In high-tech fields such as electronic devices, new energy vehicles, and LED lighting, efficient heat dissipation materials are critical. Traditional polymers generally exhibit poor thermal conductivity, failing to meet the heat dissipation requirements of high-power devices. To address this, researchers incorporate high-thermal-conductivity fillers into polymers. Boron nitride (BN) has attracted much attention due to its excellent thermal conductivity, electrical insulation, and chemical stability. However, using BN fillers alone often makes it difficult to form continuous and efficient thermal conduction pathways. Therefore, through deliberate design and regulation, starting from two aspects – "multi-dimensional filler synergy" and "three-dimensional network construction" – an effective thermal conduction network can be built at relatively low filler loadings, thereby producing high-thermal-conductivity composites.
I. Boron nitride and multi-dimensional filler compounding
For a single BN filler, the same structure and size tend to create voids in the polymer, and the poor thermal conductivity of air limits the improvement of the material's thermal performance. Using hybrid fillers offers the following main advantages:
① The synergistic effect among fillers of different shapes achieves higher thermal conductivity at lower fillings while maintaining good mechanical and processing properties of the polymer;
② Fillers can also impart other functions to the material, such as flame retardancy and hydrophobicity.
01 BN with zero-dimensional fillers: "point–plane" combination
Zero-dimensional fillers are granular. Two-dimensional BN and zero-dimensional thermally conductive fillers combine in a "point–plane" manner, filling gaps between lamellae, increasing packing density, and facilitating the formation of thermal conduction networks. Common zero-dimensional thermally conductive fillers hybridized with h-BN include silicon carbide particles (SiC), silver nanoparticles (AgNPs), alumina particles (Al₂O₃), and silica particles (SiO₂).
02 BN with one-dimensional fillers: "line–plane" combination
One-dimensional fillers have tubular or linear structures. BN and one-dimensional thermally conductive fillers combine in a "line–plane" manner, acting as "bridges" connecting the polymer matrix and h-BN, making the internal thermal conduction network denser, reducing interfacial thermal resistance, and improving heat transfer efficiency. Common one-dimensional thermally conductive fillers hybridized with h-BN include carbon nanotubes (CNT), silicon carbide nanowires (SiCNW), silver nanowires (AgNW), aramid nanofibers (ANF), and carbon fibers (CF).
03 BN with two-dimensional fillers: "plane–plane" combination
Two-dimensional materials have flake-like structures. Research on BN compounded with two-dimensional fillers mainly focuses on graphene oxide (GO). The two exhibit close interfacial bonding, good phonon spectrum matching, and low interfacial thermal resistance, synergistically enhancing in-plane thermal conductivity. The dense packing of fillers improves both in-plane and through-plane heat transfer, gradually eliminating thermal conduction anisotropy.
04 Multi-component thermally conductive fillers
Hybridizing h-BN with multiple types of thermally conductive fillers has become a research hotspot. Increasing the variety of thermally conductive fillers creates more complex thermal conduction pathways, promotes rapid heat transfer, and can impart multiple functions to the material, such as flame retardancy and hydrophobicity. However, as the types of thermally conductive fillers increase, the uncertainties in the filler architecture also amplify.
II. Construction of three-dimensional thermal conduction networks
Although composite fillers of different particle sizes and morphologies can effectively promote the formation of thermal conduction pathways inside the material, the introduction of fillers leads to increased interfacial thermal resistance. Constructing a 3D thermal conduction network not only reduces the contact area between fillers and matrix and lowers interfacial thermal resistance but also establishes a continuous and stable thermal conduction network, efficiently improving the thermal conductivity of the composite at low filler loadings. Currently, there are four main methods for constructing 3D thermal conduction networks:
01 Template method: structurally controllable, easy to operate
The template method is widely used for constructing three-dimensional structures in composites. Its advantages include precise control over the network structure, applicability to various fillers and matrices, and simple operation. However, it cannot greatly increase filler content.
Ice template method: Utilizes the directional freezing of aqueous solutions, where ice crystals grow in specific orientations, to construct a 3D thermal conduction network. It is widely applied due to its simplicity and ease of operation.
Foam template method: Uses foam as a simple template, with high-thermal-conductivity fillers as the main component. Impregnation techniques infiltrate liquid polymer into a pre‑formed negative-pressure three-dimensional network structure. Mechanical compression densifies and aligns the thermal conduction network, producing high-performance thermally conductive composites for multifunctional applications.
Sacrificial template method: Removes an initial template to create a three-dimensional interconnected thermal conduction network. Numerous studies have used salt and water-soluble sugar as sacrificial templates to prepare 3D network structures in thermally conductive composites.
02 Self-assembly method
A technique where basic structural units (molecules, nanomaterials, micron- or larger-scale substances) spontaneously form ordered structures through non-covalent interactions. Compared to the template method, it is simpler, lower in cost, and allows for a higher upper limit of filler content. However, it may introduce binders or highly conductive fillers, affecting insulation performance.
03 Hot-pressing method
Uses heating and pressing to construct an oriented 3D network structure, which can effectively enhance thermal conductivity and mechanical strength. This is generally achieved through mechanical interference. The parameters of the hot-pressing process are highly tunable, enabling orientation control, and it is applicable to a wide range of material systems while strengthening internal structural stability.
04 3D printing method
A mold-free direct writing technology characterized by high design freedom, low cost, and fast processing. During the process, melt extrusion and shear flow induce high orientation of BNNSs in the polymer matrix, resulting in better mechanical strength and thermal conductivity enhancement. This technology is widely used in both research and industrial manufacturing.
05 Other construction methods
Innovative 3D network construction techniques (e.g., electrospinning, mechanochemical methods) can significantly increase thermal conductivity while improving other properties such as mechanical and electrical performance. However, the effectiveness of these methods varies, and they face limitations such as lack of versatility or demanding experimental conditions.