Coupling of FeS2-xSex nanoparticles and foam-like carbon superstructure to achieve high-density electron flow for enhanced sodium storage performance

The advantage of FeS2 in sodium storage is constrained by its poor inherent conductivity and unstable electrochemical activity. In this work, the hierarchical structure, FeS2-xSex nanoparticles with high activity encapsulated into the foam-like carbon network, are fabricated by in-situ chelation/self-crosslinking and synchronous sulfurization/selenization strategies. Inside, the incorporation of Se into FeS2 markedly changes the local electron distribution around the Fe atoms and improves the intrinsic conductivity of FeS2. Outside, S, Se codoped foam-like carbon networks are evenly wrapped on the surface of FeS2-xSex nanoparticles, which accelerate the diffusion of internal charges into the electrolyte. Excitingly, the Se-replaced FeS2-xSex nanoparticles and carbon shell established an unobstructed pathway through robust Fe-S-C and Fe-Se-C bond connections, realizing the transmission of more charge transfer, and finally forming a high-density electron flow. This powerful charge transfer mode from the inside out realizes an overall conductivity improvement of the materials and markedly enhances the rate performance. Moreover, the obtained FeS2-xSex nanoparticles ensure high electrochemical activity, and the external carbon layer effectively manages the volume expansion during the sodium storage process. As expected, the FeS2-xSex@SSe/C(5:1) exhibits a high capacity (603.73 mAh g-1 at 1 A g-1 over 600 cycles), outstanding rate capability, and cycle performance (225 mAh g-1 at 3 A g-1 over 5231 cycles) for sodium-ion batteries.