A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium‐Sulfur Batteries

Abstract Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li−S batteries. 3D nucleation of Li 2 S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri‐sulfur (S 3 ⋅ − ) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high‐DN characteristics that trigger the S 3 ⋅ − radical pathway, and inhibit the growth of Li dendrites. Li−S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low‐capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μL electrolyte mg sulfur −1 . This work opens a new avenue for the development of electrolyte additives for Li−S batteries.