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 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: $$ . The computed cationic transference number (t₊) using the $$ is consistent with NMR experimental data. The t₊ (and the trends with temperature) computed using the $$ and ionic conductivities are in good agreement.