Nitrogen-doped carbon encapsulated trimetallic CoNiFe alloy nanoparticles decorated carbon nanotube hybrid composites modified separator for lithium‑sulfur batteries

The large-scale applications of lithium sulfur batteries have been limited by their rapid capacity loss, which can be attributed to the dissolution of polysulfide intermediates and subsequent irreversible shuttling effect. Several strategies have been attempted to the solve these problems by designing novel cell structure, including the modification of separator. Herein, a hybrid composite consisting of trimetallic CoNiFe alloy nanoparticles encapsulated with nitrogen doped carbon decorated carbon nanotubes (NC@CoNiFe/CNTs) was designed and coated on polypropylene (PP) separator for lithium sulfur batteries. The conductivity of mesoporous CNTs provide fast electronic transport and improve the sulfur utilization. The NC@CoNiFe nanoparticles can further adsorb the soluble polysulfides and serve as catalysts to promote the redox kinetics of polysulfides conversion. Benefiting from the synergism of physical confinement, chemical adsorption, and catalytic conversion, the lithium sulfur cell based NC@CoNiFe/CNTs-PP delivers excellent electrochemical performance at high sulfur loading. The lithium sulfur cell with NC@CoNiFe/CNTs-PP under 3.8 mg cm−2 sulfur loading exhibits a high initial capacity of 785.4 mAh g−1 at 0.5C and sustain a capacity of 572.4 mAh g−1 after 240 cycles, corresponding to a retention rate of 72.9 %. The cell with a high sulfur loading of 8.9 mg cm−2, it shows a discharge capacity of 8.89 mAh cm−2 and still maintains 7.24 mAh cm−2 over 100 cycles.