The Study On Preparation And Modification Of Li₄Ti₅O₁₂ As A Anode Material For Lithium Ion Batteries

As a promising anode material for lithium ion batteries,spinel Li₄Ti₅O₁₂ has a lot of advantages such as high voltage platform,stable structure,good cycle performance and high safety.However,the low electronic conductivity and Li⁺diffusion coefficient of the Li₄Ti₅O₁₂ would lead to a poor rate performance,hindering the further application in lithium ion batteries.In this dissertation,In order to overcome the significant drawbacks,it is used for nanometerization,doping modification and coating to prepare Li₄Ti₅O₁₂ anode materials with excellent rate performance and cycle performance.this study includes the following aspects:Li₄Ti₅O₁₂ was synthesized by solid-state method using Li₂CO₃ and TiO₂ as raw material,and the effects of different calcining temperature and calcination methods on the structure,surface morphology and electrochemical performance of the material were investigated.The optimal synthetic conditions was that the molar ratio n（Li）:n（Ti）=0.84:1.00,calcined at 500℃for 4 h,and then calcined at 750℃for 16 h,the electrochemical properties of the material synthesized in two-step calcination method were optimized.Li₄Ti₅O₁₂-C with different weight percent of carbon were prepared by in-situ composite method using glucose as a carbon source.The structure,surface morphology and electrochemical performance of the composites were investigated by a series of testing methods.The results show that the Li₄Ti₅O₁₂-C composite particles are homogeneous without impure phase.Li₄Ti₅O₁₂ with 3%weight percent of carbon has the best electrochemical performance,the first discharge capacity of 185.9 mAh/g when discharging at the rate of 0.5 C,its capacity remains 161.5 mAh/g after 50 cycles.Its first discharge capacity is 106.9 mAh/g when discharging at the rate of 4.0 C.On the above（1）optimum conditions,Li₄Ti_5-xCo_xO₁₂（x=0,0.05,0.1,0.3）and Li₄Ti₅O_12-yCl_y（y=0,0.05,0.1,0.3）materials were synthesized by solid state reactions,and their the structure,surface morphology and electrochemical performance were characterized.The results showed that all samples were free of other phases with uniform size and smooth surface.The sample with the cobalt doping amount x=0.05 exhibit the best electrochemical performance,the first discharge capacity was 104.1 mAh/g,which was 58 mAh/g higher than the pure phase Li₄Ti₅O₁₂at the charge-discharge rate of 10 C.Similarly,The sample with the chlorine doping amount y=0.05,the electrochemical performance of Li₄Ti₅O_11.95Cl_0.05.05 exhibit the best initial discharge capacity of 73.3 mAh/g,which was 27.1 mAh/g higher than the pure phase Li₄Ti₅O₁₂.Li₄Ti₅O₁₂ nanosheets was synthesized by hydrothermal method,and the effects of different hydrothermal time and different calcination temperature on the structure,morphology and electrochemical properties of the samples were investigated.The best conditions were as follow:the hydrothermal time is 36 h and the calcination temperature is 600℃.The results showed that the initial discharge capacity of up to182.9 mAh/g,at 0.5 C,the capacity remains 157.4 mAh/g after 50 cycles.At a high 10C,the discharge capacity is still as high as 130.70 mAh/g.