Flexible/Stretchable Supercapacitors with Novel Functionality for Wearable Electronics

Abstract

offering comfort to the user. Wearable electronics can be integrated into common textiles or be directly attached onto human skin to perform various functions, for instance, measuring pulses, sensing toxins in the environment, analyzing bodily fluids such as sweat, injecting medication, and informing the user of such activities. Aside from their biomedical purposes, wearable electronics with touchpads and displays, and smart functions, including Internet communication and facial and sound recognition, can also be developed to benefit and assist with daily activities. In addition to functionality, flexibility and stretchability are desired attributes of the components of wearable electronics so that the electronics can exhibit mechanical stability against deformation due to human motions without a deterioration in performance. Many flexible/stretchable devices were developed for integration into wearable devices such as various sensors including bio-signal [1-3] and environmental sensors, [4,5] solar cells, [6,7] energy harvesters, [8] antennas, [9,10] and radio frequency identification (RFID) tags. [11] Moreover, together with other flexible/ stretchable devices, energy storage devices used for powering the active devices on wearable electronics should also be able to withstand deformation. The energy storage devices built for wearable electronics should meet specific criteria, such as having a small size and high efficiency, and being flexible, lightweight, and biocompatible. [12,13] Among the various energy storage devices, supercapacitors are considered one of the most promising candidates in wearable electronics. Rechargeable metal-ion batteries such as lithium-ion batteries (LIBs) have been widely used as energy storage devices in commercial applications owing to their large energy density. Compared to the batteries, supercapacitors have simpler structures, faster charge-discharge time, higher power density of ≈10 kW kg −1 , and longer cycle life over 100 000 cycles. Owing to supercapacitors' uncomplicated architecture, their miniaturization has been extensively studied, resulting in micro-supercapacitors (MSCs). An MSC is a supercapacitor whose total device area is on the square millimeter or centimeter scale, and/or a supercapacitor with a thickness of <10 µm. [14] Materials with a high surface area such as foamstructured materials or nanocarbon-based materials can be utilized to reduce the size and weight of a supercapacitor and to With the miniaturization of personal wearable electronics, considerable effort has been expended to develop high-performance flexible/stretchable energy storage devices for powering integrated active devices. Supercapacitors can fulfill this role owing to their simple structures, high power density, and cyclic stability. Moreover, a high electrochemical performance can be achieved with flexible/stretchable supercapacitors, whose applications can be expanded through the introduction of additional novel functionalities. Here, recent advances in and future prospects for flexible/s...

Polypyrrole and Graphene Nanoplatelets Inks as Electrodes for Flexible Solid-State Supercapacitor

“…Over the past few decades, there has been an increasing research interest in the field of energy storage systems and, among them, a great deal of attention has been focused on supercapacitors [1][2][3][4]: devices that combine a high power density and a fast charging rate with a simple design that enables them to be flexible, stretchable, and bendable [5][6][7], qualities that make them particularly suited for wearable electronic applications [8][9][10]. Supercapacitors, which consist of a couple of electrodes impregnated with an electrolyte and spaced by an ion-permeable separator, have performances, electric behavior, and even working principles that change depending on the nature of the electrodes, of the medium interposed between the electrodes, and of the electrolyte.…”

3D-Printed highly stretchable conducting polymer electrodes for flexible supercapacitors

“…19,20 Moreover, most of these substrates are subject to the drawbacks of low capacitance and high resistance, which may result in poor electrochemical performance. 21 Another approach to achieve stretchable electrodes is applying structural engineering techniques to reduce the stresses placed on the material, e.g. modifying the geometric structure of non-stretchable materials into helical, serpentine, sponge, wavy and net congurations.…”

A Textile‐Based Temperature‐Tolerant Stretchable Supercapacitor for Wearable Electronics

“…Dramatic progress in the development of wearable electronic devices, which can be attached to bodies or embedded in clothes, has yielded numerous attempts to obtain the stability of energy storage devices under a variety of environmental conditions, that is, flexible/stretchable properties and tolerance over temperature and humidity. [1][2][3][4][5][6][7] Supercapacitors are one of the most important energy storage devices with many benefits over batteries, such as high power density, long cyclic life, excellent high-performance flexible supercapacitors based on a polyelectrolyte with tolerance over temperatures ranging from −30 to 100 °C. [31] Although these temperature-tolerant supercapacitors can be operated at extreme temperatures, there have been no reports about stretchable supercapacitors that are stable over a wide temperature range of 100 °C or higher.…”