Influence of Cation and Anion Chemistry on the Ionic Conductivity and Transference Number of Zwitterionic Polymer-Supported Ionic Liquid Electrolytes

Abstract

Polyzwitterionic (polyZI) ionogels have been demonstrated to be promising candidates for battery electrolyte applications. In this study, we used atomistic molecular dynamics simulations to study the influence of alkali metal cation (Li⁺ or Na⁺) and anion (${\mathrm{BF}}_4^{-}$, ${\mathrm{PF}}_6^{-}$, TFS^–, and TFSI^–) chemistry on the dynamic and structural properties of poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] supported ionic liquid electrolytes. With an increase in the poly(MPC) content, our simulations revealed a decrease in the diffusivities and conductivities in both the Li⁺ and Na⁺ ionogels. With the increasing polyZI content, the results show a simultaneous increase in the inverse Haven ratios and transference numbers. While varying the anion identities, our findings indicate that chemistries in which a higher fraction of alkali metal cations coordinate with the polymers result in enhanced inverse Haven ratios, while systems with stronger alkali metal cation–polyZI interactions exhibit improved transference numbers. Overall, our results shed light on the complex nature and influence of the electrostatic interactions between the polyZI, ionic liquid, and salt ions on the mobility and structural properties of polyZI ionogels.