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

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 O₂ diffusion. Moreover, to further encourage O₂ diffusion, a bio-inspired breathable cathode with progressively branching channels that balances between O₂ 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.