Fox Alina M, Vrankovic Dragoljub, Buchmeiser Michael R
Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Daimler AG, RD/EBZ, Mercedesstraße, 70327 Stuttgart, Germany.
ACS Appl Mater Interfaces. 2022 Jan 12;14(1):761-770. doi: 10.1021/acsami.1c18481. Epub 2021 Dec 31.
Silicon is one of the most promising materials when it comes to lithium-ion battery anodes because of its high theoretical capacity and the low working potential Li/Li. However, the drastic volume change during lithiation and delithiation leads to a rapid failure of the electrode. In order to accommodate the large volume change, Si@C core-shell nanocomposites have been investigated, as they efficiently protect the Si surface from being exposed to the electrolyte and thus limit side reactions and improve the cycling stability through a stable solid electrolyte interface layer. In recent years, phenolic resins have been investigated as the carbon source due to their facile synthesis and the possibility of scale-up. Here, the influence of the chemical structure of the Si-C interface on electrochemical performance has been analyzed by comparing pristine, silanol-rich and epoxide-functionalized Si/phenolic resin-derived nanocomposites. Whereas pristine Si@C exhibits the highest initial specific capacity of around 2000 mA h/g, introduction of silanol groups to the native surface leads to a more homogeneous carbon shell around the Si and thus to an overall higher Coulombic efficiency and a more stable cycling behavior. Additional epoxide functionalization, however, leads to a drastic decrease in initial capacity due to an overall increased resistance and prolongs the activation process. Nevertheless, in the long term, the additional layer leads to more stable cycling, especially at high current rates. For all nanocomposites, the electrochemical performance, characterized by cyclic voltammetry, cycling experiments, and electrochemical impedance spectroscopy, is correlated with the structure of the Si-C interface, determined by transition electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman, scanning electron microscopy, and IR-spectroscopy. To the best of our knowledge, the influence of the Si-C interface of a core-shell nanocomposite on structure and electrochemistry by chemically modifying the silicon surface is analyzed and reported for the first time.
就锂离子电池负极而言，硅因其高理论容量和低Li/Li工作电位，是最具前景的材料之一。然而，在锂化和脱锂过程中剧烈的体积变化会导致电极迅速失效。为了适应这种大体积变化，人们对Si@C核壳纳米复合材料进行了研究，因为它们能有效保护硅表面不暴露于电解液中，从而限制副反应，并通过稳定的固体电解质界面层提高循环稳定性。近年来，酚醛树脂因其合成简便且具有放大生产的可能性而被作为碳源进行研究。在此，通过比较原始的、富含硅醇的和环氧化官能化的Si/酚醛树脂衍生的纳米复合材料，分析了Si-C界面的化学结构对电化学性能的影响。原始的Si@C表现出约2000 mA h/g的最高初始比容量，而在原生表面引入硅醇基团会使硅周围形成更均匀的碳壳，从而总体上提高库仑效率并使循环行为更稳定。然而，额外的环氧化官能化会由于总体电阻增加而导致初始容量急剧下降，并延长活化过程。不过，从长期来看，额外的这一层会使循环更稳定，尤其是在高电流速率下。对于所有纳米复合材料，通过循环伏安法、循环实验和电化学阻抗谱表征的电化学性能与通过透射电子显微镜、X射线光电子能谱、X射线衍射、拉曼光谱、扫描电子显微镜和红外光谱确定的Si-C界面结构相关。据我们所知，首次分析并报道了通过化学修饰硅表面，核壳纳米复合材料的Si-C界面对结构和电化学的影响。
