## 3 Materials and Methods  
Fabrication of Highly Dispersed Ultrafine Co-Species Interspersed g-C\({}_{3}\)N\({}_{4}\) Nanosheets and Graphene Heterostructure (Co@g-C\({}_{3}\)N\({}_{4}\)/G)  
g-C\({}_{3}\)N\({}_{4}\) was prepared by direct thermal polymerization of urea in air, as referred from previous published work [41]. Co@g-C\({}_{3}\)N\({}_{4}\)/G heterostructure composites were synthesized via a one-step pyrolysis strategy. For preparation of the precursor, 25 mL of GO suspension (2.0 mg mL\({}^{-1}\)) was first sonicated and stirred for 0.5 h. Next, 50 mg of CoCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O and the as-prepared g-C\({}_{3}\)N\({}_{4}\) were added to this solution consecutively, followed by violent sonicating for another 2.0 h and vigorous stirring for another 1.0 h to produce a homogeneous mixture. Subsequently, the mixture was treated with vacuum filtration to remove the residual CoCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O and then freeze-dried to obtain the precursor (g-C\({}_{3}\)N\({}_{4}\)/GO). Finally, the dry precursor was annealed under nitrogen protection and kept at different temperatures (500, 550, and 600 \({}^{\circ}\)C) for 2 h with a ramping rate of 5 \({}^{\circ}\)C min\({}^{-1}\) to yield black products.  
For comparison, a control sample of g-C\({}_{3}\)N\({}_{4}\)/G was prepared by following the same process without addition of CoCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O. In addition, a CoO@G sample was obtained with pyrolysis of the precursor composed of CoCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O and GO. Reduced GO (rGO) was obtained by direct thermal reduction of GO powder. These three controlled samples were all calculated at 550 \({}^{\circ}\)C for 2 h with a heating rate of 5 \({}^{\circ}\)C min\({}^{-1}\) under a nitrogen atmosphere.  
Fabrication of the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP, g-C\({}_{3}\)N\({}_{4}\)/G-PP, and CoO@G-PP Separators  
Modified separators were prepared using a vacuum filtration strategy. Briefly, 18.0 mg of Co@g-C\({}_{3}\)N\({}_{4}\)/G was dispersed into 150 mL of ethanol under ultrasonic treatment for 2  
Figure 6: (**a**) Rate performances and (**b**) charge–discharge profiles at 0.1 C of Li-S cells with different separators. CV curves of (**c**) cells with g-C\({}_{3}\)N\({}_{4}\)/G-PP and Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators and (**d**) symmetric cells using two Co@g-C\({}_{3}\)N\({}_{4}\)/G electrodes. (**e.f**) Cycling performances at different rates of cells with corresponding separators. (**g**) EIS spectra of cells with PP, g-C\({}_{3}\)N\({}_{4}\)/G-PP, and Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separators. (**h**) Cycling performance at 0.2 C of the cell using the Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP separator with a high sulfur loading of 3.0 mg cm\({}^{-2}\).  
h, and then, 1.0 mL of the LA133 aqueous binder (0.2 wt%) was added to this solution to obtain a homogeneous slurry. Next, a certain volume of the prepared slurry was directly vacuum-filtered onto one surface of a commercial PP separator, followed by drying at room temperature, and finally punched into a 19-mm-diameter circular disk (Co@g-C\({}_{3}\)N\({}_{4}\)/G-PP). Similarly, the other corresponding separators were prepared using the same method. The areal mass density of the coating material was ~0.2 mg cm\({}^{-2}\).