Polyelectrolyte Membrane Enables Highly Reversible Zinc Battery Chemistry via Immobilizing Anion and Stabilizing Water

The integration of water-based electrolytes into zinc-ion batteries encounters challenges due to the limited voltage window of water, interfacial side reactions of mobile counterions, and the growth of zinc metal (Zn0) dendrites during charge. In this study, we introduce a nonfluorinated, cation-conducting polyelectrolyte membrane (PEM) designed to alleviate these challenges by suppressing the reactivities of both water and counterions. This PEM forms hydrogen bonds with water molecules through its proton-accepting side chains, thus shifting the lowest unoccupied molecular orbital (LUMO) energy of water from −0.37 to −0.14 eV and inducing a negative shift in the onset potential for hydrogen evolution by 110 mV. Additionally, it immobilizes the counteranions onto the polymer backbones via covalent bonding, hence making the Zn2+ transference number nearly unity (0.96). Meanwhile, the high modulus PEM establishes a solid-state diffusion barrier to homogenize the interfacial Zn2+ flux, leading to 3D in-plane interfacial Zn2+ diffusion and compact Zn0 plating within the (002) plane. Atomic resolution scanning transmission electron microscopy (STEM) reveals corrosion-free Zn0 deposition without electrolyte degradation, while operando transition X-ray microscopy (TXM) further illustrates the real-time dendrite-free Zn0 plating process at 5 mA/cm2. Consequently, the unique properties of this water-binding and anion-tethering PEM enable enhanced electrochemical performance without employing highly fluorinated and expensive anions. This PEM demonstrates a durability of 3800 h in Zn0–Zn0 symmetric cells and a lifetime of 6000 cycles in Zn0–LiV3O8 full cells.