# Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries
## 2 Preparation Methods of Graphene-Based Materials
### Pyrolysis
applied this strategy for the preparation of vanadium nitride/nitrogen-doped graphene (VN/NGr) in the two-stage pyrolysis of a mixture including dicyandiamide (DCDA), glucose, and NH\({}_{4}\)VO\({}_{3}\), as shown in Figure 3E. In the first stage, NH\({}_{4}\)VO\({}_{3}\) was transformed into VN gradually at 600 \({}^{\circ}\)C. Thermal decomposition of DCDA produced layered g-C\({}_{3}\)N\({}_{4}\), which bound the carbon derived from glucose and VN to its interlayer gaps to form graphene layers and meanwhile limited the aggregation of VN nanoparticles. In the second stage, the g-C\({}_{3}\)Nwas completely decomposed at 800 \({}^{\circ}\)C. The formed nitrogen was introduced into the graphene framework due to the small atomic size difference between N and C. Finally, VN/NGr nanocomposites were obtained without any post-treatment [54]. The strategy was then studied to prepare Co/N/S Tri-doped graphene [55]. [PERSON] et al. proposed a zinc-assisted solid pyrolysis (ZASP) method to produce block graphene. The authors compressed glucose powder and Zn metal (usually 1:9) into an ingot and directly pyrolyzed it to obtain graphene with a full film and excellent graphitization. In addition to the pore-forming effect of common SFAs, zinc metal introduced a stratification process on large organic matter and solid carbon, leading to the preparation of graphene sheets at high temperatures. Zinc gas can be extruded and evaporated from the carbon material at higher temperatures, thereby eliminating the formed impurities. Zinc gas also promoted the carbonization and graphitization of organic matter, realizing the recycling of metal reagents and avoiding tedious wet processing [56]. Removing redundant SFA completely is a challenging task due to potential, unpredictable side effects, which has led to the extensive study of SFA-free pyrolysis. In 2013, [PERSON] et al. developed a chemical blowing route known as sugar blowing, which uses NH\({}_{3}\) to produce struttted graphene foam. In the process of heating glucose and NH\({}_{4}\)Cl, the molten syrup gradually polymerizes into melanin, which is blown into a network of polymeric bubbles by NH\({}_{3}\). The walls of these bubbles become thinner due to blowout, drainage, and chemical elimination reactions, leading to the formation of ultra-thin graphene films in the subsequent high-temperature graphitization process. The resulting self-supporting graphene products possess high conductivity, large SSA, and superior mechanical properties [11]. In 2019, [PERSON] et al. proposed an O\({}_{2}\)-NH\({}_{3}\) reactive pyrolysis strategy to generate graphene, which transformed cellulose paper into networked carbon paper composed of graphene sheets while avoiding the production of dense carbon fiber/particles [57]. [PERSON] et al. applied flash Joule heating technology to the preparation of gram-scale graphene with a turbine tier arrangement structure between the stacked layers from cheap carbon sources in less than one second. The method has attracted the attention of researchers widely on account of its many advantages, such as superior production efficiency, high purity without a furnace, solvent, or reaction gas, and promise for industrial application [58; 59]. Graphene can also be prepared by pyrolyzing the surface of single SiC crystals pretreated by oxidization [60] or H\({}_{2}\) etching [61], in which the Si atoms are removed by evaporation and graphene grows along the surface structure of SiC. The method is also known as \"epitaxial growth\", with SiC as both the carbon source and SFA material [62]. [PERSON] et al. subjected single-crystal 6H-SiC to oxidation or hydrogen etching treatment at 1000 \({}^{\circ}\)C to eliminate surface oxides under ultra-high vacuum conditions. The sample was then maintained at a temperature range of 1250-1450 \({}^{\circ}\)C for 1-20 min, resulting in graphene with a thickness of 1-2 carbon atoms on the silicon-terminated (0001) face [63]. [PERSON] et al.