Trimethyl Phosphate for Nonflammable Carbonate‐Based Electrolytes for Safer Room‐Temperature Sodium‐Sulfur Batteries

Abstract To address the safety concern for room‐temperature sodium‐sulfur batteries, such as fires easily triggered by organic electrolytes, an applicable non‐flammable electrolyte formula was developed by introducing trimethyl phosphate (TMP) into 1.0 M NaClO 4 ‐ethylene carbonate/propylene carbonate electrolyte. It is demonstrated that the electrolyte containing 15 wt.% TMP was a optimized formula, exhibiting nonflammability, thermal stability, electrochemical compatibility and lasting cell performance. Using this optimized electrolyte formula, the sulfur cathode exhibited a stable capacity of 788 mAh g −1 at a rate of 0.1 C and excellent rate capability of 441 and 177 mAh g −1 for 200 cycles at rates of 1 C and 5 C , respectively. When the TMP content further increases to 25 wt.%, the specific capacity of batteries declined significantly due to unstable SEI. Our study can shed light on the development of flame‐retardant electrolyte for room‐temperature sodium‐sulfur or other batteries.