High-rate sodium metal batteries enabled by trifluormethylfullerene additive

Sodium metal is a promising anode for sodium batteries due to its high theoretical capacity and low cost. However, the serious Na dendrite growth and low Coulombic efficiency, especially at high current densities/cycling capacities, severely limit the application of sodium metal anodes. Herein, trifluoromethylfullerene, C₆₀(CF₃)₆, is designed as an electrolyte additive to enable the high-rate cycling of sodium metal anodes with high Coulombic efficiency. The CF₃ groups contribute to the formation of stable NaF-rich solid electrolyte interface layer, while C₆₀ cages induce the uniform distribution of sodium ions and promote the formation of smooth and compact morphology. Thus, Na||Cu cell with C₆₀(CF₃)₆ can be cycled at 2 mA·cm⁻² and 10 mAh·cm⁻² over 180 cycles with an average Coulombic efficiency of 99.9%, and Na||Na cell can be cycled at 10 mA·cm⁻² over 600 cycles. Furthermore, Na||NaV₂(PO₄)₃@C full cell exhibits high capacity retention of 84% over 2,000 cycles at 20 C (~ 3 mA·cm⁻²).