For further development of lithium–sulfur (Li–S) batteries, it is necessary to construct sulfur hosts with high sulfur utilization/loading ratios and moderate the shuttling effect of lithium polysulfides. Herein, we synthesized uniform pomegranate-like microclusters (MCs) via carbonization of a Prussian blue analogue; the MCs consist of homogeneously inlaid ultrafine Co nanoparticles in nitrogen-doped carbon subunits (Co-NPC). The hierarchical pore structure and high conductivity of the Co-NPC-MCs can immobilize sulfur species, and the ultrafine Co nanoparticles and doped nitrogen exert catalytic effects to improve the electrochemical performance of Li–S batteries. Therefore, the S/Co-NPC-MCs cathode exhibits a high initial capacity of 1192 mA h g−1 and 941 mA h g−1 after 200 cycles at 0.5C. It also exhibits excellent rate capacities at high rates of 1C and 2C; the reversible capacities remain at 650 mA h g−1 and 574 mA h g−1 after 400 cycles, respectively, demonstrating its great potential for practical applications.
The real-world application of Li–S batteries is challenged with the problems of the shuttle effect of lithium polysulfides (LiPSs) and sluggish reaction kinetics. Herein, a porous MoN@nitrogen-doped carbon (MoN-NC) nano-octahedron with a bicontinuous intertwined MoN and NC porous structure was designed as a novel S host material for Li–S batteries. With hierarchical pore structures, the NC immobilized the LiPSs by physical-chemical confinement. Moreover, the continuous MoN framework demonstrated excellent chemisorption with LiPSs as well as the electrocatalysis of the LiPS redox reactions, which was confirmed by our experimental and theoretical results. Due to the synergetic effect of the NC and MoN, the S/MoN-NC cathode with a high S content up to 77% exhibited greatly enhanced electrochemical performances. At 0.5C, the S/MoN-NC cathode delivered a long life of 895 mA h g−1 after 350 cycles, which was much higher than that of its S/MoN and S/NC counterparts (71% and 49% after 100 cycles, respectively). At a high current density of 2C, the specific capacity of S/MoN-NC was 3.2 and 1.3 times higher than that of its S/MoN and S/NC counterparts, respectively. Remarkably, with the increase in the S loading up to 6.5 mg cm−2, the high capacity retention was still maintained (0.059% capacity decay over 200 cycles). This study gives useful guidance to enable high-energy and high-power Li–S batteries for practical applications.
1 January 2019 in Journal of Electroanalytical Chemistry