Processing and characterisation of hot rolling pressed PVDF films with enhanced field-induced polarisation

Poly (vinylidene fluoride) (PVDF) based polymers are good candidates for high-power energy storage in dielectric capacitors. So far, most studies reporting PVDF with high energy density are based on solution casting, a method ill-suited for large-scale production. In this work, we develop PVDF films with high crystallinity (47 %) and ultrahigh β-phase (∼97 %) using Hot Rolling Press (HRP). During HRP, the crystallinity, fraction of β-phase, internal stress, and the piezoelectric coefficient d33 increased with rolling temperature. The anisotropic stress imposed by two rollers led to a highly preferred orientation of the HRP film along the rolling direction. Notably, the HRP film exhibits an enhanced field-induced polarisation Pin-max value (0.16 C m−2) compared to conventional PVDF films (0.10 C m−2), with an energy density of 32.6 J cm−3 at 871 kV/mm. The good low field dielectric (εr ∼19 @ 1 kHz) and piezoelectric (d33 ∼30 pC/N) properties with high-temperature stability (up to 100 °C), and its suitability for in-line continuous production, make HRP PVDF films promising for low field dielectric and piezoelectric applications.