Salt on the Mechanical and Dynamic Properties of Polyzwitterion-supported Ionogel Electrolytes*

Polyzwitterion (polyZI) supported ionogel electrolytes have emerged as alternatives for designing mechanically robust electrolytes with high room temperature conductivities. This is due to the PolyZI side chains playing a dual role as noncovalent crosslinking sites and mobile ion dissociation promoters. In this study, we used atomistic molecular dynamic simulations to probe the impact of cation identity (Li⁺vs Na⁺ ) on the elastic moduli and conductivity of single-salt (Li⁺ or Na⁺) and mixed-salt (Li⁺ and Na⁺) ionogels as a function of ZI weight percentage. Our model system is comprised of ZI poly (2-methacryloyloxyethyl phosphorylcholine) (pMPC) loaded with 0.5M X + TFSI/N-butyl-N-methylpyrrolidinium (BMP) TFSI ionic liquid electrolyte (where X ⁺ = Li⁺, Na⁺, or Li ⁺ and Na⁺ ). For both single- and mixed-salt doped ionogel electrolytes, with increasing ZI weight percentage, we observe an increasing association between Li⁺ and Na⁺ ions with the ZI polymer. This observation is accompanied by a decrease in the interaction between Li⁺ and Na⁺ ions with the ionic liquid and salt common anion. Our simulations also reveal a preferential association of Li + - ZI over Na + - ZI in both cases. We also present the probability of ion-pair associations to identify the mechanistic origins of structural and dynamical property differences in both single- and mixed-salt ionogels. Lastly, we show cluster analysis to rationalize the experimentally observed elastic moduli and conductivity results.