Unlocking a Stable, High‐Voltage Aqueous Iron‐Sulfur Battery by Engineering the Iron Anode with a Preconstructed Polymer‐Metal Hybrid Interphase and Decoupling the Electrolyte

ABSTRACT Aqueous iron‐sulfur (Fe//S) batteries are a promising next‐generation energy storage technology due to their high theoretical capacity and shuttling‐free mechanism. However, their development is hindered by dendrite growth, hydrogen evolution reaction (HER) at the anode, and low discharge voltage. Here, we address these challenges by pre‐constructing a polymer‑metal hybrid interphase on the Fe anode (polyvinylidene difluoride (PVDF)‐M@Fe, M = Bi, Pb, Cu) to stabilize the electrode/electrolyte interface, while employing an electrolyte‐decoupling strategy (FeSO 4 /CuSO 4 ) to maximize the device discharge voltage through tailoring the charge carriers at the S cathode. Combining theoretical calculations with operando spectroscopy, we demonstrate that the outer PVDF layer effectively shields Fe anode from the bulk electrolyte, suppressing HER; while the inner electron‐conductive metal layer simultaneously homogenizes the electric field and increases nucleation sites, enabling dendrite‐free and highly reversible Fe deposition. This synergistic interface regulation allows a PVDF‐Bi@Fe symmetric cell to cycle stably for 412 h at 1 mA cm −2 . The decoupled PVDF‐Bi@Fe//S@activated carbon cell achieves a maximum discharge voltage of 0.85 V (2.4 times higher than that of the conventional cell), a large capacity of 1976 mAh g Sulfur −1 at a high rate of 2 A g Sulfur −1 , and remarkable cycling stability with 85.42% capacity retention after 100 cycles.