Semihollow Core-Shell Nanoparticles with Porous SiO₂ Shells Encapsulating Elemental Sulfur for Lithium-Sulfur...

Lithium-sulfur batteries have shown great promise as next-generation high energy density power sources, but their commercial applications are hindered by short battery cycle life arising from the dissolution and shuttling of polysulfides. To address this shortcoming, we prepared two types of semihollow core-shell nanoparticles in which (1) elemental sulfur is encapsulated within a porous silica shell (S@SiO₂) and (2) elemental sulfur is encapsulated within a porous silica shell where the inner surface of the shell is decorated with small Au nanoparticles (S@Au@SiO₂). These core-shell nanoparticles, both ∼300 nm in diameter, were generated from analogous zinc sulfide-based core-shell nanoparticles (ZnS@SiO₂ and ZnS@Au@SiO₂, respectively) by converting the ZnS cores to elemental sulfur upon treatment with Fe(NO₃)₃. With a high surface area and strong host-polysulfide interaction, the SiO₂ shells effectively trap the polysulfides; moreover, the internal void space of these nanostructures accommodates the volume expansion of the sulfur core upon lithiation. By decorating ∼5-7 nm Au nanoparticles evenly on the inner surface of the porous SiO₂ shells (i.e., S@Au@SiO₂), electron transport is enhanced, with consequently enhanced sulfur conversion kinetics at high current rates. Studies of battery performance showed that the S@SiO₂ cathode can deliver an initial capacity of 1153 mA h g^-1 under 0.2 C and retain 816 mA h g^-1 after 100 cycles. More importantly, the Au-decorated S@Au@SiO₂ cathode can deliver a high capacity of 500 mA h g^-1 under 5 C.