Robust Electron-Donating Organic Compounds for Non-Aqueous Redox Flow Batteries

Abstract

The development of robust electro-active materials is critical for a variety of electrochemical energy storage applications. Phenothiazines, phenoxazines, carbazoles, and triphenylamines are among some of the numerous electron-donating aromatic compounds that have been studied for numerous applications in organic electronics, photovoltaics, and electrochemically-mediated synthesis. Their use as electrolyte components and electrode materials has only been studied by a few groups, yet these materials are easy to functionalize, enabling tuning their electronic properties, solubility, and stability. My research group initially explored derivatives of these compounds as redox shuttles for overcharge protection of lithium-ion batteries. With systematic variations in structure, our efforts combining analytical techniques with density functional theory calculations have enabled us to identify decomposition products and to predict reasonable mechanisms that lead to failure in neutral and oxidized states. Our development of robust derivatives that survived for thousands of hours of overcharge was a result of the design rules that came from these studies. Recently we have expanded our use of these compounds as catholyte components for non-aqueous redox flow batteries. In one to three steps from commercially available materials, we have prepared highly soluble phenothiazine derivatives (solubility of 1-2 M in organic electrolytes) that can serve as one- and/or two-electron donors with long lifetimes in the charged states. This presentation will focus on the synthesis, spectroscopic, and electrochemical analysis of these materials as electron donors for redox flow batteries.