Free-Energy-Gradient-Driven Iodine Regeneration toward Ultrastable Zinc-Iodine Batteries

Rechargeable aqueous Zn-I2 batteries are attractive for safe, low-cost energy storage but remain fundamentally limited by severe self-discharge and poor cycling stability because sluggish ZnI2 oxidation impedes efficient iodine regeneration during charging. Herein, we confine highly dispersed iodine quantum dots within a Fe(CN)64--doped polypyrrole/polyaniline framework to establish a free-energy-gradient-driven regeneration pathway. During discharge, Fe-cyanide and N-rich sites immobilize polyiodide intermediates, suppressing shuttle and self-discharge. More importantly, during charging, the in situ generated ZnxFeIII(CN)6/Znx+1FeII(CN)6 redox couple establishes an intrinsic free-energy gradient that couples Zn2+ transfer with iodide oxidation, thereby directing iodine regeneration and limiting aggregation. The resulting cathode delivers 238.2 mAh g-1 at 0.5 A g-1, maintains approximately 217 mAh g-1 at 10 A g-1, retains 92.6% capacity after 50,000 cycles with nearly 100% Coulombic efficiency, and supports stable pouch-cell and flexible microbattery operation. These results establish free-energy-gradient engineering as a strategy for regulating reversible halogen conversion beyond static confinement.