硫—石墨烯复合正极材料的制备及性能研究

发布时间：2018-06-19 15:45

  本文选题：热剥离石墨烯 + 还原氧化石墨烯　； 参考：《华中科技大学》2014年硕士论文

【摘要】：锂二次电池是具有极大潜力和应用前景的次世代便携储能器件，而以硫作为正极储能材料的锂硫电池体系是近年来发展最为迅速，表现最为优秀的体系之一。本文分别分析探索了一种硫-石墨烯复合正极材料和一种潜力巨大的全固态锂硫电池，分析了其性能影响因素。 本实验利用两种不同形态的石墨烯材料与单质硫进行复合，制备了一系列表现优良的硫碳复合材料。通过大量的实验证明：这种材料在保证了较高硫负载量的同时，表现出了优良的电化学性能，同时也较为有效的克服了锂硫电池正极材料存在的：导电性差、循环性能差等缺点，并在一定程度上抑制了穿梭效应带来的负面影响，同时也进一步改善了石墨烯材料存在的负载量和利用率较低的缺陷。 我们利用热剥离石墨烯这种超薄的二维材料作为基底负载了单质硫，在硫单质表面形成了一层保护层，这种保护层既能极大的提高其导电性能又能够有效的防止循环过程中活性材料的流失。我们进一步在这种片层材料的外层包覆了还原氧化石墨烯（一种具有优良导电性能和物理性质的薄膜材料），实验结果表明，该方法能够明显提高单质硫的利用率，前50个循环的电化学性能全面优于未包覆材料。本文中还同时研究了含硫量、包覆量、不同粘结剂，不同热剥离石墨烯基底的制备条件等变量对电化学性能影响。 实验结果表明，在不计其他变量影响的前提下，存在一个最佳的包覆量，，以及最佳的含硫量（60%-70%）和最佳的正极片厚度（10-15μm）使电化学性能达到最佳，而过多的含硫量会造成介孔的堵塞和片层结构的损伤。氧化石墨在1050℃下的剥离程度和孔径均优于1000℃和950℃下剥离的样品，而在气氛保护下进行分段式预热剥离得到的石墨烯的剥离程度和孔径优于在马弗炉无气氛保护下一次剥离得到的石墨烯。 由于电解质的选择对于锂硫电池性能的影响较大，我们以此正极硫碳复合材料为基础设计了一种全新的全固态锂硫电池作为探索和对比。由固态电解质和电极之间的多点接触问题导致的高接触电阻一直是困扰全固态锂硫电池发展的因素之一，本体系采用了实验室制备的LATP陶瓷固态电解质和CPE半固态电解质，以CPE半固态电解质作为缓冲区，以缓冲层的形式置于电极和电解质之间，提高接触面的电导率，并减少LATP材料和负极Li片接触时造成电解质损失。以球磨BP2000与硫制得的复合材料为对照组，对比多种正极以及有无缓冲层对固态电池性能的影响。 试验结果表明：在全固态电池体系中石墨烯-硫复合材料首次放电比容量不如对照组材料，但其循环稳定性的表现却优于对照组，表现出石墨烯-硫复合材料较好的循环稳定性。而没有使用缓冲层的电池的性能表现和使用了缓冲层的电池差距较大，这说明此缓冲层在全固态电池中起着重要的作用。
[Abstract]:Lithium secondary battery is the next generation portable energy storage device with great potential and application prospect, and the lithium sulfur battery system with sulfur as positive energy storage material is one of the most rapid development and best performance in recent years. In this paper, a sulfide-graphene composite cathode material and an all-solid-state lithium-sulfur battery with great potential are investigated, and the factors affecting the performance of the battery are analyzed. In this experiment, a series of excellent sulfur / carbon composites were prepared by combining two kinds of graphene materials with simple sulfur. Through a large number of experiments, it is proved that this material not only guarantees high sulfur loading, but also exhibits excellent electrochemical performance. At the same time, it also effectively overcomes the existence of cathode materials for lithium sulfur batteries: poor conductivity, The poor cycle performance and so on can restrain the negative effects of the shuttle effect to a certain extent and further improve the defects of the graphene material with low load and low utilization ratio. We use thermal stripping graphene, a thin two-dimensional material, as a substrate to load elemental sulfur and form a protective layer on the surface of sulfur. The protective layer can greatly improve its conductivity and effectively prevent the loss of active materials during cycling. We further coated the outer layer of this lamellar material with reduced graphene (a thin film with excellent conductivity and physical properties). The experimental results show that this method can significantly improve the utilization rate of elemental sulfur. The electrochemical performance of the first 50 cycles is better than that of the uncoated material. At the same time, the effects of sulfur content, coating amount, different binder and different preparation conditions on the electrochemical properties of graphene substrate were also studied. The experimental results show that the optimum coating amount, the optimum sulfur content and the optimum thickness of the cathode sheet (10 ~ 15 渭 m) can achieve the best electrochemical performance without taking into account the influence of other variables. Excessive sulphur content can cause mesoporous blockage and lamellar structure damage. The peeling degree and pore size of graphite oxide at 1050 鈩

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