Poly(vinyl alcohol)-Assisted Exfoliation and Grafting\nModification of Boron Nitride Nanosheets with a High Aspect Ratio\nvia a Continuous Production Method for Energy Storage and Thermal\nManagement

Hexagonal\nboron nitride nanosheets (BNNS) integrating many extraordinary\nproperties are usually combined with polymers to fabricate multifunctional\ndielectric materials for energy storage and thermal management. Unfortunately,\nthe existing technologies for producing BNNS generally have the disadvantages\nof inefficiency and low product quality, which significantly hinder\nthe wide application of high-value nanocomposites. Herein, a novel\npoly(vinyl alcohol) (PVA)-assisted pan-milling method based on the\ninnovative solid-state shear milling (S<sup>3</sup> M) technology\nis reported for the production of high-quality BNNS. The uniform three-dimensional\n(3D) shear force field generated by pan milling not only ensured the\nhigh aspect ratio of BNNS (the average lateral size of ∼954\nnm and the average thickness of ∼3.7 nm) but also induced the\nmechanochemical reaction between PVA and BNNS to achieve in situ grafting\nmodification on the BNNS surface. The simultaneous high-quality exfoliation\nand surface modification of BNNS positively contributed to the mechanical,\ndielectric, and thermal conduction properties of BNNS/PVA nanocomposites.\nAt the BNNS content of 10 wt %, the BNNS/PVA composite film exhibited\nexcellent robustness (Young’s modulus of 5305 MPa and the tensile\nstrength of 83 MPa), with a satisfactory breakdown strength (<i>E</i><sub>b</sub> of 134.7 MV/m) and dielectric constant (∼5\nat 1000 Hz). In addition, the substantial improvement of thermal conductivity\n(from 0.88 to 5.59 W·m<sup>–1</sup>·K<sup>–1</sup>) guaranteed the stability of the dielectric properties of the nanocomposites\nat high temperatures. This pan-milling method characterized by green\nand efficiency is highly scalable to other two-dimensional (2D) layered\nmaterials, providing a practical strategy for the industrial fabrication\nof nanocomposites in elevated-temperature energy storage.