Enhancement of Overall Kinetics by Se-Br Chemistry in Rechargeable Li-S Batteries.

The sluggish kinetics of lithium-sulfur (Li-S) batteries severely impedes the application in extreme conditions. Bridging the sulfur cathode and lithium anode, the electrolyte plays a crucial role in regulating kinetic behaviors of Li-S batteries. Herein, we report a multifunctional electrolyte additive of phenyl selenium bromide (PhSeBr) to simultaneously exert positive influences on both electrodes and the electrolyte. For the cathode, an ideal conversion routine with lower energy barrier can be attained by the redox mediator and homogeneous catalyst derived from PhSeBr, thus improving the reaction kinetics and utilization of sulfur. Meanwhile, the presence of Se-Br bond helps to reconstruct a loose solvation sheath of lithium ions and a robust bilayer SEI with excellent ionic conductivity, which contributes to reducing the de-solvation energy and simultaneously enhancing the interfacial kinetics. The Li-S battery with PhSeBr displays superior long cycling stability with a reversible capacity of 1164.7 mAh g after 300 cycles at 0.5 C rate. And the pouch cell exhibits a maximum capacity of 845.3 mAh and a capacity retention of 94.8 % after 50 cycles. Excellent electrochemical properties are also obtained in extreme conditions of high sulfur loadings and low temperature of -20 °C. This work demonstrates the versatility and practicability of the special additive, striking out an efficient but simple method to design advanced Li-S batteries.