Aligned Bilayer of Single-Walled Carbon Nanotubes Suppresses the Polysulfide Shuttle in Li-S Batteries

Abstract

Lithium-sulfur (Li-S) batteries have attracted much attention due to their high energy density and cost efficiency. However, the drawbacks such as the polysulfide shuttle effect and low electrical conductivity of active sulfur material result in poor cycling performance. In this work, we endeavored to overcome these problems by applying a highly engineered bilayer of single-walled carbon nanotubes (SWCNTs). Two monolayers of aligned SWCNTs were deposited on a glass fiber separator using a modified Langmuir-Schaefer method. The deposited bilayer forms a mesh pattern that acts as a spatial filter to mitigate the polysulfide shuttle effect. To confirm the improvement, we assembled cells with modified glass fiber separators coated by SWCNT bilayers and compared their electrochemical performance with unprotected cells with pristine glass fiber separators. The electrochemical results revealed that the discharge capacity increased significantly for the battery with the modified separator. After 50 cycles (0.5 C), the battery with the coated separator had the same discharge capacity as the battery with the pristine separator after only 20 cycles (600 mA h/g), indicating a significant difference of 30 cycles in capacity retention. This implies that an ultrathin bilayer of SWCNTs on the conventional glass fiber separator significantly suppresses the polysulfide shuttle effect.