Enhancing energy density in thin-film nanocomposite dielectric capacitors through surface functionalization of nanoparticles

In this work, barium titanate nanoparticles were chemically functionalized to increase the energy density of polypropylene-based nanocomposite film capacitors. The nanoparticles were treated with: i) nitric acid or hydrogen peroxide to hydroxylate the surface of nanoparticles, ii) organic surface agents, i.e., silane, amine, phosphorous acid, dopamine hydrochloride, and maleic anhydride, iii) polypropylene coating, iv) grafting of polypropylene co-polymer with maleic anhydride. Nanocomposite dielectrics were manufactured by spin-coating a polypropylene gel with dispersed nanoparticles on a conductive substrate, which resulted in a thickness of the dielectric layers below 1 µm. Functional capacitor devices were fabricated by deposition of aluminium on top of the dielectric layers. The electrical testing data indicated that devices with functionalized nanoparticles showed an up to 47 % increase in capacitance, a 36 % improvement in the dielectric constant, and a doubling of the breakdown voltage with respect to capacitors with unfunctionalized nanoparticles. Overall, the energy densities reached up to 5.2 J cm⁻³, which was four times higher than untreated counterparts. These data highlight the importance of chemical functionalization of nanoparticles for achieving high energy density of nanocomposite film capacitors and show the way forward to high-efficiency power electronics devices with reduced weight and volume.