Multivalent MoxC coupling with Ni@CNT hetero-crystals as promoting polysulfide chemisorption and catalytic conversion layer for advanced Li-S batteries

Lithium-sulfur batteries (LSBs), known for its high theoretical specific capacity and energy density, have been considered as the most promising electrochemical energy storage system. However, the heavy shuttle effect of the polysulfides and the retarded reaction kinetics are significant challenges for the future application of Li-S batteries. In this manuscript, a heterostructured catalysts of nickel and molybdenum carbide wrapping into nitrogen doping carbon nanotubes (Ni@MoxC@CNTs) were prepared through high temperature annealing selfcatalyzed process. The obtained Ni@MoxC@CNTs were then employed as the modifier for commercial PP separators, which greatly increased the catalytic sites for polysulfide conversion and mitigated the shuttle effect of polysulfides by facilitating ion transfer due to its excellent conductivity and electron transport properties. Furthermore, nitrogen-doped CNTs wrapping dispersive Ni@MoxC offered enough physical adsorption sites on the surface and inner of nanotubes for polysulfides and the Ni@MoxC hetero-nanocrystals further anchor the diffused polysulfides through chemisorption for the facilitation of the catalytic conversion of polysulfides. Specifically, a high discharge capacity of 703 mAh/g is achieved at the current density of 3C. Moreover, Ni@MoxC@CNTs/PP battery maintains a remarkably high discharge capacity of 711 mAh/g even after 300 cycles at a current density of 0.5C with a capacity decay rate of only 0.12 % per cycle. After 300 cycles at the current density of 1C, the battery of Ni@MoxC@CNTs/PP separator achieves the discharge capacity of 690 mAh/ g with the capacity degradation rate of as low as 0.1 % for each cycle. This manuscript provides a new idea and method for the preparation of metal and carbide synergistic catalyst for high-performance LSBs separator modification through improving chemisorption and catalytic conversion.