Overcoming Conductivity-Stretchability Trade-Off in Soft Conductive Composites through Liquid Metal Junctions

Soft conductive composites are significant components of soft and wearable electronics. Existing soft conductive composites encounter difficulties in attaining 10% of copper's electrical conductivity while maintaining high stretchability. In this work, a novel "soft conductive junction" concept is introduced to overcome the conductivity-stretchability trade-off. This new paradigm of soft, conductive composites consists of an interwoven copper fiber network embedded in a compliant elastomer matrix. The fiber junctions are connected using a liquid metal bridge, which significantly lowers the junction resistance without influencing the stretchability of the fiber network. These hybrid composites uphold ultrahigh and strain-insensitive conductivity that is around 60,000 S/cm under 55-75% stretch. Notably, the stretchability of these composites can be further enhanced by 2-5 times via tuning the mesh angles through prestrain, while maintaining high conductivity of 27,000-58,000 S/cm. Potential applications of the composites in stretchable circuitry, wearable interconnects, capacitance tactile sensors, and highly stretchable Joule heaters are presented.