Effect of graphite structures on the productivity and quality of few-layer graphene in liquid-phase exfoliation

Liquid-phase exfoliation (LPE) is a promising technique for commercializing graphene production because of its simplicity and cost-effectiveness. However, the low yield of graphene in laboratory-scale production, less than 10 g/h, necessitates modifications to the process for it to be feasible for commercial applications. Natural graphite has various size distribution, crystallite sizes, and interlayer space, making the choice of initial graphite very important. Five types of natural graphite with different structures were prepared for the experiment. The structural parameters of graphite such as crystallite size and d-spacing were precisely determined based on a standard procedure of X-ray diffraction measurements for carbon materials. The effects of graphite flake size and crystallite size on the productivity and quality of few-layer graphene (FLG) were investigated. The results showed that small graphite was easier to fragment and exfoliate. FLG productivity improvement up to 1500% was attained when graphite with smaller flakes was used instead of graphite with large flakes. The crystallite size of graphite was manipulated by plenary ball milling, and the effect of crystallite on FLG productivity in LPE process was also discussed.