The rechargeable all-solid-state Na–O₂ battery is one of the most promising candidates for next-generation energy storage devices owing to its high theoretical specific energy, safety, electrochemical stability, and abundant Na resources. However, the practical implementation of current all-solid-state Na–O₂ batteries is still limited by low-resistance interfaces, low energy efficiency, and poor cycle life. Herein, an all-solid-state Na–O₂/H₂O battery that can sustain highly reversible cycling with a low overpotential is reported. Using a customized silver–polymer composite cathode, this battery can be operated under ≈7% relative humidity (RH) at 80 ^°C and cycled for more than 100 times with a low overpotential (≈75 mV at 100th cycle) and high round trip efficiency >97% at 100th cycle) at an energy density of 20 mA g⁻¹. Furthermore, mechanistic insight that the RH intimately controls the type and hydration state of the discharge product is also provided, and thereby the charge kinetics and battery performance are modulated. It is also revealed that silver catalyst can efficiently reduce the reaction barrier of NaOH decomposition. With the further optimization, this battery potentially can be implemented in real-world applications and confer practical applicability that can extend to other energy-storage systems, such as other metal–air batteries.

https://doi.org/10.1002/adfm.202202518