Porous PVDF-Based Piezoelectric Films Applied in Human Motion Detection Exhibit Excellent Piezoelectric Properties

In recent years, the exploration of ways to enhance flexible piezoelectric sensors through the use of nanofillers and electrospinning has garnered significant attention. This paper presents the development of lead-free flexible piezoelectric sensors based on polyvinylidene fluoride (PVDF)/K_0.5Na_0.5NbO₃ (KNN), augmented with bismuth chloride to further promote the formation of the PVDF β-phase and enhance its conductivity. The sensor was fabricated via electrospinning, with KNN synthesized through a hydrothermal reaction at 180°C. Fourier transform infrared spectroscopy and x-ray diffraction were employed to characterize the β-phase content and crystallinity of the PVDF-based flexible piezoelectric sensors. The results revealed that the piezoelectric composite film containing 2 wt.% BiCl₃ and 2 wt.% KNN exhibited the optimal piezoelectric phase, significantly enhancing its piezoelectric performance. Subsequently, four types of nanofiber-based piezoelectric sensors [PVDF, PVDF/KNN (KP), PVDF/BiCl₃ (BP), and PVDF/BiCl₃/KNN (BKP)] were analyzed to systematically explore the factors influencing the flexible piezoelectric sensors. It was observed that with the incorporation of fillers, the voltage output progressively increased from the original (V = 0.41 V, I = 5.90 nA) to BKP (V = 5.89 V, I = 54.94 nA). Ultimately, the developed BKP was applied to various parts of the human body, generating output voltages of 2.1 V, 3.6 V, 4 V, and 0.32 V at the elbow, knee, neck, and throat, respectively, when stretched at specific angles, thereby demonstrating its practical applicability.