All-carbon solid-state yarn supercapacitors from activated carbon and carbon fibers for smart textiles

Abstract

Smart textiles are intelligent devices that can sense and respond to environmental stimuli. They require integrated energy storage to power their functions. An emerging approach is to build integratable fiber/yarn-based energy storage devices. Here, we demonstrated all-carbon solidstate yarn supercapacitors using commercially available activated carbon and carbon fiber yarns for smart textiles. Conductive carbon fibers concurrently act as current collectors in yarn supercapacitors and as substrates for depositing large surface area activated carbon particles.Two hybrid carbon yarn electrodes were twisted together in polyvinyl alcohol/H 3 PO 4 polymer gel, which is used as both electrolyte and separator. A 10-cm long yarn supercapacitor, with the optimum composition of 2.2 mg/cm activated carbon and 1 mg/cm carbon fiber, shows a specific length capacitance of 45.2 mF/cm at 2 mV/s, an energy density of 6.5 µWh/cm, and power density of 27.5 µW/cm. Since the yarn supercapacitor has low equivalent series resistance at 4.9 Ω/cm, longer yarn supercapacitors up to 50 cm in length were demonstrated, yielding a high total capacitance up to 1164 mF. The all-carbon solid-state yarn supercapacitors also exhibit excellent mechanical flexibility with minor capacitance decreases upon bending or being crumpled.Utilizing three long yarn supercapacitors, a wearable wristband was knitted; this wristband is capable of lighting up an LED indicator, demonstrating strong potential for smart textile applications.An emerging approach of building energy storage devices for smart textiles is to directly incorporate energy storage materials at the formation stage of textile fibers, and then integrate multiple fibers into energy storage fabrics. Researchers are exploring different nanomaterials for energy storage, such as carbon nanotubes, graphene, and many metal oxide nanoparticles.However, different nanomaterials have their specific weakness which limits their practical applications, for example, the high cost of single walled carbon nanotubes, the lack of scalable production of amorphous Ni(OH) 2 , 1 the potential health and environmental toxicity of RuO 2 and some other carbon nanomaterials. 2-4 Activated carbon derived from biomaterials or polymer precursors is the most widely used electrode material in commercial supercapacitors nowadays.Carbon fibers with excellent electrical conductivity and mechanical strength, made from polyacrylonitrile or pitch, are produced in large quantity with billions of dollars market. We envisage that it is a practical and promising approach to efficiently incorporate activated carbon into weavable/knittable carbon fiber yarns, which combines the good capacitive energy storage property of activated carbon with excellent electrical conductivity and mechanical flexibility of carbon fibers. Yarn supercapacitors can be assembled using such hybrid carbon fibers of activated carbon and carbon fibers as electrodes, which unveil strong potential for smart textile applications in the near future.conducting polymers...

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“…Impressively, a highly flexible fabric‐based supercapacitor was woven from two 40 cm long coaxial fibers, paving the way to future wearable ESTs (Figure a‐v,a‐vi). Zhai et al fabricated a wearable wristband by knitting three long yarn‐shaped supercapacitors together. In their study, an all‐carbon electrode was prepared by drop‐casting an activated carbon suspension onto CF yarns (Figure b‐i, left).…”

“…b‐iii) Photo of a woven supercapacitor wristband worn on the wrist lighting an LED. b) Reproduced with permission . Copyright 2015, Royal Society of Chemistry.…”