The effect of supporting electrolytes on redox flow battery performance

In the current global transition to renewable energy sources, large scale of energy storage technologies are needed. Solar and wind energy are available intermittently, thus there is a mismatch between energy production and societal demand. Redox flow batteries (RFBs) are an attractive energy storage option, as they can decouple capacity (tank size) and power (stack size) for installation at any scale. Furthermore, RFBs offer long operational lifetime and higher safety than other batteries such as lithium-ion devices. RFBs using earth-abundant elements (carbon, iron, etc.) are being explored as new, inexpensive active species, but these new materials require compatible electrolytes, long-term stability, high solubility and optimal reaction kinetics. This work studies RFBs using different supporting electrolytes to understand their effect on performance of the battery. In RFBs all active species are dissolved in liquid electrolytes which can affect their performance. Specifically, RFBs contain two electrolytes, anolyte and catholyte, which are comprised of the solvent (e.g. water), the redox active compound (e.g., Fe(bpy)32+ or anthraquinone-2,6-disulfonate AQDS), and a supporting electrolyte containing cations (Li+, Na+, K+, or NH4+) and anions (Cl- or NO3-). The electrolyte is pumped through an electrochemical stack where the active species are oxidized or reduced to charge or discharge the battery. This research project be quantifies achievable current densities, long- term capacity fade rates, as well as diffusion coefficients and reaction kinetics as a function of supporting salt identity.