Polyimide-coated MgO nanoparticles improves high-temperature energy storage performance in polyetherimide-based nanocomposite films

Enhancing the energy storage capacity of dielectric polymers can be achieved by the introduction of inorganic nanoparticles. However, the difference in surface energy often influences the interfacial compatibility of nanoparticles with polymers, consequently limiting their comprehensive dielectric properties. Here, the magnesium oxide (MgO) nanoparticles were coated with polyimide (PI) shells via in-situ polymerization, which is beneficial to improve the scattered particles in the polyether imide (PEI) matrix. The PI buffer shell is tightly bound to the PEI matrix through automatic electrostatic interaction making the defects decrease, together with the increased dielectric permittivity (εr) attributed to MgO, significantly enhancing the discharged energy density (Udis) and storage efficiency (η) of the PI@MgO/PEI nanocomposite films in harsh conditions. Thus, the maximal Udis of the PI@MgO/PEI nanocomposites is 4.33 J/cm3 at 150 °C, twice that of the pristine PEI. Even if an η exceeds 90 %, the Udis of 3.83 J/cm3 of 1 vol%-PI@MgO/PEI at 500 MV/m and 150 °C is better than that of the most advanced dielectric polymers.