【作者】 王娜；

【导师】 戴长松；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 硕士

【摘要】 针对Li₄Ti₅O₁₂材料电子导电性比较低,且作为负极来说,其充放电电压相对较高的缺点,本文采用流变相法合成了Li₄Ti₅O₁₂负极材料,通过SEM、TEM等测试考察并优化了合成工艺、碳源、掺杂比例和金属离子的掺杂对Li₄Ti₅O₁₂材料性能的影响。首先,考察了Li₄Ti₅O₁₂材料的液相合成方式,通过与溶胶-凝胶法相比,流变相法的操作周期更短,制备的粒子更小,电化学性能也最好。然后研究了流变相法烧结气氛、烧结时间和烧结温度等工艺条件对材料性能的影响。结果表明,以流变相法制备的材料,在氩气的烧结气氛下,烧结温度为700℃,烧结时间为6 h,钛酸四丁酯与无水乙醇的体积比为1:5,能制备出纯相的尖晶石结构的Li₄Ti₅O₁₂材料,首次充电比容量为159 mAh·g^-1（1C）和133 mAh·g^-1（5C）,循环20次后,材料的容量保持率为98%和89%。其次,研究了碳源的加入对Li₄Ti₅O₁₂材料在高倍率下充放电的性能影响。结果表明,包覆碳能极大的改善材料的循环性能,且均能减小Li₄Ti₅O₁₂/C复合材料的颗粒粒径。以葡萄糖为碳源时,加入量为5mass%时,此条件下合成的Li₄Ti₅O₁₂复合材料性能最佳。当以蔗糖为碳源时,最佳加入量为6mass%。当以超细石墨为碳源时,由于有杂质生成,超细石墨没有提高材料的容量,但是提高了材料的容量保持率。当以PEG为碳源时,12mass%含量的PEG性能最好。PEG能均匀的包覆在Li₄Ti₅O₁₂/C复合材料表面。材料的首次充电容量能达到166 mAh·g^-1（1C）和156 mAh·g^-1（5C）。20次循环的容量保持率为100%和98%。经历了大倍率充放电后,容量能恢复到161 mAh·g^-1,为1C充放电的96%。最后,为了降低材料的相对电压,掺杂了金属Cr。掺杂Cr能很好的提高材料的容量和容量保持率。当掺杂量为0.2时,材料有最好的容量和循环性能。相对锂离子电压降低了0.4V。材料的首次充电容量为164 mAh·g^-1（1 C）和157 mAh·g^-1（5C）。20次循环的容量保持率为100%和99%。经历了大倍率充放电后,容量能恢复到1C充放电的99%。当放电倍率为20C,此时容量能达到163 mAh·g^-1。总之,包覆碳和掺杂金属离子均能提高材料的电子导电性,掺入Cr后明显的降低了材料的电压。更多还原

【Abstract】 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.更多还原