Molecular Dynamics (MD) Simulation of Electrolytes
Prediction of crystal structure and transport properties in bulk and at interfaces
Molecular dynamics (MD) computer simulations were employed to illuminate molecular details of solvent and electrolytes transport in bulk and at interfaces. [1,2] This detailed nanoscale information is out of reach of any experiment and is useful to optimize solvent properties and uncover the structural fundamentals behind transport and charge transfer in battery systems, in particular within electrodes.
For this, we developed the first reliable MD force-field for the state-of-the-art solvent employed in Li/S batteries, namely LiNO3/TFSI in DME/DIOX mixtures. We also computed the transport of molecular solutes through 1 nm wide slit-shaped pores carved out of solid substrates of silica. The results showed that the solute permeability through the solvated pores is strongly dependent on the solid-substrate surface structure. Detailed analysis of the simulated systems reveals that local properties of confined solvent, including its structure, and more importantly, evolution of solvation free energy and hydrogen-bond structure are responsible for the pronounced differences observed. A multi-scale approach was then implemented to demonstrate that a Smoluchowski one-dimensional model is able to reproduce the molecular-level results for short pores when appropriate values for the local self-diffusion coefficients are used as input parameters. We propose that the model can be extended to predict solute transport through solvated pores of macroscopic length and various geometries. On-going work extends the models developed to the specific case of lithium migrating to carbon electrodes. When verified by experiments, our simulation results could have important implications in predictions of lithium migration through electrode materials.