Pan Junkun, Charnay Aaron P, Zheng Weizhong, Fayer Michael D
Department of Chemistry, Stanford University, Stanford 94305, United States.
State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China.
J Am Chem Soc. 2024 Dec 25;146(51):35329-35338. doi: 10.1021/jacs.4c13423. Epub 2024 Dec 11.
Optimizing lithium-ion battery (LIB) electrolytes is essential for high-current applications such as electric vehicles, yet experimental techniques to characterize the complex structural dynamics responsible for the lithium transport within these electrolytes are limited. In this study, we used ultrafast infrared spectroscopy to measure chemical exchange, spectral diffusion, and solvation structures across a wide range of lithium concentrations in propylene carbonate-based LiTFSI (lithium bis(trifluoromethanesulfonimide) electrolytes, with the CN stretch of phenyl selenocyanate as the long-lived vibrational probe. Phenyl selenocyanate is shown to be an excellent dynamical surrogate for propylene carbonate in Li solvation clusters. A strong correlation between exchange times and ionic conductivity was observed. This correlation and other observations suggest structural diffusion as the primary transport mechanism rather than vehicular diffusion. Additionally, spectral diffusion observables measured by the probe were directly linked to the desolvation dynamics of the Li clusters, as supported by density functional theory and molecular dynamics simulations. These findings provide detailed molecular-level insights into LIB electrolytes' transport dynamics and solvation structures, offering rational design pathways to advanced electrolytes for next-generation LIBs.
优化锂离子电池（LIB）电解质对于电动汽车等大电流应用至关重要，但用于表征这些电解质中负责锂传输的复杂结构动力学的实验技术有限。在本研究中，我们使用超快红外光谱来测量基于碳酸丙烯酯的双（三氟甲烷磺酰）亚胺锂（LiTFSI）电解质中广泛锂浓度范围内的化学交换、光谱扩散和溶剂化结构，以苯基硒氰酸酯的C≡N伸缩振动作为长寿命振动探针。结果表明，苯基硒氰酸酯是锂溶剂化簇中碳酸丙烯酯的优良动力学替代物。观察到交换时间与离子电导率之间存在强相关性。这种相关性和其他观察结果表明，结构扩散是主要的传输机制，而非车辆扩散。此外，正如密度泛函理论和分子动力学模拟所支持的那样，探针测量的光谱扩散可观测量与锂簇的去溶剂化动力学直接相关。这些发现为LIB电解质的传输动力学和溶剂化结构提供了详细的分子水平见解，为下一代LIB的先进电解质提供了合理的设计途径。
