Next-Generation Regenerable Fluorine-Free Membrane for Zinc-Polyiodide Redox Flow Batteries

Abstract

Zinc-polyiodide redox flow batteries (ZIFBs) are promising for large-scale grid energy storage applications. The membrane plays a vital role by enabling selective ion transport while preventing polyiodide crossover, ensuring the long-term performance of the system. Widely used perfluorosulfonic acid membranes, such as Nafion, are expensive and, due to their fluorinated nature, raise environmental concerns. In this work, a fluorine-free sulfonated polyethylene-styrene-co-divinylbenzene (S-PE-PSt-DVB) regenerable interpolymer membrane is designed for ZIFB as an alternative to fluorine-containing membranes such as Nafion. A ZIFB assembled with this membrane demonstrates a volumetric capacity of 20 Ah L^–1 at 40 mA cm^–2 on a 100 cm² cell, with 87% capacity retention even after 500 cycles. Notably, this work demonstrates the first validation of membrane reusability (other than Nafion, to the best of our knowledge) in ZIFB via simple water cleaning, thereby enabling recovery of membrane functionality after cycling. These results highlight the potential of the S-PE-PSt-DVB regenerable membrane for durable and scalable ZIFB. To the best of our knowledge, this study demonstrates a large-area cell with decent areal capacity that achieved over 500 cycles.