Flexible graphite films with high cross-plane thermal conductivity prepared by graphitization of polyimide catalyzed by Ni-coated-CNTs

Abstract

Graphite films are widely used in microelectronic devices as heat-dissipation materials due to their high thermal conductivity, low thermal expansion coefficient and lightweight. In the 5G era, the miniaturization and integration of microelectronic devices are continuously improving, so there are higher requirements for heat-dissipation materials. Therefore, flexible graphite films with high thermal conductivity are urgently needed. In this work, nickel-coated CNTs (Ni@CNTs) were prepared first as additives to be incorporated into the PI matrix via in situ polymerization, and then the Ni@CNTs/PI composite films were carbonized and graphitized at high temperature to form graphite films. In this composite system, nickel particles can effectively improve the graphitization degree of the obtained graphite films, which is beneficial to the improvement of their thermal conductivity, as well as the CNTs can effectively enhance the cross-plane thermal conductivity and mechanical strength of the graphite films. The graphite films obtained from the graphitization of PI/Ni@CNTs (0.4 wt%) have a perfect graphene structure and optimal properties. The optimal layer thickness of graphene is 0.3354 nm, while the d-spacing of the graphite layers is around 0.3358 nm. The in-plane thermal conductivity is 1.13 times greater than that of the graphite film made from the pure PI film (G0 film), which has a value of 1198.5 W m⁻¹ K⁻¹. The cross-plane thermal conductivity is 6.26 W m⁻¹ K⁻¹, which is 2.96 times that of the G0 film (2.11 W m⁻¹ K⁻¹). The bending strength is 72.3 Mpa, which is 2.28 times that of the G0 film (31.7 Mpa). The introduction of Ni@CNTs greatly improves the comprehensive properties of graphite films, and the preparation technology has an important guiding significance for the preparation of high thermal conductivity flexible graphite films and important industrial application value.