Grafting polysulfides into a functional N-halo compound for high-performance lithium—sulfur battery

Abstract

Due to its high energy density, lithium-sulfur (Li-S) battery is considered as the most promising candidate for the energy storage systems, but its practical application is hindered by the dissolution of lithium polysulfides in the electrolyte. In this work, N-bromophthalimide (C8H4NO2Br, NBP), an aromatic molecule with carbophilic, sulfiphilic, lithiophilic, and solvophilic nature, is introduced into active graphene (AG) to fabricate the sulfur composite cathode. The carbophilic NBP is anchored readily on the AG surface via π−π stacking interaction. During discharging, the dissolved lithium polysulfide anion (LiS− ) is grafted into the sulfiphilic NBP spontaneously via SN2 substitution reaction to form C8H4NO2SnLi, which brings the dissolved LiS− back to the AG surface in the composite cathode. Moreover, the lithiophilic and solvophilic nature of NBP improve the wettability of the porous composite cathode, and the electrolyte molecule is easily penetrated into the micro-mesopores of AG to facilitate the diffusion of the electrolyte. Thus, NBP, as a multi-functional compound in Li-S battery, can immobilize LiS− and enhance the diffusion of the electrolyte. The above features of NBP endow the sulfur composite cathode with improved electrochemical performance in the cycling stability.