High p- and n-type thermopowers in stretchable self-healing ionogels

Abstract

Flexible ionic thermoelectric materials with large thermopowers show great promise for ultrasensitive thermal detection in wearable devices. Here large and tunable p- and n-type thermopowers are reported in stretchable and self-healing ionogels made of a fluorocarbon elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), an ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and a salt acting as the thermopower regulator. Particularly, a self-healing n-type ionic thermoelectric material is developed for the first time. The thermopower of the resultant ionogels varies from + 30 mV K−1 to − 21 mV K−1 at 90% relative humidity. Meanwhile, the ionogels exhibit excellent stretchability up to 1700% and appropriate Young’s modulus of around 0.26 MPa. Both the mechanical and thermoelectric properties can self-heal spontaneously after damage. Taking advantage of the large p and n-type thermopowers, the stretchable self-healing ionogels are integrated as a flexible thermoelectric detector with 10 pairs of p- and n-type legs on copper electrodes, showing a total thermopower of 0.25 V K−1 operating with a low temperature difference of 1–2 K.