A Young Choi

Flexible Supercapacitor Made of Carbon Nanotube Yarn with Internal Pores

Electrochemical deposition of MnO2 onto carbon nanotube (CNT) yarn gives a high-performance, flexible yarn supercapacitor. The hybrid yarns blended structure, resulting from trapping of MnO2 in its internal pores, effectively enlarges electrochemical area and reduces charge diffusion length. Accordingly, the yarn supercapacitor exhibits high values of capacitance, energy density, and average power density. Applications in wearable electronics can be envisaged.

Stretchable, weavable coiled carbon nanotube/MnO2/polymer fiber solid-state supercapacitors

Fiber and yarn supercapacitors that are elastomerically deformable without performance loss are sought for such applications as power sources for wearable electronics, micro-devices, and implantable medical devices. Previously reported yarn and fiber supercapacitors are expensive to fabricate, difficult to upscale, or non-stretchable, which limits possible use. The elastomeric electrodes of the present solid-state supercapacitors are made by using giant inserted twist to coil a nylon sewing thread that is helically wrapped with a carbon nanotube sheet, and then electrochemically depositing pseudocapacitive MnO2 nanofibers. These solid-state supercapacitors decrease capacitance by less than 15% when reversibly stretched by 150% in the fiber direction, and largely retain capacitance while being cyclically stretched during charge and discharge. The maximum linear and areal capacitances (based on active materials) and areal energy storage and power densities (based on overall supercapacitor dimensions) are high (5.4 mF/cm, 40.9 mF/cm2, 2.6 μWh/cm2 and 66.9 μW/cm2, respectively), despite the engineered superelasticity of the fiber supercapacitor. Retention of supercapacitor performance during large strain (50%) elastic deformation is demonstrated for supercapacitors incorporated into the wristband of a glove.

Corrugated Textile based Triboelectric Generator for Wearable Energy Harvesting

Triboelectric energy harvesting has been applied to various fields, from large-scale power generation to small electronics. Triboelectric energy is generated when certain materials come into frictional contact, e.g., static electricity from rubbing a shoe on a carpet. In particular, textile-based triboelectric energy-harvesting technologies are one of the most promising approaches because they are not only flexible, light, and comfortable but also wearable. Most previous textile-based triboelectric generators (TEGs) generate energy by vertically pressing and rubbing something. However, we propose a corrugated textile-based triboelectric generator (CT-TEG) that can generate energy by stretching. Moreover, the CT-TEG is sewn into a corrugated structure that contains an effective air gap without additional spacers. The resulting CT-TEG can generate considerable energy from various deformations, not only by pressing and rubbing but also by stretching. The maximum output performances of the CT-TEG can reach up to 28.13 V and 2.71 μA with stretching and releasing motions. Additionally, we demonstrate the generation of sufficient energy from various activities of a human body to power about 54 LEDs. These results demonstrate the potential application of CT-TEGs for self-powered systems.

Triboelectric generator for wearable devices fabricated using a casting method

In this study, we fabricate an efficient triboelectric generator (TEG) using inexpensive materials that are readily available in our surroundings. By casting polydimethylsiloxane (PDMS), we perform micropatterning on the surface of sandpaper. We use aluminum foil as an electrode and electrified body. To improve the durability and resilience of the aluminum foil, we use a polyethylene terephthalate (PET) film. PET/Al electrodes may act on the bottom and top performing the role of an electrode, and at the same time as an electrified body. We applied an external force of 1 N using the pushing tester on the TEG created using the PDMS, and we then connected an external resistor to confirm the output power. Based on the patterning TEG, we confirmed that there was an increase in the output voltage by a factor of about 10 compared to the flat TEGs output voltage of 15 V. We turned on 79 LEDs by hand pushing, and produced an output voltage of more than 250 V. In addition, we turned on 39 LEDs by performing a bending test with an average output voltage of more than 100 V.

Conductive functional biscrolled polymer and carbon nanotube yarns

Biscrolling aligned electrospun fiber (AEF) sheets and carbon nanotube (CNT) sheets were fabricated for conductive, functional yarns by a versatile dry composite method. Our biscrolling (twist-based spinning) method is based on spinnable polymer fiber sheets and spinnable CNT sheets unlike the previous biscrolling technique using unspinnable nanopowders and spinnable CNT sheets. The CNT sheet in composite yarns acted as effective electrical wires forming dual Archimedean multilayer rolled-up nanostructures. The weight percent of the electrospun polymer fibers in the composite yarns was over 98%, and the electrical conductivity values of the composite yarns was 3 orders higher than those of other non-conducting polymer/CNT composite fibers which were electrospun from polymer solutions containing similar loading of CNTs. We also demonstrate that biscrolled yarns having various structures can be fabricated from spinnable AEF sheets and spinnable CNT sheets.

