Engineering Electrolytes\nwith Transition Metal Ions\nfor the Rapid Sulfur Redox and In Situ Solidification of Polysulfides\nin Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have been\npursued\ndue to their high theoretical energy density and superb cost-effectiveness.\nHowever, the dissolution–conversion mechanism of sulfur inevitably\nleads to shuttle effects and interface passivation issues, which impede\nLi–S battery practical application. Herein, the approach of\nadopting transition metal salts (CoI<sub>2</sub>) to engineering the\nelectrolyte is proposed. Different from anchored transition metal\ncatalysts in the cathode, soluble cobalt ions can chemically reduce\nand solidify polysulfides, alleviating the dependence of sulfur conversion\non the conductive interface while suppressing the shuttle effect.\nImportantly, all elements in CoI<sub>2</sub> are in the lowest valence\nstate and solid complexes are formed after the redox reaction, which\nprevents the migration of high valent Co<sup>3+</sup> to the anode,\nthus overcoming the poor compatibility between redox mediator and\nLi anode. Notably, I<sub>3</sub><sup>–</sup> has the function\nof eliminating dead sulfur and dead lithium, which we apply to Li–S\nbatteries. After activating I<sub>3</sub><sup>–</sup> at a\ncertain frequency, Li–S batteries indeed achieve a longer and\nmore stable cycle life. By combining the regulatory behavior of anions\nand cations, the electrolyte is engineered for Li–S batteries\nwith high capacity, long lifespan, and excellent rate performance.