Sodium-ion batteries (NIBs) are a promising energy storage technology, but their insufficient low-temperature and fast-charging cycling performance has limited their widespread adoption in broader application scenarios. This work reports the use of sodium fluorosulfonate (NaFSO₃) as an electrolyte additive to reduce the electrode/electrolyte interfacial resistance and enhance the low-temperature and fastcharging performance of NIBs. The results show that NaFSO₃ exhibits good solubility in carbonate solvents, reaching almost 1 M in propylene carbonate/methyl ethyl carbonate (4/6, weight ratio) mixtures. Most of the dissolved NaFSO₃ remains in an undissociated state, contributing little to ionic conductivity, thus making it suitable as an additive rather than a main salt. Due to the strong interaction between FSO₃^- and Na⁺, FSO₃^- can participate in the passivation reaction on the electrode surface to form an inorganic-rich, mainly Na₂SO₄ and Na₂SO₃, thin, uniform, and mechanically robust interphase film. This passivation film can significantly reduce the initial interfacial resistance of both the cathode and anode, and effectively suppress electrolyte decomposition and the increase in interfacial resistance during cycling. Consequently, the cycling and storage performance of layered oxide/hard carbon NIBs are significantly improved, and their low-temperature cycling and high-rate cycling performance are also greatly enhanced. Compared with DTD, another typical lowimpedance additive, NaFSO₃ shows superior enhancement in low-temperature charging and fast-charging cycling. After incorporating NaFSO₃ into the electrolyte, the commercial 32140 cylindrical cells retain 92% of their capacity after 2222 cycles under 2 C fast-charging at room temperature, and stable charging cycling can be achieved at -20 ℃ at 0.1 C. This study provides an effective strategy for improving the lowtemperature charging and fast-charging cycling performance of NIBs, which is of great significance for promoting their widespread application.