Ultrasmall CoS nanoparticles embedded in heteroatom-doped carbon for sodium-ion batteries and mechanism explorations via synchrotron X-ray techniques

A composite containing ultrasmall CoS nanoparticles (∼7 nm) embedded in heteroatoms (N, S, and O)-doped carbon framework was synthesized and it exhibited remarkable sodium storage performance. Moreover, the structural transformation and Co valence evolution during cycling were revealed with advanced synchrotron X-ray techniques.