Highly Transparent and Flexible All-Nanofiber-Based Piezocomposite Containing BaTiO₃-Embedded P(VDF-TrFE) Nanofibers for Harvesting and Monitoring Human Kinetic Movements

We developed kinetic energy-harvestable and kinetic movement-detectable piezoelectric nanogenerators (PENGs) consisting of piezoelectric nanofiber (NF) mats and metal-electroplated microfiber (MF) electrodes using electrospinning and electroplating methods. Percolative non-woven structure and high flexibility of the NF mats and MF electrodes allowed us to achieve highly transparent and flexible piezocomposites. A viscoelastic solution, mixed with P(VDF-TrFE) and BaTiO₃, was electrospun into piezoelectric NFs with a piezoelectric coefficient d₃₃ of 21.2 pC/N. In addition, the combination of electrospinning and electroplating techniques enabled the fabrication of Ni-plated MF-based transparent conductive electrodes (TCEs), contributing to the high transparency of the resulting piezocomposite. The energy-harvesting efficiencies of the BaTiO₃-embedded NF-based PENGs with transmittances of 86% and 80% were 200 and 240 V/MPa, respectively, marking the highest values in their class. Moreover, the output voltage driven by the coupling effect of piezoelectricity and triboelectricity during finger tapping was 25.7 V. These highly efficient energy-harvesting performances, along with the transparent and flexible features of the PENGs, hold great promise for body-attachable energy-harvesting and sensing devices, as demonstrated in this study.