NSF-DFG Confine: Structure, dynamics, and electrochemical stability of concentrated electrolytes in confined spaces

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This project will investigate the fundamental role of confinement on the ionic structure and dynamics in highly concentrated electrolytes, and reveal how confinement impacts performance of battery systems. Confinement occurs when the dimension of a physical feature, such as a pore, is comparable to the dimensions of the molecules present. Porous electrodes are common in batteries, with pore sizes that are often smaller than 50 nanometers. Ions need to navigate and react electrochemically inside this confined pore space for electrical current to flow. Therefore, in battery systems the electrolyte dynamics and reactivity within pores is central to the device performance. Highly concentrated electrolytes are a burgeoning field driven by groundbreaking opportunities for safer and higher energy density electrochemical devices, in particular for new directions in aqueous batteries, which use water instead of a flammable solvent. Despite their promises, highly concentrated electrolytes bring their own set of challenges that are exacerbated within the confined settings of battery systems. A poor understanding of transport properties in highly concentrated electrolytes suggest that there are unique structure-property relationships at play that warrant further investigation, especially under confinement. This project will yield advancements in electrolyte engineering and offers insights into improved electrode materials/structures for better batteries. Beyond batteries, the results will have important implications for colloidal gels, ionic and polymeric liquids, and generally molecules under confinement. Insights from studying the water-based electrolytes may also aid in environmental remediation applications like brine management. This project will also provide training at several levels. Undergraduate and graduate student researchers will gain unique perspectives from the international collaboration and local elementary students will learn about battery basics through outreach programs. This collaborative project will uncover fundamental structure-property relationships for confined concentrated electrolytes using experiments, theories, and models. The team will isolate contributions from the anion, cation, valency, as well as the dielectric constant of the solvent to obtain a clear understanding of the underlying structure and dynamics. The Berkeley team will focus on the fundamental aspects leading to novel theoretical frameworks and validated models for the electric double layer and transport dynamics under confinement using experimental techniques such as the Electrochemical Surface Force Apparatus (ESFA), impedance spectroscopy, molecular simulations, and recently developed Onsager transport theory. Insights from these studies will provide input to the Münster team who will address the role of EDLs on non-Faradaic processes in porous electrode systems and its influence on the reactivity on metallic electrodes from a chemical and electrochemical standpoint using different electrochemical and spectroscopically methods including Raman (including in situ surface enhanced) and IR spectroscopy, as well as in situ NMR and laser spectroscopy. This project involves a novel combination of experimental techniques and theoretical descriptions for the forces, relaxation and transport behaviors of electrolytes under confinement. This project was awarded through the “NSF-DFG Lead Agency Activity in in Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.