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Room‐temperature sodium–sulfur (RT Na–S) batteries have attracted extensive attention because of their low cost and high specific energy. RT Na–S batteries, however, usually suffer from sluggish reaction kinetics, low reversible capacity, and short lifespans. Herein, it is shown that chain‐mail catalysts, consisting of porous nitrogen doped carbon nanofibers (PCNFs) encapsulating Co nanoparticles (Co@PCNFs), can activate sulfur via electron engineering. The chain‐mail catalysts Co@PCNFs with a micrograde hierarchical structure as a freestanding sulfur cathode (Co@PCNFs/S) can provide space for high mass loading of sulfur and polysulfides. The electrons can rapidly transfer from chain‐mail catalysts to sulfur and polysulfides during discharge–charge processes, therefore boosting its conversion kinetics. As a result, this freestanding Co@PCNFs/S cathode achieves a high sulfur loading of 2.1 ± 0.2 mg cm−2, delivering a high reversible capacity of 398 mA h g−1 at 0.5 C (1 C = 1675 mA g−1) over 600 cycles and superior rate capability of an average capacity of 240 mA h g−1 at 5 C. Experimental results, combined with density functional theory calculations, demonstrate that the Co@PCNFs/S can efficiently improve the conversion kinetics between the polysulfides and Na2S via transferring electrons from Co to them, thereby realizing efficient sulfur redox reactions.

All‐solid‐state sodium batteries (ASSBs) are regarded as the next generation of sustainable energy storage systems due to the advantages of abundant sodium resources, and their exceptional and high energy density. Nevertheless, there are still grand challenges to realize their practical applications, such as the limited types of solid‐state electrolytes (SEs), low ionic conductivity of SEs, high charge‐transfer impedance, interfacial issues, and Na dendrite growth. Herein, the recent progress and challenges of various SEs for ASSBs are summarized, including solid polymer electrolytes, inorganic solid electrolytes (including oxides, sulfides, and boron hydrides), and their combinations. Furthermore, recent reports on various cathodes materials and corresponding cathode/SE interfacial issues are comprehensively reviewed. Current trends and future perspectives on sodium metal anodes are discussed in detail with an emphasis on the anode interface protection and innovative SEs with good Na compatibility. Finally, future opportunities for the development of ASSBs are outlined.