The ultrahigh discharge efficiency and energy density of P(VDF-HFP): Via electrospinning-hot press with St-MMA copolymer

Poly(vinylidene fluoride) (PVDF) based fluoropolymers possess high permittivity and breakdown strength (Eb), and have been extensively studied because of their dielectric applications. However, their practical applications are greatly hampered by the low energy density (Ue) and efficiency (η). Herein, using an electrospinning-hot press strategy, a novel P(VDF-HFP)/MS (poly(vinylidene fluoride-hexafluoropropylene)/poly(methyl methacrylate-co-styrene)) composite film with concomitantly enhanced Ue of 20 J cm-3 and discharge efficiency (η ≈ 81%) was fabricated. Due to the strong electrostatic force and confining effect during electrospinning, two polymers exhibit substantially enhanced compatibility and form a much more homogeneous microstructure as compared with the blend control, leading to higher Eb and more even electric field distribution as simulated by the finite element analysis. Strikingly, composite films containing 30 wt% MS copolymer exhibit typical relaxor polarization behaviors (and thus improved Eb and Ue), which are 157% and 262% that of the pristine P(VDF-HFP), respectively. Moreover, the η of composite films can be well retained, even if it is under a high Eb of 550 MV m-1, and is still greater than previous reported values. This work provides a straightforward and scalable strategy to achieve PVDF-based dielectrics with both high Ue and η for the applications of energy storage capacitors.