Zinc-air battery efficiency

Why Zync-air rechargeable batteries suffer for low efficiencies? Is it an inherent problem of all metal-air batteries? There also seem to be a large difference between Coulombic efficiency (around 90%) and roundtrip voltage efficiency (around 55%). Is there any ways to solve this problem somehow?

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Electrically reversing the reaction at a bi-functional air cathode, to liberate oxygen from discharge reaction products, is difficult; membranes tested to date have low overall efficiency. Charging voltage is much higher than discharge voltage, producing cycle energy efficiency as low as 50%. Providing charge and discharge functions by separate uni-functional cathodes, increases cell size, weight and complexity. https://en.wikipedia.org/wiki/Zinc–air_battery

Edited May 21, 20196 yr by Moreno