Pressure-induced ultrahigh-aspect-ratio boron nitride nanosheets via combustion synthesis: enabling high orientation and enhanced in-plane thermal conductivity of flexible heat spreaders

The rapid advancement of high-power-density integrated circuits and electronic devices demands thermally conductive yet electrically insulating composites to effectively mitigate “hot spot” issues. Hexagonal boron nitride nanosheets (BNNS) are promising fillers for dielectric polymer composites to enhance their thermal conductivity. However, constructing high thermal conduction networks and scalably, efficiently synthesizing BNNS remain challenging, which seriously hinders further improvement in the thermal conductivity of BNNS/polymer composites. Herein, we report the preparation of highly thermally conductive and electrically insulating BNNS/cellulose nanofiber (CNF) composite films via vacuum-assisted filtration followed by cold-pressing, in which highly crystalline and ultrahigh-aspect-ratio BNNS were fabricated by a combustion synthesis method. The subsequent cold-pressing step further improved the BNNS orientation and established closer contact between BNNS, forming an interconnected thermal “expressway”. The composite exhibits a high in-plane thermal conductivity of 74.97 W m −1 K −1 . As a heat spreader in high-power LED modules, it demonstrates effective cooling performance (A sharp drop of 28.4 ℃ in LED temperature and a reduction of 5.06 ℃ in the practical computer application). These findings provide an alternative route for producing high-quality BNNS and thermally conductive polymer composites, with promising applications in thermal management for modern electronics.