A Highly Stretchable, Fiber‐Shaped Supercapacitor

Abstract

Flexible and portable devices are a mainstream direction in modern electronics and related multidisciplinary fields. To this end, they are generally required to be stretchable to satisfy various substrates. [1,2] As a result, stretchable devices, such as electrochemical supercapacitors, [3][4][5][6] lithium-ion batteries, [7] organic solar cells, [8] organic light-emitting diodes, [9,10] field-effect transistors, [11] and artificial skin sensors [12] have been widely studied. However, these stretchable devices are made in a conventional planar format that has largely hindered their development. For the portable applications, the devices need to be lightweight and small, though it is difficult for them to be made into efficient microdevices. In particular, it is challenging or even impossible for them to be used in electronic circuits and textiles that are urgently required also in a wide variety of other fields, such as microelectronic applications.Recently, some attempts have been made to fabricate wire-shaped microdevices, such as electrochemical supercapacitors. They have been generally produced by twisting two fiber electrodes with electrolytes coated on the surface. [13][14][15][16][17][18][19] Several examples have been also successfully shown to make fiber-shaped supercapacitors with a coaxial structure. [20,21] Compared with their planar counterparts, the wire or fiber shape enables promising advantages such as being lightweight and woven into textiles. Although the wire and fiber-shaped supercapacitors are also flexible with high electrochemical performance, they are not stretchable, which is critically important for many applications. For instance, the resulting electronic textiles could easily break during the use if they were not stretchable.To the best of our knowledge, herein we have, for the first time, developed a novel family of highly stretchable, fibershaped high-performance supercapacitors. Aligned carbon nanotube (CNT) sheets that are sequentially wrapped on an elastic fiber serve as two electrodes. The use of aligned CNT sheets offers combined remarkable properties including high flexibility, tensile strength, electrical conductivity, and

Toward Soft Skin‐Like Wearable and Implantable Energy Devices

“…This is because reversible oxidation/reduction reaction(s) will occur at the electrode/ electrolyte interface of the pseudocapacitor, giving 10-100 times more capacitance than that of pure carbon-based EDLC. [61] To date, various novel materials with intrinsic stretchability (e.g., carbon nanotubes, carbon nanofibers, graphene, and metal nanowires) [18,45,46,51] and structural designs (e.g., wire configuration, [62] film configuration, [12] and textile configuration) [37] have been proposed for the purpose of developing stretchable and implantable supercapacitors. We will discuss several viable configurations.…”

“…There are mainly two configurations for wire-shaped stretchable supercapacitors: coaxial design [46,62] and non-coaxial design [41,63] (Figure 7). The first coaxial, stretchable, wire-shaped supercapacitors was developed in 2013 (Figure 7a).…”

“…The first coaxial, stretchable, wire-shaped supercapacitors was developed in 2013 (Figure 7a). [62] The stretchability was achieved by wrapping an aligned CNT sheets layer, a thin gel electrolyte layer, and another CNT sheets layer coaxially onto elastic fibres ( Figure 7b). This design could maintain high contact areas and low contact resistance between the electrode and electrolytes, resulting in a high specific capacitance of 19.2 F g −1 .…”

“…The Reproduced with permission. [62] Copyright 2013, Wiley-VCH. c) Photographs of a 1D wire-like twist stretchable supercapacitor stretched with different strain (up to 370%).…”

“…Interestingly, the capacitance for the device based on the bare CNT-wrapped elastic wire electrodes increased by 13% as the tensile strain increased from 0 to 250%, presumably because of the strain-induced enhancement in the contact between the two twisted electrodes upon stretching. [62,63] Further stretching (250-350%) caused a slight decrease in the capacitance, though it was still 10% higher than the initial capacitance. Graphene microfibers has also been chose as electrode materials for 1D wire-based stretchable supercapacitor.…”