Fig. 4: Reversible Na plating/stripping behavior on bare Al and BiF₃@Al.

a CEs of Na plating/stripping of Na||Al and Na||BiF₃@Al cells at 1 mA cm⁻²@1 mAh cm⁻² at 25 °C. Insets: voltage profiles of Na||Al and Na||BiF₃@Al cells at the 100th and 1000th cycles. b Voltage profiles of Na||BiF₃@Al cells at the 10th and 1000th cycle at 25 °C. Inset: corresponding nucleation and deposition overpotential. c CEs of Na plating/stripping of Na||Al and Na||BiF₃@Al cells at 1 mA cm⁻²@5 mAh cm⁻² at 25 °C. Inset: voltage profiles of the 10th cycle. d CEs of Na plating/stripping of Na||Al and Na||BiF₃@Al cells at 20 mA cm⁻²@2 mAh cm⁻² at 25 °C. e Voltage profiles of Na||Al and Na||BiF₃@Al cells at −30 °C and 0.5 mA cm⁻²@1 mAh cm⁻². f CEs of Na plating/stripping of Na||Al and Na||BiF₃@Al cells at −30 °C and 0.5 mA cm⁻²@1 mAh cm⁻².