Synthesis And Properties Of Lithium Titanate As Anode Material For Lithium Ion Batteries

As a new anode material for lithium ion battery, spinel-structured lithium titanate (Li₄Ti₅O₁₂) has attracted much interest because of its excellent cycling stability and safety. However, its low electronic conductivity and Li+diffusion coefficient limit its practical applications. Therefore, how to effectively improve its electrochemical performance has attracted increasing attention.In this work, Li₄Ti₅O₁₂ nanoclusters, open hollow mesoporous microspheres, mesoporous nanoparticles and Li₄Ti₅O₁₂@PANI core-shell nanoparticles were synthesized via the coprecipitation method, hydrothermal method, microwave hydrothermal method and in situ synthesis. The influences of preparation conditions on the physical and electrochemical properties of the products were studied and the results are as follows:（1） Li₄Ti₅O₁₂ nanoclusters were prepared by a coprecipitation method with C16H36O4Ti and LiOH as the starting materials. Large sized Li₄Ti₅O₁₂ particles with poor electrochemical performance was obtained at the high calcination temperature during long times. In this study, the Li₄Ti₅O₁₂ nanoclusters with the diameter of around 100-250 nm were prepared by calcined at 700℃ for 1 h and they exhibited discharge capacities of 115.9 mAhg^-1 and 70.9 mAhg^-1 at 0.1 C and 10 C, respectively.（2） Li₄Ti₅O₁₂@PANI core-shell nanoparticles were synthesized by an in situ synthesis with Li₄Ti₅O₁₂ and C6H7N as the raw materials. The PANI contents of the products were increased with high polymerization proportion during long times; nimiety PANI would influence the electrochemical properties of the composites. In this study, the Li₄Ti₅O₁₂@PANI core-shell nanoparticles with the average particle size of 150-250 nm were prepared with the polymerization ratio of 1:50 in 12 h; electrochemical results show that appropriate ratio of PANT coating would significantly improve Li+ diffusion coefficient and electrical conductivity as well as reduce the degree of polarization of the material.（3） Li₄Ti₅O₁₂ open hollow mesoporous microspheres were synthesized by a hydrothermal method with the preform TiO2 and LiOH as the starting materials. The products could not be fully transformed into Li₄Ti₅O₁₂ at the low calcination temperature during short times; the structure of products would be destroyed at excessively high temperature during long times. In this experiment, the Li₄Ti₅O₁₂ open hollow mesoporous microspheres with the diameter of about 1.2 mm, assembled by nanoparticles with the size of around 60 nm, were prepared by calcined the hydrothermal products at 400℃ for 2 h; they exhibited a discharge capacitiy of 86 mAhg^-1 at 40 C.（4） Li₄Ti₅O₁₂ mesoporous nanoparticles were prepared by a microwave hydrothermal method with the preform TiO2 and LiOH as the raw materials. The calcined products could not be fully transformed at the low calcination temperature during short times; the structure of products became loose at the high temperature during long times. In this study, Li₄Ti₅O₁₂ mesoporous nanoparticles with the diameter of around 40 nm and the average pore size of about 8 nm were prepared by reacting at 180℃ for 120 min after calcination, and they exhibited discharge capacities of 173.7 mAhg^-1 and 90.2 mAhg^-1 at 1 C and 60 C, respectively.（5） For the preparation technology, the calcination temperatures and times of Li₄Ti₅O₁₂ were reduce significantly by using the preform TiO2 prepared by this experiment, which was mainly due to its porous structure and the nano-sized sticks would be beneficial to react with other ions in the solution. In addition, Li₄Ti₅O₁₂ prepared by microwave hydrothermal method can remarkably shorten the production cycle and improve the production efficiency under the condition of increasing the reaction temperature appropriately.