Lithium-sulfur (Li-S) batteries are considered to be one of promising next-generation energy storage systems. Considerable progresses have been achieved in the sulfur composite cathodes, but high cycling stability and discharging capacity at the expense of volumetric capacity have offset their advantages. 

In a study published inAdv. Energy Mater., the research group led by Prof. WANG Ruihu from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences (CAS) reported a functional separator by coating cobalt-embedded nitrogen-doped porous carbon nanosheets and graphene on one surface of commercial polypropylene separator (Co-Nx@NPC/G-PP). 

The researchers found that the coating layer is not only suppressing polysulfides shuttle effect through chemical affinity but also functions as an electrocatalyst to propel catalytic conversion of intercepted polysulfides.  

The cell with Co-Nx@NPC/G-PP separator exhibits significantly improved cycling stability and sulfur loading capability compared with that of PP separator. 

What’s more, the freestanding carbon nanofibers/sulfur cathode provides high discharging capacity of 1190 mA h g^-1 and volumetric capacity of 1136 mA h cm^-3 at high sulfur loading of 10.5 mg cm^-2. The electrochemical performance is comparable with or even superior to those in the state-of-the-art carbon-based sulfur cathodes.  

This separator holds great promises for the development of high-energy-density Li-S batteries. 

Schematic cell configuration of the Co-Nx@NPC/G-PP separator with chemisorption and catalytic effects toward polysulfides. (Image by Prof. WANG’s Group)