Artificially engineered, bicontinuous anion-conducting/-repelling polymeric phases as a selective ion transport channel for rechargeable zinc-air battery separator membranes

Zinc (Zn)-air batteries have recently attracted a great deal of attention as a promising energy storage system to fulfill our ever-increasing demand for higher energy density power sources. Despite commercial success of primary Zn-air batteries, performances of rechargeable Zn-air batteries are still far below practically satisfactory levels. Among critical challenges facing the electrochemical rechargeability, the crossover of zincate (Zn(OH)₄^2-) ions from the Zn anode to the air cathode (via separator membranes) is a formidable bottleneck. Here, as a facile and scalable polymer architecture strategy to address this ion transport issue, we demonstrate a new class of polymer blend electrolyte membranes with artificially engineered, bicontinuous anion-conducting/-repelling phases (referred to as "PBE membranes"). As an anion-conducting continuous phase, an electrospun polyvinyl alcohol (PVA)/polyacrylic acid (PAA) nanofiber mat is fabricated. Into the PVA/PAA nanofiber mat, Nafion bearing pendant sulfonate groups is impregnated to form an anion-repelling continuous phase. Such bicontinuous phase-mediated structural uniqueness enables the PBE membrane to act as a selective ion transport channel, i.e., effectively suppresses Zn(OH)₄^2- crossover (by a continuous Nafion phase offering the Donnan exclusion effect) with slightly impairing OH^- conduction (predominantly through the PVA/PAA nanofiber mat), eventually improving the cycling stability (cycle time = over 2500 min for the PBE membrane vs. 900 min for a conventional polypropylene separator). The PBE membrane featuring the selective transport of OH^- and Zn(OH)₄^2- ions is anticipated to pave a new route that leads us closer toward rechargeable Zn-air batteries.