The design of electrolyte materials with both tunable redox potential and high solubility is critical for boosting the energy density of aqueous redox flow batteries (ARFBs) for stationary energy storage. A redox-active material lithium ferrocyanide (Li4[Fe(CN)6]) is designed. Li4[Fe(CN)6] has an improved solubility of 2.3 M compared to other ferrocyanide salts due to week intermolecular interactions. The constructed Li4[Fe(CN)6]-based ARFB system demonstrates high average capacity retention (nearly 100%) over 1365 hours and an unprecedented volumetric capacities up to 62.2 Ah/L in H2O. A zinc-ferricyanide (Zn/[Fe(CN)6]3-) ARFB, using a Nafion 117 membrane, achieves an unprecedented catholyte capacity of 61.4 Ah/L at neutral pH, surpassing the performance of most known ARFBs. In addition, the prepared ARFB shows a low electrolyte cost of $24 per kWh. This work provides a promising option for developing sustainable energy storage technology with high efficiency and a low cost.
Lithium Ferrocyanide Catholyte for High-Capacity Aqueous Redox Flow Batteries