【作者】 时志强；

【导师】 王成扬；

【作者基本信息】 天津大学 ， 化学工艺， 2004， 硕士

【摘要】 本课题以开发性能优异而价格低廉的锂离子电池负极材料为目的，以具有良好嵌锂性能（372mAh/g）但与电解液的相容性却较差的天然石墨为研究对象，对其进行了系统深入的研究；针对其循环效率低的缺点，尝试了气相氧化和液相氧化改性；针对天然石墨振实密度偏低的缺陷，采用物理包覆和化学包覆的方法有效提高了天然石墨振实密度，并对制备出的复合石墨材料进行了初步的电化学性能的研究。 采用 SEM、XPS、循环伏安和恒电流充放电测试等方法，对 HT10 在 EC/EMC和 3EC/3EMC/4PC 作溶剂的两种电解液中的充放电行为的研究结果表明：虽然SEM 观察到了部分石墨片层发生剥落的现象，但循环伏安和恒电流充放电测试的结果证实，首次循环中形成的 SEI 膜能阻止了溶剂的进一步分解，避免了石墨片层在含 40%PC 的电解液中的大量剥落，保证了石墨电极的良好充放电循环，因此，含有菱形石墨相的天然石墨 HT10 在两种电解液中均表现出良好的充放电性能。 采用空气和双氧水对天然石墨进行了氧化改性研究。结果表明，空气氧化增加了嵌锂位置，石墨颗粒变得更规整；嵌锂位置的增加提高了锂离子的嵌入量，颗粒的规整化有利于形成稳定、均匀的 SEI 膜，防止石墨结构在充放电过程中由于溶剂的嵌入而发生剥落。双氧水氧化通过改变天然石墨表面的官能团而降低了表面的氧含量，有利于减少首次充电时形成 SEI 膜时锂离子的消耗，抑制溶剂和电解质的分解，提高首次充放电的循环效率。氧化改性后的天然石墨 HONG 的首次不可逆容量由氧化前的 52.9mAh/g降低到 38.8mAh/g，可逆放电容量也保持在 340mAh/g以上，首次的充放电效率达到 89.8%。 物理包覆和化学包覆的方法都能有效的提高天然石墨的球形度和振实密度，复合天然石墨电极的电化学性能也有一定程度的改善。尤其是化学包覆的天然石墨CPNG11，其振实密度由原来的0.61g/cm3提高到0.87g/cm3，首次的放电容量达到338mAh/g，首次的循环效率达到86.4%左右。更多还原

【Abstract】 In the present study, natural graphite, which has good lithium storage performanceand bad compatibility with electrolyte, was deep investigated for preparing excellentperformance and low-cost anode materials for Lithium ion battery (LIB). Naturalgraphite was modified by gas-phase oxidation and liquid-phase oxidation which wereattempted to improve coulombic efficiency. The methods of chemical coating andphysical coating which were used to improve tap density were introduced to solve thedeficiencyof small tap densityof the natural graphite. Two natural graphite compositematerials with large tap density were prepared, and their electrochemicalperformances were studied primarily. X-ray diffraction (XRD), Scanning electron microscope (SEM), X-rayphotoelectron spectroscopy (XPS), cyclic voltammograms and constantcharge-discharge were used to analyze the structure and electrochemical performanceof many kinds of typical natural graphite in China, especially to studycharge/discharge behavior of the sample HT10 in EC/EMC and 3EC/3EMC/4PCsolvent. Exfoliation product from partial graphite flake was observed by SEM. Theformation of solid electrolyte interface (SEI) film in the first cycle was analyzed bycyclic voltammograms and constant charge-discharge tests. It was proved that SEI caninhibit the decompositionof solvent further and avoid the exfoliation of graphite flakein the electrolyte containing 40% PC solvent which can make the anode performstable charge/discharge cycling. Therefore, natural graphite HT10 containingrhombohedral phase can exhibit excellent performance in two kinds of electrolyte. Oxidation treatment in which natural graphite was modified by air and H2O2 wasinvestigated. It was demonstrated that lithium storage sites increased and the particlesize became more uniform by air oxidation because these changes make the insertioncapacity increase and is benefit to form stable and uniform SEI film which can inhabitthe cointercalation of solvent in the cycling process. It was proved that the oxygencontent on the surface of the graphite decreased with the change of surface functionalgroup by oxidation treatment. At the same time, the change of surface structure wasbeneficial to decrease the consumption of lithium ion in the process of the formationof SEI film. Furthermore, this change inhibited the decomposition of solvent andelectrolyte and improved the coulombic efficiency in the first cycle. The first<WP=5>irreversible capacity of HONG which was modified by H2O2 was decreased from52.9mAh/g to 38.8mAh/g, the reversible capacity kept above 340mAh/g, and thecoulombic efficiency reached 89.8% in the first cycle. Two methods of chemical coating and physical coating can also improve thesphericityand tap density of natural graphite，and the electrochemical performance ofcomposite materials were enhanced to a certain extent. Especially the tap density ofthe graphite CPNG11 which was modified by chemical coating was increased from0.61g/cm3 to 0.87g/cm3, the discharge capacity reached 338mAh/g and the coulombicefficiencyattained 86.4% in the first cycle.更多还原