Pomegranate-Structured Silica/Sulfur Composite Cathodes for High-Performance Lithium-Sulfur Batteries

Porous materials have many structural advantages for energy storage and conversion devices such as rechargeable batteries, supercapacitors, and fuel cells. When applied as a host material in lithium-sulfur batteries, porous silica materials with a pomegranate-like architecture can not only act as a buffer matrix for accommodating a large volume change of sulfur, but also suppress the polysulfide shuttle effect. The porous silica/sulfur composite cathodes exhibit excellent electrochemical performances including a high specific capacity of 1450 mA h g^-1 , a reversible capacity of 82.9 % after 100 cycles at a rate of C/2 (1 C=1672 mA g^-1 ) and an extended cyclability over 300 cycles at 1 C-rate. Furthermore, the high polysulfide adsorption property of porous silica has been proven by ex-situ analyses, showing a relationship between the surface area of silica and polysulfide adsorption ability. In particular, the modified porous silica/sulfur composite cathode, which is treated by a deep-lithiation process in the first discharge step, exhibits a highly reversible capacity of 94.5 % at 1C-rate after 300 cycles owing to a formation of lithiated-silica frames and stable solid-electrolyte-interphase layers.