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 ( ε r ) of polypropylene (PP) restricts the increase of the energy density . Introducing high ε r particles to prepare PP composites is a prospective strategy. But the introduction of high ε r 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 ε r particles. Here, the high ε r 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 ε r coating. A maximum ε r of 4.2 and a maximum E b 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 BOPP-based 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.