At a current density of 100 mA/g,the first discharge specific capacity of the composite material was as high as 1298 mAh/g,even after the100th cycles,the reversible capacity was still as high as 528 mAh/g,and the coulombic efficiency was 99.3%.At a current density of 500 mA/g,the reversible capacity capacity can still be maintained at 276 mAh/g,and the coulombic efficiency can still reach over 99.0%.The excellent cycle stability and rate performance of SnO₂/C composites can be attributed to the one-dimensional nanowire structure and the introduction of glucose as a carbon source.Micron silicon powder,polyacrylonitrile,graphite,aluminum nitrate nonahydrate as raw materials,a double-carbon coated silicon/carbon composite material doped with alumina was successfully synthesized through mechanical ball milling,low temperature pre-oxidation and high temperature heat treatment.At a current density of 200 mA/g,the first discharge specific capacity was as high as 1293 mAh/g,the charge specific capacity was 1044 mAh/g,the first coulombic efficiency was as high as 80.8%,even after 100 charge-discharge cycles,its reversible specific capacity still maintained a high capacity of 901 mAh/g,and the reversible specific capacity can still be maintained at265 mAh/g at a high current density of 3200 mA/g.The excellent cycle stability and rate performance shown can be attributed to the synergy of Al₂O₃,graphite and amorphous carbon,which improved the conductivity and structural stability of the composite material.