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

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li-S batteries. 3D nucleation of Li2S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S-3(center dot-)) 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(center dot-) 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 mu L(electrolyte)mg(sulfur)(-1). This work opens a new avenue for the development of electrolyte additives for Li-S batteries.