Batteries: Towards High‐Performance Nonaqueous Redox Flow Electrolyte Via Ionic Modification of Active Species (Adv. Energy Mater. 1/2015)

High concentrations of electroactive materials are essential to achieve high energy densities in redox flow batteries. In article number 1400678, Wu Xu, Wei Wang, and co-workers describe a molecular engineering strategy that introduces a polar ionic group to the ferrocene, leading to a 20-fold increase in its solubility and thus energy density. When tested in a non-aqueous Li-organic flow cell with a Li-graphite hybrid anode, the redox electrolyte produces an energy density of 50 Wh L−1 and an energy efficiency >75% with decent cyclability.