The large piezoelectricity and high power density of a 3D-printed multilayer copolymer in a rugby ball-structured mechanical energy harvester

Piezoelectric polymers are characterized by their flexibility and ease of processing into shapes, however, their piezoelectric coefficients, such as d₃₃, are quite low (∼24 pC N^-1). Here we report a 3D-printed multilayer β-phase PVDF-TrFE copolymer which does not require high temperature annealing or complicated transfer processes and exhibits a much higher effective piezoelectric coefficient (d₃₃ ∼ 130 pC N^-1 for six 10 μm layers). In order to confirm its high power density, a rugby ball-shaped energy harvester, which operates via a flextensional mechanism, was prepared using the multilayer copolymer. The experimental results show that it can produce a peak voltage of ∼88.62 V_pp and a current of 353 μA, which are 2.2 and 10 times those of a single-layer PVDF-TrFE harvester, respectively, under a pressure of 0.046 MPa. Notably, its peak output power density was as high as 16.4 mW cm^-2 (according to P_peak = (V_peakI_short)/2); while at a load of 568 kΩ, it was still 5.81 mW cm^-2. The proposed copolymer processing method and flextensional mechanism in a rugby ball configuration show great potential for future micro-energy development in flexible, wearable electronic devices and wireless sensor networks.