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Achieving relatively uniform dispersion in organic-inorganic composites with overwhelming differences in surface energy is a perennial challenge. Herein, novel eliminated polyvinylidene fluoride (EPVDF)/EPVDF functionalized barium titanate nanoparticles (EPVDF@BT) flexible piezoelectric nanogenerators (PENGs) with strong interfacial adhesion are developed via thermal stretching following sequential click chemistry. Thanks to the strong interfacial adhesion, the optimal PENGs containing ultra-high β-phase content (97.2%) exhibit not only optimized mechanical and dielectric behaviors but also excellent piezoelectric properties with high piezoelectric output (V = 10.7 V, I = 216 nA), reliable durability (8000 cycles), ultrafast response time (20 ms), and good sensitivity (2.09 nA kPa -1 ), far outperforming most reported PVDF-based composites. Furthermore, COMSOL finite element simulations (FEM) confirm that the elevated stress transfer efficiency induced by the strong interfacial adhesion is the main driving force for enhanced piezoelectric performances. For practical applications, self-powered PENGs can simply but stably capture mechanical energy, drive tiny electronic devices, and serve as potential multifunctional and durable sensors for detecting human physiological motions. This work opens a pioneering avenue to break the trade-offs between piezoelectric and other properties, which is of great importance for developing self-powered flexible sensors., (© 2024 Wiley‐VCH GmbH.)

With the rapid development of wearable self-powered devices, the piezoelectric materials having deformable and switchable characteristics are attracting extensive attention. Herein, the cross-linked polyvinylidene fluoride (cPVDF) was fabricated through an alkali-catalyzed defluorination and chemical cross-linking method by introducing trimethylhexamethylenediamine (THDA). The system filled with 1 wt % THDA (CP1) was proved to possess balanced cross-linking density and crystallinity, which would play a crucial role in achieving a switchable piezoelectric effect. In comparison to pristine PVDF, the cross-linked one exhibited repeatable shape memory characterization due to restrained plastic deformation above the melting transition. Both the shape-fixing and shape-recovery ratios were stably maintained above 90%. More significantly, the thermo-mechanical program also triggered the α-β-α crystal transition accompanied by the variation of conformational entropy. The largest amount of β crystals was produced in the temporary shape, whereas the original and recovery shapes were dominated by α crystals. Such structural transition occurred repeatedly in the successive shape memory cycles, which thereby induced the periodic fluctuation of the piezoelectric constant ( d 33 ). For the CP1 sample, its d 33 was only about 2 pC/N in the original and recovery shapes but reached up to 9.4 pC/N in the temporary shape. When the latter one was fabricated into a piezoelectric device, alternating voltage and current were generated by performing periodic impact force and were demonstrated to be capable of monitoring some pressure-related motions in real time without an external power supply. Finally, the switchable piezoelectric effect of the CP1 at different shape memory stages was further revealed through its electroactive response to the sinusoidal voltage stimulation. This work offers a special perspective in tailoring piezoelectric performance through the structural transition in shape memory progress, which is of great significance for enriching the types and applications of piezoelectric polymers.