Topological Engineering Electrodes with Ultrafast Oxygen Transport for Super‐Power Sodium‐Oxygen Batteries

Abstract Sodium‐oxygen battery has attracted tremendous interest due to its extraordinary theoretical specific energy (1605 Wh kg −1 NaO2 ) and appealing element abundance. However, definite mechanistic factors governing efficient oxygen diffusion and consumption inside electrolyte‐flooded air cathodes remain elusive thus precluding a true gas diffusion electrode capable of high discharge current (i.e., several mA cm −2 ) and superior output power. Herein, 3D‐printing technology is adopted to create gas channels with tailored channel size and structure to demystify the diffusion‐limited oxygen delivery process. It is revealed that as the clogging discharging products increase, large channel size, and interconnected channel structure are essential to guaranteeing fast O 2 diffusion. Moreover, to further encourage O 2 diffusion, a bio‐inspired breathable cathode with progressively branching channels that balances between O 2 passage and reaction is 3D printed. This elaborated 3D electrode allows a sodium‐oxygen cell to deliver an impressive discharging current density of up to 4 mA cm −2 and an output power of 8.4 mW cm −2 , giving rise to an outstanding capacity of 18.4 mAh cm −2 . The unraveled mystery of oxygen delivery enabled by 3D printing points to a valuable roadmap for the rational design of metal‐air batteries toward practical applications.