Design, progress and challenges of 3D carbon-based thermally conductive networks

Abstract

The advent of the 5G era has stimulated the rapid development of high power electronics with dense integration. Three-dimensional (3D) thermally conductive networks, possessing high thermal and electrical conductivities and many different structures, are regarded as key materials to improve the performance of electronic devices. We provide a critical overview of carbon-based 3D thermally conductive networks, emphasizing their preparation-structure-property relationships and their applications in different scenarios. A detailed discussion of the microscopic principles of thermal conductivity is provided, which is crucial for increasing it. This is followed by an in-depth account of the construction of 3D networks using different carbon materials, such as graphene, carbon foam, and carbon nanotubes. Techniques for the assembly of two-dimensional graphene into 3D networks and their effects on thermal conductivity are emphasized. Finally, the existing challenges and future prospects for 3D carbon-based thermally conductive networks are discussed.

1. Introduction

Heat is a ubiquitous part of our daily lives, acting as a double-edged sword in the realm of technology. With the continuous advancement of science and technology, electronic equipment has ushered in an era of high-power and highly integrated electronic components[1,2]. However, the enhanced functionality and integration of these devices eventually result in substantial heat generation. Inadequate heat dissipation can significantly degrade the performance and lifespan of electronic components, posing as a hindrance in the development of complex electronic devices and integrated circuits. Furthermore, in the domains like solar energy storage, thermal energy management[3] plays a pivotal role in the efficient storage and conversion of energy. Therefore, developing materials with high thermal conductivity has become all the more urgent.

Traditionally, the thermal conductivity of materials, denoted by the coefficient kc, is a benchmark for their heat management capabilities, encompassing the metals, non-metals and polymers. For instance, conventional polymers such as polyethylene glycol and paraffin exhibit thermal conductivities between 0.1 and 0.5 W·m−1·K−1[4], whereas metals like Cu, Ag and Al demonstrate far superior conductivities ranging from 200 to 400 W·m−1·K−1[5]. Nevertheless, the metals are expensive, carry significant weight, and exhibit limited malleability. Recently, the shift towards non-metallic, particularly carbon-based thermally conductive materials[6] has been significant due to their substantial advantages over metals, including orders-of-magnitude higher thermal conductivities and meeting the stringent insulation requirements for electronic product security. Carbon-based materials, spanning from one-dimensional (1D) carbon nanotubes (CNTs)[7–9] and two-dimensional (2D) graphene[10,11] to 3D carbon foam[12], exhibit remarkable thermal conductivities. At room temperature, the theoretical thermal conductivity of a single multi-walled CNT can soar to 3 000 W·m−1·K−1[13], and that of single-layer suspended graphene can range from 3 000 to 5 300 W·m−1·K−1[14,15], with carbon foam aligned along a highly graphitized framework reaching up to 1 800 W·m−1·K−1[16]. However, the anisotropic nature of these materials limits their thermal conductivity in directions other than the axial direction.

Addressing this limitation involves the strategic construction of highly interconnected 3D thermally conductive networks, enhancing phonon transport and thus the overall thermal conductivity[17,18]. The creation of more efficient and comprehensive heat transfer channels is paramount. By tailoring the design and microstructure of these networks whether by developing anisotropic networks for directional heat dissipation or isotropic networks for uniform heat spreading, it is possible to achieve optimal thermal management in various applications.