Novel Nano/micro Hierachical Li₄Ti₅O₁₂ Anode For Application In High-Rate Lithium Ion Battery

Lithium ion battery has many merits (e.g., higher voltage, higher energy density, and longer cycle life) compared with traditional rechargeable batteries. Considerable attention has been paid to electrochemical energy storage devices with the ability to withstand fast charge-discharge over an adequate cycle life, because of their potential use in future electric vehicle (EV) or hybrid EV (HEV). Thus, the research and development of Lithium ion battery with outstanding high-rate performance is desirable and significative.As the performance of high–rate lithium ion battery these devices depends intimately on the properties of their materials, considerable attention has been paid to the research and development of key materials. Although spinel Li4Ti5O12 has a good reversibility and exhibits a very small volume change during charge–discharge process, the future importance of high-power applications encourages investigation of the high-rate performance of the material. Electrode materials with nano/micro hierarchical structures are the best systems of choice to improve high rate capability, because they have large specific surface area, short distance for lithium ion diffusion, good stability and easy of fabrication. Novel Li4Ti5O12 with nano/micro hierarchical structure may give an ideal host material for the rapid intercalation and deintercalation of Lithium ions and provide the possibility of efficient transport of electrons in the high-rate lithium ion batteries. The major research content is as follows: The flower-like spinel Li4Ti5O12 consisting of nanosheets was synthesized by a hydrothermal process in glycol solution and following calcination. The cycle voltammetric results of the electrodes indicate enhanced electrochemical kinetics for lithium insertion by reducing the distance of lithium ion diffusion in solid-state body. The capacity of the sample used as anode material for lithium ion battery was measured. This structured Li4Ti5O12 exhibited a high reversible capacity and an excellent rate capability of 165 mAhg-1 at 8 C. Besides the flower-like Li4Ti5O12, the Li4Ti5O12 hollow microspheres consisting of nanosheets have also been synthesized via a hydrothermal route and following calcination. The formation mechanism for the hollow microspheres was studied by tracking the crystallization and morphology of the product at different reaction stages. Because of the favorable transport properties of this hollow structure, when the Li4Ti5O12 hollow microspheres assembled by nanosheets were used as the anode material in lithium ion battery, they exhibited superior rate performance and high capacity even at a very high rate (131 mAhg-1 at 50 C), indicating potential application for high-rate lithium ion batteries.Mesoporous spinel lithium titanate Li4Ti5O12 microspheres were prepared by template-free hydrothermal process in ethanol-water mixed solution and subsequent heat treatment. The role of ethanol helps the formation of a mesoporous structure during the hydrothermal process. In general, well-defined mesoporous spheres can hardly be produced when r(EtOH vol% in the solvent of EtOH-H2O) is lower than 30%. A mechanism analogous to the Kirkendall effect was proposed to account for the template-free formation of these mesoporous nanostructures. As anode materials for high-rate lithium ion battery, the Li4Ti5O12 mesoporous spheres exhibited superior high-rate performance of 114 mAhg-1 at 30 C and good capacity retention of 125mAhg-1 after 200 cycles at 20 C.A facile synthesis route was developed to prepare hierarchical hollow microspheres assembled by titanate nanotubes. Especially, H2O2 was found to be an efficient agent that can facilitate the roll of titanate sheets into nanotubes under low concentrated NaOH conditions. And the similar structured hydrogen titanate was prepared via acid washing of sodium titanate. After calcination, the hydrogen titanate can be transformed into TiO2 nanotube-based hollow spheres, and similar structured Li4Ti5O12 can be prepared by hydrothermal ion-exchange between lithium ion with hydrogen titanate and following calcination. When the hierarchical structured TiO2 were used as the anode material in lithium ion battery, they exhibited a high capacity and cycle stability of 160 mAhg-1 after 100 cycles at 1 C and a good rate performance of 90 mAhg-1 at 8 C.