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).