Revealing Localized Electrochemical Transition of Sulfur in Sub-nanometer Confinement

Current concerns of the pressing environmental pollution issues and limited fossil energy resources have increased the R&D interest and investment in clean energy technologies. LIBs, as commonly used clean energy storage devices, have transformed portable electronic devices and electric transportation greatly, but have limitations of high cost and relatively low specific energy [1]. Due to advantages such as high capacity, extremely low cost, and nontoxicity, sulfur has received considerable attention as a positive electrode material in Li–S batteries. Li–S batteries can deliver a very high theoretical specific energy of 2567 Wh kg or 2199 Wh L and dramatically outperform current LIBs [1, 2]. However, the low electronic/ionic conductivity of sulfur and the discharge products, large volume change (*80%) of sulfur during the lithiation/delithiation processes, and the shuttling of dissolved lithium polysulfides (Li2Sx, 3 ≤ x ≤8) between the sulfur cathode and the lithium–metal anode during cycling severely impede the practical applications of Li–S batteries [3, 4]. These problems not only lead to poor cycling stability, inferior rate capability, and low Coulombic efficiency, but also cause the deposition of insulating Li2S/Li2S2 on both electrodes, resulting in low sulfur utilization and even triggering a series of safety problems [5–7]. Most current research has focused on solving the problems of polysulfide dissolution by reducing polysulfide solubility and/or adsorbing dissolved polysulfides in the cathode. The use of polymer-based or ionic liquid-based electrolytes eliminates the need for organic solvents in which polysulfides have high solubility [8–11], however the increased electrolyte viscosity and resistivity are detrimental to rate performance. Metal oxides, polymers, and silica can chemically or physically