Interatomic Interactions and Ion-Transport in a Polyoligomeric Silsesquioxane-based Multi-Ionic Salt Electrolyte for Lithium-Ion Batteries.

Abstract

Polyoligomeric silsesquioxane (POSS) tailored with trifluoromethanesulfonylimide-lithium and solvated in tetraglyme (G4) is a potential electrolyte for Li-ion batteries. Using classical MD simulations, at different G4/POSS(-LiNSO2CF3)8 molar ratios, the interactions of Li+ ions with the oxygen atoms of G4 and, oxygen/nitrogen sites of the pendant tails, the behavior of POSS(--NSO2CF3)8 anion, and the mobility of species are investigated. The RDFs showed that there exist competing interactions of the O(G4), O(POSS), and N(POSS) sites with Li+ ions. The lifetime analysis indicated that Li+---O(POSS) and Li+--- N(POSS) interactions are longer-lived compared to Li+---O(G4). The morphology changes of the POSS tails upon interaction with Li+ ions were analyzed using rotational lifetimes, coiling, and end-to-end distances. The ion-speciation analysis indicated the presence of solvent-separated ion pairs (SSIPs), contact ion pairs (CIPs), and higher-order ion clusters, with SSIPs being the more dominant species at 32/1. The self-diffusion coefficients for the 32/1 system, which showed the least cation-anion interaction, followed the trend: [[EQUATION]] > [[EQUATION]] > [[EQUATION]] > [[EQUATION]]. The computed cationic transference number (t+) using the [[EQUATION]] is consistent with NMR experimental data. The t+ (and the trends with temperature) computed using the [[EQUATION]] and ionic conductivities are in good agreement.