Multinuclear magnetic resonance investigation of cation-anion and anion-solvent interactions in carbonate electrolytes
Multinuclear magnetic resonance investigation of cation-anion and anion-solvent interactions in carbonate electrolytes
复制标题
DOI：
10.1016/j.jpowsour.2018.07.095
复制
发表时间：
2018-09
影响因子：
9.2
通讯作者：
Jing Peng;Mallory P Gobet;M. Devany;K. Xu;A. Cresce;O. Borodin;S. Greenbaum
中科院分区：
文献类型：
--
作者：
Jing Peng;Mallory P Gobet;M. Devany;K. Xu;A. Cresce;O. Borodin;S. Greenbaum
电解质中的离子-溶剂相互作用的研究对于基本理解通过本体电解质的离子传输以及两个电极上的界面形成过程至关重要，这决定了锂离子电池（LIB）的性能。本文采用核磁共振（NMR）方法研究了两种典型锂盐（六氟磷酸锂（LiPF 6）和四氟硼酸锂（LiBF 4））溶解在碳酸乙烯酯（EC）/碳酸二甲酯（DMC）混合物中的溶剂化行为。随着两个体系中盐浓度和DMC百分比的增加，19 F NMR随J 31 P− 19 F和J 11 B− 19 F的减少而沿着发生高场位移，这证明了在高介电介质存在减少的环境中Li+和F−之间的相互作用更强。11 B的四极弛豫机制优于19 F的弛豫机制，表明LiBF 4在高盐浓度或低极性介质中主要以离子对形式存在。通过7 Li，19 F，1HNMR扩散测量表征了阳离子、阴离子和溶剂分子的相对迁移率，结果支持了上述结论。在LiBF 4体系中，盐浓度和溶液极性对阴阳离子聚集和溶剂化的影响比在LiPF 6体系中大得多。
The investigation of ion-solvent interaction in electrolytes is crucial for basic understanding of ion transport through the bulk electrolyte as well as interphase formation processes on both electrodes, which dictate performances of lithium ion batteries (LIBs). In this report, nuclear magnetic resonance (NMR) was used to study the solvation behaviors of two typical lithium salts (lithium hexafluorophosphate, or LiPF 6, and lithium tetrafluoroborate, or LiBF 4) dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) mixtures. With increasing salt concentration and DMC percentage in both systems, 19 F NMR experiences an upfield shift along with decreasing J 31 P− 19 F and J 11 B− 19 F, which evidence the stronger interaction between the Li+ and F− in an environment with diminishing presence of high dielectric medium. The quadrupolar relaxation of 11 B dominates the 19 F relaxation mechanism and demonstrates that LiBF 4 mainly exists as ion pairs in solution either at high salt concentration or in a medium of low polarity. 7 Li, 19 F, 1 H NMR diffusion measurements were conducted to characterize the relative mobility of cation, anion and solvent molecules, the results of which support the conclusion above. Salt concentration and solution polarity have a much stronger effect on cation-anion aggregation and solvation in the LiBF 4 system than in the LiPF 6 system.