From Industrially Weavable and Knittable Highly Conductive Yarns to Large Wearable Energy Storage Textiles

Abstract

Wearable electronic textiles that store capacitive energy are a next frontier in personalized electronics. However, the lack of industrially weavable and knittable conductive yarns in conjunction with high capacitance, limits the wide-scale application of such textiles. Here pristine soft conductive yarns are continuously produced by a scalable method with the use of twist-bundle-drawing technique, and are mechanically robust enough to be knitted to a cloth by a commercial cloth knitting machine. Subsequently, the reduced-graphene-oxide-modified conductive yarns covered with a hierarchical structure of MnO2 nanosheets and a polypyrrole thin film were used to fabricate weavable, knittable and wearable yarn supercapacitors. The resultant modified yarns exhibit specific capacitances as high as 36.6 mF cm(-1) and 486 mF cm(-2) in aqueous electrolyte (three-electrode cell) or 31 mF cm(-1) and 411 mF cm(-2) in all solid-state two-electrode cell. The symmetric solid-state supercapacitor has high energy densities of 0.0092 mWh cm(-2) and 1.1 mWh cm(-3) (both normalized to the whole device) with a long cycle life. Large energy storage textiles are fabricated by weaving our flexible all-solid-state supercapacitor yarns to a 15 cm × 10 cm cloth on a loom and knitting in a woollen wrist band to form a pattern, enabling dual functionalities of energy storage capability and wearability.

A General Electrode Design Strategy for Flexible Fiber Micro‐Pseudocapacitors Combining Ultrahigh Energy and Power Delivery

“…Various carbonaceous materials like activated carbon,9, 10 carbon nanotubes (CNTs),11, 12, 13 reduced graphene oxide (rGO),14, 15, 16 and our recently developed rGO/CNT hybrids17, 18 were exploited as active materials for fiber m‐SCs, yet their applications are restricted by the low capacitance of <200 mF cm −2 . Alternatively, incorporating pseudocapacitive materials into fiber m‐SCs is a superior solution to achieve high‐density energy due to 10–100 times higher theoretical capacitance than carbon materials 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36. Due to the poor conductivity for pseudocapacitive materials, composite electrode design by depositing active materials on one‐dimensional (1D) conductive scaffolds including carbon‐based fibers19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or metal‐based wires,31, 32, 33, 34, 35, 36 was employed to improve the electron transport.…”

“…Alternatively, incorporating pseudocapacitive materials into fiber m‐SCs is a superior solution to achieve high‐density energy due to 10–100 times higher theoretical capacitance than carbon materials 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36. Due to the poor conductivity for pseudocapacitive materials, composite electrode design by depositing active materials on one‐dimensional (1D) conductive scaffolds including carbon‐based fibers19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or metal‐based wires,31, 32, 33, 34, 35, 36 was employed to improve the electron transport. Despite some progresses, the improvements in the areal energy density for these fiber m‐SCs are still too modest to cater for many practical requirements and often come at the expense of sacrificing their rate capability or power density 1, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36.…”

“…Due to the poor conductivity for pseudocapacitive materials, composite electrode design by depositing active materials on one‐dimensional (1D) conductive scaffolds including carbon‐based fibers19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or metal‐based wires,31, 32, 33, 34, 35, 36 was employed to improve the electron transport. Despite some progresses, the improvements in the areal energy density for these fiber m‐SCs are still too modest to cater for many practical requirements and often come at the expense of sacrificing their rate capability or power density 1, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36. This impedes their broad practical applications where both high power and energy densities are required.…”

“…However, such crucial design concern is often ignored in previous carbon‐based fiber m‐SCs, thus leading to a major bottleneck in performance (typically <200 mF cm −2 and <1 mW cm −2 ) 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. As compared, metallic scaffold was recognized as the best candidate for long‐range electron transport 31, 32, 33, 34, 35, 36. For instances, bare Ni wires were often utilized as conductive skeletons to load various active materials like Ni(OH) 2 /rGO,[[qv: 36b]] CuCo 2 O 4 nanowires,[[qv: 36c]] and rGO15 for fiber m‐SCs.…”

“…For instances, bare Ni wires were often utilized as conductive skeletons to load various active materials like Ni(OH) 2 /rGO,[[qv: 36b]] CuCo 2 O 4 nanowires,[[qv: 36c]] and rGO15 for fiber m‐SCs. However, these bare metallic wires are solid and often suffer from limited surface area,31, 32, 33, 34, 35, 36 also commonly seen in carbon‐based fiber electrodes 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. This undoubtedly restricted allowable active material loading, since thicker active material layer may cause poor adhesion, inferior mechanical stability, and high resistivity.…”