Free-Volume Regulation Enables Significantly Enhanced Electrical Breakdown via Short-Chain Molecular...

The peculiar molecule-structural units with ferroelectric ordering render poly(vinylidene fluoride) (PVDF) a crucial functional polymer, but the existence of the free volume in PVDF (also for many other polymers) would interrupt the long-range molecule chains, leading to the declined electrical functionality (e.g., electric breakdown), and also the thermal, mechanical, and chain relaxation properties. Herein, to regulate the free volume for electrical tuning, a molecular spatial-positioning shimming strategy is developed in terms of intercalating shortchain molecules polyethylene wax (PE wax) into the spherulite gap region of PVDF. The PE wax/PVDF films are fabricated by a multi-layer folding coupled hot pressing route that allows the complex crystalline structure modulation (e.g., phase, morphology, spherulite formation, amorphous and free-volume status etc.), which are comprehensively investigated. Upon free volume regulation, the fabricated PE wax/PVDF film exhibits significantly improved breakdown strength (E_b = 735.1 MV m^-1). Meanwhile, ultrahigh energy density (32.67 J cm^-3) and energy storage efficiency (78.02%) are synergistically achieved. With ultrafast energy release (t_0.9 = 38.5 ns) and exceptional power density (138 MW cm^{- 3}), the charge-discharge performance competes favorably with leading polymer/hybrid-based films. This work offers a novel model to design new PVDF (or other polymer) based films with generating superior functionality.