Atmospheric Water Harvesting Enables High-Performance Metal–Air Batteries

Aqueous metal–air batteries offer an ultrahigh theoretical energy density, intrinsic safety, and abundant metal resources, making them ideal for wearable electronics and emergency power applications. However, their deployment is constrained by excessive liquid electrolyte requirements to compensate for water consumption during discharge and evaporation from the open-air cathode. This reliance severely reduces the practical energy density and accelerates the parasitic corrosion of reactive metal anodes. Here, we demonstrate metal–air batteries that harvest both H2O and O2 directly from ambient air during discharge, eliminating the need for excess liquid electrolyte. The liquid-free storage state prevents corrosion and enables repeated on-demand activation. Consequently, magnesium–air batteries can achieve a practical energy density exceeding 400 Wh·kg–1 and a 10-fold enhancement in storage stability. This water-harvesting strategy is readily extended to zinc–air and aluminum–air batteries, offering a general approach to lightweight, durable, and self-sustaining metal–air energy systems.