Failure Mechanism of High‐Temperature Li–S Batteries in Localized High‐Concentration Electrolytes

Abstract Conventional ether‐based electrolytes struggle to sustain steady operation of lithium–sulfur (Li–S) batteries at high temperatures due to inferior thermal durability and aggravated parasitic reactions. Although localized high‐concentration electrolyte (LHCE) has emerged as a promising strategy to enhance thermal stability, its deployment in high‐temperature (HT) Li–S batteries has met with limited success. Herein, the failure mechanism of HT Li–S batteries in LHCE is revealed via probing sulfur redox reactions and electrolyte solvation chemistry. Slow reaction kinetics and high polysulfide reactivity are determined to be the dominant factors causing the rapid capacity deterioration at high temperatures. To this end, a diethylene glycol dibutyl ether‐based localized medium concentration electrolyte (B‐LMCE) with suitable anion concentration and weakly solvating effect is developed. The new electrolyte concurrently achieves fast cathode kinetics and stable anode/electrolyte interface. With the assistance of a tailored electrochemical voltage range of 1–3.8 V, Li–S batteries sustain a durable cycling performance over 250 cycles at 60 °C. They also showcase superior wide‐temperature operation (0 °C–80 °C) while enabling feasible fabrication of Ah‐level pouch cells. Our study opens a new avenue for designing extreme‐temperature electrolytes toward pragmatic Li–S batteries.