Pre-Formed Organic SEI Protected Sodium Metal Anode Exclusively Confined in Reduced Graphene Oxide Host.

The combination of Na metal with a 3D scaffold has effectively solved the long-standing problems of sodium metal batteries, including dendrite formation and volume change. However, uncontrollable interfacial reaction and morphology degradation caused by the high surface area of the scaffold are still unsolved. Here, a solvent pretreatment strategy is reported to generate a pre-formed solid electrolyte interface (SEI) protected Na exclusively confined in the scaffold. This pre-formed SEI prevents the reactive Na from the direct contact with the electrolyte, thereby mitigating side reactions. Meanwhile, by removing the highly reactive Na nanoparticles, as well as their low ionic conductivity derivatives on the surface, this exclusively confined Na structure enhances the uniformity of Na plating/stripping and the corresponding ion transport kinetics. Benefiting from this pre-formed SEI optimization, a thin and NaF-riched SEI can be further evolved during cycling. Compared to the pristine counterpart, Na₃V₂(PO₄)₃ coupled with the anode protected by pre-formed SEI exhibits a 14.9% and 18.9% increase in specific capacity at 25 and -30 °C, respectively. The pre-formed SEI strategy solves the prolonged interfacial issues of high surface area Na metal composite anodes, and brings a new perspective to the plating/stripping behaviors.