Synergistic effect of selectively etched CoFe and N-doped hollow carbon spheres for high performance lithium-sulfur batteries

Abstract

Lithium-sulfur batteries (LSBs) feature benefits of high theoretical specific capacity, but they are severely constrained by the shuttle effect of lithium polysulfides and volume expansion in the process. To address these issues, CoFe nano particles covered in N-doped carbon (SE-CoFe@NC) layer were prepared by bimetallic-organic skeleton pyrolysis method and used as cathode matrix for LSBs. The nitrogen-carbon shell layer and polar CoFe-alloy nanoparticles provide plentiful chemisorption sites for polysulfides, and the alloy is essential for accelerating the redox conversion of polysulfides. Nitrogen-doped carbon layer promotes ion/electron transport and the nitrogen doping is generally considered to have a strong adsorption effect on polysulfides, with the hollow carbon spheres acting synergistically in promoting electrolyte penetration, enhancing sulfur loading capacity and accommodating sulfur expansion during cycling. Take advantage of these benefits, the S@CoFe/NC-80 composite cathode exhibits strong adsorption capability of lithium polysulfides (LiPSs), efficient reaction kinetics and stable cycling performance (reversible capacity of 617 mAh g−1 at 0.2C after 200 cycles, and when the charging/discharging rate reaches 1C, it maintains a reversible discharge capacity of 490 mAh g−1 after 1000 cycles with a per-cycle decay rate of only 0.05%). The synergistic effect of the dual properties of the catalytic activity of the CoFe alloy and the conductive hollow nitrogen-carbon layer provides a viable solution for the appropriate design of bimetallic alloy structures and promotes further applications.