Solid‐to‐Solid Zn Anode and Interhalogen Iodine Cathodes for High‐Voltage Fluoride‐Ion Batteries

Abstract

ABSTRACT Fluoride ion batteries (FIBs) operated at room temperature typically suffer from low output voltages (< 0.5 V) due to the lack of reversible, suitable electrode chemistries in liquid electrolytes. Here, we report a high‐voltage aqueous FIB system delivering an output voltage of ∼1.3 V by coupling a zinc/zinc hydroxyfluoride (Zn↔ZnOHF) anode with an iodine cathode undergoing reversible I − ↔I 2 F − interhalogen conversion in an NH 4 F‐based methanol/water hybrid electrolyte. At the anode, strong complexation between NH 4 + and Zn 2+ activates a reversible solid‐to‐solid Zn↔ZnOHF conversion. Meanwhile, methanol effectively suppresses HER and accelerates fluoride‐ion desolvation, leading to fast kinetics and high reversibility. As a result, the ZnOHF/Zn anode exhibits remarkable durability for over 1100 h at 1 mA cm −2 and 2 mAh cm −2 . At the cathode, tetrahexylammonium iodide (THAI) induces the formation of insoluble THAI 2 F during the fluorination of I 2 cathode, effectively immobilizing iodine species and suppressing shuttle effects. The proposed fluoride‐ion‐shuttled Zn/I 2 cells deliver a high specific capacity of 168 mAh g −1 at 2 A g −1 and retain 81% capacity after 2500 cycles. This work establishes interhalogen chemistry and electrolyte‐regulated solid‐state fluorination as viable strategies for designing high‐voltage, long‐life FIBs.