Yang Xiaohua, Liu Xiangyang, Han Jinhui, Liu Zhiping, Zhang Xianren
State Key Laboratory of Organic-Inorganic Composites, School of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
J Phys Chem B. 2023 Apr 6;127(13):3026-3040. doi: 10.1021/acs.jpcb.3c00475. Epub 2023 Mar 28.
It is critical to design the solvents or additives to provide high oxidation stability of electrolyte and good solid-electrolyte interphase (SEI) in lithium secondary batteries. In this work, we used quantum chemical calculations to evaluate carbonates with various fluorinated patterns to satisfy the requirements of antioxidation, stabilize SEI films, and modify solvation structures. The thermodynamic cycle method was used to calculate the oxidation and reduction potentials of a series of fluorinated linear (dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) and cyclic carbonates (ethylene carbonate, propylene carbonate, and 2,3-butanediol cyclic carbonate) vs Li/Li. Both quantity and position of fluorine substitutions have a significant impact on the oxidation and reduction potentials according to correlation analyses. The instinctive causes for the potential change were the influence of the fluorinated position on the frontier orbital. We further studied lithium-ion coordinated fluorinated carbonates and found that the binding energy is mostly determined by electrostatic interaction according to the energy decomposition analysis. Fluorination will weaken the coordination ability of carbonates, which is demonstrated by their electrostatic potential distributions. Furthermore, it was found that the linear carbonate fluorinated at the α-position under reduction reaction easily produces LiF in situ, which was beneficial to the construction of good SEI. Finally, we provide some suggestions for the development of fluorinated carbonates based on the theoretical studies in this work.
设计溶剂或添加剂以提供锂二次电池中电解质的高氧化稳定性和良好的固体电解质界面（SEI）至关重要。在这项工作中，我们使用量子化学计算来评估具有各种氟化模式的碳酸酯，以满足抗氧化、稳定SEI膜和改变溶剂化结构的要求。采用热力学循环法计算了一系列氟化线性碳酸酯（碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯）和环状碳酸酯（碳酸乙烯酯、碳酸丙烯酯和2,3-丁二醇环状碳酸酯）相对于Li/Li的氧化和还原电位。相关性分析表明，氟取代的数量和位置对氧化和还原电位有显著影响。电位变化的内在原因是氟化位置对前线轨道的影响。我们进一步研究了锂离子配位的氟化碳酸酯，根据能量分解分析发现，结合能主要由静电相互作用决定。氟化会削弱碳酸酯的配位能力，这通过它们的静电势分布得到证明。此外，发现在还原反应下α位氟化的线性碳酸酯容易原位生成LiF，这有利于构建良好的SEI。最后，基于本工作中的理论研究，我们为氟化碳酸酯的开发提供了一些建议。
