【作者】 孙蕾；

【导师】 唐致远；

【作者基本信息】 天津大学 ， 应用化学， 2009， 硕士

【摘要】 尖晶石型Li₄Ti₅O₁₂是一种理想的嵌入型电极材料,被称作“零应变”材料。它具有充电次数多、充电过程快、安全性高等优点,因而成为目前锂离子电池负极材料研究和开发的热点。本课题是以研制比容量高、循环稳定性好、大电流充放电性能佳、制备工艺简单且成本低廉的锂离子电池负极材料Li₄Ti₅O₁₂,分析其电化学性能的影响因素为目的。本实验主要采用固相反应法和直接融盐法制备Li₄Ti₅O₁₂,利用TG-DTA、XRD、SEM等测试对电极材料进行表征,使用恒流充放电、CV和EIS等电化学测试手段,确定其最佳合成工艺条件,并通过碳掺杂、碳包覆和金属元素掺杂对其进行改性研究。采用固相反应法,结合二次煅烧的方法,制备Li₄Ti₅O₁₂的最佳合成工艺条件为:采用Li₂CO₃和锐钛矿型TiO₂为原料,先于450℃预烧4h,再于900℃煅烧12h。在0.1C倍率下首次放电比容量达165.05mAh·g^-1,经20次循环放电比容量仍保持在159.90 mAh·g^-1。采用直接融盐法制备Li₄Ti₅O₁₂,以CH₃COOLi·2H₂O和锐钛矿型TiO₂为原料,先于70℃保温5h,再于700℃保温2h,从而得到的3#样品的电化学性能最佳。在0.1C倍率下首次放电比容量达到160.77 mAh·g^-1,经20次循环放电比容量仍保持在154.68 mAh·g^-1。利用石墨粉作为单质碳源进行碳掺杂,最佳掺杂量为10%wt;利用葡萄糖作为有机碳源进行碳包覆,最佳掺杂量为20%wt;在Li⁺位上掺杂Mg²⁺,最佳掺杂量为x=0.2;在Ti⁴⁺位上掺杂Sn⁴⁺,最佳掺杂量为x=0.10。与未掺杂的纯Li₄Ti₅O₁₂材料相比,掺杂改性后的样品首次放电比容量和充放电效率高,电荷转移阻抗和容量衰减小,可逆性和循环稳定性好,倍率性能佳。更多还原

【Abstract】 The spinel lithium titanate (Li₄Ti₅O₁₂), which was called as“zero-strain”material, was a sort of perfect insertion electrode material. Owing to its excellent characteristic of reversibility, fast kinetics of charge-discharge process, and safety performance, Li₄Ti₅O₁₂ has recently been the hotspot of research and development of negative electrode materials for lithium ion batteryThe purposes of the dissertation were to prepare Li₄Ti₅O₁₂ as negative electrode material for lithium ion battery, which has high energy density, long term cycling ability, high current charge-discharge ability, simple synthesis technology and low cost, to analyze the factors which might affect the electrochemical performances of Li₄Ti₅O₁₂. Work has been done in order to find the optimal synthesis conditions of Li₄Ti₅O₁₂ which was synthesized by solid-state reaction and direct molten-salt method. The materials were characterized by TG-DTA, XRD and SEM, and investigated by constant current charge-discharge test, CV and EIS. Carbon doping, carbon coating and metal ion doping were adopted to improve the performance of Li₄Ti₅O₁₂.Li₄Ti₅O₁₂ has been prepared by solid-state reaction combined with second- calcining. The best material was obtained by pre-heating Li₂CO₃ and anatase TiO₂ at 450℃for 4h, subsequently calcined at 900℃for 12h. The discharge specific capacity is 165.05mAh·g^-1 after first cycle at 0.1C, and 159.90 mAh·g^-1after 20 cycles.Li₄Ti₅O₁₂ has been synthesized by solid-state reaction. The best sample 3# was obtained by heating CH₃COOLi·2H₂O and TiO₂ at 70℃for 5h, subsequently calcined at 700℃for 2h. The discharge specific capacity is 160.77mAh·g^-1 after first cycle at 0.1C, and 154.68 mAh·g^-1after 20 cycles.Taking graphite and dextrose as carbon resource, the optimal doping quantity is respectively 10%wt and 20%wt. The optimal doping quantity of Mg²⁺ and Sn⁴⁺ is respectively x=0.2 and x=0.10. Compared with the pure Li₄Ti₅O₁₂, the doped Li₄Ti₅O₁₂ has high first discharge specific capacity, high charge-discharge efficiency, low charge transfer resistances, low capacity attenuation, excellent reversibility, cyclic stability and high rate capability.更多还原