An in-situ formed stable interface layer for high-performance sodium metal anode in a non-flammable electrolyte

Sodium metal batteries (SMBs) have huge potential for applications in large-scale energy storage systems because of their high energy density, low cost and abundant resources. However, SMBs suffer from challenging problems, such as low reversibility and dendrite growth during plating/stripping. In this work, we report that a non-flammable electrolyte with Fluoroethylene carbonate (FEC) and 1,3,2-Dioxathiolane 2,2-dioxide (DTD) can in-situ generate a stable solid-electrolyte-interface (SEI) layer, which effectively suppresses the side reactions and prevents dendrite growth. This is attributed to the synergy of the multi-component of SEI layer including S-containing compounds (Na2S, Na2SO3 and organic S-containing salts), NaF and phosphate (Na3PO4). The DTD additive significantly promotes the stability and integrity of the formed SEI layer, which not only enables the dendrite-free Na plating/stripping with an average CE as high as 93.4% for 250 cycles, but also makes the Na||Na symmetric cell stable over more than 1350 h at 1 mAh cm−2 and 720 h even at 5 mAh cm−2.