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: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>G</mml:mi> <mml:mn>4</mml:mn></mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>L</mml:mi> <mml:mi>i</mml:mi> <mml:mo>+</mml:mo></mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>F</mml:mi> <mml:mfenced><mml:mi>P</mml:mi> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> <mml:mi>S</mml:mi></mml:mfenced> </mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>P</mml:mi> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> <mml:mi>S</mml:mi></mml:mrow> </mml:msub> </mml:mrow> <mml:annotation>${{D}_{G4}\char62 {D}_{Li+}\char62 {D}_{F\left(POSS\right)}\char62 {D}_{POSS}}$</mml:annotation> </mml:semantics> </mml:math> . The computed cationic transference number (t₊) using the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>F</mml:mi> <mml:mfenced><mml:mi>P</mml:mi> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> <mml:mi>S</mml:mi></mml:mfenced> </mml:mrow> </mml:msub> <mml:annotation>${{D}_{F\left(POSS\right)}}$</mml:annotation> </mml:semantics> </mml:math> is consistent with NMR experimental data. The t₊ (and the trends with temperature) computed using the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>D</mml:mi> <mml:mrow><mml:mi>P</mml:mi> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> <mml:mi>S</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{D}_{POSS}}$</mml:annotation> </mml:semantics> </mml:math> and ionic conductivities are in good agreement.