Solvent–Solvent Interaction Regulation Enables a Practical Ultra‐Low‐Temperature Electrolyte for Sodium‐Ion Batteries

ABSTRACT

Organic electrolytes encounter critical challenges at low temperatures (LT), such as solvent crystallization and sluggish Na ⁺ transport kinetics. While most studies have primarily focused on low‐viscosity ethers or highly fluorinated solvents for LT performance, their practical applications remain limited by inadequate stability and environmental and safety concerns. In this work, a low‐cost, highly safe electrolyte for LT applications was designed based on sodium‐ion pouch cells. Through methyl substitution at α‑H, the polarity of ethyl butyrate was enhanced, promoting interactions with propylene carbonate to construct a highly stable electrolyte with low solvation energy barriers. It exhibits an ultra‐low freezing point (−130°C) and superior kinetics, demonstrating excellent electrochemical performance in Ah‐scale pouch cells, including: a discharge capacity retention of nearly 70% at −60°C; maintaining 90% of initial capacity after 200 cycles of continuous discharge at 1C and −30°C; and a fast‐charge/discharge capacity retention of over 90% at 10C and 25°C. Furthermore, systematic analysis of sodium plating behavior on anodes at LT revealed that the electrolyte has significant advantages in suppressing sodium plating. Finally, successful engineering‐scale validation was conducted in a 5 Ah pouch cell, providing a safe, reliable, and practical electrolyte design strategy for LT sodium‐ion batteries.