Highly stretchable fiber-based single-electrode triboelectric nanogenerator for wearable devices

Fiber- or thread-based triboelectric nanogenerators are suitable for wearable applications such as clothes embedded with communication devices or other electronic textiles. Unfortunately, previously reported fiber-based triboelectric nanogenerators had poor stretchability, because of which they were not suitable for weaving applications. In this paper, we propose a new structure of a fiber-based single-electrode triboelectric nanogenerator (FSTENG). The proposed FSTENG uses silicone rubber as the negative part and a conductive thread as the electrode of the TENG. The electrical output of the FSTENG is generated by the continuous contact and separation between human skin and silicone rubber. A prototype of the proposed FSTENG showed an electrical output of 28 V and 0.56 μA, when in contact with human skin, and exhibited a high strain of up to 100%. In addition, we fabricated a woven structure with dimensions of 45 mm × 45 mm, incorporating the FSTENG, and confirmed its power generation capabilities using LEDs and an electronic watch. The proposed FSTENG can be applied to various products ranging from wearable and stretchable energy harvesters to smart clothing, by facilitating the manufacture of large textiles.

Flexible fiber-based triboelectric generator for self-powered sensors

This paper presents a fiber-based triboelectric generator (FTEG) that can not only harvest energy, but also function as a self-powered sensor. It consists of elastic silicon rubber and conductive fiber. Triboelectricity is generated by the regular contact and noncontact between the relatively positive conductive fiber and negative silicon rubber. The flexible FTEG showed an output voltage of 3.31V at a strain rate of 34%, which was 75% more efficient than the original state. As it is easy to fabricate, cost-efficient, and has flexible property, the FTEG is expected to possess the potential to harvest energy from human motion.

Flexible single-strand fiber-based woven-structured triboelectric nanogenerator for self-powered electronics

Textile or woven-structured triboelectric nanogenerators (TENGs) convert the mechanical energy generated from human motion into electrical energy and they can be used as efficient power sources for wearable and portable devices. However, the existing weaving-based woven-structured TENGs require multiple strands of fibers and have limited stretchability. In this paper, we propose highly stretchable and flexible single-strand fiber-based woven-structured TENGs (FW-TENGs). The proposed FW-TENGs can generate ∼34.4 µW/cm2 power from the continuous contact and separation from skin and demonstrate durability and potential for application in electronic devices. We successfully integrated the proposed FW-TENG into a shoe and harvested the mechanical energy generated from human motion. The FW-TENG is expected to find use in various applications such as e-textiles and smart clothing because it can be manufactured on a large scale.Textile or woven-structured triboelectric nanogenerators (TENGs) convert the mechanical energy generated from human motion into electrical energy and they can be used as efficient power sources for wearable and portable devices. However, the existing weaving-based woven-structured TENGs require multiple strands of fibers and have limited stretchability. In this paper, we propose highly stretchable and flexible single-strand fiber-based woven-structured TENGs (FW-TENGs). The proposed FW-TENGs can generate ∼34.4 µW/cm2 power from the continuous contact and separation from skin and demonstrate durability and potential for application in electronic devices. We successfully integrated the proposed FW-TENG into a shoe and harvested the mechanical energy generated from human motion. The FW-TENG is expected to find use in various applications such as e-textiles and smart clothing because it can be manufactured on a large scale.

Stretchable and flexible cylindrical-fiber-based triboelectric nanogenerator

With the depletion of energy sources and an increase in the demand for portable electronic devices, energy harvesting is receiving more attention. In particular, fiber/textile triboelectric energy harvesters are flexible and lightweight, and thus, they are easy to wear on the human body. Traditional fiber-based triboelectric nanogenerators have an active triboelectric material and electrodes placed outside the fiber, causing problems such as short-circuiting, when made as a textile. To solve this problem, a cylindrical-fiber-based triboelectric nanogenerator (CFTENG), with an active triboelectric material and electrodes placed inside the fiber, has been fabricated and its applicability as an energy source has been confirmed. The CFTENG had 140% elasticity, and generated 5.4 V and 31.2 V in stretching and pushing motions, respectively. Due to its high elasticity, the CFTENG is expected to find applications in power generation and self-powered sensing.

Correction: Triboelectric generator for wearable devices fabricated using a casting method

Correction for ‘Triboelectric generator for wearable devices fabricated using a casting method’ by Chang Jun Lee et al., RSC Adv., 2016, 6, 10094–10098.