Enhancing reversibility of zinc metal for Zn||I2 aqueous battery via nanophase-clustered perfluorosulfonic acid layers with tuned sulfonic acid densities

Zinc metal batteries (ZMBs) are considered promising candidates for large-scale energy storage systems due to zinc's natural abundance, low cost, and intrinsic safety. However, the commercialization of ZMBs is hampered by uncontrolled Zn dendrite growth and interfacial instability, which result in poor cycling performance and safety concerns. Although perfluorosulfonic acid (PFSA) polymers have been previously used as protective layers, the fundamental relationship between their sulfonic acid group density and Zn plating behavior has remained unclear. In this study, we unveil a previously unexplored mechanism by which the sulfonic acid group density governed by the equivalent weight (EW) of PFSA dictates the formation of nanophase-separated ionic clusters that directly influence Zn 2+ ion transport, transference number, and plating morphology. We reveal that optimized PFSA structures not only suppress dendrite formation but also promote preferential Zn deposition along the (002) lattice plane, rather than the conventional (100) orientation. This lattice-oriented growth leads to significantly improved Zn anode reversibility and stability. As a result, the PFSA-Zn||I 2 full cell demonstrates long-term cycling over 1489 cycles at 4.3 mAh cm −2 , maintaining 88.8 % capacity retention and a high Coulombic efficiency of 99.8 %. • Sulfonic acid density in PFSA controls Zn 2+ transport and plating. • Optimized PFSA promotes (002) Zn growth, enhancing reversibility and stability. • PFSA-Zn||I 2 cell retain 88.8 % capacity over 1489 stable cycles.