Highly stretchable three-dimensional thermoelectric fabrics exploiting woven structure deformability and passivation-induced fiber elasticity

Abstract

Accommodating localized strains and deformations imposed by human body movements is indispensable to reliable operation of wearable thermoelectric (TE) fabrics. Despite their inherent flexibility and conformability, TE fabrics can suffer from significantly compromised TE performance and mechanical reliability at large applied strains, owing to the limited stretchability of the constituting fibers/components. Here, we propose threedimensional woven fabrics of high TE performance and exceptional mechanical reliability, encouraged simultaneously by passivation of TE fibers. Immersion-coating in carbon nanotube (CNT) ink effortlessly deposits TE sheath layers on polyurethane (PU) core fibers. PU passivation layers are encapsulated on the coated fibers not only to enhance the intrinsic fiber stretchability by enabling fiber reorientation of individual CNTs, but also to augment the TE properties by regulating heat transfer along PN legs. The passivated fibers are woven into threedimensional fabrics that harvest heat in the out-of-plane direction with the highest normalized open-circuit voltage of 8.0 mV K-1 and normalized power per leg of 1.1 x 10(-4) mu W K-2 among the reported woven-type TE fabrics. The woven structure deformability and the passivation-induced fiber elasticity cooperatively achieve reliable fabric mechanical stability against bending and stretching up to 100% strain. Conforming seamlessly to the curved human forearm, the TE woven fabrics hold promises for efficient body heat harvesting to realize self-powered wearable electronics.