Abstract
Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications. Here, we report weavable carbon nanotube yarn supercapacitors having high performance because of high loadings of rapidly accessible charge storage particles (above 90 wt% MnO2). The yarn electrodes are made by a biscrolling process that traps host MnO2 nanoparticles within the galleries of helically scrolled carbon nanotube sheets, which provide strength and electrical conductivity. Despite the high loading of brittle metal oxide particles, the biscrolled solid-state yarn supercapacitors are flexible and can be made elastically stretchable (up to 30% strain) by over-twisting to produce yarn coiling. The maximum areal capacitance of the yarn electrodes were up to 100 times higher than for previously reported fibres or yarn supercapacitors. Similarly, the energy density of complete, solid-state supercapacitors made from biscrolled yarn electrodes with gel electrolyte coating were significantly higher than for previously reported fibre or yarn supercapacitors.
Highlights
Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications
The fundamental problem is that only the shell is utilized as an effective loading site for active materials, while the bulk core of the fibre does not participate in the electrochemical charge/discharge processes[2]
Biscrolling dramatically expands the achievable loading of active particles in yarns to as high as 99 wt%, and both the high loading levels and retention of useable strength has enabled the development of biscrolled yarn superconductors[33], bio-fuel electrodes[34] and battery electrodes[32]
Summary
Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications. Performance is enhanced by balancing the competing demands for maximizing the interfacial area between active electrode material and electrolyte without compromising mechanical robustness or electronic conductivity Pseudocapacitive active materials, such as manganese dioxide (MnO2), provide increased intrinsic capacitance, but need to be employed as fine powder or thin films because thick MnO2 layers can significantly degrade areal and volumetric capacitances and rate capability due to intrinsic low electrical conductivity[31]. Active material loadings have to date been restricted to o20 wt%, even when nano-structured core fibres have been used, such as twist-spun carbon nanotube (CNT) yarns[2,4,5,6] and CNT-coated, coiled nylon fibre[3] To achieve both high discharge rate and high energy storage capabilities, we utilize a powerful technology called biscrolling[32]. The biscrolled MaannnddOCE2VV/C1⁄41⁄4N15T5.45y1aFmrcnmWs hÀha3cv)measÀnpde3)ceinfithecracgta,yptdaoecniotsauintricekessn(o(ECwAAl1⁄4e1⁄4d3g85e8.,89emmxWcFeeccdmmtÀÀhe[22] previously reported performances of fibre-based supercapacitor electrodes
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