Functional CNTs@EMIM⁺‐Br⁻ Electrode Enabling Polysulfides Confining and Deposition Regulating for Solid‐State Li‐Sulfur Battery

Abstract With an extremely high theoretical energy density, poly(ethylene oxide) (PEO)‐based solid‐state lithium‐sulfur (Li‐S) batteries are emerging as one of the most feasible and safest battery storage systems. However, the long‐term cycling performance is severely impeded by polysulfides (Li₂S_n, n = 4–8) shuttling and terrible electrode passivation from the electronic insulating Li₂S. Here, a novel cathode through chemically grafted 1‐Ethyl‐3‐methylimidazolium bromide (EMIM⁺‐Br⁻) to carbon nanotube (CNTs) for PEO‐based Li‐S batteries is reported (CNTs@EMIM‐Br/S). Concretely, bi‐functional mediator EMIM⁺‐Br⁻ not only inhibits the polysulfides shuttling by strong chemical interactions via EMIM⁺, but also facilitates the electrochemical kinetics for promoting the formation of 3D particulate Li₂S through high donor anion (Br⁻). Satisfactorily, dual‐function CNTs@EMIM‐Br/S cathode exhibits high sulfur utilization with the capacity of up to 1298 mAh g⁻¹, and keeps high capacity retention of 80.2% at 0.2 C after 350 cycles, exceeding that of many reported PEO‐based solid‐state Li‐S batteries. This work will open a new door for rationally designed architecture to enable the practical applications of advanced Li‐S batteries.