## 2 Results and Discussion
### Electrochemical Performance of Li-S Batteries with the Modified Separators
Four distinct redox peaks could be observed, even up to a scan rate of 3 mV s\({}^{-1}\), in the Co@g-C\({}_{3}\)N\({}_{4}\)/G symmetrical cells, implying rapid kinetics conversion for polysulfide redox reactions in the Co@g-C\({}_{3}\)N\({}_{4}\)/G interface [25; 66]. Therefore, these positive results confirm that the Co@g-C\({}_{3}\)N\({}_{4}\)/G heterostructure can well propel the kinetic conversion of intermediate polysulfides in a working Li-S cell. Figure 6e displays the cycling performances of the three cells with corresponding functional separators at 1.0 C, and it was obviously seen that the cell assembled with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separator exhibited the best cycling stability among the three cells, delivering the highest initial capacity of 900 mAh g\({}^{-1}\) and still maintaining a specific capacity of 657 mAh g\({}^{-1}\) after 400 cycles, with a capacity decay rate of \(\sim\)0.067% per cycle and a high coulombic efficiency of above 98.0%. In addition, the cycling performance of cells with Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators at low rates of 0.2 and 0.5 C were investigated, all exhibiting superior cycling stability, as shown in Figure 6f. There was moderate capacity fading in the first 30 cycles under the corresponding rates and then low capacity decay in the following appointed cycling numbers. Specifically, a specific capacity of 1040 mAh g\({}^{-1}\) was delivered after a 0.1 C low rate activation and still remained at 928 mAh g\({}^{-1}\) over 250 cycles at a 0.2 C rate, with a capacity-fading rate of 0.043% per cycle. At a 0.5 C rate, a stable capacity of 815 mAh g\({}^{-1}\) was achieved after 350 cycles, with a low capacity attenuation of 0.035% per cycle. The comparison in Table S2 shows that the electrochemical performances of the cell with the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separator have some advantages over other relevant functional-separator-assembled Li-S cells in the recent literature. Overall, these favorable results manifest a good promise of the as-designed separator in the improvement of the performance of Li-S batteries. Considering the superiority of the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators, a cell using the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separator and a high-sulfur-loading S/KB cathode (3.0 mg cm\({}^{-2}\)) was prepared and its cycling stability was further explored (Figure 6h). The cell could deliver a high specific capacity of 1110 mAh g\({}^{-1}\) at 0.1 C low rate activation and then undergo stable cycling at 0.2 C, still maintaining a capacity of 785 mAh g\({}^{-1}\) after 150 cycles. These good electrochemical performances obtained can be attributed to two major aspects: (1) High-conductivity graphene can ensure fast electron transfer, which is conducive to accelerating the redox conversion of captured polysulfides occurring on the active sites of Co-species during the electrochemical process, and (2) the residual g-C\({}_{3}\)N\({}_{4}\) supplies rich N sites for efficient adsorbing polysulfides, thus alleviating the shuttle effect and improving sulfur use. Hence, the lithium-sulfur batteries assembled with Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators can possess a high capacity and stable cycling performance.