Constructing 3D g-CNNS network in epoxy for enhanced thermal conductivity and breakdown strength for high high-voltage applications

Abstract

Ultra-high integration density of power electronics leads to severely localized heat accumulation, critically threatening the safe operation and lifetime of devices. Traditional high thermal conductivity (TC) polymer composites always suffer from deteriorated breakdown strength (E_b). Nowadays, effective decoupling regulation and synchronous enhancement of TC and E_b still is a formidable challenge in polymer composites. To tackle this problematic issue, in this work, the graphitic carbon nitride nanosheet (g-CNNS) was prepared using a thermal oxidation method, and the g-CNNS/cellulose nanofiber (CNF)/epoxy (EP) nanocomposites were prepared via ice-templating and infiltration methods. It is found that the uniformly distributed three-dimensional CNF supporting g-CNNS skeletons were constructed in EP even at low filler loadings. The CNFs can physically crosslink with EP groups and form hydrogen bonds with g-CNNS, not only enhancing the interfacial interactions but also restricting the EP chain mobility, subsequently leading to concurrently improved TC and E_b in g-CNNS/CNF/EP. The 10.4 wt% g-CNNS/CNF/EP exhibits a concurrently high TC and E_b of 1.06 W/(m·K) and 34.7 kV/mm, along with a low permittivity (ε) and dielectric loss (tanδ) of 2.47 and 0.022 at 10³ Hz, respectively. This work reveals the underlying heat conduction and charge migration mechanisms, provides deep insight into the design and preparation of EP nanomaterials with simultaneously high TC and E_b coupled with low ε and tanδ, presenting appealing applications in power systems and high frequency microelectronic devices.