Manipulating the electrocatalytic activity of sulfur cathode via distinct cobalt sulfides as sulfur host materials in lithium-sulfur batteries.

For the better development of lithium-sulfur (Li-S) batteries, it is necessary to fabricate sulfur hosts with cheap, rapid sulfur reaction dynamic and inhibiting the shuttling effect of lithium polysulfides (LiPSs). Herein, four hollow cubic materials with two kinds of nitrogen-doped carbon derived from Prussian blue analogues (PBA) precursor, CoS/MnS/NC@NC-400, CoS/MnS/NC@NC-500, CoS/MnS/NC@NC-600 and CoS/MnS/NC@NC-700, are reported when the vulcanization temperatures are regulated at 400 °C, 500 °C, 600 °C and 700 °C, respectively. Among them, CoS/MnS/NC@NC-400, CoS/MnS/NC@NC-500 and CoS/MnS/NC@NC-600 have the similar hollow cubic structure, which can physically confine the LiPSs's shuttle, however, the Co vacancies of CoS in the CoS/MnS/NC@NC-600 can promote the rearrangement of surface electrons, which is beneficial to the diffusion of Li/e, improving the electrochemical reaction kinetics. As for the CoS/MnS/NC@NC-700 with the same substance but almost collapsed structure, the CoS/MnS/NC@NC-600 can accommodate the volume expansion of sulfur conversion. In the four sulfur-host materials, the CoS/MnS/NC@NC-600 not only displays the outstanding adsorption ability on LiPSs, but also presents the best electrocatalytic activity in the LiS potentiostatic deposition experiments and active sulfur reduction/oxidation conversion reactions, greatly promoting the electrochemical performances of Li-S batteries. The S@CoS/MnS/NC@NC-600 cathode can deliver 1010.2 mA h g at 0.5 C and maintain 651.1 mA h g after 200 cycles. In addition, the in-situ X-ray diffraction (in-situ XRD) test reveals that the sulfur conversion mechanism is the processes of the α-S → LiS → β-S (first cycle), then β-S ↔ LiS during the subsequent cycles. Based on the fundamental understanding of the design and preparation of CoS/MnS/NC@NC hosts with the desired adsorption and catalysis functions, the work can provide new insights and reveal the defect-engineering to develop the advanced Li-S batteries.