Low-temperature and high-rate sodium metal batteries enabled by electrolyte chemistry

High-rate cycling of alkali metal batteries at subzero temperature is essential for their practical applications in extreme environments. Here, we realize high-rate low-temperature sodium metal batteries (LT SMBs) through modulating electrolyte chemistry. By introducing a weak Na⁺ solvating co-solvent, tetrahydrofuran/1,2-Dimethoxyethane (THF/DME), the kinetic barrier for Na⁺ desolvation is significantly mitigated. Furthermore, an anion-derived NaF-rich solid-electrolyte interphase (SEI) film generated on the sodium electrode suppresses the dendrite growth and guarantees stable cycling of SMBs down to -60°C. In consequence, the symmetric Na/Na batteries achieve a high current density of 3 mA cm⁻² at -20°C and 2 mA cm⁻² at -40°C. Meanwhile, they exhibit an outstanding cumulative cycling capacity of 1350 mAh cm⁻² (-20°C) and 285.5 mAh cm⁻² (-40°C), which outperforms the previously reported LT alkali metal symmetric batteries. Moreover, the Na-NaTi₂(PO₄)₃ (NTP) full batteries exhibit a power density of 1396.5 W kg⁻¹ at 46.2 Wh kg⁻¹ (based on NTP) under -40°C.