Designing multifunctional artificial SEI layers for long-term stability of sodium metal anodes

Sodium metal batteries, which are low-cost and have great potential for large-scale energy storage, face challenges such as shortened battery life and safety issues due to the uncontrolled growth of sodium dendrites and extensive side reactions during the cycling of sodium metal anodes. In this work, we address these challenges by introducing SnF₂ to the surface of the sodium metal, which in situ generates a stable composite interfacial layer (NaSn@NaF). This interfacial layer contains Na-Sn alloy with a potential gradient and electrically insulating NaF, which promotes uniform deposition of Na⁺ ions and effectively suppresses dendrite formation and side reactions. Additionally, In addition, the average Young’s modulus of the modified artificial solid electrolyte interface layer (SEI) is about 6.9 Gpa, which is about 2.7 times higher than that of bare sodium (2.4GPa). This artificial/natural composite interfacial layer significantly enhances the performance of sodium electrodes. Symmetric battery cycling tests demonstrated that the electrode with the composite interfacial layer could sustain continuous charging and discharging for 870 h, a significant improvement compared to the 95 h achieved by the pristine sodium metal anode. Furthermore, the full-cell configuration (Na|NaSn@NaF||NVP) exhibited remarkable long-cycle stability, maintaining around 80 % capacity retention after 1100 cycles at a 2C rate, with minimal capacity degradation. This research presents a straightforward and efficient method that enhances the practical application potential of sodium metal anodes.