# Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries
## 2 Preparation Methods of Graphene-Based Materials
### Cvd
In addition, structural oxides have also been studied as a template. [PERSON] et al. developed graphene nanocages from the in situ decomposition of magnesium oxide templates with alkaline magnesium carbonate [29]. As reported by [PERSON], graphene could be grown bottom-up on MgO at a temperature as low as 325 \({}^{\circ}\)C using cyclohexane as the carbon source (Figure 2F) [30]. Graphene can also be prepared by CVD using porous metal oxide as a template. Thus, a large number of mesopores can be obtained through the self-assembled microporous framework of the template, and the metal oxide can be used as a catalyst to produce micropores. CaO has a similar structure to MgO and can also be used as a template for the preparation of graphene. [PERSON] et al. reported the CVD growth of porous graphene materials on CaO templates at 950 \({}^{\circ}\)C by feeding CH\({}_{4}\) (Figure 2G) [31]. [PERSON] et al. used scallops, conch, starfish, and other biomass rich in CaCO\({}_{3}\) to prepare porous CaO substrates at high temperatures. By controlling the morphology of CaO substrates, the microstructure and corresponding properties of the graphene foam were changed [32]. Similarly, strategies that adopted ZnO [33] and layered double oxide [34; 35] as the template have also been reported. SiO\({}_{2}\) is a suitable template for the nucleation and growth of graphene as well. [PERSON] et al. reported the preparation of graphene by using kieselguhr as a template, which inherited the naturally curved surface of kieselguhr and overcame the problem of interlayer stacking [36]. [PERSON] et al. reported graphene with a tetrahedral-connected cell structure via SiO\({}_{2}\) aerogel templates, which showed a tubular network of several graphene layers with hollow tetrahedral connections (Figure 2H) [37]. [PERSON] et al. presented the fabrication of free-form graphene foam by a combination of 3D printing and CVD. The porous SiO\({}_{2}\) templates were prepared by digital photo processing methods and polymerization of resins. The stencil porosity was governed by a gluing and burning process, whose product is inherited from an interconnected network with excellent electrical conductivity and mechanical performance [38]. [PERSON] et al. proposed a plasma-enhanced CVD scheme to prepare a highly oriented pyrolytic graphite (HOPG) with H\({}_{2}\) plasma known to etch graphene from the edges. HOPG has been grown directly on SiO\({}_{2}\)/Si substrate without a catalyst at a temperature as low as 300 \({}^{\circ}\)C when using C\({}_{2}\)H\({}_{4}\) as the carbon source [39]. Figure 2: CVD for graphene preparation. **(A)** Synthesis of a GF and integration with PDMS [13]. Reproduced with permission: Copyright 2011, Springer Nature. **(B)** Flowchart for the preparation of GF/epoxy composites [17]. Reproduced with permission: Copyright 2014, American Chemical Society. **(C) (i)** Image of a CVD-grown graphene film on iron foil and (inset) AFM image of graphene; **(ii)** SEM image of the graphene; **(iii)** AFM image of graphene on an iron substrate which reveals its surface morphology [22]. Reproduced with permission: Copyright 2011, Springer Nature. **(D) (i)** Schematic diagrams of the growth process of carbon isotope labeled graphene; **(ii)** High-resolution TEM image of the graphene [23]. Reproduced with permission: Copyright 2012, American Chemical Society. **(E) (i)** CVD growth of single-layer graphene on Ni-Mo substrate, and the numbers from 1 to 4 represent the elementary steps in the Ni-Mo-CVD process; **(ii)** TEM image and the selected area electron diffraction pattern (inset) reveal the nice crystallinity of single-layer graphene grown on the Ni-Mo alloy; **(iii)** AFM image of the grown graphene [25]. Reproduced with permission: Copyright 2011, Springer Nature. **(F) (i)** Image of a CVD-grown graphene film on MgO; **(ii)** Graphene island on the surface of a MgO crystal; **(iii)** Magnified region from the box in panel C highlighting graphene structure [30]. Reproduced with permission: Copyright 2010, American Chemical Society.