Investigation On Synthesis And Modification Of Li₄Ti₅O₁2 Anode Material For Lithium Ion Battery

Carbon anode materials, widely used in commercial lithium ion batteries, could result in lithium plating on the surface of anode and the decomposition of electrolyte during overcharge of lithium ion batteries because of their lower lithium-intercalation potential, and could make lithium ion batteries, especially power lithium ion batteries, unsafe, and therefore impede their applications. Due to higher lithium-intercalation potential than that of carbon and excellent cycle performance resulting from zero-strain lithium intercalation, spinel lithium titanate (Li₄Ti₅O₁₂) has been considered as one of the promising anode materials. However, the poor conductivity of Li₄Ti₅O₁₂ degrades the high rates electrochemical performance and impedes its commercial applications. In order to improve the electrochemical performance by enhancing the conductivity of Li₄Ti₅O₁₂, the Li₄Ti₅O₁₂ and Li₄Ti₅O₁₂/C composite were prepared by modified synthesis methods and the electrochemical performance of the prepared-anode materials was studied in details.Li₄Ti₅O₁₂ was prepared by a traditional solid-state method and the factors influencing physical and electrochemical performances of the Li₄Ti₅O₁₂ were investigated. The results show that performance of Li₄Ti₅O₁₂ significantly depends on raw material ratios and calcination temperature. Lithium salt excessive percentage, calcination temperature and reaction time for optimal conditions are 8 wt.%, 800℃and 12 h, respectively, and the Li₄Ti₅O₁₂ synthesized at optimal conditions has average particle size of 1.1μm. The capacity of the Li₄Ti₅O₁₂ remains 135.8 mAh/g and 102.5 mAh/g after 50 cycles at 0.2 C and 1 C, respectively, and the corresponding capacity retentions during 5-50th are 91.4% and 76.9%, respectively.Li₄Ti₅O₁₂ was prepared by a hydrothermal method followed by solid state calcination using triethanolamine as a structure-directing agent. The effects of raw material ratios and calcination conditions on the structure and electrochemical performance of Li₄Ti₅O₁₂ were investigated. The pure Li₄Ti₅O₁₂ was prepared at the conditions of 1:0.82:1:20 for ratio of butyl titanate/lithium acetate/ triethanolamine, calcination temperature of 800℃and reaction time of 18 h, and exhibits 200 nm of average particle size. The capacity of the Li₄Ti₅O₁₂ prepared by hydrothermal method retains 149.3 mAh/g and 110.2 mAh/g after 50 cycles at 0.2 C and 1 C, respectively, and the corresponding capacity retentions during 5-50th are 97.3% and 88.4%, respectively. In order to improve the conductivity and electrochemical performance of Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C composite was synthesized by a solid-state method using glucose as carbon source and the effects of carbon content on the structure and electrochemical performance of Li₄Ti₅O₁₂/C were investigated. The results indicate that addition of carbon does not change the spinel structure of Li₄Ti₅O₁₂ and the sample is of uniform particle size of 0.68μm. Compared with the pure spinel Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C composite with 10 wt.% carbon has higher capacity, better cycle performance and reversibility. The capacity of Li₄Ti₅O₁₂/C composite keeps 153.2 mAh/g and 147.6 mAh/g after 50 cycles at 0.2 C and 1 C, respectively, and the corresponding capacity retention rates of 5-50th are 98.8% and 92.7%, respectively. Moreover, the Li₄Ti₅O₁₂/C composite displays initial discharge capacity high as 108.5 mAh/g even at high rate of 5 C.