Lithium-ion batteries have been widely applied in portable electronics due to its high energy density. [1] It is essential to improve the state-of-the-art LIBs, which are far from their maximum theoretical energy density, in order to power up electric vehicles. [2] Researchers have shown that the physiochemical properties, such as conductivity, electrochemical window and ability to form solid electrolyte interphase (SEI), depend on the solution structures of the electrolyte. [3] Thus, it is crucial to determine the solution structures of the electrolyte and the relative solvating ability of various solvents for designing advanced electrolyte systems.

Novel method utilizing specific 2D-NMR technique was successfully developed to probe the solvation state of different electrolyte solvents. The result obtained by this technique agreed with the measurement by vibrational spectroscopy. Most importantly, unlike the vibrational spectroscopy measurement, this method can be easily applied to electrolyte system with two or more electrolyte solvents. For example, it is not impossible to determine the solvation state of a ternary-solvent electrolyte comprising EC, EMC and DMC by vibrational spectroscopy due to the severe overlapping of peaks. However, the solvation state can be easily determined with the new method developed. Therefore, this new technique provides an important experimental tool in examining the solvation state of different electrolyte solvents. Application of this newly developed technique in revealing the electrochemical performance of various electrolytes on Li-ion batteries will also be discussed.

References:

[1] (a) Tarascon, J.-M.; Armand, M., Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359-367. (b) Armand, M.; Tarascon, J.-M., Building Better Batteries. Nature 2008, 451, 652-657.

[2] Goodenough, J. B.; Park, K.-S., The Li-Ion Rechargeable Battery: A Perspective. Journal of the American Chemical Society 2013, 135, 1167-1176.

[3] (a) Seo, D. M.; Reininger, S.; Kutcher, M.; Redmond, K.; Euler, W. B.; Lucht, B. L., Role of Mixed Solvation and Ion Pairing in the Solution Structure of Lithium Ion Battery Electrolytes. The Journal of Physical Chemistry C 2015, 119 (25), 14038-14046. (b) Xu, K., Electrolytes and interphases in Li-ion batteries and beyond. Chemical reviews 2014, 114 (23), 11503-618.