Fluorinated Artificial Solid–Electrolyte–Interphase Layer for Long-Life Sodium Metal Batteries

Abstract

Sodium metal batteries have garnered significant attention due to their high theoretical specific capacity, cost effectiveness, and abundant availability. However, the propensity for dendritic sodium formation, stemming from the highly reactive nature of the sodium metal surface, poses safety concerns, and the uncontrollable formation of the solid–electrolyte interphase (SEI) leads to large cell impedance and battery failures. In this study, we present a novel approach where we have successfully developed a stable fluorinated artificial SEI layer on the sodium metal surface by employing various weight percentages of tin fluoride in a dimethyl carbonate solution, utilizing a convenient, cost-effective, and single-step method. The resulting fluoride-rich protective layer effectively stabilized the Na metal surfaces and significantly enhanced cycling stability. The engineered artificial SEI layer demonstrated an enhanced lifetime of Na metal symmetric cells of over 3.5 times, over 700 h at the current density of 0.25 mA/cm2, in cycling performance compared to the untreated sodium, which is attributed to the suppression of dendrite formation and the reduction of undesired SEI formation during high-current cycling.

A Critical Review on Room‐Temperature Sodium‐Sulfur Batteries: From Research Advances to Practical Perspectives

“…For instance, it has been reported that the SnF 2 coating layers can be converted into NaF and Na‐Sn rich protective layer on the Na metal, which could significantly enhance the cycling stability of the Na metal anodes. [ 119 ]…”

“…[109] A composite SEI layer with Na 2 Te, NaTe, TeO 2 , TeF 4 , Na 2 TeO 4, and other organic components could be observed, which exhibited good structural stability to enable stable cycling of the Na metal anodes in carbonate electrolyte for 700 h. A series of Na + conductive transition metals (In, Bi, Zn, Sn) have been investigated as protective coating layers for Na metal anodes, and the results demonstrated that the Na-In composite anode delivered the most stable cycling performance for 800 h at 5 mAh cm −2 with a low nucleation potential and regulated Na + flux. [108] Many transition metal compounds have also been reported as coating layers for Na metal anodes, including SnF 2 , [119] SbF 3 , [120] V 2 S 3 , [116] Mo 6 S 8 , [121] MoS 2 , [122] V 2 P, [117] BiVO 4 , [156] etc. The compounds could be converted into intermetallic alloys to regulate Na metal plating and inorganic sodium salts as components for stable SEI layers.…”

“…For instance, it has been reported that the SnF 2 coating layers can be converted into NaF and Na-Sn rich protective layer on the Na metal, which could significantly enhance the cycling stability of the Na metal anodes. [119] Several reports have demonstrated that Na + conductive oxides, such as Al 2 O 3 and Ti 0.87 O 2 could also be applied as protective layers for Na metal anodes. [114,115] Significantly, a few layers of Al 2 O 3 coating (2.8 nm) can be fabricated on Na metal via atomic layer deposition (ALD), which serves as an artificial SEI layer and enables stable cycling of Na metal anodes in ester-based electrolytes for more than 400 h. [114] The ultrathin protective layer could significantly reduce the side reactions between the Na metal and the electrolyte, resulting in dendrite-free Na metal plating.…”