Song Linhu, Li Shiyou, Wang Jie, Zhu Junlong, Wang Yinong, Cai Xingpeng, Zong Feifei, Wang Hui, Cui Xiaoling, Zhao Dongni
School of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, P. R. China.
Key Laboratory of Low Carbon Energy and Chemical Engineering of Gansu Province, Lanzhou 730050, P. R. China.
ACS Appl Mater Interfaces. 2023 Oct 25;15(42):49727-49738. doi: 10.1021/acsami.3c08704. Epub 2023 Oct 16.
Si@C as a high specific capacity anode material for lithium batteries (LIBs) has attracted a lot of attention. However, the severe volume change during lithium de-embedding causes repeated rupture/reconstruction of the solid electrolyte interphase (SEI), resulting in poor cycling stability of the Si-based battery system and thus hindering its application in commercial batteries. Using electrolyte additives to form an excellent SEI is considered to be a cost-effective method to meet this challenge. Here, the classical film-forming additive vinyl carbonate (VC), and the newly emerging lithium salt additive lithium difluorophosphate (LiDFP), are chosen as synergistic additives to improve the electrode-electrolyte interface properties. Final results show that the VC additive generates flexible polycarbonate components at the electrode/electrolyte interface, preventing the fragmentation of Si particles. However, the organic components show high impedance, inhibiting the fast transport of Li. This defect can be supplemented from the decomposition substances of the LiDFP additive. The derived inorganic products, such as LiF and LiPO, can strengthen the reaction kinetics of the electrode, reduce the interfacial impedance, and promote the Li transport. Thus, the synergistic effect of VC and LiDFP additives builds an effective SEI with good flexibility and high ionic conductivity and then significantly improves the cycling and rate stability of Si@C anodes. The experimental results show that the utilization of LiDFP and VC additives to modify the Si@C anode interface enhances the capacity retention of the Si@C/Li half-cell after 100 cycles from 68.2% to 85.1%. Besides, the possible mechanism of action between VC and LiDFP is proposed by using the spectral characterization technique and density functional theory (DFT) calculations. This research opens up a new possibility for improvement of SEI, and provides a simple way to achieve high-performance Si-based LIBs.
硅碳复合材料作为一种用于锂电池（LIBs）的高比容量负极材料已引起广泛关注。然而，在锂脱嵌过程中严重的体积变化会导致固体电解质界面（SEI）反复破裂/重构，从而导致硅基电池系统的循环稳定性较差，进而阻碍其在商用电池中的应用。使用电解质添加剂来形成优异的SEI被认为是应对这一挑战的一种经济有效的方法。在此，选择经典的成膜添加剂碳酸亚乙烯酯（VC）和新兴的锂盐添加剂二氟磷酸锂（LiDFP）作为协同添加剂来改善电极-电解质界面性能。最终结果表明，VC添加剂在电极/电解质界面生成柔性聚碳酸酯成分，防止硅颗粒破碎。然而，有机成分显示出高阻抗，抑制了锂的快速传输。这一缺陷可由LiDFP添加剂的分解产物来补充。衍生的无机产物，如LiF和LiPO，可增强电极的反应动力学，降低界面阻抗，并促进锂的传输。因此，VC和LiDFP添加剂的协同作用构建了具有良好柔韧性和高离子电导率的有效SEI，进而显著提高了硅碳复合材料负极的循环稳定性和倍率性能。实验结果表明，利用LiDFP和VC添加剂对硅碳复合材料负极界面进行改性，使硅碳复合材料/锂半电池在100次循环后的容量保持率从68.2%提高到85.1%。此外，通过光谱表征技术和密度泛函理论（DFT）计算，提出了VC和LiDFP之间可能的作用机理。该研究为改善SEI开辟了新的可能性，并提供了一种实现高性能硅基锂电池的简便方法。
