Investigation Of Ti-based Compounds As Anode Materials For Lithium-ion Batteries

Lithium-ion batteries anode materials Li4Ti5O12and TiO2have very specificcharacteristics, such as small volume variation during insertion/desertion of Li+, highsafety and excellent cyclic stability. However, both of them have low electricconductivity. Generally, Li4Ti5O12is synthesized using TiO2with high price as Tisource, which makes high fabrication cost of Li4Ti5O12. In this dissertation, low-priceH2TiO3is exploited as Ti source to synthesis carbon-coated Li4Ti5O12/C rather thanTiO2. Two methods have been used to mix the starting materials, one is supersonicmixing, and the other is vacuum-assisted infiltration. In addition, TiO2mixed withgrapheme(TiO2/GNs) has been synthesized as well as carbon-coated TiO2(TiO2/C)with different carbon content has been synthesized using hydrothermal method. XRD,SEM, TEM, discharge/charge cycling、cyclic voltammetry and AC impedence methodhave been employed to characterize their microstructure and electrochemicalproperties. The results can be summarized as follows:(1) Carbon-coated spinel Li4Ti5O12/C has been synthesized using H2TiO3as Tisource through supersonic mixing and vacuum-assisted infiltration, respectively. Thetwo kinds of Li4Ti5O12/C exhibit secondary aggregate morphology. The aggregationdegree of Li4Ti5O12/C synthesized using supersonic mixing is higher thanvacuum-assisted infiltration. The thickness of the carbon-coating layer is23nm.(2) The electrochemical performance of the vacuum-assisted Li4Ti5O12/C is betterthan that fabricated by supersonic mixing, which has first-cycle charge capacity of169.0mAh/g and coulombic efficiency of99.5%. The discharge capacity retention is97.2%after100cycles at0.1C.(3) Hydrothermally synthesized TiO2using Ti(SO4)2as Ti source is anatase type,which display secondary aggregate morphology. After graphene is added, theaggregate degree of TiO2/GNs composite decreases and graphene is embedded in theTiO2particles.(4) The discharge/charge capacity and rate capability of TiO2/GNs are higher thanTiO2. However, addition of graphene results in low first-cycle coulombic efficiency.(5) The carbon-coated anatase TiO2/C with different carbon content has beensynthesized using glucose as carbon source and Ti(SO4)2as Ti source throughhydrothermal method followed by carbonization at700oC. The aggregate degree ofTiO2/C is low. (6) TiO2/C with carbon content21.39%exhibits the best electrochemical properties.Its reversible capacity is229.0mAh/g after100cycles at0.2C.