Preparation Ang Modification Of The Li₄Ti₅O₁2 Material For High Rate Lithium-Ion Batteries

Spinel Li₄Ti₅O₁₂ is a great potential anode material for power lithium ion battery. However, the ionic and electronic conductivity of the material is low, its capacity fades quickly at high rate charge/discharge, and the rate performance is much poor, which limits its applications. Therefore, to accelerate its commercialization, it is necessary to the improvement its rate performance by modification.In the work, lithium titanate material was prepared though solid-state reaction using the anatase TiO₂ and LiCO₃ as raw materials. The sintering temperature of as-prepared sample has been initially identified by TG-DTA analysis. The performance of the as-prepared materials were examined by XRD,SEM,CV,EIS, and charge-dischage test, as well as the carbon content-assisted analysis.Using the solid-state method, effects of the paticle sizes of the anatase TiO₂, the time and temperatures of the low and high termperatures sintering process on the electrochemical performance of the pure phase Li₄Ti₅O₁₂ were studied. The experimental results show that the pure spinel Li₄Ti₅O₁₂ prepared from the particle size of 70 nm TiO₂ has the best rate performance. At the charge-discharge rate of 1 C and 10 C , its discharge capacities are 91.6 mAh·g^-1 and 28.7 mAh·g^-1, respectively. The capacity retention of the 10 C compared to 1 C is 31.33%. The diacharge capacities of the material at 2 C, 10 C, and 20 C deteriorate slightly after 100 or 500 cycles, the coulombic efficiencies are nearly 100%. However, the rate capacity of 20 C is not high, the coulombic efficiency fluctuates evidently. The condition of 600 oC calcined for 8 h, and then 800 oC calcinated for 4 h is the best, the material prepared under this condition, its rate performance is the best, and its rate capacity increases greatly. At the charge-discharge rate of 1 C and 10 C, its discharge capacities are 155.0 mAh·g^-1 and 101.6 mAh·g^-1, respectively. Its capacity retention at 10 C compared to 1 C is 65.55%. Its cycling performance at 2 C, 10 C and 20 C is very stable. Its diacharge capacity decays after 100 or 500 cycles, and the coulombic efficiencies are nearly 100%.Using the optimized synthetic conditions, the Li₄Ti₅O₁₂ materials are coated by carbon modification. The result shows that the actual rate of carbonation by different carbon sources is different, when using citric acid as a carbon source, the theoretical amount of carbon package is 7% (denoted 7% citric acid), its actual carbon content is 1.35%, and its rate performance is the best, the cycle stability is also good. At the charge-discharge rate of 1 C and 10 C , its discharge capacities are 168.7 mAh·g^-1 and 143.2 mAh·g^-1, respectively. The capacity retention of the 10 C compared to 1 C is 84.88%. The cycling performance of materials at 2 C, 10 C and 20 C is stable, the diacharge capacities decay little after 100 or 500 cycles, the coulombic efficiencies are nearly 100%.Using the best carbon source and coated carbon amount which has been optimized, (MgCO₃)₄·Mg(OH)₂·6H₂O is used as a doping modification material, influence of Mg²⁺ doping amount on the performance of synthetic material is investigated. The result shows that using the 7% citric acid to produce Li₄Ti₅O₁₂/C with doping Mg²⁺, its rate performance is not good, but declines, which is related to the reaction between acidic carbon source and alkaline magnesium source when ball milling. In contrast, 4% glucose is used as a carbon source, doping 1% Mg²⁺, the rate performance of the mateial has been greatly improved, its cycle stability is also very good. At the charge-discharge rate of 1 C and 10 C , its discharge capacities are 185.5 mAh·g^-1 and 151.7 mAh·g^-1, respectively. The capacity retention of the 10 C compared to 1 C is 81.78%. The cycling performance of materials at 2 C, 10 C and 20 C is stable, the diacharge capacities decay little after 100 or 500 cycles, the coulombic efficiencies are nearly 100%.