Oxidation States Regulation of Cobalt Active Sites through Crystal Surface Engineering for Enhanced Polysulfide Conversion in Lithium–Sulfur Batteries

Abstract In this work, unique Co3O4/N‐doped reduced graphene oxide (Co3O4/N‐rGO) composites as favorable sulfur immobilizers and promoters for lithium–sulfur (Li–S) batteries are developed. The prepared Co3O4 nanopolyhedrons (Co3O4‐NP) and Co3O4 nanocubes mainly expose (112) and (001) surfaces, respectively, with different atomic configurations of Co2+/Co3+ sites. Experiments and theoretical calculations confirm that the octahedral coordination Co3+ (Co3+Oh) sites with different oxidation states from tetrahedral coordination Co2+ sites optimize the adsorption and catalytic conversion of lithium polysulfides. Specially, the Co3O4‐NP crystals loaded on N‐rGO expose (112) planes with ample Co3+Oh active sites, exhibiting stronger adsorbability and superior catalytic activity for polysulfides, thus inhibiting the shuttle effect. Therefore, the S@Co3O4‐NP/N‐rGO cathodes deliver excellent electrochemical properties, for example, stable cyclability at 1 C with a low capacity decay rate of 0.058% over 500 cycles, superb rate capability up to 3 C, and high areal capacity of 4.1 mAh cm−2. This catalyst's design incorporating crystal surface engineering and oxidation state regulation strategies also provides new approaches for addressing the complicated issues of Li–S batteries.