Timescale-Decoupled Polarization Kinetics Guide the Design of Polarization-Resistant Cathode Hosts for Zinc–Iodine Batteries

Severe voltage polarization limits the deployment of zinc–iodine batteries by collapsing energy/power output under high iodine loadings (> 10 mg cm −2 ) and current densities (> 3 A g −1 ). Yet its origins remain unresolved because ohmic, charge-transfer, and mass-transport losses evolve concurrently during operation. Here we establish a timescale-decoupled polarization framework that quantitatively differentiates these overlapping voltage losses in operando and links them to electrode design principles. The analysis reveals that concentration-polarization dominates under practical high-loading and high-rate conditions. Guided by this insight, we design a polarization-resistant cathode host consisting of Fe single atoms anchored on porous graphene (Fe@PG). The architecture integrates a conductive graphitic framework for rapid electron transport, atomically dispersed Fe–N 4 sites for accelerated I − /I 3 − redox conversion, and hierarchical pores with strong iodine affinity for efficient mass transport and species confinement, thereby concurrently suppressing ohmic, activation, and concentration polarization. At an iodine loading of 14.1 mg cm −2 , the I 2 /Fe@PG‖Zn cell delivers a low polarization loss of 0.43 V at 70.5 mA cm −2 (5 A g −1 ), 29.5% lower than the control, together with energy/power densities of 214.1 Wh kg −1 /1761.4 W kg −1 , and 82.0% capacity retention after 3000 cycles. This work provides a generalizable strategy for decoding and regulating polarization kinetics in conversion-type Zn–halide batteries.