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

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 behaviour of POSS(--NSO2CF3)(8), 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 morphological changes of the POSS tails upon interaction with Li+ ions were analysed 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: D-G4 > DLi+ > D-F(POSS) >D-POSS. The computed cationic transference number (t(+)) using the D-F(POSS) is consistent with NMR experimental data. The t(+) (and the trends with temperature) computed using the and ionic conductivities are in good agreement.