Largely enhanced energy density of BOPP-OBT@CPP-BOPP sandwich-structured dielectric composites

Biaxially oriented polypropylene (BOPP) is the most widely used polymer dielectric in film capacitors due to its excellent dielectric advantages and competitive cost-performance. However, how to significantly improve its low dielectric constant while retaining its high breakdown strength and low dielectric loss is still a great challenge. In this study, a dielectric coating was formulated using barium titanate modified with octyltriethoxysilane (OBT) as a high-dielectric filler and chlorinated polypropylene (CPP) as a binder. The dielectric coating was then applied on a commercial BOPP dielectric film, and a sandwich-structured BOPP-OBT@CPP-BOPP composite film was successfully fabricated through lamination of the coated BOPP films. In this configuration, the middle OBT@CPP layer effectively boosted the dielectric constant and the outer BOPP layers provided high breakdown strength and low dielectric loss. The experimental results showed that the highest energy density of BOPP-OBT@CPP-BOPP was up to 7.17 J cm(-3) at 450 MV m(-1) with 40 wt% OBT in the OBT@CPP layer, which was 2.6 times higher than that of BOPP. Besides, the charge-discharge efficiency remained as high as 81%. This study presents a facile, scalable, and industrially compatible roll-to-roll process to largely improve the energy density of the commercial BOPP film capacitors.