Porosity vs carbon shell number: Key factor actually affecting the performance of multi-shelled hollow carbon nanospheres in Li-S batteries

Abstract

• The pores in the carbon shells of HCNs play a key role in the Li + diffusion and Li 2 S x confinement. • Simply increasing the shell number in HCNs can not effectively confine the leakage of Li 2 S x from the S cathode. • Porous 1S-HCNs endow the S cathode with better cycling stability and rate capability than the oligoporous 2S-HCNs and 3S-HCNs do. • After 700 cycles, a capacity of 759 mAh g -1 with 63% retention is achieved for the S@1S-HCNs cathode at 0.2 C. As a type of sulfur host for lithium-sulfur batteries (LSBs), hollow carbon nanospheres (HCNs) are of particular interest due to their high electrical conductivity, available cavities, and unique morphology. However, there is a lack of in-depth study about the pivotal factors affecting their performance in LSBs. Herein, a series of multi-shelled HCNs have been prepared by a template-free method and the corresponding sulfur cathodes have been systematically investigated. A positive dependence of electrochemical properties on the specific surface area and pore volume of HCNs is confirmed. In case of low porosity of carbon shell, increasing the shell numbers in HCNs could not accelerate the Li + diffusion and restrict the dissolution of lithium polysulfide in the S@HCNs cathode. As a result, the highly porous 1S-HCNs endow the sulfur cathode with better cycling stability and rate performance than the oligoporous 2S-HCNs and 3S-HCNs do. This work may not only provide a useful reference in the design of novel sulfur hosts but also shed a light on the understanding of the complicated mechanism behind the sulfur redox reactions.