Thermally Conductive Polyelectrolyte Nanocomposite for Electrical Insulation

As electric vehicles continuously advance, higher demands are put on the thermal transport and dielectric properties of dielectric materials to increase electric motor efficiency and power density. Furthermore, due to the increasingly complex winding architectures found in electric motors, traditional insulating procedures struggle to deposit conformal insulation layers. In this work, the layer-by-layer (LbL) assembly of polyethylenimine, mica clay, poly(acrylic acid), and hexagonal boron nitride is exploited to provide a thermally conductive (through-plane thermal conductivity ≈ 1.8 W×m^-1×K^-1) yet electrically insulating (breakdown strength ≈ 155 kV×mm^-1) dielectric material. A remarkably high through-plane thermal conductivity (i.e., perpendicular to the substrate) is obtained due to mica and hexagonal boron nitride platelets stretching through multiple layers, a result of “jagged” deposition. The nanocomposite’s heat removal efficiency is demonstrated on a mock electric aircraft motor showing reduced max temperatures across the winding-heat sink interface at high power densities when compared to the state-of-the-art polyimide insulation. This is one of the first reports of a thermally conductive yet electrically insulating polyelectrolyte-based self assembled nanocomposite.