Largely improved dielectric energy performances and safety of BOPP film via surface engineering

Biaxially-orientated polypropylene (BOPP) film is the state-of-the-art material for energy storage capacitors. However, the low permittivity (epsilon(r)) of polypropylene (PP) restricts the increase of the energy density. Introducing high epsilon(r) particles to prepare PP composites is a prospective strategy. But the introduction of high er particles generally sacrifices the breakdown strength (E-b) and the biaxially-stretchability of the PP matrix, because of the electric field concentration and stress concentration near composite interfaces around the high epsilon(r) particles. Here, the high er particles are loaded on the outer surface of pure BOPP film by plasma-assisted coating to solve these problems. The barium titanate (BT) particles are mixed with polyvinyl alcohol (PVA) to prepare the high epsilon(r) coating. A maximum er of 4.2 and a maximum Eb of 470 MV/m are achieved in PVA/BT coated BOPP films, enabling a high energy density of 2.90 J cm(-3) at 400 MV/m, which is at the advanced level of the reported BOPPbased films. Simulation reveals that the surface coating can remove the high electric fields in traditional composites and produce a higher Eb. Coated BOPP film behaves with excellent flexibility, endurance, additional flame resistance, and puncture resistance.