Mixed electronic-ionic conductors with high flexibility and stretchability can serve as key materials in rapidly emerging applications such as soft electronics and soft robotics. The combined use of two functional liquid materials, ionic liquids (ILs) and liquid metals (LMs), is of significant interest in the development of highly deformable mixed conductors. In this study, composite gels embedded with both IL and LM are prepared for the first time using a Ga-In eutectic (eGaIn), 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide, and poly(vinylidene fluoride-co-hexafluoropropylene) as the LM, IL, and polymer matrix, respectively. The composite gels exhibit low electronic conductivities of the order of 10 −3 S cm −1 . The addition of an optimal amount of Ni particles (NiPs) improve the electronic conductivity to ≈25 S cm −1 while retaining mechanical flexibility. The electronic conductivity is further enhanced upon elongation due to the reversible alignment and elongation of the LM in the gel matrix along the stretching direction. Owing to a bicontinuous structure composed of the IL-based gel and metal component phases, the composite gels exhibit high ionic conductivity of the order of 10 −3 S cm −1 . This study demonstrates a rational approach for designing stretchable mixed conductors using ILs and Ga-based LMs.

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Ga-based liquid metals (LMs) are expected to be suitable for wiring highly deformable devices because of their high electrical conductivity and stable resistance to extreme deformation. Injection and printed wiring, and wiring using LM–polymer composites are the most popular LM wiring approaches. However, additional processing is required to package the wiring after LM patterning, branch and interrupt wiring shape, and ensure adequate conductivity, which results in unnecessary wiring shape changes and increased complexity of the wiring methods. In this study, we propose an LM–polymer composite comprising LM particles and ion gel as a flexible matrix material with low viscosity and specific gravity before curing. Moreover, the casting method is used for wire patterning, and the material is cured at room temperature to ensure that the upper insulative layer of the ion gel self-assembles simultaneously with the formation of LM wiring in the lower layer. High conductivity and low resistance change rate of the formed wiring during deformation are achieved without an activation process. This ion gel–LM bilayer wiring can be used for three-dimensional wiring by stacking. Furthermore, circuits fabricated using ion gel–LM bilayer wiring exhibit stable operation. Therefore, the proposed method can significantly promote the development of flexible electronic devices.