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

Abstract 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 NiCo2O4 to expose more catalytic sites to accelerate the lithium polysulfides (LiPSs) conversion. And the oxygen deficient in NiCo2O4 with spinel type structure (space group Fd3m) leads to the excellent chemical affinity of NiCo2O4-x for LiPSs. Moreover, because of the optimal distribution of electron on (3 1 1) plane of NiCo2O4-x, the Gibbs free energies of the evolution from S8 to Li2S on (3 1 1) plane of NiCo2O4-x is much lower than that of NiCo2O4, illustrating the NiCo2O4-x with the higher catalytic activity. Therefore, the cell with the NiCo2O4-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 NiCo2O4-x become the efficient catalyst of LSBs. And the results promote the development of bimetallic oxides as catalyst in LSBs.