Stretchable Ionic Double Layer at the Interface Between Crosslinked Networks of Ionic Liquids

Polymerized ionic liquids (PILs) are an emerging class of ion conducting materials wherein one of the ionic moieties in the ionic liquids is covalently attached to a polymer backbone. Crosslinked networks of ionic liquids (NILs) allows solid-state electrolyte that can selective conduct single ions. Herein, two oppositely charged NILs were prepared based on 1-ethyl-3-methyl imidazolium (3-sulfopropyl) acrylate ([ES]) and (1–(2–acryloyloxy–ethyl)–3–buthyl–imidazolium bis(trifluoromethane) sulfonimides ([AT]). At the interface of [ES]/[AT], we show that an ‘ionic double layer’ (IDL) is formed. The mobile ions are diffused away from the interfacial region, resulting in a build-up of excess fixed charges with a capacitance of ~ 1 mF/cm². This IDL leads to asymmetric current flow when the polarity of the bias voltage is altered, analogous to the electrical rectification of a semiconductor diode. Moreover, the elastic properties of NILs allow a physical deformation which provides an electrical response that can be used for strain sensing or energy harvesting without the need for an external bias voltage. Our finding serves as a fundamentally new platform for a liquid-free, elastic and stretchable ionic diode that can harvest ambient mechanical energy such as human motion