The Modification Of Li₄ Ti₅ O₁2 As Anode Material Ror Li-Ion Battery

In this thesis, pure phase spinel Li₄Ti₅O₁₂ composite were prepared by two-step solid-state reaction using industrial grade TiO2 and battery grade Li2CO3 as raw materials. The structure, morphology and electrochemical properties of Li₄Ti₅O₁₂ were characterized by XRD, SEM, galvanostatic charge-discharge tests, in order to finding the optimal synthesis process to getting Li₄Ti₅O₁₂ materials with more excellent electrochemical performance.At first, the effect of the different carbon sources such as glucose and solvable starch on the carbon modification samples was researched. The results indicated that solvable starch combined with bath-heat process has the best effect to improve electrochemical properties of Li₄Ti₅O₁₂/C, this due to the inherent character of solvable starch. A series of single-factor experiments, such as the atom ratio of Li and Ti, the second step calcinations temperature and reaction time, were investigated. The detailed process was: the raw materials with a atom ratio of Li/Ti was 4.08:5(excessive by 2%), calcined at 600℃holding 4h for the first step, then calcined at 800℃holding 6h for the second step, both calcine processes were under N2 atmosphere.Based on the results, the effect of starch content on the carbon modification was researched, the experiments results indicated that the carbon content increased, the particle size was becoming smaller, electric conductivity was rising, and tap density was turning lower with starch content rising. At the same time, discharge capacity was first increased and then decreased. The sample with 4 wt% (aim content in Li₄Ti₅O₁₂/C) displayed the best electrical performance, a 178.2mAh/g of specific capacity was obtained at 0.2C rate, while 161, 155.1 and 141.8mAh/g at 1, 2 and 5C rate, the capacity retention was 97.7% after 50 cycles.The samples with Mg²⁺, Al³⁺ and V⁵⁺ doping were synthesized via the pure phase calcine process. The results showed that none of the three doping changed the crystal structure of Li₄Ti₅O₁₂, but the electrochemical properties were improved in varying degree. The sample with Mg²⁺ doping displayed the best electrochemical performance, this due to the favorable ionic radius of it and smaller lattice distortion.At last, the effect of Mg²⁺ doping combined with carbon coating at the optimal ratio using starch as carbon source was investigated. The results demonstrated that the effect of combined modification was better than other single-way modification, with a 163, 155.1 and 144.2mAh/g specific capacity at 1C, 2C and 5C rate respectively, the capacity retention rate was 97.6% after 50 cycles. These results indicated that the combination of two methods had improved the electrochemical properties by its own way.