# Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries
## 2 Preparation Methods of Graphene-Based Materials
### Others
#### 2.3.2 Liquid Phase Exfoliation  
The liquid phase exfoliation (LPE) method has been widely investigated due to its high yield, low defect, low cost, and suitability for large-scale production. Combining the cavitation effect of ultrasound and the intercalation effect of solvent molecules to exfoliate graphite to prepare graphene, i.e., ultrasound-assisted LPE (ULPE), is the most common LPE strategy. [PERSON] et al. demonstrated that graphite fragmentation and exfoliation occurred in three different stages: (1) graphite flake rupture and kink band formation; (2) peeling off of thin graphite strips; and (3) exfoliation to thin flakes during ultrasound-assisted LPE in which the kink band-induced exfoliation process was a critical step (Figure 4B) [68]. [PERSON] et al. systematically investigated the effects of three liquid phase systems (i.e., organic solvent system, aqueous surfactant system, and ionic liquid system) on graphene preparation and discussed the exploration of new solvents and improvement measures for the ULPE method [69]. [PERSON] et al. achieved a high yield of monolayer graphene with low basal plane defects. The graphene solution was prepared through mild ultrasonication in N-methylpyrrolidone (NMP) for an extended period [70]. [PERSON] et al. introduced graphene oxide (GO) as a dispersant into ULPE for the first time to prepare graphene nanoflakes (GNFs) with a low oxygen content, few defects, and high electrical conductivity. The GO/graphene complexes formed by wrapping the graphene nanosheets with GO effectively improved the exfoliation rate and dispersion of graphene in an aqueous solution, thus avoiding the restacking of graphene sheets into graphite, and the retained GO in solution could be removed and recycled by centrifugation [71].  
Shear-induced LPE has also been investigated for its simplicity of process and feasibility in preparing graphene/polymer composites in situ. [PERSON] et al. demonstrated that large amounts of high-quality, unoxidized graphene suitable for industrial production could be obtained by shear mixing without prior intercalation expansion. They also developed a quantitative model to scale up graphene production using this method [72]. [PERSON] et al. prepared graphene-enhanced polymer matrix composites (G-PMCs) directly in molten thermoplastic polymers where high-speed shear stress was applied to exfoliate graphite [73]. Based on [PERSON]'s study, [PERSON] et al. prepared graphene nanoplatelets (GNPs) for high-performance supercapacitors by the high-speed shear-induced exfoliation of graphite in an aqueous medium mixed with GO dispersant, then the GO retained in solution could be converted to reduced graphene oxide (rGO) by thermal or chemicalreduction [74]. [PERSON] et al. put forward a nanoparticle-assisted liquid phase exfoliation strategy to prepare graphene with a controlled layer number, which utilized the strong shear forces resulting from the collision of Fe\({}_{3}\)O\({}_{4}\) particles with graphite particles and intense ultrasonic waves to enhance the exfoliation of graphite [75].