Sandwiched C@SnO2@C hollow nanostructures as an ultralong-lifespan high-rate anode material for lithium-ion and sodium-ion batteries

SnO2 is considered a promising anode candidate for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), but suffers from the low electrical conductivity and severe volume variation during repetitive cycling. To circumvent these issues, we developed novel interconnected sandwiched carbon-coated hollow nanostructures, i.e., carbon-shell/SnO2-nanocrystal-layer/hollow-carbon-core (C@SnO2@C HNSs), in which ultrasmall SnO2 nanocrystals (2-5 nm) were tightly confined between the carbon shell and the hollow carbon core. Such a unique structure can not only protect the active materials from direct exposure to the electrolyte as well as restrain the migration and pulverization of the SnO2, but also offer rich void space for buffering the volume changes and complement the electron conductivity of the active materials, thus achieving remarkably enhanced electrical conductivity and structural integrity of the whole electrode. As a consequence, this C@SnO2@C HNS electrode exhibited an extremely outstanding long-life high-rate cycling stability for both LIB and SIB anodes, such as only 8% capacity loss after 1000 cycles at 10 A g(-1) for LIB anode and only 10% capacity loss after 3000 cycles at 4.6 A g(-1) for SIB anodes. As far as we know, this is the best high-rate cycle performance ever reported for SnO2-based SIB anodes.