# Macroporous Activated Carbon Derived from Rapeseed Shell for Lithium-Sulfur Batteries
## 3 Results and Discussion
The AC sample showed a broad diffraction peak at approximately 26\({}^{\circ}\), implying the amorphous character of AC. For the pure sulfur sample, sharp diffraction peaks indicated its crystal form. After impregnation into AC frameworks, sulfur-associated crystalline diffraction peaks were not observed in the AC/S sample. The results demonstrated that sulfur existed in an amorphous state inside the nanopores of AC. The sulfur content of the AC/S composite was analyzed by TGA measurements (Figure 3b). The weight of sublimed sulfur decreased sharply in the range of 180 \({}^{\circ}\)C to 360 \({}^{\circ}\)C. However, for AC/S composite, the loss of weight started at 180 \({}^{\circ}\)C and ended at 390 \({}^{\circ}\)C. Sulfur in the AC matrix was more thermally stable than that in the normal state, indicating the restraining effect of AC frameworks. TGA analysis indicated that the sulfur content in the composite closely approximated that of our design. AC/S composite was also characterized by N\({}_{2}\) isotherm adsorption-desorption analysis. After the encapsulation of sulfur into AC nanopores, the nitrogen absorption volume decreased markedly (Figure 3c). For the BJH pore size distribution curve of AC/S composite, the main peak significantly decreased (Figure 3d), demonstrating that sulfur deeply impregnated the AC nanopores. The pore volume and BET surface area of AC/S composite measured 0.03 cm\({}^{3}\) g\({}^{-1}\) and 10 m\({}^{2}\) g\({}^{-1}\), respectively. Notable diminution of these two parameters also suggests that sulfur was infused into the nanopores of the AC hosts. Figure 4a,b exhibit SEM images of AC/S composite at various magnifications. The macroporous structure of AC was partially destroyed due to the grinding treatment during the preparation of AC/S composite. Bulky sulfur was not observed on the surface of AC/S particles. Figure 4c-e present SEM images of the composite and corresponding energy dispersive spectroscopy (EDS) mapping for elemental carbon and sulfur. Sulfur was evenly dispersed in the AC/S composite. To evaluate the electrochemical performance of AC/S composite, coin cells were assembled with AC/S composite as the cathode. Figure 5a shows CV curves of AC/S during the initial two cycles at 0.05 mV s\({}^{-1}\) from 1.7 V to 2.7 V. During the discharge process, two peaks at potentials of 2.29 and 2.03 V corresponded to reductions of sulfur to soluble lithium polysulfides (Li\({}_{2}\)S\({}_{n}\), \(4\leq n\leq 8\)) and low-order  
Figure 3: (**a**) XRD patterns of elemental sulfur, AC, and activated carbon/S (AC/S) composite; (**b**) Thermogravimetric analysis (TGA) profiles of elemental sulfur and AC/S composite; (**c**) N\({}_{2}\) adsorption–desorption isotherms and (**d**) BJH pore size distribution curves from the adsorption branch of AC and AC/S composite. polysulfides to solid-state Li\({}_{2}\)S\({}_{2}\)/Li\({}_{2}\)S. During the subsequent charge process, the sample showed two peaks at potentials of 2.33 and 2.36 V, corresponding to oxidations of Li\({}_{2}\)S\({}_{2}\)/Li\({}_{2}\)S to Li\({}_{2}\)S\({}_{n}\) (4 \(\leq n\leq\) 8) and Li\({}_{2}\)S\({}_{n}\) (4 \(\leq n\leq\) 8) to sulfur, respectively [39]. Figure 5b shows typical voltage versus capacity curves at 200 mA g\({}^{-1}\) for the first and second cycles. The discharge curves exhibit two plateaus, which can be ascribed to the multistep reduction of sulfur to lithium sulfides. The two plateaus coincide with the two peaks in CV curves obtained during the discharge process. The composite electrode delivered an initial discharge capacity of 1065 mAh g\({}^{-1}\). The cell was further tested at various charge/discharge current densities. With increasing current densities, voltage versus capacity curves for AC/S composite maintained the typical two-plateau characteristic (Figure 5c). Figure 5d shows that AC/S composite delivered specific discharge capacities of 980, 840, 750, 680, and 590 mA h g\({}^{-1}\) at 200, 400, 800, 1600 and 3200 mA g\({}^{-1}\), respectively.