High Potential Organic Materials for Battery Applications

There is a large and rapidly growing need for electrical energy storage in modern society. Lithium ion batteries (LIBs) are ubiquitous, powering everything from our cell phones to power tools to cars. However, there are still some safety concerns, often related to the danger presented by LIB overcharge. Thus, numerous research groups have explored the development of “redox shuttles” that allow charging current to pass while limiting cell voltage to values at or just above that expected at a state of charge (SOC) = 100%. These additives are generally organic compounds that undergo reversible electrochemical oxidation at potentials near the maximum design value. However, many of the compounds studied to date are either too expensive or not sufficiently durable for commercial applications.

At the same time, redox-active organic materials are being investigated in order to develop non-aqueous redox flow batteries (RFBs) for inexpensive grid-level electrical energy storage systems. Indeed, because such materials must exhibit reversible oxidation at high potential, many candidates for redox shuttles have also been employed as catholytes in RFB applications. Also, they display highly reversible electrochemical oxidation and very good solubility in carbonate solvents, making them particularly attractive for flow battery applications.

In this poster, we describe ongoing efforts to develop heterocyclic systems with high oxidation potentials and very stable radical cation states for both redox shuttle and RFB applications. One part of our strategy includes “tuning” oxidation potentials by using steric factors and considering the changes in molecular geometry that occur upon oxidation. We also describe the synthesis and characterization of several novel phenothiazine-5,5-dioxide derivatives that exhibit reversible electrochemical oxidation at potentials above 4.2 V vs. Li/Li⁺.