真空—液相法制备沥青炭包覆石墨负极材料的研究

发布时间：2018-05-24 14:46

  本文选题：石墨负极材料 + 人造石墨　； 参考：《湖南大学》2015年硕士论文

【摘要】：锂离子电池具有电压高、比能量高、自放电少、绿色环保、无记忆效应等优点,被誉为“21世纪最具有竞争力的动力电源”,不仅广泛应用于便携式电子产品中,还被应用于航天航空、军事、电动汽车和储能等领域。石墨材料具有比容量高、循环性能好、嵌脱锂平台低、成本低廉等优点,成为最具有商业价值的锂离子电池负极材料。但是由于石墨与有机溶剂电解液的相容性很差,使得负极材料表面形成过多的SEI膜,过量的SEI膜不仅消耗大量的锂,产生较大的不可逆容量损失,还使界面阻抗增大,引起电化学动力学障碍,使石墨层解理乃至剥落,导致容量衰减和循环性能下降。因此,为进一步改善石墨负极材料的性能,本文采用真空-液相包覆法对石墨材料进行沥青炭包覆改性处理。采用XRD、SEM和多种电化学测试方法考察了软化点较低的中温沥青和改质沥青炭包覆对石墨结构、形貌和电化学性能的影响。实验结果表明:采用真空-液相包覆法能够制备出具有良好的“核-壳”结构复合材料。沥青炭种类和包覆量对石墨样品的结构和电化学性能影响很大,中温沥青包覆微晶石墨,改质沥青包覆人造石墨,在石墨颗粒表面可以形成良好的无定形炭包覆层,提高石墨材料的电化学性能,随着包覆量的增加,石墨颗粒团聚性增加,表面平整度增加;经过包覆改性可以提高石墨材料的首次库伦效率,并保持可逆容量基本不变。而采用改质沥青炭包覆天然微晶石墨和采用中温沥青炭包覆人造石墨,包覆效果都较差。中温沥青炭包覆微晶石墨的最佳包覆量为6%,改质沥青炭包覆人造石墨的最佳包覆量为9%。沥青浓度越高,天然微晶石墨包覆样品电化学性能越好,本实验最佳沥青浓度为0.1g/ml。炭化升温速率也会影响天然微晶石墨包覆样品的电化学性能,炭化升温速率过快或过慢都不利于电化学性能的提高,最佳炭化升温速率为2℃/min。炭化温度越高,人造石墨包覆样品的电化学性能越好,本实验的最佳炭化温度为1100℃。真空-液相包覆人造石墨的改性效果优于固相包覆人造石墨的改性效果。经过包覆改性后,石墨材料电化学性能得到明显改善,微晶石墨和人造石墨的首次库伦效率分别从原来的86.5%和90.0%提高到92.7%和93.4%,循环性能得到改善。
[Abstract]:Li-ion battery has the advantages of high voltage, high specific energy, less self-discharge, green environment protection, no memory effect and so on. It is praised as "the most competitive power supply in the 21st century", which is not only widely used in portable electronic products. They are also used in aerospace, military, electric vehicles and energy storage. Graphite has many advantages, such as high specific capacity, good cycling performance, low platform and low cost, so it has become the most valuable anode material for lithium ion batteries. However, due to the poor compatibility between graphite and organic solvent electrolyte, too much SEI film is formed on the surface of anode material. The excess SEI film not only consumes a large amount of lithium, but also results in a large irreversible loss of capacity, and increases the interface impedance. It causes electrochemical kinetic obstacles, cleavage and even exfoliation of graphite, resulting in capacity attenuation and decreased cycling performance. Therefore, in order to further improve the performance of graphite anode materials, the vacuum liquid phase coating method was used to modify graphite materials by bituminous carbon coating. The effects of carbon coating on graphite structure, morphology and electrochemical properties were investigated by XRDX SEM and various electrochemical methods. The experimental results show that a good "core-shell" structure composite can be prepared by vacuum-liquid phase coating method. The structure and electrochemical properties of graphite samples are greatly affected by the type and amount of bituminous carbon. A fine amorphous carbon coating layer can be formed on the surface of graphite particles by medium temperature bitumen coated with microcrystalline graphite and modified asphalt coated with artificial graphite. With the increase of coating amount, the agglomeration of graphite particles increases and the surface smoothness increases, and the first Coulomb efficiency of graphite material can be improved by coating modification, and the reversible capacity remains unchanged. However, the coating effect of modified bituminous carbon coated with natural microcrystalline graphite and medium temperature bituminous carbon coated with artificial graphite is poor. The optimum coating amount of medium temperature bituminous carbon coated microcrystalline graphite is 6 and that of modified asphalt carbon coated artificial graphite is 9. The higher the asphalt concentration, the better the electrochemical performance of the sample coated with natural microcrystalline stone ink. The optimum asphalt concentration in this experiment is 0.1 g 路ml ~ (-1) 路L ~ (-1) 路L ~ (-1). The carbonization heating rate also affects the electrochemical performance of the sample coated with natural microcrystalline stone ink. Too fast or too slow carbonization temperature rise rate is not conducive to the improvement of the electrochemical performance. The best carbonization temperature rise rate is 2 鈩，

本文编号：1929432