Supercapacitors are known to have superior power densities over batteries due to their surface-centered charge-discharge processes. Recently, increasing attention has accumulated in the fiber or yarn shaped supercapacitor (FSC) systems, mainly due to their high flexibility and pliable nature, leading to potential applications in wearable electronics, microrobots, medical implants, and smart textiles. However, one of the major limitations that occurs when supercapacitors are made into fiber/yarn shapes, is the increased equivalent series resistance (ESR) due to the fibrous geometry adopted here. For instance, even the best FSC reported will exhibit several hundred ohms of resistance at one-meter length, which however is usually neglected by researchers in their publication.

To directly tackle this issue, here we report our strategies of using a metallic core filament in the yarn supercapacitors development in our lab. With detailed materials and process engineering, we are able to boost the power density by one order of magnitude. Sealing strategies and other alternative solutions for this issue will also be discussed.