Carbonaceous-Material-Induced Gelation of Concentrated Electrolyte Solutions for Application in Lithium-Sulfur Battery Cathodes.

Lithium-sulfur (Li-S) batteries can theoretically deliver high energy densities exceeding 2500 Wh kg. However, high sulfur loading and lean electrolyte conditions are two major requirements to enhance the actual energy density of the Li-S batteries. Herein, the use of carbon-dispersed highly concentrated electrolyte (HCE) gels with sparingly solvating characteristics as sulfur hosts in Li-S batteries is proposed as a unique approach to construct continuous electron-transport and ion-conduction paths in sulfur cathodes as well as achieve high energy density under lean-electrolyte conditions. The sol-gel behavior of carbon-dispersed sulfolane-based HCEs was investigated using phase diagrams. The sol-to-gel transition was mainly dependent on the amount of the carbonaceous material and the Li salt content. The gelation was caused by the carbonaceous-material-induced formation of an integrated network. Density functional theory (DFT) calculations revealed that the strong cation-π interactions between Li and the induced dipole of graphitic carbon were responsible for facilitating the dispersion of the carbonaceous material into the HCEs, thereby permitting gel formation at high Li-salt concentrations. The as-prepared carbon-dispersed sulfolane-based composite gels were employed as efficient sulfur hosts in Li-S batteries. The use of gel-type sulfur hosts eliminates the requirement for excess electrolytes and thus facilitates the practical realization of Li-S batteries under lean-electrolyte conditions. A Li-S pouch cell that achieved a high cell-energy density (up to 253 Wh kg) at a high sulfur loading (4.1 mg cm) and low electrolyte/sulfur ratio (4.2 μL mg) was developed. Furthermore, a Li-S polymer battery was fabricated by combining the composite gel cathode and a polymer gel electrolyte.