Enhanced Output Performance of Piezoelectric Composites via Plasma Annealing Treatment

Piezoelectric energy harvesters (PEHs) which can convert the electricity from the external stress have attracted attention, because it is one of the promising candidates for the sustainable and semi-permanent power source for consumer electronics and wireless sensors. To overcome the limitations that PEH based on piezoceramics with bulky and rigid characteristics hinder the energy applications into flexible and wearable self-powered systems, many researches has been actively conducted on the demonstration of composites-based PEHs made of organic polymeric matrices with excellent flexibility and inorganic piezoelectric nanostructures.<br/>However, despite the remarkable potential for use as f-PEHs by adopting the elastomers with naturally flexible properties and inorganic nanoparticles with high piezoelectricity, they still show insufficient piezoelectricity/flexibility and low energy conversion performance due to use of thick non-piezoelectric polymers. To achieve the enhanced flexibility and piezoelectric conversion performance, some researchers have demonstrated the organic-inorganic hybrid piezoelectric composite with low content of piezo-ceramics by replacing non-piezoelectric matrices with piezo-polymers, such as PVDF and P(VDF-TrFE). In addition, for implementing the enhanced output performance of f-PEHs based on organic-inorganic hybrid composites, there are attempts to increasing the crystallinity of piezo-polymers. Although the various methods have been proposed to increase the crystallinity of the piezo-polymers, the complicated and time-consuming annealing processes impede the practicality of f-PEHs for power sources of consumer electronic devices.<br/>To resolve the above-mentioned issues, plasma annealing (PA) has emerged as a new strategy for enhancing the crystallinity of polymers. Plasma treatment has been shown to enhance material crystallinity by increasing the surface temperature, thereby facilitating the rearrangement of polymer chains into more ordered structures. Recent research has reported on improving the crystallinity and properties of polymers through PA processes. These studies indicate that plasma annealing is a promising approach to overcome the limitations of the complicated and time-consuming traditional annealing process and can be effectively utilized to enhance the crystallinity and performance of polymeric materials.<br/>In this study, we introduce and optimize a relatively short PA process for polyvinylidene fluoride (PVDF)-BaTiO3 composites to increase piezoelectric performance. Therefore, we fabricated flexible-piezoelectric energy harvesters (f-PEH) by phase transforming the amorphous structure of polymer into a crystalline structure through a 10-minute plasma annealing process on PVDF BaTiO3 nanoparticles composite fibers. Subsequently, f-PEH, subjected to a poling process for 4 hours at an electric field of 200 kV/cm, generated an output voltage of approximately 6 V and a current of approximately 115 nA under mechanical bending deformation. We also demonstrated its use as a vibration detection sensor capable of detecting differences in flow velocity within pipes used in circulators. Furthermore, we converted vibrations generated by a flow rate of 28.0L/m into electrical signals and charged commercial capacitors. These results suggest an efficient method for developing f-PEH with increased crystallinity in a short time.