Highly stretchable, strain-stiffening, self-healing ionic conductors for wearable sensors

Wearable sensors based on flexible ionic conducive materials have attracted increasing attention in the past decade. However, most of the reported ionic conductors are mechanically weak, vulnerable under large deformation, and more importantly, lack the ability to self-heal or adhere to metal and tissue surfaces, which limited their applications and integration at the human–machine interfaces. Herein, we report a series of ionic conductor materials that exhibit high mechanical strength (up to 6.37 MPa) and toughness (up to 22.36 MJ/m3), enormous stretchability (>2000%), high transparency (>92% in the visible region) and skin-like strain-stiffening behavior. Composed of a hydrogen-bonded polymeric network of poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) doped with lithium bis(trifluoromethane sulfonimide) (LiTFSI), the resulting PAA-PEO-Li ionic conductors show excellent self-healing ability, strong adhesion to metal and tissue surfaces, and good ionic conductivity (up to 8.78 mS/cm). Wearable sensors based on these ionic conductors are capable to precisely monitor human body motions and temperature change in real time by recording the resistance or capacitance variation, which may find applications as ionic skin in wearable ionotronic devices and health-care monitoring.