Yang Yaozong, Wang Jie, Li Zhaolin, Yang Zhao, Wang Bo, Zhao Hailei
School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People's Republic of China.
Beijing Municipal Key Laboratory of New Energy Materials and Technologies, Beijing 100083, People's Republic of China.
ACS Nano. 2024 Mar 12;18(10):7666-7676. doi: 10.1021/acsnano.4c00998. Epub 2024 Feb 28.
Constructing a robust solid electrolyte interphase (SEI) is extremely critical to developing high-energy-density silicon (Si)-based lithium-ion batteries. However, it is still elusive how to accurately manipulate the chemical composition and structure of the SEI layer. Herein, a LiF-dominated SEI film intertwined by a highly elastic polymer is achieved by regulating the defluorination mechanism of the fluorinated carbonate additive on the Si electrode surface. The experimental and computational results confirm that the decomposition route of -difluoroethylene carbonate (DFEC) molecules can be significantly altered in the presence of lithium difluoro(oxalato)borate (LiDFOB) additive. The induction of direct defluorination of DFEC step by LiDFOB, as opposed to the breaking of C-O bonds without LiDFOB addition, is crucial in ensuring the exclusive formation of LiF-dominated SEI and maintaining the cyclic structure of DFEC. The defluorinated DFEC easily polymerizes to form poly(vinylene carbonate), enhancing the elasticity of the SEI. The resulting LiF-dominated SEI film with a polymer interwoven outer layer shows enhanced ionic conductivity and mechanical stability, which can effectively accelerate electrode reaction kinetics and maintain the structural stability of the Si electrode. As a result, the Si electrode with the electrolyte containing the designed dual-additive exhibits superior cycling stability and excellent rate performance, delivering a high reversible capacity of 1487.3 mAh g after 1000 cycles at 2 A g.
构建坚固的固体电解质界面（SEI）对于开发高能量密度的硅基锂离子电池极为关键。然而，如何精确调控SEI层的化学成分和结构仍不清楚。在此，通过调控含氟碳酸酯添加剂在硅电极表面的脱氟机制，实现了由高弹性聚合物交织而成的以LiF为主导的SEI膜。实验和计算结果证实，在二氟草酸硼酸锂（LiDFOB）添加剂存在下，二氟碳酸乙烯酯（DFEC）分子的分解途径会发生显著改变。与不添加LiDFOB时C-O键断裂不同，LiDFOB诱导DFEC直接脱氟对于确保以LiF为主导的SEI的独家形成以及维持DFEC的环状结构至关重要。脱氟后的DFEC易于聚合形成聚碳酸亚乙烯酯，增强了SEI的弹性。所得的具有聚合物交织外层的以LiF为主导的SEI膜表现出增强的离子导电性和机械稳定性，能够有效加速电极反应动力学并维持硅电极的结构稳定性。结果，含有设计的双添加剂电解质的硅电极表现出优异的循环稳定性和出色的倍率性能，在2 A g下1000次循环后可提供1487.3 mAh g的高可逆容量。
