Synthesis Of Li₄Ti₅O₁₂ Anode Materials By Rheological Phase Method And Its Modification Study

To overcome the defect of poor electronic conductivity of Li₄Ti₅O₁₂ and its high relatively potential, this paper used a new route-rheological phase method to synthesis Li₄Ti₅O₁₂ cathode material. Through the test of SEM,TEM and BTS,to check the effect of synthesis technology,carbon source and metallic ion doping.Firstly, the synthesis manners between rheogical phase methode and sol-gel method were compared.The sol-gel methode's complexing agent is triethanolanmine.From the test, the rheological phase method has shorter operating time, smaller particle and better electrochemical properties.Then, researched the effect of sintering atmosphere,sintering time and sintering temperature and so on to the ptoperties of material.The result shoes that ,the material made by rheological pgase method,when its sintering temperature is 700℃, sintering time is 6h,the volume rate of tetrabutyl titanate and ethanol is 1:5, the pure spinel phase Li₄Ti₅O₁₂ materials can be prepared.The first charge and capacity is 159 mAh·g-1(1C) and 133 mAh·g^-1(5C). After 20 cycles, the material capacity can maintain 98% and 89%.Then, the effect of the addition of carbon source on Li₄Ti₅O₁₂ material at high charge and discharge rate is researched. The results shows that, carbon coating can greatly improve the cycling performance and can reduce the particle size of the Li₄Ti₅O₁₂/C composite material. When using glucose as carbon source, and the best amount is 5mass%, under these conditions, the best performance of Li₄Ti₅O₁₂/C composite material can be synthesized. When using sucrose as the carbon source and the best addition quantity is 6mass%. When the carbon source is nano graphite, because of impurity generation, the Li₄Ti₅O₁₂/C composite material didn't increase the capacity, but improved the capacity retention rate of material. When the addition amount is 6mass%, the composite material with the best performance can be synthesised. As with PEG as the carbon source, the 12mass% PEG content has the best performance. PEG can be uniformly coated in Li₄Ti₅O₁₂/C composite material surface. The first charge capacity can reach 166 mAh·g^-1(1C) and 156 mAh·g^-1(5C). After 20 cycles, the loop retention rate is 100% and 98%. Through high rate charge and discharge, the capacity can restore to 161 mAh·g^-1(1C).Finally, in order to reduce the relative voltage of the material, metal ion Cr is doped. Cr-doping can improve the material's capacity and its loop retention. When the doping content is 0.2, the material has the best capacity and cycling performance. The potential vs. Li⁺/Li is 0.4V lower than the materiasl is 164 mAh·g^-1(1C) and 157mAh·g^-1(5C). After 20 cycles, the loop retention is 100% and 99%. Experinced large rate of charge and diacharge, the capacity of doping-Cr composite material can restore to 99% of the 1C capcacity. The limite rate is 20C, this point the first capacity can reach 128 mAh·g^-1and the capacity conservation rate is 75%.In short, carbon coated and metal ion doped can enhance the electronic conductivity of the material. Doping Cr can significantly the potential of the material vs. Li+/Li.