A silk sericin-confined in-situ synthesis strategy: Fe7S8 inserted N,S co-doped carbon nano-aggregates for high-performance sodium storage

Owing to the low cost and renewability, biomass-derived hard carbons (B-HCs) are attractive anode candidates for sodium-ion batteries (SIBs). Although the specific capacity of B-HCs can be further improved by incorporating transition metal sulfides, it also brings out other issues, including the sluggish kinetics, “shuttle effect” of sodium polysulfides and voltage failure. Herein, a facile in-situ synthesis strategy for Fe7S8 inserted N,S co-doped carbon nano-aggregates (Fe7S8-NS/C) is developed. The strong adsorption of sericin to Fe3+ ensures the dispersive distribution of Fe7S8 nanoparticles in carbon matrix, contributing to fast Na+ transport kinetics. The first principles calculations demonstrate the self-doped pyridine N (3.45 at%) and pyrrolic N (7.91 at%) is conducive to Na adsorption, which promotes sodium storage. More importantly, the polar C-S and C-N bonds in the carbon matrix can effectively immobilize sodium polysulfides and inhibit abnormal voltage failure. As an anode material for SIBs, the elaborate Fe7S8-NS/C composite offers high reversible capacity (477 mAh g−1 at 1 A g−1 over 500 cycles) and excellent rate capability (326 mAh g−1 at 5 A g−1). The simple synthesis method and outstanding electrochemical performances make the Fe7S8-NS/C an attractive candidate for SIBs.