Multiredox Polyoxovanadate‐Based Ionic Liquids for Nonaqueous Redox Flow Batteries

Redox-active ionic liquids (ILs) represent a promising class of energy carriers due to their intrinsic ionic conductivity, negligible volatility, and electron-transfer capability. However, the design of ILs capable of reversible multielectron storage is still in its infancy. In this work, we report a family of mixed-valence polyoxovanadate-based ionic liquids (POV-ILs) obtained by combining the highly redox-active, mixed-valence cluster ($n$Bu$_4$N)$_4$)$_8$[V$_{14}$O$_{34}$Cl][(MgOH)V$_{13}$O$_{33}$Cl] with a series of bulky quaternary ammonium cations. Cation exchange transforms the solid precursor into liquid-like POV-ILs, dramatically enhancing solubility in organic solvents, such as acetonitrile, THF, and glymes, making them ideal compounds for nonaqueous redox flow batteries (NRFBs). Electrochemical studies demonstrate that these POV-ILs retain the reversible multielectron redox activity of the parent cluster across a wide potential window, enabling their use as symmetric electrolytes in NRFBs. Flow-cell demonstration confirms stable multielectron cycling, with electrolyte remixing mitigating capacity fading. By integrating the redox versatility of POVs with the solubility and processability of ILs, this work establishes a new design strategy for redox-active electrolytes and highlights the promise of POV-ILs for next-generation, high-energy-density NRFBs.