Multiple heteroatoms co-doped carbon layers coupled with Janus sulfides (CoS2@NPSC@MoS2) for super Na+/K+ storage.

ABSTRACT

As the most promising anodes for Na+/K+ batteries (SIBs/PIBs), transitional metal sulfides present the advantages of high capacity, straightforwardly-controlled morphology and abundant redox reaction sites. However, maintaining the structural integrity of the electrode materials during cycling and improving the cycle life still face great challenges. Herein, CoS2@NPSC@MoS2 nano-spindle heterostructure with multiple heteroatoms co-doped carbon layers coupled with Janus metal sulfides (CoS2 and MoS2) were successfully fabricated via the successive organic coating, gas-phase phosphorization and the final hydrothermal reaction processes. Benefiting from the uniformly dispersed CoS2 nanocrystals in the interior of carbon layer and the MoS2 nanosheets arrays in the exterior, Na+/K+ diffusion distances are remarkedly shortened and the reaction kinetics are greatly improved, which also provide more active sites on the surface for exposure to the electrolyte. The presence of heterogeneous atomic N/P/S co-doped carbon layer greatly improves the electrochemical conductivity of the heterostructure and provide additional buffer space for volume changes, which is conducive to retaining the integrity of the electrode structure during the cycling processes. When used as the anode material for SIBs/PIBs, it reached the reversible specific capacity of 340.44 mAh g-1 at 5.0 A g-1 after 1000 cycles for SIBs and 37.53 mAh g-1 at 5.0 A g-1 after 800 cycles for PIBs. This work demonstrates a reliable and simple strategy for the rational design of Janus metal sulfides heterostructures for high performance Na+/K+ storage application.