3D Printing of Free-Standing “O₂ Breathable” Air Electrodes for High-Capacity and Long-Life Na–O₂ Batteries

Superoxide-based Na–O₂ batteries have been considered as some of the most promising candidates for next-generation energy storage systems due to their high theoretical energy density and energy efficiency. However, to fully realize the advantages of Na–O₂ batteries, the underutilization of air electrodes and poor cycling performance caused by limited O₂ transport in the air electrodes must be addressed. In this work, 3D printing of a reduced graphene oxide (rGO)-based air electrode with a hierarchical porous structure was first demonstrated as being “O₂ breathable” for Na–O₂ batteries. The unique cathode structure features noncompetitive and continuous pathways for O₂, Na⁺ ions, and electrons. The macropores provide smooth passages to facilitate O₂ access across the whole electrode, while the micropores between rGO sheets serve as electrolyte reservoirs and accommodate NaO₂. The efficiently packed rGO sheets ensure sufficient electronic conductivity within the 3D architecture. Na–O₂ batteries using these “O₂ breathable” electrodes can achieve a high capacity of 13484.6 mAh g^–1 at 0.2 A g^–1 and a stable cycling performance over 120 cycles with a cutoff capacity of 500 mAh g^–1 at 0.5 A g^–1. The 3D-printed “O₂ breathable” electrodes evidently demonstrate the importance of a refined balance between electronic conductivity and O₂ transport for high-performance Na–O₂ batteries.