Supporting Electrolyte Design for a Stable Nonaqueous Redox Flow Battery Analyte

Non-aqueous redox flow batteries (NRFB) are of interest due to their enhanced potential for large energy densities compared to aqueous redox flow batteries. In this work, we compare the effects of several commonly used supporting electrolytes on the cycling stability of our previously reported active organic electrolyte. We report on the effects of various common cations and anions, and on the combined effects of various pairs. We find that non-coordinating anions and cations provide the most stable battery configurations. Cation and anions that will be discussed include 1-ethyl-3-methylimidazolium (EMIM) and 1-butyl-3-methylimidazolium (BMIM), tetrabutyl ammonium (Bu 4 N), and also trifluromethanesulfonate (OTf), tetraphenylborate (BF 4 ) and triflimide (Tf 2 N). In most cases we see that stability correlates independently with the cation and the anion identity, but there are cases where the combination of certain cation and anion pairs provides an unexpected result. Our results describing battery performance and stability will include charging and discharging studies, measurements of electron transfer rate, diffusions coefficients, solution stability absent applied current, conductivity and viscosity measurements.