Ladder-structured boron nitride nanosheet skeleton in flexible polymer films for superior thermal conductivity

Highly efficient heat transfer combined with electrical insulation is extremely important in electronic devices. Hexagonal boron nitride (h-BN) has both excellent in-plane thermal conductivity and electrical insulation and is considered one of the most promising fillers for thermal interface materials. However, BN-based composite films usually suffer from poor through-plane thermal transport behavior since the fillers are hard to align vertically, which limits their practical applications. Herein, we report a novel flexible composite film with ladder-structured boron nitride nanosheet (BNNS) skeleton structure using an ice-press assembly strategy. This unique structure is composed of a vertically aligned BNNS embedded on the upper and lower horizontal BNNS lamellae, and presents an unprecedentedly high thermal conductivity of 9.6 W m−1 K−1 and 11.2 W m−1 K−1 in the through-plane and in-plane directions, respectively, combined with excellent flexibility and inherent electrical insulation. This study offers a novel design strategy to enhance the performance of thermal interface materials by improving the filler assembly structure.