Anisotropic high thermal conductivity of flexible graphite sheets used for advanced thermal management materials

This work was to prepare the high purity exfoliated graphite particles and use them to prepare the anisotropic high thermal conductivity of flexible graphite sheets by mechanically roll-compacting method. Scanning electron microscopy (SEM) was used to analysis the surface morphology. The thermal diffusivity both parallel and perpendicular to the pressing direction were measured by Laser flash method (NETZSCH LFA-447). The thermal conductivity was calculated indirectly. Moreover, the thermal resistance performance of the flexible graphite sheets and copper and aluminum were investigated. The results indicated that the adjacent graphite micro layers orientation inside the sample was preferentially perpendicular to the pressing direction. As the density of the material increased, the thermal conductivity increased along the in-plane direction and decreased along the cross-plane direction, 486 W/m.K and 4.77 W/m.K, respectively. The effect of graphite micro layers orientation, structure porosity and impurity distribution played a significant role on thermal transport properties of the materials. Compared with the copper and aluminum, the flexible graphite sheets had lower thermal dissipation resistance along the in-plane direction. The flexible graphite sheets with high thermal conductivity, low thermal expansion coefficient, lightweight and low-cost are promising thermal management materials for applications in HCPV solar cell heat dissipation.