Challenges in regulating interfacial‐chemistry of the sodium‐metal anode for room‐temperature sodium‐sulfur batteries

Post‐Li ion battery technologies are gaining importance due to their high theoretical energy density and high specific capacity of the electrode materials. Due to fundamental limitations, the existing Li‐ion batteries cannot fulfill rigorous requirements, like cost‐effectiveness and high storage capacities. Room‐temperature sodium‐sulfur battery (RT‐Na/S), in particular, is an emerging candidate with the high theoretical specific capacity of sodium (~1166 mAh/g) and sulfur (~1675 mAh/g) and naturally high abundance of both the electrode materials. Sodium metal, combined with sulfur, is a cheap and energy‐dense option to the existing battery technologies. In recent years, this has garnered much interest in the scientific community due to a wide range of possibilities for altering battery performance. With the invention of the high‐temperature sodium‐sulfur batteries, Na metal‐based chemistries remain in oblivion. However, due to increasing concerns over the safety of high‐temperature sodium‐sulfur batteries, Na metal anode is revived in recent years with the ever‐growing demands for high energy density and improved safety. Despite that current Na metal anode still lacks high‐reversibility, efficiency, and room‐temperature stability due to limited or no control over the interfacial chemistry of the Na metal anode. The electrochemical reduction of Na+ ions is accompanied by the inevitable reduction of organic species, which leads to the growth of the solid‐electrolyte interphase (SEI) with Na‐deposits. The SEI is inherently unstable due to the localized fluctuations in its chemical and physical properties. A deep understanding of challenges associated with the SEI's localized interfacial chemistry is of prime importance toward developing practical Na metal anodes for RT‐Na/S batteries. This minireview highlights critical challenges in developing a stable Na metal anode and further sheds light on its mechanistic aspects. In addition to that, novel approaches to precisely tune the interphase's physicochemical properties are highlighted to pave path for developing a stable and long‐life Na‐metal anode for RT‐Na/S batteries.