Study On The Preparation And Characteristics Of TiO₂-based Anode Materials Of Lithium-ion Batteries In Energy Storage Systems For Vehicles

In recent years,as one of the means of transportation,new energy vehicles with the advantages of environmental friendliness have been strongly support by the government and achieved rapid development.As one of the main energy storage systems for new energy vehicle,lithium-ion battery is widely favored due to its a series of advantages,such as good cycle stability,high energy density,environmental friendliness,no memory effect,and ease of assembly.At present,lithium-ion batteries with graphite as the anode have serious safety hazards.With the frequent reports of news about the burning or explosion of lithium-ion batteries in recent years,the safety issues of lithium-ion batteries have further attracted the attention of researchers.As an intercalation type anode material,TiO₂can effectively avoid the formation of lithium dendrites due to its high lithium insertion potential,which greatly improves the safety performance of lithium ion batteries.Therefore,in order to improve the electrochemical performance of TiO₂,this paper prepared four TiO₂-based composite materials through reasonable microstructure construction and regulation,and the relationship between structure and electrochemical performance is deeply studied.The main research work and results are as follows:（1）Using titanyl sulfate as the titanium source and mixing organic alcohols as the solvent,hierarchical HMR-TiO₂@C microrods composed of nanosheets are synthesized through a one-step solvothermal method followed by a calcination process.The effects of carbon layer and calcination temperature on the structure morphology,electrochemical performance and kinetic performance of the composite material were studied.The results show that the presence of the carbon layer prevents the breakage of the nanosheets and inhibits the crystal growth of TiO₂,which effectively improves the cycle stability and rate performance of the composite material.The composite material delivers a reversible specific capacity of 484.7 m A h g^-1with a capacity retention rate of 85.8%after 100 cycles at a current density of 0.2 A g^-1.It still exhibits a high reversible specific capacity of 276.3 m A h g^-1at a high current density of 5.0 A g^-1.The kinetic results show that the presence of the carbon layer reduce the charge transfer steric hindrance of the composite material and increase the lithium ion diffusion rate.The electrochemical performance of composite material is seriously affected by the calcination temperature,in which the too low or too high temperature is harmful to its electrochemical performance.When the calcination temperature is 500°C,the composite material exhibits the best electrochemical performance.（2）In order to effectively utilize the pseudocapacitive lithium storage effect induced by nano-TiO₂and study the influence of carbon layer thickness on electrochemical performance and kinetic performance of TiO₂,the ultrafine TiO₂nanoparticles prepared by the microemulsion method are used as the basis,and phenolic resin is used as the carbon source.The porous SNs-TiO₂@C composites with different carbon coating thicknesses were prepared by adjusting the dosage of SNs-TiO₂.The results are shown as follows:In the composite material,the SNs-TiO₂are completely confined in the carbon coating layer.The existence of the carbon coating layer not only prevents the collapse of the composite material structure,but also effectively inhibits the agglomeration of TiO₂,which greatly increases the contribution of the pseudocapacitor lithium storage.The calculation shows that when the CV scan rate is 1 m V s^-1,its pseudocapacitive contribution is as high as 69.78%.The difference thickness of the carbon layer has no effect on the cycle stability of composite material.It affects the overall reversible specific capacity and dynamic performance of the composite material.When the dosage of SNs-TiO₂is 0.4 g,the thickness of the carbon coating layer is moderate,showing the best electrochemical lithium storage performance.An excessively thick carbon layer not only reduces the diffusion rate of Li⁺,but also causes a reduction of overall specific capacity due to the high proportion of carbon.When the carbon layer is too thin,it will increase the charge transfer steric hindrance,which decreasing the electrochemical performance of the composite material.（3）In order to increase the volumetric energy density and first coulombic efficiency of TiO₂,tetrabutyl titanate was used as the titanium source,phenolic resin was used as the carbon source,and low-porosity LP-TiO₂@C microspheres were prepared based on the surface-restricted in-situ growth mechanism.The structure and electrochemical lithium storage and sodium storage performance of the composite material are studied.The results show that:in this structure,TiO₂particles with oxygen vacancies are uniformly embedded in the interior and surface of the carbon microspheres.Benefiting from this highly composite structure,when the LP-TiO₂@C is used as a lithium-ion battery anode material,its coulombic efficiency is increased to 75%for the first time.At the same time,it also exhibits excellent electrochemical lithium storage performance.The reversible specific capacity is 426.7 m A h g^-1with a capacity retention rate of 91.5%after 200 cycles at a current density of 0.2 A g^-1.When the current density is 5 A g^-1,it delivers a reversible specific capacity is 210.1 m A h g^-1.As a anode material for sodium ion batteries,it also exhibits excellent sodium storage performance.The reversible specific capacity is 301 m A h g^-1after 200 cycles at a current density of 0.1 A g^-1,and the reversible specific capacity is 150 m A h g^-1when the current density increased to 2 A g^-1.（4）In order to further increase the energy density of the TiO₂-based composite material,TiO₂@Sn O₂@C composite materials with a controllable Ti/Sn ratio are prepared base on the surface-restricted in-situ growth mechanism.The effect of Ti/Sn ratio on the electrochemical lithium storage performance of composite materials was studied.The results show that:in the composite material,the presence of TiO₂not only acts as a mechanical buffer,but also greatly increases the reduction potential of Sn O₂to Sn.When the proportion of TiO₂in the composite material is too low,the large volume expansion of Sn O₂cannot be well alleviated,which causes the gradual attenuation of its reversible capacity.When the proportion of TiO₂is too high,it can well alleviate the volume expansion of Sn O₂and obtain a high capacity retention rate.However,the overall reversible specific capacity of the composite material is low.When the ratio of Ti/Sn is 1:1,the composite material shows the best electrochemical lithium storage performance.The reversible specific capacity is 769.1 m A h g^-1with a capacity retention rate of 85.5%after 100 cycles at a current density of 0.2 A g^-1.When the current density is increased to 10 A g^-1,it still exhibits a high reversible specific capacity of 422.3 m A h g^-1.