Tiny amounts of fluorinated carbon nanotubes remove sodium dendrite for high-performance sodium‒oxygen batteries

Metallic sodium battery is regarded as a promising alternative of metallic lithium battery due to abundance in Na resources. However, similar to Li, metallic Na suffers from severe dendrite growth during cycling, which hinders its practical applications. Here, we report a Na composite anode composed of metallic Na and tiny amounts of fluorinated carbon nanotubes (FCNTs, 1~1.5 wt%). Compared with bare Na, Na/FCNTs electrode exhibits lower polarization voltage, lower surface resistance, and longer cycle life. The Na/FCNTs electrode can sustain a stable cycling at 2 mA cm–2 with a capacity as high as 5 mAh cm–2 for 1700 h. Scanning electron microscope (SEM) and in-situ optical microscope observation confirm dendrite-free stripping/plating of metallic Na during cycling. The inhibition effect of Na dendrites can be attributed to the NaF-rich solid electrolyte interface (SEI) layer on the Na surface which is in-situ formed from the reactions between Na and FCNTs. Na‒O2 cellwith Na/FCNTs anode can be stably cycled for 112 cycle sat 400 mA g–1 with a limited capacity of 1000 mAhg–1, while that with bare Na anode can be stably cycled only for 62 cycles. The obviously enhanced cycling stability of the cell with Na/FCNTs anode is due to the protective effect of the in-situ fabricated NaF-rich SEI layer.