Chelation Mediated Outer‐Sphere Electron Transfer for High‐Voltage and Long‐Lifespan Neutral Zinc‐Iron Flow Batteries

ABSTRACT Neutral zinc‐iron flow batteries (ZIFBs) are promising candidates for grid‐scale energy storage due to their safety, low cost, and sustainability. However, their cycle stability and energy density are restricted by zinc dendrite growth, hydrogen evolution, and more positive Zn anode potential in neutral media compared to alkaline conditions. Herein, we propose a ligand‐coordination strategy using tetrasodium iminodisuccinate (IDs) to rationally tune the redox behavior of Zn 2+ . The formation of a stable [H 4 Zn(C 8 H 7 NO 8 ) 2 ] 2− complex converts the conversional Zn(H 2 O) 6 2+ structure into a chelate‐dominated configuration, inducing an outer‐sphere electron transfer pathway by preventing direct Zn‐electrode interactions. Meanwhile, it results in a significant negative shift in redox potential of 350 mV (from −0.814 to −1.164 V vs. SHE), enabling a record‐high cell voltage of 1.63 V in neutral ZIFBs. The stabilized coordination environment facilitates highly reversible Zn plating/stripping while suppressing hydrogen evolution, dendrite formation and other side reactions. As a result, such high‐voltage ZIFB demonstrates a remarkable energy efficiency of 88.77% at 40 mA cm −2 and excellent cycling stability over 320 cycles, advancing durable and high‐performance neutral ZIFBs.