Agarose-based Gel Electrolytes for Sustainable Primary and Secondary Zinc-Air Batteries

•Gel 2 wt% agarose 8 M KOH presents superb performance in primary Zn-air batteries.•Gel 8 M KOH has unprecedented Zn utilization in the literature, approaching 95–97%.•In secondary Zn-air batteries, this gel can sustain from loose to severe cycling.•Encouraging metrics per cycle are proven for first-time at high areal capacities.•Further enhancement in secondary Zn-air cells can be achieved by design optimization.