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

In this work, unique Co(3)O(4)/N‐doped reduced graphene oxide (Co(3)O(4)/N‐rGO) composites as favorable sulfur immobilizers and promoters for lithium–sulfur (Li–S) batteries are developed. The prepared Co(3)O(4) nanopolyhedrons (Co(3)O(4)‐NP) and Co(3)O(4) nanocubes mainly expose (112) and (001) surfaces, respectively, with different atomic configurations of Co(2+)/Co(3+) sites. Experiments and theoretical calculations confirm that the octahedral coordination Co(3+) (Co(3+) (Oh)) sites with different oxidation states from tetrahedral coordination Co(2+) sites optimize the adsorption and catalytic conversion of lithium polysulfides. Specially, the Co(3)O(4)‐NP crystals loaded on N‐rGO expose (112) planes with ample Co(3+) (Oh) active sites, exhibiting stronger adsorbability and superior catalytic activity for polysulfides, thus inhibiting the shuttle effect. Therefore, the S@Co(3)O(4)‐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.