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钛酸锂/石墨烯复合负极材料的制备及电化学性能研究
张利辉
Subtype硕士
Thesis Advisor徐宇兴
2018
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword锂离子电池,Li4ti5o12负极材料,固相法,石墨烯
Abstract

钛酸锂(Li4Ti5O12)作为锂离子电池负极材料,与石墨等碳电极材料相比具有热稳定性好、安全性能高和循环寿命长等优点,被认为是一种极具发展潜力的动力型锂离子电池负极材料。但是Li4Ti5O12固有的电子导电率较低(10-13 S cm-2),导致其在大电流充放电条件下容量衰减快和倍率性能较差,限制了其规模化应用。为解决Li4Ti5O12材料在实际应用中容量衰减快和倍率性能差等问题,本论文采用球磨法和砂磨法两种方法制备钛酸锂/石墨烯复合负极材料。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能量色谱仪(EDS)、透射电子显微镜(TEM)和拉曼光谱(Raman)等表征手段研究其结构和形貌的变化,采用蓝电电池测试系统和电化学工作站测试其电化学性能,具体研究结果如下:采用两步球磨法,分别制备Li4Ti5O12/graphene(LTO-G)和Li4Ti5O12/N-doped graphene(LTO-NG)复合材料。相比添加石墨烯而言,氮掺杂的石墨烯能够提供更多的自由电子,提高LTO-NG样品的电子导电性,对比纯相Li4Ti5O12、LTO-G和LTO-NG,LTO-NG具有较好的倍率性能及循环稳定性,在0.2C、0.5C、1C、3C、5C、10C和20C倍率下充电比容量依次为164、161.5、157.9、144.6、127.8、104.4和80.5 mAh/g,5C倍率下循环200次后的容量保持率为92%。通过CV测试和计算,表明LTO-NG样品具有最小的极化程度和最大锂离子扩散系数(5.76 × 10?10 cm2 s?1)。采用一步球磨及喷雾干燥相结合的方法,制备了球形的不同石墨烯添加量的Li4Ti5O12/graphene复合材料,当石墨烯添加量为1wt.%时,Li4Ti5O12/graphene复合材料(LTO-G-2)具有优异的倍率性能及循环稳定性。LTO-G-2样品在0.2C、0.5C、1C、3C、5C和10C倍率下的充电比容量为172.9、165.7、163.5、157.4、154.0和143.5 mAh/g,5C倍率下循环200次后,容量保持率为94.8%。CV实验结果表明LTO-G-2样品具有最小的极化程度,阻抗测试结果也表明LTO-G-2样品的电荷转移阻抗Rct(69.6 Ω)是最小的。采用一步砂磨法,制备了不同石墨烯添加量的Li4Ti5O12/graphene复合材料,当石墨烯添加量为0.93wt.%时,Li4Ti5O12/graphene复合材料(GLTO-2)具有优异的倍率性能及循环稳定性。GLTO-2样品在0.2C、0.5C、1C、3C、5C、10C、15C、20C和30C倍率下的充电比容量为175.2、175.8、71.9、167.9、166.4、164.1、 161.4、159.4和150.8 mAh g?1,10C倍率下循环900次后,容量保持率为89.4%,5C倍率下循环2000次后,容量保持率仍有80.2%。CV实验结果表明GLTO-2样品具有最小的极化程度和最大的锂离子扩散系数(1.04 × 10?9 cm2 s?1),同时,阻抗测试结果也表明GLTO-2样品的电荷转移阻抗Rct(47.3 Ω)是最小的。;As an anode material of lithium ion battery, Li4Ti5O12 exhibits good thermal stability, high electrochemical security and long cycling life compared with graphite and other carbon electrode materials. It is considered to be a potential anode material for high-power lithium ion battery. Unfortunately, the inherent low electronic (10-13 S cm-2) conductivity, which leads to the capacity decaying and poor rate performance under the high current charge and discharge process, greatly hinders its practical application.In order to enhance the specific capacity and rate capability of Li4Ti5O12, the Li4Ti5O12/graphene composites have been successfully prepared by three solid-state methods. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), Raman spectra, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge tests and electrochemical workstation were used to confirm the structure and electrochemical performance of the materials. The results of the study are shown as follows:Li4Ti5O12/graphene (LTO-G) and Li4Ti5O12/N-doped graphene (LTO-NG) composites have been synthesized by an two-step ball milling method. Compared with the graphene, the nitrogen doped graphene can provide more free electrons and improve the electronic conductivity of LTO-NG. Comparing the electrochemical performances of the three materials, the LTO-NG exhibits excellent rate capability and cycling stability, with specific capacities of 164, 161.5, 157.9, 144.6, 127.8, 104.4, and 80.5 mAh g?1 at rates of 0.2, 0.5, 1, 3, 5, 10, and 20 C, respectively. Moreover, LTO-NG shows a charge capacity retention of 92% after 200 cycles at a rate of 5 C. Cyclic voltammetry (CV) tests show that LTO-NG has a smallest polarization degree and a largest Li+ diffusion coefficient (5.76 × 10?10 cm2 s?1).Li4Ti5O12/graphene composites with different amount of graphene have been synthesized by an one-step solid-state ball milling and spray drying method. When the amount of graphene is added to 1 wt.%, the Li4Ti5O12/graphene composite (LTO-G-2) exhibits excellent performance with charge capacities of 172.9、165.7、163.5、157.4、154.0 and 143.5 mAh/g at 0.2, 0.5, 1, 3, 5 and 10 (1 C = 160 mAh g?1). Moreover, LTO-G-2 shows a charge capacity retention of 94.8% after 200 cycles at 5 C. Cyclic voltammetry tests (CV) show that the polarization degree of GLTO-2 is the smallest. Electrochemical impedance (EIS) tests also show that the charge transfer resistance of LTO-G-2 (69.6 Ω) is the lowest.Li4Ti5O12/graphene composites with different amount of graphene have been synthesized by an one-step sand milling method. When the amount of graphene is added to 0.93 wt.%, the Li4Ti5O12/graphene composite (GLTO-2) exhibits excellent performance with charge capacities of 175.2, 175.8, 171.9, 167.9, 166.4, 164.1, 161.4, 159.4, and 150.8 mAh g?1 at 0.2, 0.5, 1, 3, 5, 10, 15, 20, and 30 C (1 C = 160 mAh g?1). Moreover, GLTO-2 shows a charge capacity retention of 89.4% after 900 cycles at 10 C and 80.2% after 2000 cycles at 5 C. Cyclic voltammetry tests (CV) show that the polarization degree of GLTO-2 is the smallest and the Li+ diffusion coefficient (1.04 × 10?9 cm2 s?1) is the largest . Electrochemical impedance (EIS) tests also show that the charge transfer resistance of GLTO-2 (47.3 Ω) is the lowest.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40736
Collection中国科学院过程工程研究所
Recommended Citation
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张利辉. 钛酸锂/石墨烯复合负极材料的制备及电化学性能研究[D]. 中国科学院大学,2018.
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