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 (Zn 0 ) 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 Zn 2+ transference number nearly unity (0.96). Meanwhile, the high modulus PEM establishes a solid-state diffusion barrier to homogenize the interfacial Zn 2+ flux, leading to 3D in-plane interfacial Zn 2+ diffusion and compact Zn 0 plating within the (002) plane. Atomic resolution scanning transmission electron microscopy (STEM) reveals corrosion-free Zn 0 deposition without electrolyte degradation, while operando transition X-ray microscopy (TXM) further illustrates the real-time dendrite-free Zn 0 plating process at 5 mA/cm 2 . 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 Zn 0 –Zn 0 symmetric cells and a lifetime of 6000 cycles in Zn 0 –LiV 3 O 8 full cells.