Turning wastewater treatment into a fluorine-rich interphase for over 10 Ah prismatic zinc-ion batteries

Summary Zinc-ion batteries promise safe, low-cost grid storage but are constrained by unstable interphases and dendritic zinc. Current fluorinated interphase strategies often use costly, toxic, or brittle reagents that hinder scale-up. Here, we report a scalable interfacial approach that uses poly(diallyl dimethyl ammonium) (PDDA), an inexpensive water-treatment polymer, as a precursor to an in situ ZnF₂-enriched solid-electrolyte interphase (SEI). Via electrostatic association with triflate, PDDA forms a PDDA-OTf complex that uniformly coats zinc and, under cycling, undergoes field-assisted dealkylation to yield a robust, flexible, fluorine-rich SEI. The interphase promotes highly oriented Zn(002) deposition, suppresses parasitic reactions, and accelerates Zn²⁺ transport, delivering 2,528 h symmetric-cell life at 1 mA cm⁻² and 99.2% Coulombic efficiency over 800 cycles. A prismatic Zn@PDDA-OTf||VO₂ cell (>10 Ah) retains 96.2% capacity after 100 cycles at 2.86 C. This cost-effective route links laboratory advances to industrially relevant zinc-ion batteries.