Preparation And Electrochemical Performance Of Li₄ Ti₅O₁₂ Anode Materials For Lithium-Ion Batteries

Recently, the spinel-structured Li₄Ti₅O₁₂ is being considered as a promising anode material for lithium-ion batteries due to its zero-strain structure, excellent cycle performance, good safety and high thermostability. However, the low electronic conductivity affects its rate performance. In this paper, high rate performance Li₄Ti₅O₁₂ was synthesized by two ways and modified by carbon coating. In addition, the micro-structure and morphology was analyzed by XRD, SEM, TEM, TG; and the electrochemical performance was analyzed by galvanostatic charge-discharge test, cycle voltammagram and AC Impedance.The pure Li₄Ti₅O₁₂ was synthesized by solid-state method with lithium hydroxide, anatase TiO2 as raw materials. The effects of Li/Ti mole ratio, milling time, calcination temperature on the properties of Li₄Ti₅O₁₂ were investigated. The optimal experimental conditions were: Li/Ti mole ratio was 0.82, the milling time was 1h and calcination temperature was 800℃. Under this condition, the Li₄Ti₅O₁₂/C with different carbon content was synthesized by adding phenanthroline to the raw materials. After carbon-coated, the particles became smaller and the rate performance was improved significantly. The Li₄Ti₅O₁₂/C with 7.9% carbon content had the best electrochemical performance. The discharge capacity can reach to 148.6 mAh/g at the rate of 0.5C and 117.3 mAh/g at the rate of 10C which was much higher than the pure Li₄Ti₅O₁₂ at the same rate.The pure Li₄Ti₅O₁₂ was also synthesized by hydrothermal method with lithium hydroxide, anatase TiO2 as raw materials. The preparation condition such as lithium hydroxide concentration, hydrothermal time, calcination temperature and calcination time were investigated. The optimal experimental conditions were : lithium hydroxide concentration was 0.2M, hydrothermal time was 12h, calcination temperature was 700℃, calcination time was 5h. The Li₄Ti₅O₁₂ prepared under the optimal experimental conditions had an excellent electrochemical performance: the discharge capacity can reach to 165.3mAh/g at the rate of 0.5C and 122.5mAh/g at the rate of 40C, and it also had excellent cycle performance even at the rate of 30C. The synthesis mechanism of Li₄Ti₅O₁₂ was discussed, the formation of Li₄Ti₅O₁₂ can be divided into hydrothermal process and high temperature heat treatment process. In the hydrothermal process, LiTiO2 and Li-Ti-O compounds was generated from TiO2. In the high-temperature heat treatment process: firstly, the reaction of LiTiO2, Li-Ti-O compounds with TiO2 to form Li2TiO3, then the Li₄Ti₅O₁₂ was generated with the reaction of TiO2 with Li2TiO3.