Roll your own – nano-nanocomposite capacitors

Abstract

Commercial and liquid-feed flame spray pyrolysis (LF-FSP) processed nano-BaTiO₃ with average particle sizes (APSs) of 50 nm were mixed with [glycidylSiMe₂OSiO_1.5]₈ (OG, Q cage epoxy) and diaminodiphenylmethane (DDM) at loadings of 30, 40 and 50 vol% (69, 77 and 83 wt%) to form nano-nanocomposites. We demonstrate processing flexible films at 10–13 μm thicknesses on a variety of substrates but especially 40 μm thick aluminum foil. The octafunctional glycidyl silica cage epoxy resin combines very high flexibility needed for rolling with the potential to impart good-to-excellent breakdown voltages and hence higher energy densities. Nanopowders and cast films with and without nano-BaTiO₃ were characterized by FTIR, TGA, SEM, XRD etc. The dielectric constants of the cast films were also characterized providing dielectric constants (loss tangents) of 18 (0.05), 21 (0.06) and 16 (0.11) for 30, 40 and 50 vol% films, respectively at 100 KHz. Only 30 and 40 vol% films were cast on Al foil for processing to wound capacitors as 50 vol% films exhibited excessive porosity resulting from agglomeration induced during curing/coating of the resin. Rolled capacitors were fabricated by simply stacking two strips of nanocomposite cast Al foil and rolling them around a metal rod used as a mandrel. The found energy storage of the capacitors ranged from 80–90 nanofarads (33–37 nF cm⁻²) whereas that of equivalent biaxially oriented polypropylene (BOPP) capacitors at the same thicknesses would exhibit only 9–12 nanofarads (4–5 nF cm⁻²) at similar voltages. Current work provides the first example of a rolled BaTiO₃/epoxy nanocomposite capacitor with excellent potential for replacing commercially available counterparts. Furthermore, the potential to achieve much higher energy densities through further optimization suggests the possibility of reducing the dimensions of any given capacitor.