A molecular dynamics study of a fully zwitterionic copolymer/ionic liquid‐based electrolyte: Li+ transport mechanisms and ionic interactions

Abstract The development of polymer electrolytes (PEs) is crucial for advancing safe, high‐energy density batteries, such as lithium‐metal and other beyond lithium‐ion chemistries. However, reaching the optimum balance between mechanical stiffness and ionic conductivity is not a straightforward task. Zwitterionic (ZI) gel electrolytes comprising lithium salt and ionic liquid (IL) solutions within a fully ZI polymer network can, in this context, provide useful properties. Although such materials have shown compatibility with lithium metal in batteries, several fundamental structure‐dynamic relationships regarding ionic transport and the Li + coordination environment remain unclear. To better resolve such issues, molecular dynamics simulations were carried out for two IL‐based electrolyte systems, N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) with 1 M LiTFSI salt and a ZI gel electrolyte containing the IL and a ZI copolymer: poly(2‐methacryloyloxyethyl phosphorylcholine‐co‐sulfobetaine vinylimidazole), poly(MPC‐co‐SBVI). The addition of ZI polymer decreases the [TFSI] − –[Li] + interactions and increases the IL ion diffusivities, and consequently, the overall ZI gel ionic conductivity. The structural analyses showed a large preference for lithium‐ion interactions with the polymer phosphonate groups, while the [TFSI] − anions interact directly with the sulfonate group and the [BMP] + cations only display secondary interactions with the polymer. In contrast to previous experimental data on the same system, the simulated transference numbers showed smaller [Li] + contributions to the overall ionic conductivities, mainly due to negatively charged lithium aggregates and the strong lithium‐ion interactions in the systems.