Study On The Preparation And Modification Of Anode Material Li₄Ti₅O₁₂ For Lithium-Ion Battery

The spinel Li₄Ti₅O₁₂ which has three-dimensional diffusion channel of lithium ion channels and"zero-strain"property has excellent cycling performance with high rate capability and long cycle life. Its raw material is wide variety of sources and inexpensive. In this paper, Li₄Ti₅O₁₂ spinel was synthesized by solid-state method and modified by carbon coating and metal ions doping. The phase composition and crystal structure was analysed by X-Ray Diffraction (XRD). The superficial morphology and coating effects was observed by Scanning Electron Microscope (SEM) and Transmission Electron Microscope(TEM). The X-ray Photoelectron Spectroscopy(XPS) was employed to study the valence of sample and the Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscope (EIS) was used to discuss the behavior of Li ion insertion and extraction. The specific capacity and cyclic properties was studied by charge-discharge test.First of all, the Li₂CO₃ and TiO₂ were chose as the raw material to get the best performance. The influence of sintering temperature and time were studied and the results showed that the optimal performance could be achieved by sintering at 650℃for 16 hours. Its reversible capacity was 165mAh·g^-1 (1C),164mAh·g^-1 (3C),137mAh·g^-1 (5C) and 120mAh·g^-1 (10C). The spinel Li₄Ti₅O₁₂ showed excellent cycling performance, after 1600 cycles, capacity retention rates were 98%(1C),91%(3C) and 89%(5C), respectively.Second, lithium titanate with carbon coating was researched. Sucrose,graphite,CNTs and Super-P-Li were used as carbon source to increase the conductivity of lithium titanate. The SEM images showed that the Super-P-Li particles joined together and formed three-dimensional carbon network which prevented Li₄Ti₅O₁₂ particles to grow up. The Li₄Ti₅O₁₂/Super-P-Li composite had better rate performance and the capacity was 160mAh·g^-1 (0.5C),156mAh·g^-1 (3C),135mAh·g^-1 (5C),124mAh·g^-1 (10C). The TEM analysis showed that the sucrose could form uniform carbon film on Li₄Ti₅O₁₂ particles which improved the conductivity. The capacity of the sample was 165mAh·g^-1,145mAh·g^-1,127mAh·g^-1,115mAh·g^-1 at the rate of 1C,3C,5C,10C. The Li₄Ti₅O₁₂/C composite as negative electrode and LiFePO₄ as positive electrode were assembled into battery and its performance was researched. The Li₄Ti₅O₁₂ matched well with the system, the discharge platform of the battery was 1.8V and charging platform was 2.0V. After 50 cycles, the capacity retention was 92% (0.5C).At last, Mg and Ti₂O₃ were adopted to improve electrochemical performance of Li₄Ti₅O₁₂. The X-Ray Diffraction test indicated that Mg doping causesd the lattice parameters of Li₄Ti₅O₁₂ to become larger and produce TiO2 which has negative effect on material conductivity and Li ion diffusion. The capacity of Li_4-2xMgxTi₅O₁₂(x=0.1) was 156mAh·g^-1. Ti₂O₃ doping can creat Ti³⁺/Ti⁴⁺ which increase material conductivity. The X-Ray Diffraction test showed that there were characteristic diffraction peaks of LiTi₂O₄ in products, and the XPS test also certificated the existence of Ti³⁺. The sample doped with 1% Ti₂O₃ exhibited the best electrochemical performance, the capacity is 155mAh·g-¹at the rate of 1C.