Target construction of ultrathin graphitic carbon encapsulated FeS hierarchical microspheres featuring superior low-temperature lithium/sodium storage properties

Although numerous electrode materials based on conversion-reactions have been investigated for lithium/sodium ion batteries (L/SIBs), the low-temperature performance is still a big challenge for their practical application in cold climates. Herein, every individual small FeS sphere wrapped by several graphitic carbon layers in a micro-nano system (FeS@g-C) is designed and explored. The in situ generated FeS@g-C delivers excellent electrochemical performance over a wide temperature range. For instance, the reversible capacity of FeS@g-C can reach 562 mA h g(-1) at 0.2 A g(-1) for LIBs at -20 degrees C. And for SIBs, it exhibits a capacity of 311 mA h g-1 at 0.05 A g(-1) even when operated at a cryogenic temperature of -25 degrees C. In addition, when paired with a Na3V2(PO4)(2)O2F cathode as a full cell for SIBs, it also works well, revealing great application prospects. This good electrochemical performance of the FeS@g-C can be attributed to the short ion-diffusion paths provided by the ultrasmall FeS nanospheres along with the more important g-C coating, which guarantees the high conductivity of FeS@g-C. In addition, the perfectly shaped and porous hierarchical FeS spheres can effectively accommodate the volume variation during electrochemical processes, thus endowing the FeS@g-C with a robust structural stability.