Preparation Of Lithium Titanate Composite And Its Electrochemical Properties

With the appearance of energy crisis and environmental pollution problems caused by fossil energy, lithium ion battery representing clean energy has become an important research direction, and has been gradually applied electric vehicles、 hybrid electric vehicles and so on. "Zero strain" materials of spinel lithium titanate Li₄Ti₅O₁₂ has good cycle performance, high voltage and large energy density, but low theoretical capacity（175mAh/g） and conductivit（10-13Scm-1） limit its commercial development. To get fast kinetics for both transported Li+ ions and electrons,Li₄Ti₅O₁₂/TiO2 nanocomposites、Li₄Ti₅O₁₂/RGO nanocomposites and RGO/AB （acetylene black） mixed conductives are designed 。The precursor of Li₄Ti₅O₁₂/TiO2 is prepared by hydrothermal method at 130℃ for 24h with a Li/Ti molar ratio of 4:5. The effects of TiO2 on Li₄Ti₅O₁₂/TiO2 nanocomposites are studied under different calcination temperature and time.The precursor is first calcined at 400℃ for 5h and then heated at 500℃ for 5h in air.The SEM image clearly shows that the products are nanosheets, well-crystallized, and a mean thickness 20 nm. The corresponding lithium ion diffusion coefficients are calculated to be 7.27*10-14 cm2 s- 1. At the current density of 0.1C, the discharge capacity of the nanocomposite is 189.5 mAh/g. Importanly, the discharge capacity at 50C still remains 120.0 mAh/g with retention ratios of 98.6% after 50 cycles, which shows the as-prepared Li₄Ti₅O₁₂/TiO2 have superior electrochemical performances in terms of specific capacity, cycling performance, and rate performance.The Li₄Ti₅O₁₂/RGO nanocomposites with 5% RGO are successfully synthesized by hydrothermal reaction and heat treatment. The products are stacked nanosheets morphology with a mean thickness 15 nm. The Li₄Ti₅O₁₂/RGO nanocomposite deliver a discharge capacity of 243.0 mAhg-1 at 0.1C, and 125.4mAhg-1 at 40 C. After 200 cycles at 40C, the discharge capacity remains at100.2mAh/g, and shows better capacity retention ratios of 80.0%。The effects of the mixed conductive additives of AB and RGO on the Li₄Ti₅O₁₂ and LiFePO4 are investigated. The results indicate that the addition of RGO plays an important role at high charge/discharge rate. Adopting the mixture of A B and RGO as conductive additives, it forms better conductive network and larger contacting area, and alleviates the degree of cathode polarization. The mixed conductive additives with 1% shows better high rate performance.