Tailored nanocomposite energy harvesters with high piezoelectric voltage coefficient through controlled nanowire dispersion

Abstract

Composites composed of piezoelectric nanomaterials dispersed in a flexible polymer have emerged as promising materials for highly durable and flexible energy harvesters and sensors. Although piezoelectric materials in their bulk form have a high electromechanical coupling coefficient and can efficiently convert mechanical energy to electrical energy, the ceramic form has low fracture toughness and thus they are limited in certain applications due to difficulty in machining and conforming to curved surfaces. Recently, additive manufacturing processes such as direct write, have been developed to incorporate piezoelectric nanowires into a polymer matrix with controlled alignment to realize printed piezoelectrics. Given the multiphase structure of a nanocomposite, it is possible to control the material structure such that the piezoelectric coupling and dielectric properties can be varied independently. In this paper, experimentally validated finite element (FE) and micromechanics models are developed for calculation and optimization of the piezoelectric voltage coefficient, g31, of a nanocomposite. It is shown that by using high aspect ratio nanowires with controlled alignment, the piezoelectric coupling can be disproportionately increased with respect to the dielectric constant which yields a g31 coefficient that can be enhanced more than seven times compared to the bulk piezoelectric material. Moreover, it is demonstrated that the use of high aspect ratio nanowires in the energy harvester resulted in significant improvement on the output electrical power of an energy harvester.