Achieving highly stable sodium metal batteries with self-adapting and high-ionic-mobility ceramic fiber membranes

[Display omitted] •Al2SiO5 CF membranes with superb thermal durability, electrolyte wettability and mechanical robustness guarantee large Na+ conductivity and high security for sodium metal batteries.•CF-spaced SMBs showcase a superior ionic transfer number of 0.65 to that of GF or PP case, permitting more free Na+ moving through membranes and hence lowering the concentration polarization of SMBs.•Aluminous components in CF membranes can spontaneously interact with F-based molecules in electrolyte, and release Al3+ species that would be electrochemically deposited onto Na surfaces, positively influencing Na+ plating/stripping behaviors and anodic geometric features. Tough issues like sodium (Na) dendrite growth and poor anode reversibility hinder the practical application of sodium metal batteries (SMBs) with moderate liquid electrolytes. To settle these problems, using a smart self-adapting Al2SiO5 ceramic fiber (CF) membrane is demonstrated to enable homogeneous Na depositions and inhibit the dendritic growth. This inorganic membrane itself has superb thermal stability, high ionic mobility (Na+ transference number: 0.65) and electrolyte wettability over traditional glass fiber (GF) or polymeric ones, guaranteeing the low voltage polarization (14 mV) and long-cyclic lifetime (over 600 h) in symmetric cells testing. Notably, aluminous components in CF membranes would interact with F-based molecules in the electrolyte phase, thereby releasing some Al3+ species that can be electrochemically deposited onto the anodic interface. The packed (+)Na3V2(PO4)3|CF|Na(−) full SMBs exhibit far superior cyclic stability (capacity retention over 78.7 % after 600 cycles at 1C) than other counterparts. The in-situ detection/postmortem analysis reveal that Al/F-based inorganics formed in as-built SEI layers play a vital role in Na metal anode protection. This work may provide a viable strategy to overcome the constraints of high-energy SMBs in practical applications.