Scalable ultrathin sodium metal anodes

Sodium-ion batteries have been attracting extensive attention in both academic and industrial fields. However, the lack of large-area and ultrathin sodium (Na) metal foil hinders basic research on and commercialization of energy-dense Na-ion batteries. Here we successfully fabricated a metre-length, ultrathin (≤50 μm), mechanically strengthened Na metal foil by a roll-to-roll calendaring process with interfacial lubrication and functional modification. By developing self-lubricating polydimethylsiloxane as the multifunctional agent, the poor processibility of metallic Na is addressed by forming a mechanically strong interface as well as a surface lubricant film during rolling. Furthermore, polydimethylsiloxane-derived (Si–O) n -Na interphases can guide Na + -ion interfacial diffusion and enable a robust solid electrolyte interphase. Consequently, the large-area ultrathin Na foil exhibits a stable electrode potential and stripping capacity, as well as prolonged lifespan compared with bare Na anodes. This approach enables the realization of amp-hour-level Na metal pouch cells under a low negative-to-positive capacity ratio of 1.9, showing an energy density of 180.2 Wh kg −1 . This scalable ultrathin Na foil establishes a materials foundation for fundamental studies on Na-ion batteries and the potential manufacture of high-energy-density Na metal batteries.