Precise solid-phase synthesis of CoFe@FeOx nanoparticles for efficient polysulfide regulation in lithium/sodium-sulfur batteries

Complex metal nanoparticles (NPs) distributed uniformly on supports demonstrate distinctive physicochemical properties and thus attract a wide attention for applications. The commonly used synthesis approaches are the wet chemistry methods, yet they display limitations to achieve the NPs structure design and uniform dispersion simultaneously. Solid synthesis serves as an interesting strategy which can achieve the fabrication of complex metal NPs on supports. Herein, the solid synthesis strategy is developed to precisely synthesize uniformly distributed CoFe@FeOx core@shell NPs via thermal syngas treatment. Fe atoms are preferentially exsolved from CoFe alloy bulk to the surface and then be carburized into a FexC shell under thermal syngas atmosphere, subsequently the formed FexC shell is passivated by air, obtaining CoFe@FeOx with a CoFe alloy core and a FeOx shell. This strategy is universal for the synthesis of MFe@FeOx (M=Co, Ni, Mn). The CoFe@FeOx exhibits bifunctional effect on regulating polysulfides as the separator coating layer for both Li/Na-S batteries. This method could be developed into solid synthetic systems to construct well distributed complex metal NPs.