# Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries
## 2 Preparation Methods of Graphene-Based Materials
### Pyrolysis  
On an industrial scale, pyrolysis using liquid or solid carbon sources can be more efficient and economical than the CVD template method, which requires a gaseous carbon source and more sophisticated equipment, or the solution method, which necessitates a solvent to disperse graphene oxide (GO) flakes to obtain large amounts of graphene. However, pore size cannot be precisely controlled in pyrolysis. To address this issue, the addition of in situ pore-building additives at high temperatures has been explored as a competitive strategy. For instance, [PERSON] et al. developed a simple method to produce a fluorescent graphene layer by pyrolyzing amide salt [40]. [PERSON] et al. prepared a high-performance magnetic graphene aerogel doped with nickel nanoparticles (GA@Ni) through a simple one-pot hydrothermal route and in situ pyrolysis process. The product revealed a low density and microwave absorption (Figure 3A) [41]. [PERSON] et al. fabricated vertically structured graphene sheets with 2-10 layers by bombarding polyethylene powder with a microwave plasma emission device and demonstrated that increasing the calcination temperature in an inert or low-oxygen atmosphere enhanced the crystallization of graphene sheets [42]. Pore-forming agents and shape-forming agents (SFA) are commonly employed in the pyrolysis process to fabricate graphene materials with diverse structures while precisely controlling the pore size and distribution [43]. For instance, [PERSON] et al. generated copper templates in situ during the pyrolysis process by mixing Cu\({}_{2}\)(OH)\({}_{2}\)CO\({}_{3}\) with polymethyl methacrylate (PMMA) and subsequently induced PMMA to yield few-layer graphene [44]. [PERSON] et al. prepared porous iron-nitrogen functionalized graphene (Fe/N/GR) utilizing ZnO as both the adsorbent and pore-forming agent for GO. The pyrolysis of ZnO/GO in the presence of a nitrogenous precursor and Fe source produced porous Fe/N/GR, in which the Fe species and ZnO were removed, as shown in Figure 3B [45]. [PERSON] et al. employed nickel nanoparticles (Ni-NPs) as the SFA material to synthesize multilayer graphene balls (GBs) by Ni-induced carbon separation [46]. [PERSON] et al. reported the bottom-up construction of ordered mesoporous graphene framework (MGF) thin films in which the oleylamine ligands were pyrolyzed into amorphous carbon shells in the presence of Fe\({}_{3}\)O\({}_{4}\) nanocrystal (Fe\({}_{3}\)O\({}_{4}\) NCs) superlattice films and further transferred into MGF after removing Fe\({}_{3}\)O\({}_{4}\) NCs [47]. Considering the previously mentioned relatively complicated treatments for metal or metal oxide after pyrolysis, salt SFAs have attracted the attention of researchers due to their low cost and high solubility in water. [PERSON] et al. used Na\({}_{2}\)CO\({}_{3}\) as the skeleton to build the framework structure in which the fumaric acid particles were directly converted into graphene frameworks (GFs) through rapid decomposition [48]. [PERSON] et al. introduced NaCl into the pyrolysis of sodium polyacrylate precursor, which led to the introduction of nitrogen and sulfur atoms into the interlayer of carbon material to prepare nitrogen-sulfur co-doped porous carbon (NSPC) through a simple liquid-solid absorption method (Figure 3C) [49]. [PERSON] et al. reported a reverse-solvent method strategy to prepare the ferric phthalocyanine (FePc)/KCl precursor. Graphene loaded with Fe particles was formed by surface pyrolysis of FePc (Figure 3D) [50]. [PERSON] et al. studied the strategy of ferric chloride hexahydrate as the pore-forming agent [51], and muti-templates schemes [52] were also studied. Self-sacrificing SFAs that can be removed or eliminated from the major material during pyrolysis without subsequent elution have also been explored. [PERSON] et al. proposed a strategy to use self-sacrificing graphitic carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) as the stratification agent and pore-forming agent for graphene preparation [53]. [PERSON] et al.