Lithium–sulfur (Li–S) batteries are considered as a highly promising energy storage system due to their ultrahigh theoretical energy density. However, the sluggish kinetics of the complex multi-electron sulfur redox reactions seriously hinders the actual battery performance especially under practical working conditions. Homogeneous redox mediation, through elaborately designing the additive molecules, is an effective approach to promote the sulfur redox kinetics. Herein a promoter of mixed organodiselenides (mixed-Se) is proposed to comprehensively improve the sulfur redox kinetics following the redox comediation principles. Concretely, diphenyl diselenide promotes the liquid–liquid conversion between polysulfides and the solid–liquid conversion regarding lithium sulfide oxidation to polysulfides, while dimethyl diselenide enhances the liquid–solid conversion regarding lithium sulfide deposition. Consequently, the mixed-Se promoter endows a high discharge capacity of 1002 mAh g⁻¹ with high sulfur loading of 4.0 mg cm⁻², a high capacity retention of 81.6% after 200 cycles at 0.5 C, and a high actual energy density of 384 Wh kg⁻¹ at 0.025 C in 1.5 Ah-level Li–S pouch cells. This work affords an effective kinetic promoter to construct high-energy-density Li–S batteries and inspires molecular design of kinetic promoters toward targeted energy-related redox reactions.