▎ 摘　　要

Boron nitride nanosheets (BNNSs) have been regarded as promising fillers to fabricate polymer-based composites for thermal management. However, the thermal resistance between BNNSs seriously restricts the further improvement of thermal conductivity (TC) for BNNS-based polymer composites. Herein, a rapid and high-yield method based on a combustion synthesis technique is developed to combine BNNSs and graphene (G) tightly as a hybrid filler, in which G was in-situ grown on the surface and interlayer of BNNSs, forming a special G@BNNS heterojunction structure. A foldable and thermal conductive composite film made of such G@BNNS filler and cellulose nanofiber (CNF) matrixes through filtration exhibits high in-plane and through-plane TC of 125.0 and 2.1 W/(m K), respectively. Such high TC is attributed to the reduced interfacial thermal resistance because of the high order and strong bridging effect of G with BNNSs. By utilizing this composite film as a heat spreader, heat dissipation is demonstrated effectively in high-power LED devices under high-power conditions over numerous cycles and heat dissipation can be carried out uniformly in the in-plane direction. Our findings indicate that G@BNNS/CNF films can meet both performance of maintenance and heat dissipation for thermal management, which are much needed for modern electronic devices.