Deformation-tolerant metal anodes for flexible sodium–air fiber batteries

Although flexible sodium–air (Na–air) batteries with high theoretical energy density offer promising opportunities for next-generation smart electronics, enhancing the safety and efficiency of flexible sodium metal anodes under dynamic and continuous deformation remains a challenge. Here, a flexible sodiated carbon nanotube layer to suppress dendrite growth under various deformations is demonstrated through a Fermi level-driven spontaneous synthetic process. The resulting sodiated carbon nanotube layer, which has a spontaneously formed solid–electrolyte interface and a robust interlocked structure, creates a uniformly distributed electric field and stable interface even under deformation, affording dendrite-free flexible Na metal anodes. With this deformation-tolerant Na metal anode, we have constructed a new family of highly flexible Na–air fiber batteries with excellent cycling performance for 400 cycles at a current density of 1000 ​mA·g−1 and a capacity limit of 500 mAh·g−1 under dynamic deformation. These Na–air fiber batteries can be further woven into self-powering systems to support flexible electronic devices.