Exceptional high thermal conductivity of inter-connected annular graphite structures†
Based on the experimentally observed templating effects in CNTs containing carbon fibers, new types of inter-connected annular graphite structures are proposed and designed in order to significantly improve the cross-plane thermal conductivity of graphite. The calculations of the thermal conductivity of the newly designed structures were carried out by combining macroscopic continuous equations and microscopic molecular dynamic (MD) simulations. First, MD simulation was used to examine the influence of bending curvature on the in-plane thermal conductivity of a graphene sheet along and perpendicular to the rolling direction. Next, various types of annular graphite structures with single and inter-connected double/triple multi-layered graphite sheets were designed. Finally, finite element analysis was used to calculate the effective out of plane thermal conductivities of these structural models. The cross-plane thermal conductivity of a common graphite film is 2–3 orders of magnitude lower than its in-plane thermal conductivity, which strongly restricts its heat dissipation ability. However, the formation of annular graphite structures and the inter-connections of the outer layers lead to a dramatic improvement of effective out of plane thermal conductivity from 2.3 W m−1 K−1 to 799.8 W m−1 K−1 in this work, which is superior to common metal materials, especially considering the relatively lower density of carbon materials. These results would be valuable for designing and fabricating highly thermally conductive carbon materials for heat dissipation and temperature management.