## 2 Results and Discussion
### Electrochemical Performance of Li-S Batteries with the Modified Separators  
For the Co@g-C\({}_{3}\)N\({}_{4}\)/G material calcined at different temperatures, it was found that there was an obvious difference in the component and micromorphology based on our analyses. First, the performances of Li-S cells assembled with different Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators were investigated. The electrochemical performances were tested using CR2016-type coin cells prepared by the corresponding separators and S/KB cathodes with a final sulfur content up to \(\sim\)70 wt%. Figure 5a presents the rate properties of the corresponding Li-S cells recorded at various rates from 0.2 to 2.0 C. The cell using the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (550 \({}^{\circ}\)C) separator delivered discharge-specific capacities of 1213, 1020, 935, and 860 mAh g\({}^{-1}\) at a 0.2, 0.5, 1.0, and 2.0 C rate, respectively, suggesting an excellent rate property. Moreover, a reversible capacity of 1149 mAh g\({}^{-1}\) was well recovered when the current density switched back to 0.2 C, demonstrating an effective confinement ability toward sulfur species at a high rate. In comparison, the cells with the other two functional separators exhibited inferior rate capabilities. Figure 5b and Figure S5 compare the voltage profiles of Li-S cells equipped with different separators under different current rates, and it can be observed that the cells with corresponding separators all retain a clear two-plateau discharge profile, even at a considerable rate of up to 2.0 C, but the capacities of both high- and low-voltage plateaus (Q\({}_{\mathrm{H}}\) and Q\({}_{\mathrm{L}}\)) for the cell with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (550 \({}^{\circ}\)C) separator are much higher than those of the other two controlled cells, especially at faster rates, revealing an effective capture and catalytic conversion capability of the Co@g-C\({}_{3}\)N\({}_{4}\)/G (550 \({}^{\circ}\)C) interlayer toward polysulfide species [59; 60]. Long cycling tests of cells assembled with corresponding separators were also performed (Figure 5c), and the cell with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (550 \({}^{\circ}\)C) separator exhibited the best cycling stability in comparison with the other two controlled cells. It delivered an initial specific capacity of 900 mAh g\({}^{-1}\) and maintained a specific capacity of 657 mAh g\({}^{-1}\) after 400 cycles at a 1.0 C rate, with a slow decline rate of 0.067% per cycle (capacity retention rate of 73.0%). In particular, a high and stable coulombic efficiency could be obtained concurrently in the whole cycling process, which indicates good electrochemical reversibility in the cell with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (550 \({}^{\circ}\)C) separator. Besides, it was seen that the cell with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (500 \({}^{\circ}\)C) separator delivered a relative low capacity, and another cell using the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP (600 \({}^{\circ}\)C) separator had severe capacity fading in later cycling (Figure 5c). Most possibly, the root reason for these results is a dual influence of electrical conductivity and Li ion transfer capacity in the Co@g-C\({}_{3}\)N\({}_{4}\)/G interlayer. Specifically, Co@g-C\({}_{3}\)N\({}_{4}\)/G possesses  
Figure 4: (**a**) Photographs of Li\({}_{2}\)S\({}_{6}\) solution contacting with Co@g-C\({}_{3}\)N\({}_{4}\)/G and g-C\({}_{3}\)N\({}_{4}\)/G. (**b**) Photographs of PP, g-C\({}_{3}\)N\({}_{4}\)/G-PP, and Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators. SEM images of (**c**) PP and (**d,e**) Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators. (**f**) Cross-sectional SEM image of Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators. much more g-C\({}_{3}\)N\({}_{4}\) and a relative low reduction degree of graphene after calcining at 500 \({}^{\circ}\)C, exhibiting limited electrical conductivity and thus leading to congested electronic transmission in the discharge-charge process [60].