Nitrofullerene as an electrolyte-compatible additive for high-performance sodium metal batteries

Electrolyte additives have an important impact on the cycling stability of sodium metal batteries , but their applications are severely impeded by the poor compatibility with different electrolytes. Herein, rational incorporation of nitro groups on fullerene (C 60 ) cage yields nitrofullerene (C 60 (NO 2 ) 6 ) as an effective additive, which displays high compatibility with different electrolytes and can enable highly reversible and dendrite-free plating/stripping of sodium metal anodes (SMAs). In-situ optical observation of Na electrodeposition confirms a great improvement in the cycling stability of metallic Na anodes with the C 60 (NO 2 ) 6 additive, which not only promotes the formation of stable protective layers on SMAs, but also facilitates the uniform Na deposition and effectively suppresses the Na dendrite growth. As a result, the Na||Na symmetrical cells with C 60 (NO 2 ) 6 show low voltage hysteresis , high rate capability and prolonged cycle life in both carbonate and ether electrolytes. Even at 5 mA cm –2 and 5 mAh cm –2 , the Na||Cu half cells can stably cycle over 450 h in the ether electrolyte. Furthermore, a significantly improved cycling stability of the high loading Na||Na 3 V 2 (PO 4 ) 3 @C (8.7 mg cm –2 ) full cell is achieved in the carbonate electrolyte.