Molten Salt Planarizing of Graphene Wrinkles for Efficient Thermal Dissipation

Macroscopic graphitic films made from graphene platelets have been widely utilized in the thermal management of electronic devices, yet the thermal conductivity of the films is often deteriorated by imperfections such as structural defects, misalignment, and porosity. Previous efforts have been dedicated to optimizing the size of graphene platelets and minimizing the microscopic voids, while the control of graphene wrinkles at the graphitization stage has been less investigated due to the high processing temperatures up to 3000°C. Here we report a sodium molten salt strategy to planarize graphene wrinkles for the preparation of ultraflat graphene platelets in macroscopic films. We identify the melting and intercalation procedure of sodium salts, which are generated from the reaction between purposely added sodium hydroxide and acid residue in the precursor graphene oxide. The wrinkle planarizing is elucidated based on the relaxed compressive strain and the improved interlayer interaction between graphene layers. As a result, an ultrahigh thermal conductivity of 1994 W m^-1 K^-1 is obtained for graphitic films with a final thickness of 10 µm, and the expansion of thickness in the graphitization is largely alleviated. Our finding provides a wrinkle engineering strategy for macroscopic graphitic films toward high-performance thermal management applications.