Embedding anion-doped Fe7S8 in N-doped carbon matrix and shell for fast and stable sodium storage

In order to enhance the electrochemical activity of transition metal chalcogenide anodes for sodium ion batteries (SIBs), anion-doping and carbon modification are demonstrated to be effective methods. In this work, using polydopamine (PDA) coated metal organic framework of MIL-88-Fe (MIL-88-Fe/PDA) as self-template, N-doped Fe7S8 embedded in N-doped carbon (N-Fe7S8@NC) are successfully fabricated, through a high-temperature sulfurization process. Benefited from the PDA coating, integral peapod-liked nanoarchitecture can be preserved, and N atoms are doped both in the Fe7S8 lattice and the carbon matrix and shell. This stable peapod-liked N-Fe7S8@NC nanoarchitecture with continuous carbon protection, shows fast Na+ insertion/extraction reaction kinetics, demonstrating as fast and stable anode material for SIBs. It displays highly stable capacities of 312.7 mAh g(-1) at 5.0 A g(-1) after 2000 cycles, giving a capacity retention of 98.1%. Even at ultrahigh current of 10.0 A g(-1), after long-term cycling (4000 cycles), a capacity of 238.4 mAh g(-1) can be maintained, giving an impressive capacity retention of 81.5%. For the possible kinetics mechanism, the ultrafast pseudocapacitive contribution and higher adsorption energy induced by the anion-doping, may promote its high-rate sodium storage capability.

Automated summary

Anion-doping and carbon modification have been shown to enhance the electrochemical activity of transition metal chalcogenide anodes for sodium ion batteries. By using polydopamine coated metal organic framework of MIL-88-Fe as self-template, N-doped Fe7S8 embedded in N-doped carbon are successfully fabricated, resulting in a stable peapod-liked nanoarchitecture with fast and stable anode material performance for SIBs. This nanoarchitecture exhibits highly stable capacities even at ultrahigh current, showing impressive capacity retention due to ultrafast pseudocapacitive contribution and higher adsorption energy induced by anion-doping.