Modeling of Complex Electrolytes and the Impact of Electric Double Layer (EDL) on SEI Formation

Next-generation electrolytes designed for high-energy batteries with Li-metal electrodes or operating under extreme conditions (e.g. fast charging and low temperature) can no longer be viewed and simulated as a dilute system with fully solvated ions.<br/>In this talk, we first categorize homogenous electrolytes, based on the solvent-ion interactions, salt concentration, solubility limit, and the availability of free solvents, into low-concentration electrolytes (LCE); high-concentration electrolytes (HCE) or medium concentration electrolytes (MCE). Heterogeneous structures can form in liquid electrolytes when combined with non-ion-solvating diluents. We named these heterogeneous structures as “micelle-like structures” in localized HCE and localized MCE, as LHCE and LMCE, respectively.<br/>This talk will discuss the computational design of these chemically and compositionally complex electrolytes as well as the solid electrolyte (SEI) interface they form in batteries. The structures of the complex electrolytes were obtained first by Molecular Dynamics (MD) simulations. Starting from different initial configurations with salt-solvent clusters with varying sizes embedded in diluent, instead of randomly mixed structures, accelerated the process to identify the lowest energy configurations<br/>Ion transport in these electrolytes is strongly coordinated in these complex electrolytes. Ion correlations must be considered, e.g. via the Green-Kubo relationship to accurately predict the experimentally measured ion conductivities as a function of concentration. We will show how ionic conductivity varies in the formation, percolation, and branching of salt-solvent clusters.<br/>The formation of the solid electrolyte interphase (SEI) is influenced by the Electric Double Layer (EDL) structure, which is dramatically different from their bulk structures. Therefore, the MD simulated EDL structures were feedback to ab initio calculations to determine the species will be reduced and form SEI.