Solvated metal complexes for balancing stability and activity of sulfur free radicals

Abstract

Free radicals can improve the reaction rate, but most of them are unstable due to unpaired electrons. Simultaneously maintaining their stability and activity is challenging. Herein, taking sulfur (S) radicals as an example, we propose a strategy in which solvated metal complexes constructed by Al(acetylacetonate)₃ and different solvents can stabilize high concentrations of S radicals with good activity through ion–dipole interactions. Based on this strategy, it is first demonstrated that ${S_4}^{·-}$ is selectively stabilized by controlling the configurations of the solvated complexes. As a result, the reaction rate of S↔Li₂S is increased by 8 times, and the energy efficiency and rate capability of the Li–S batteries are significantly improved, especially the 5-fold increase in cell capacities at a low electrolyte/sulfur ratio. This work provides an important strategy in which solvated metal complexes balance the activity and stability of free radicals to accelerate reactions and their application in various fields.