A Facilely Synthesized NiCo2S4 with Two Mutually Reinforcing Active Sites for High-Performance Lithium-Sulfur Batteries.

The shuttle effect and slow conversion kinetics of soluble polysulfides hinder the commercial application of lithium-sulfur batteries (LSBs). In this context, we propose a three-dimensional lamellar-stacked nanostructure of nickel cobalt sulfide (D-NiCo2S4) enriched with lattice defects by manipulating the cations in spinel sulfides. It has an obvious synergistic promotion mechanism for the adsorption and catalysis of lithium sulfides. Specifically, Ni3+ on tetrahedral (Td) sites with strong Ni-S covalency anchors LiPSs, whereas Co3+ on octahedral (Oh) sites promotes a highly efficient catalytic conversion of LiPSs, which is confirmed by experimental results and density functional theory (DFT) calculations. Besides, the crystal defects and distortions in the lamellar region could expose more active sites and enhance the redox reaction kinetics of polysulfides. Hence, Li-S batteries with D-NiCo2S4@S as the cathode show outstanding cycle stability; upon cycling at 1 A/g, the battery achieves a high initial specific capacity of 1001.12 and 655.31 mAh g-1 after 1000 cycles (decay rate as low as 0.05% per cycle), as well as a high initial areal capacity of 3.15 mAh cm-2 under high S loading (4.2 mg cm-2). This work provides a viable scheme for designing efficient bimetal sulfide catalysts and furnishes a rational strategy for constructing LSB cathodes with high specific capacity and high area capacity.