Grafting and Depositing Lithium Polysulfides on Cathodes for Cycling Stability of Lithium-Sulfur Batteries

Based on dissolution/deposition chemistry, together with multielectron redox reactions, lithium-sulfur (Li-S) batteries have been demonstrated as a promising energy storage system. However, the diffusion of soluble lithium polysulfide intermediates (LiPSs) to bulk electrolyte results in the fast capacity fade of a Li-S cell. How to confine the LiPSs within the cathode while retaining high reversible capacity remains a huge challenge. In this work, N-bromophthalimide, an organic molecule with an aromatic heterocyclic ring and a reactive halogen bond, is introduced as an electrolyte additive to conquer the excessive dissolution and diffusion of LiPSs by in situ formation of an organopolysulfide deposition layer. This electrochemically active layer not only maintains the internal sulfur conversion but also prevents LiPSs from diffusing into the electrolyte bulk, thereby improving the cycling and rate performance of Li-S batteries. This study provides a feasible strategy for regulating the reaction region and path for high-performance Li-S batteries.