# Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries
## 2 Preparation Methods of Graphene-Based Materials
### Cvd  
CVD is appropriate for preparing graphene-based materials with a regular and controlled structure, which can ensure the integrity of the lattice of the graphene sheets forming the structure with minimal defects. When the products are prepared by CVD, the morphology relies on the template material, while the structural stability depends on the type and concentration of the carbon source employed. The use of metals, structural oxides, salts, and combinatorial templates as hard templates for the preparation of graphene-based materials by CVD has been widely reported. In the utilization of metal temples, Ni and Cu templates have been widely studied for large-scale, high-quality graphene preparation. [PERSON] et al. achieved CVD growth of graphene foam (GF) on a Ni foam template with CH\({}_{4}\) as the carbon source and polymethyl methacrylate (PMMA) as the support. After etching off Ni with hydrochloric acid and removing PMMA with acetone, a highly conductive graphene foam was obtained (Figure 2A) [13]. An analogous method was used by [PERSON] et al. to prepare nanoporous nickel (np-Ni) templates to manufacture small-bore graphene [14]. By imprinting the Rosette-type Ni and Si substrates as templates, network graphene films can be prepared [15]; graphene fibers can be made with Cu wires [16], and foams can be prepared with Ni or Cu foams (Figure 2B) [17]. Graphene with an internal cross-linking structure can be obtained by controlling the number of layers, size, and assembly angle of multilayer Ni stencils [18]. [PERSON] et al. prepared large-area single-layer graphene sheets with excellent quality using benzene as the carbon source and electropolished Cu foil as the template at a low temperature [19]. Kong  
Figure 1: Graphical abstract for the current preparation method and application of graphene-based materials for the separator functionalization of lithium-ion/metal/sulfur batteries. reported the preparation of a large-area continuous graphene film using polycrystalline Ni films. The Ni films were electron-beam evaporated onto SiO\({}_{2}\)/Si substrates and annealed before CVD synthesis [20]. In the same year, [PERSON] et al. used a mixture of methane and hydrogen to achieve the growth of graphene films on Cu substrates at 1000 \({}^{\circ}\)C. The size of these films reached the centimeter scale, most of which were single-layer structures [21]. For the advantages of low cost, availability of easy etching methods, and controllability with the guide of the Fe-C phase diagram, [PERSON] et al. synthesized few-layer graphene on a Fe foil template coated with PMMA. The Fe foil was removed by an aqueous solution of FeNO\({}_{3}\)/FeCl\({}_{3}\) (Figure 2C) [22]. Despite the progress achieved by single metal substrates, as previously mentioned, the great challenge for them is controlling the layer number and uniformity of graphene. Hence, the preparation of graphene by CVD on alloy substrates has rapidly developed due to the advantage of multiple metal templates. [PERSON] reported the CVD growth of graphene on \"90-10\" Cu-Ni alloy, where a higher temperature, longer deposition time, and slower cooling rate helped to increase graphene coverage on Cu-Ni alloy foil (Figure 2D) [23]. [PERSON] successfully realized the control of the graphene layer thickness by adjusting the proportion of Ni in the Cu-Ni alloy [24]. As shown in Figure 2E, [PERSON] et al. designed a combined Ni-Mo system with a layer of Ni deposited onto Mo. In this structure, all of the excess carbon atoms were captured by Mo in the form of MoC, which overcomes the limitation of uneven growth of graphene layers on Ni [25]. In addition, Co-Cu [26], Au-Ni [27], Ni-Ge [28], and other binary alloys have also been reported as excellent systems for controlling the number of graphene layers. These alloy systems are typically composed of a carbon-soluble surface material (Ni or Co coating) and a carbon-insoluble substrate (Ge or Cu foil). Combining the advantages of both, high-quality graphene with controllable layers can be prepared.