Molecular Simulation Studies of Solvent-in-Salt Electrolytes for Energy Storage Applications

Significant efforts have been made to improve the performance of capacitive energy storage devices, which exhibit high power density but low energy density. Traditional organic electrolytes display relatively high conductivities, but low electrochemical stabilities which negatively impact the rate handling capabilities of these energy storage devices. Ionic liquids have been extensively studied in recent years due to their high electrochemical stability, but suffer from slow dynamical properties. Solvent-in-salt electrolytes (SISE), defined as highly concentrated salt solutions, have recently emerged as promising electrolytes for capacitive energy storage devices due to having high electrochemical stabilities while also displaying relatively high conductivity¹.

Here we present an integrated study of SISE² through various computational and experimental approaches to better understand the molecular behavior that drives dynamical properties. Specifically, neutron scattering and NMR experiments are performed to measure ion diffusivity, while impedance spectroscopy is conducted to measure the ionic conductivity of these electrolytes. Accompanying these experiments is a series of Molecular Dynamics (MD) simulations which provide an analysis of ion pairing and structuring to better understand the atomistic origins of ionic conductivity. Furthermore, the role of confinement on the dynamical properties is investigated through studies of SISE in novel MXenes³, which are a family of two-dimensional metal carbides and nitride materials. Included are Grand Canonical Monte Carlo (GCMC) and Gibbs Ensemble Monte Carlo (GEMC) simulations to better understand how SISE fill and interact with the interlayer spacings of MXenes.

1. Suo, L., Hu, Y.S., Li, H., Armand, M., Chen, L. (2013). A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries. Nature Communications. 4(1481).
2. Popov, I., Sacci, R. L, Sanders, N. C., Matsumoto, R. A., Thompson, M. W., Osti N. C., Kobayashi, T., Tyagi, M. S., Mamontov, E., Pruski, M., Cummings, P. T., Sokolov, A. (2020). Critical Role of Anion-Solvent Interactions for Dynamics of Solvent-in-Salt Solutions. Journal of Physical Chemistry C. https://doi.org/10.1021/acs.jpcc.9b10807
3. Anasori, B., Lukatskaya, M. R., Gogotsi, Y. (2017). 2D metal carbides and nitrides (MXenes) for energy storage. Nature Review Materials. 2.