Effect of Zwitterionic Molecules on Ionic Transport under Electric Fields: A Molecular Simulation Study

Zwitterionic molecules can aßociate with both cations and anions in electrolytes. This ability can be leveraged to manipulate ionic aßociations and transport if we understand the related mechanisms. We investigate the effect of zwitterionic molecules on ionic aßociations and transport in the electrolytes composed of 1:1 Li salts (anions: [TFSI]^- and [BETI]^-) and zwitterionic molecules containing imidazolium and sulfonate groups under 0-1.1 V/nm electric fields using molecular dynamics simulations. The ionic aßociations and transport in the electrolytes are analyzed using Li⁺-zwitterion and Li⁺-anion radial distribution functions, aßociation number and lifetimes, and diffusion coefficients of Li⁺, anion, and zwitterionic molecules. The simulation results show a close correlation between the ionic aßociation and transport. Small Li⁺ ions and large anions diffuse at the same level with the presence of zwitterionic molecules. The electric field must be stronger than a threshold to influence diffusion and aßociations of ions and zwitterionic molecules.