Lithium Ferrocyanide Catholyte for High-Energy and Low-cost Aqueous Redox Flow Batteries.

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.