含硫有机溶剂对基于硼基锂盐电解液性能的影响及机理研究

Constitutes of electrolytes in lithium-ion batteries have a huge effect on battery performances. Results of previous research indicate that there is a good synergistic effect between alkyl boron-based lithium salt and sulfur-containing organic solvents. Electrolytes based on them can dramatically improve the interfacial property between electrode and electrolyte materials and then improve comprehensive properties of batteries. But there is still no complete explanation on the mechanism of this process. This project aims to clarify the formation processes of interfacial films during charging and discharging tests of batteries with this electrolyte system, as well as the respective role, mutual effect and influence mechanism of boron-based lithium salt and sulfur-containing organic solvents during film-forming process, by experimental analysis and theoretical calculation. The implementation methods include tracking reaction mechanism of sulfur components in electrode interface, the influence to film-forming process as well as membrane properties of boron-based salt because of introducing sulfur, and the influence on battery performance of membrane properties. The project would further identify beneficial interface reaction and illuminate synergism effects of salt-solvent and solvent-solvent systems, respectively. Based on the research results, the relational model among electrolyte compositions (such as the molecular structures of boron-based lithium salt, sulfur-containing solvent and other components, and the important quantum chemical parameters), interfacial properties and cell’s performances will be built. Besides, the findings of the study can be extrapolated to guide studies of similar system. And furthermore, research conclusions will contribute to guide the optimization of the electrolyte system.

锂离子电池的电解液组成，会在很大程度上影响电池性能。已有的研究结果表明，烷基硼酸锂盐与含硫有机溶剂间存在协同促进效应。基于它们的电解液，可明显改善电解液/电极材料的界面性能，进而提升电池综合性能。但对这一过程，尚无完整的机理解释。项目拟采用传统测试表征手段与量子化学计算相并重的方法，通过跟踪研究含硫组分在电极界面的反应历程、含硫组分的引入对硼基锂盐反应成膜过程及膜性质的影响、膜性质对电池性能的影响，揭示此类电解液体系在充放电过程中界面膜形成的具体历程，并揭示硼基锂盐、含硫有机溶剂在成膜过程中各自发挥的作用、相互间的影响及影响机理，从而明确有益的界面反应及盐-溶剂、溶剂-溶剂间的协同促进机理。根据研究结果，建立起硼基锂盐、含硫溶剂、其他组分的分子结构、重要量子化学参数与界面性能、电池性能间的关联模型。进一步地，将研究结论外推，指导类似体系的相关研究。研究结论有助于指导电解液体系的配方优化。

具有螯合结构的烷基硼酸锂（下文简称硼基锂盐），如双草酸硼酸锂（LiBOB）、草酸二氟硼酸锂（LiODFB），是近年来的研究热点之一。但是，硼基锂盐/碳酸酯的电解液体系在电极表面所形成固态电解质（SEI）膜相对较厚，阻抗偏高，严重限制了电池的低温性能及倍率性能。相较于结构相似的碳酸酯，含硫溶剂通常具有更活泼的性质。而且，已有的研究结果表明，当 SEI 膜中含有种类适当的适量含硫组分时，界面上的锂离子电导率、热力学稳定性均会得到显著改善。因此，通过添加含硫溶剂来改善界面性能，是目前电解液组成优化的一个重要思路。如添加环丁砜（SL）、硫酸乙烯酯（DTD）亚硫酸丁烯酯 (BS)、硫酸二甲酯（DMS）、丙烯基-1，3-丙磺酸内酯（PES）等，均被报道可在碳基负极材料表面形成致密、有效且低阻抗的 SEI保护膜。本研究通过跟踪研究含硫组分在电极界面的反应程、含硫组分的引入对硼基锂盐反应成膜过程及膜性质的影响、膜性质对电池性能的影响，揭示此类电解液体系在充放电过程中界面膜形成的具体历程，并揭示硼基锂盐、含硫有机溶剂在成膜过程中各自发挥的作用、相互间的影响及作用机理，从而明确有益的界面反应及盐-溶剂、溶剂-溶剂间的协同促进机理。根据研究结果，可建立起硼基锂盐、含硫溶剂、其他组分的分子结构、重要量子化学参数与界面性能、电池性能间的关联模型。研究结论可为电解液组分的选用、各组分配比的确定，甚至锂盐、溶剂物质的分子设计提供依据。这对构建匹配于各类电极材料的新型高性能电解液体系意义重大。