(648g) Effect of Electric Field on Competitive Associations in Zwitterionic Electrolytes: A Molecular Simulation Study

Manh Tien Nguyen, Qing Shao

Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506

ABSTRACT: High-performance lithium-ion batteries have been recognized as an important ingredient for realizing the sustainable development of society. One challenge for lithium-ion batteries is to develop non-flammable electrolytes with high Li⁺conductivity. Zwitterionic molecules emerge as new electrolytes due to their unique chemical structures. They possess both cationic and anionic groups, and present high dipole moment and zero net charge. However, it remains unclear how zwitterions associate with lithium ions and counterions, and how their associations influence the ion conductivity. To fill this knowledge gap, we investigate the competitive associations among zwitterionic molecules, lithium ions and counterions and their diffusion under an external electric field (0-1.8 V/nm) using molecular dynamics simulations. We also investigate the influence of electrostatic interactions on the propertiesof zwitterionic electrolytes by scaling the partial charges of these molecules and ions. The simulation results show that zwitterionic molecules change the effect of electric fields on associations and diffusion of lithium ions and counterions. Enhancing electric field strength increases self-diffusions of lithium ions and counterions with the presence of zwitterionic molecules, while only that of lithium ions without zwitterionic molecules. Zwitterionic molecules induce a “cooperative diffusion” mode for lithium ions and counterions by associating with both of them. This diffusion mode help resolve the traditional issue that lithium ions and counterions may aggregate on different locations in electrolytes under an electric field.