(526g) Percolated Aggregate Sturcture and Ion Transport in Precise Sulfophenylated Polyethylene Ionomers

Ionomers present an attractive potential alternative to standard electrolytes in Li ion batteries due to their capacity to function as single-ion conductors. When the spacing between adjacent pendant groups is precisely controlled, ionic groups within ionomers have been shown to self-assemble to form aggregates with well-ordered morphologies. The structure of these aggregates can have a significant impact upon ion conductivity. In order to better understand the system in microscopic detail, we perform fully atomistic molecular simulations to probe the assembled ionic aggregates of sulfophenylated polyethylene ionomers with a spacing of five carbon atoms between pendant groups (p5PhS), neutralized with a series of cations (Li, Na, and Cs). We find that fully neutralized polymers form ionic aggregates that percolate the system for each ion species. Li and Na aggregates adopt branching ribbon-like configurations, while Cs aggregates are more disordered. We utilize graph-based techniques to better quantify these structural differences. Good agreement between the computed structure factors and x-ray scattering data provides support for the validity of the atomistic models used. Finally, the dynamics in each system reveal that the ions slowly diffuse from sulfonate group to sulfonate group through the percolated aggregates, with larger ions exhibiting larger mean-squared displacements.

This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of energy (DOE) Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government. SAND2020-3928 A