Sulfur-doped sunflower disk-like Fe3O4/Fe3N@NC heterostructure as enhanced-performance anode for potassium-ion storage

To obtain a high-performance negative electrode for potassium-ion hybrid capacitors (PIHCs), a sunflower disk- like S-Fe3O4/Fe3N@NC heterostructure was synthesized by encapsulating Fe3O4/Fe3N nanoparticles within a nitrogen-doped carbon shell via a sulfurization process. The C-S-C enhances the interplanar spacing of the nitrogen-doped carbon shell, thereby providing active sites for potassium storage. The C-S-C and C-SOx bonds interact with the Fe atoms, thereby intensifying the built-in electric field of the Fe3O4/Fe3N@NC. This interaction results in enhanced reaction kinetics and improved structural stability of the heterostructure. The distinctive structure and synergistic effects of S doping enable the S-Fe3O4/Fe3N@NC heterostructure to achieve outstanding potassium storage performance. As anticipated, when utilized in potassium-ion batteries, the SFe3O4/Fe3N@NC heterostructure demonstrates a reversible capacity of up to 251.7 mAh/g at 0.1 A/g, and exhibits exceptional rate performance, retaining a capacity of 125.2 mAh/g even at 2 A/g. Furthermore, the SFe3O4/Fe3N@NC//AC PIHC demonstrates a remarkable energy density of 53.3 Wh kg- 1 and an impressive power density of 1166.7 W kg- 1 , alongside sustaining 2000 cycles at 1 A/g without notable capacity degradation. The proposed specialized structural design and functional group modulation strategy offer novel perspectives for the advancement of sophisticated heterostructure electrodes in future practical applications.