Synergetic Protective Effect of the Ultralight MWCNTs/NCQDs Modified Separator for Highly Stable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are highly attractive due to their high energy density, potentially low cost, and environmental compatibility. However, their commercialization has been greatly hindered by their poor cycle life and severe self-discharge, which can be attributed to the polysulfides dissolution. To overcome these issues, much effort has been devoted to engineering the electrode structure and composition to improve the performance which is often expensive and laborious. In this study, an ultralight multiwall carbon nanotube/N-doped carbon quantum dot (MWCNT/NCQD)-coated separator is first designed, which is cost effective and facile. The MWCNTs/NCQDs-coated separator is then applied in Li-S batteries. The MWCNTs/NCQDs coating provides a physical shield against polysulfide shuttling and chemical adsorption of polysulfides by MWCNTs and NCQDs. The synergetic effect of MWCNTs and NCQDs enables the production of Li-S cell with a relative high initial discharge capacity of 1330.8 mA h g(-1) and excellent cyclic performance with a corresponding capacity fade rate of as low as 0.05% per cycle at 0.5 C over 1000 cycles. Excellent rate capability and anti-self-discharge behavior are also displayed. The design of MWCNTs/NCQDs-coated separator is a viable approach for successfully developing practical Li-S batteries.