Precipitation-Printed High-β Phase Poly(vinylidene fluoride) for Energy Harvesting

Poly(vinylidene fluoride) (PVDF) possesses outstanding piezoelectric properties, which allows it to be utilized as a functional material. Being a semicrystalline polymer, enhancing the piezoelectric properties of PVDF through the promotion of the polar β phase is a key research focus. In this research, precipitation printing is demonstrated as a scalable and tailorable approach to additively manufacture complex and bulk 3D piezoelectric energy harvesters with high-β phase PVDF. The β-phase fraction of PVDF is improved to 60% through precipitation printing, yielding more than 200% improvement relative to solvent-cast PVDF films. Once the precipitation-printed PVDF is hot-pressed to reduce internal porosity, a significant ferroelectric response with a coercive field of 98 MV m^-1 and a maximum remnant polarization of 3.2 μC cm^-2 is observed. Moreover, the piezoelectric d₃₃ and d₃₁ coefficients of printed then hot-pressed PVDF are measured to be -6.42 and 1.95 pC N^-1, respectively. For energy-harvesting applications, a stretching d₃₁-mode energy harvester is demonstrated to produce a power density of up to 717 μW cm^-3, while a printed full-scale heel insole with embedded d₃₃-mode energy harvesting is capable of successfully storing 32.2 μJ into a capacitor when used for 3 min. Therefore, precipitation printing provides a new method for producing high-β phase PVDF and bulk piezoelectric energy harvesters with the advantages of achieving geometry complexity, fabrication simplicity, and low cost.