Dual-regulation strategy to enhance electrochemical catalysis ability of NiCo2O4-x for polysulfides conversion in Li-S batteries.

• A dual strategy for NiCo 2 O 4 with unique morphologies and oxygen defects is used for Li-S batteries. • The NiCo 2 O 4-x exhibits the synergy of adsorption and catalysis for LiPSs. • The cell with NiCo 2 O 4-x modified separator shows the excellent electrochemical stability. Recently, lithium-sulfur batteries (LSBs) have been considered as the most potential energy storage system, but the application of LSBs is still confronted with significant challenges. One among the significant challenges is the low kinetics. In this work, we design the urchin-like structure of NiCo 2 O 4 to expose more catalytic sites to accelerate the lithium polysulfides (LiPSs) conversion. And the oxygen deficient in NiCo 2 O 4 with spinel type structure (space group Fd3m) leads to the excellent chemical affinity of NiCo 2 O 4-x for LiPSs. Moreover, because of the optimal distribution of electron on (3 1 1) plane of NiCo 2 O 4-x , the Gibbs free energies of the evolution from S 8 to Li 2 S on (3 1 1) plane of NiCo 2 O 4-x is much lower than that of NiCo 2 O 4 , illustrating the NiCo 2 O 4-x with the higher catalytic activity. Therefore, the cell with the NiCo 2 O 4-x modified separator exhibits a superior rate performance (632 mAh g−1 at 2.5 C) and a long cycle life (404 mAh g−1 at 1 C after 800 cycles) with excellent Li+ ion diffusion coefficient. The rational structural optimization makes NiCo 2 O 4-x become the efficient catalyst of LSBs. And the results promote the development of bimetallic oxides as catalyst in LSBs. [ABSTRACT FROM AUTHOR]