A thin and multifunctional CoS@g-C₃N₄/Ketjen black interlayer deposited on polypropylene separator for boosting the performance of lithium-sulfur batteries

The sluggish redox kinetic and shuttle effect of polysulfides still obstruct the commercial application of lithium-sulfur (Li-S) batteries. Herein, a nanocomposite consisting of well-dispersed and lamellar-like shape CoS anchored on g-C₃N₄ nanosheets (CoS@g-C₃N₄) is prepared firstly, and then it is integrated on a polypropylene membrane combined with little conductive Ketjen black (KB) to fabricate a multifunctional and quite thin interlayer, with a thickness of only ∼ 2.1 um and areal mass loading of ∼ 0.07 mg·cm⁻². The as-prepared interlayer firstly can capture polysulfides by Li-N bond as well as Lewis acid-base interaction between CoS and polysulfide anions (S_n^2-), and more importantly, it also displays a positive effect on catalyzing the redox conversion of intermediate polysulfides. As expected, a Li-S cell assembled with this modified separator and high sulfur content cathode displays an excellent electrochemical performance, with specific capacity of ∼ 1290 mAh g⁻¹ at 0.2C and a low fading rate of 0.03% per cycle after 500 cycles at 1.0C. Furthermore, a high sulfur mass loading of ∼ 4.0 mg·cm⁻² electrode paired with this multifunctional separator exhibits a stable specific capacity of ∼ 600 mAh g⁻¹ after 250 cycles under 0.1C. This work can give some guides to rational design a quite thin and light interlayer for improving the utilization of sulfur species, with little damage to the energy density and Li ion transportation in Li-S batteries.