Highly Ordered and Dense Thermally Conductive Graphitic Films from a Graphene Oxide/Reduced Graphene Oxide Mixture

Abstract

© 2020 Elsevier Inc.We report a new approach to making highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O). By introducing small-diameter reduced graphene oxide (rG-O) flakes into the graphene oxide starting material, we found that after heat treatment at 3,000°C, the sample density and atomic order substantially improved over a film composed, at the outset, only of pure G-O flakes. A subsequent mechanical press increased the density but reduced the atomic order. A second 3,000°C heat treatment restored the graphitic structure with graphitization metrics exceeding even those of the first heat treatment. The optimized graphitic film with an original concentration of 15 wt % reduced G-O in G-O gave well-oriented graphitic films with a density of 2.1 g cm−3, cross-plane thermal conductivity of 5.65 W m−1 K−1, and in-plane thermal conductivity of 2,025 ± 25 W m−1 K−1. Highly oriented graphitic films are used as thermal interface materials in portable electronics. Graphitic films derived from graphene oxide (G-O) could provide advantages, but graphitization of these films results in significant expansion due to heat-induced decomposition of functional groups on G-O. We report methodology that significantly improves the quality of graphitic films derived from G-O. By incorporating a small fraction of “very small”-diameter reduced G-O platelets prior to film casting, we observed less expansion and higher densities after graphitization. Mechanical pressing of these G-O-derived graphitic films can increase density but introduced defects. A subsequent heat treatment improved the crystallinity beyond that prior to mechanical pressing. Combining both approaches yielded a dense, high-quality graphitic film. The addition of reduced G-O could be used in other heat-treated G-O materials where increased density is desirable, e,g., G-O-derived carbon fibers. A new approach to make graphitic thin films from graphene oxide (G-O) is presented. By incorporating small-diameter, reduced G-O platelets with G-O, graphitized films show improved density and crystalline order when compared with pure G-O. Mechanical pressing of the graphitized films increased density but decreased crystallinity. A subsequent high-temperature heat treatment improved atomic order beyond that seen before mechanical pressing. In-plane thermal conductivity is on par with highly oriented pyrolytic graphite and exceeds commercially available graphite-based thermal interface materials