Investigation of the structure and dynamics of a localized high-concentration electrolyte
Anne HOCKMANN1, Diddo DIDDENS2, Isidora CEKIC-LASKOVIC2, Monika SCHÖNHOFF1
1University of Münster, Münster, Germany
2Helmholtz Institute Münster (IEK-12), Forschungszentrum Jülich GmbH, Münster, Germany
In recent years high-concentration liquid electrolytes (HCEs) received much attention in the battery research due to their good performance in lithium-based batteries. HCEs offer lots of advantages comprising, among others, broad electrochemical stability window, current collector protection, high safety, an effective solid electrolyte interface (SEI) formation, and therefore a high rate capability and stable galvanostatic cycling.[1] However, due to the high conducting salt content, HCEs are very viscous thus resulting in low ionic conductivity. This is why the concept of localized high-concentration electrolytes (LHCEs) was developed and published by Chen et al. in 2018.[2] Here, a third component, the diluent, is added to the system. The diluent reduces the viscosity but does not participate in the ion solvation. Thus, the local environment of the ions, which is responsible for the described benefits of a HCE, remains unchanged and the main disadvantage, the low ionic conductivity, is improved.
However, the structural heterogeneity of the LHCEs and the complexity of their composition require further research to gain an understanding of the structure and ion dynamics in order to reach the full potential of this electrolyte formulation. Therefore, in this work a LHCE consisting of the conducting salt lithium bis(fluorosulfonyl)imide (LiFSI), the solvent 1,2-dimethoxyethane (DME), and the diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was investigated by systematically varying the molar ratios of the three components in order to gain information about the structure and lithium dynamics in the electrolyte. A combination of different spectroscopic methods, namely NMR, Raman, and impedance spectroscopy, was used and supported by molecular dynamics (MD) simulations. Since MD simulations can confirm the experimental findings and provide additional information on a molecular level, this combination is very powerful to elucidate the structure, composition, and dynamics of this new type of electrolyte.
References
[1] Y. Yamada, J. Wang, S. Ko, E. Watanabe, A. Yamada, Nat Energy 4 (2019), 269–280.
[2] S. Chen, J. Zheng, D. Mei, K. S. Han, M. H. Engelhard, W. Zhao, W. Xu, J. Liu, J.-G. Zhang, Adv. Mater. 30 (2018), 1706102.