context: Over the past several decades, rechargeable lithium-ion batteries (LIBs) have been widely used in the energy storage market of portable electronic devices and electric vehicles. However, the scarcity and rising costs of Li raw materials have restricted the further large-scale commercialization of LIBs, and thus have spurred extensive research in seeking cost-effective and more reliable energy storage systems. Among various promising alternatives, Na-ion batteries (NIBs) have attracted considerable attention because of the high abundance and low cost of Na resources. Of various anode candidates for NIBs, Na metal anodes are prized for their high specific capacity (1166 mA h g−1) and low electrochemical potential (−2.714 V vs. standard hydrogen electrode). However, the naturally formed solid electrolyte interphase (SEI) that originates from the instantaneous reaction between the highly reactive Na and electrolyte solvents is generally non-uniform and fragile. The heterogeneous feature easily causes uneven Na deposition and the formation of Na dendrites, and thus brings about serious safety issues. Additionally, the fragile SEI cannot tolerate huge volume changes upon the repetitive plating/stripping process, which gives rise to repeated breakdown/repair of the SEI, leading to a low coulombic efficiency (CE) and short cycle life. These issues impede the practical applications of Na metal anodes.