Li Qi, Liu Xiangsi, Han Xiang, Xiang Yuxuan, Zhong Guiming, Wang Jian, Zheng Bizhu, Zhou Jigang, Yang Yong
Xiamen Institute of Rare Earth Materials , Haixi Institutes, Chinese Academy of Sciences , Xiamen 361024 , P. R. China.
Canadian Light Source , 44 Innovation Boulevard , Saskatoon , Saskatchewan S7N 2V3 , Canada.
ACS Appl Mater Interfaces. 2019 Apr 17;11(15):14066-14075. doi: 10.1021/acsami.8b22221. Epub 2019 Apr 8.
Silicon-based anodes have the potential to be used in next-generation lithium ion batteries owing to their higher lithium storage capacity. However, the large volume change during the charge/discharge process and the repeated formation of a new solid electrolyte interface (SEI) on the re-exposed Si surface should be overcome to achieve a better electrochemical performance. Fluoroethylene carbonate (FEC) has been widely used as an electrolyte additive for Si-based anodes, but the intrinsical mechanism in performance improvement is not clear yet. Here, we combined solid-state NMR, X-ray photoelectron spectroscopy, and X-ray photoemission electron microscopy to characterize the composition, structure, and inhomogeneity of the SEI on Si/C composite anodes with or without the FEC additive. Similar species are observed with two electrolytes, but a denser SEI formed with FEC, which could prevent the small molecules (i.e., LiPF, P-O, and Li-O species) from penetrating to the surface of the Si/C anode. The hydrolysis of LiPF leading to Li PO F and further to LiPO could also be partially suppressed by the denser SEI formed with FEC. In addition, a large amount of LiF could protect the cracking and pulverization of Si particles. This study demonstrates a deeper understanding of the SEI formed with FEC, which could be a guide for optimizing the Si-based anodes for lithium ion batteries.
由于具有更高的锂存储容量，硅基阳极有潜力应用于下一代锂离子电池。然而，为了实现更好的电化学性能，需要克服充电/放电过程中的大体积变化以及在重新暴露的硅表面上反复形成新的固体电解质界面（SEI）的问题。氟代碳酸乙烯酯（FEC）已被广泛用作硅基阳极的电解质添加剂，但其性能改善的内在机制尚不清楚。在此，我们结合固态核磁共振、X射线光电子能谱和X射线光电子发射显微镜来表征有或没有FEC添加剂的Si/C复合阳极上SEI的组成、结构和不均匀性。两种电解质观察到类似的物质，但FEC形成了更致密的SEI，这可以防止小分子（即LiPF、P-O和Li-O物质）渗透到Si/C阳极表面。由FEC形成的更致密的SEI也可以部分抑制LiPF的水解，导致LiPOF以及进一步生成LiPO。此外，大量的LiF可以保护硅颗粒的开裂和粉化。这项研究表明对由FEC形成的SEI有了更深入的理解，这可以为优化锂离子电池的硅基阳极提供指导。
