Composition-programmable graphitized carbon networks for tunable thermal conduction anisotropy in thermally conductive phase change composites

A programmable graphitized carbon network tunes anisotropy without route changes. • Competing graphene and CF networks redirect heat from through-plane to in-plane. • The composite reaches 11.7 W m −1  K −1 and retains 155 J g −1 of melting enthalpy. • Paraffin leakage is suppressed, and the composite lowers LED temperature by 25.6 °C. Phase change composites (PCCs) must combine latent-heat buffering with directional heat transport for advanced thermal management, yet the preferred heat flow direction in anisotropic PCCs is typically imposed by external alignment fields, templates, or processing geometry, making directional redesign dependent on the changes in fabrication conditions. Herein, we design composition-programmable graphitized carbon networks in paraffin wax-based PCCs to tune the preferred heat conduction direction. The conduction networks integrate one-dimensional carbon fiber (CF) backbones with two-dimensional graphene-derived bridges. By regulating the concentration of graphene oxide (GO) and the loading of CFs, the relative dominance of conductive components can be tuned to reconstruct heat transfer pathways without changing the fabrication route. Increasing the GO concentration at a low CF loading can generate a vertically aligned network, and its paraffin wax composite exhibits a through-plane thermal conductivity of 11.7 W m −1  K −1 ; whereas, increasing the CF loading at a high GO concentration can redirect the heat transport toward the in-plane direction, endowing the paraffin wax composite with an in-plane thermal conductivity of 9.3 W m −1  K −1 . Besides, the resultant PCC retains high melting enthalpy, satisfactory shape stability, and cycling durability. As a thermal interface material for high-power LEDs, it can decrease the operating temperature by 25.6 °C and increase the equivalent heat-transfer coefficient by 184%. This work demonstrates the effective tuning of heat transfer pathways in PCCs by compositional regulation of thermally conductive networks.