# Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications
## 3 Device Applications
### Energy-Harvesting/Storage Devices
Each energy unit showed a length-specific capacitance density of 13.42 mF cm\({}^{-1}\), stable charging/discharging cycling (-96.6% loss), maximum power generation of 2.5 uW, and good tactile sensitivity of 1.003 V kPa\({}^{-1}\) (below 23 kPa) [74]. The demonstration of a soft and multifunctional energy fiber makes it an attractive option for human-machine interactive systems, intelligent robots, and smart tactile-sensing clothes [74]. Among promising energy storage devices for future wearable applications, fiber-shaped supercapacitors have attracted significant attention in recent years due to their good electrochemical stability under mechanical deformation. They can be easily assembled into 3D fabric structures and integrate into cloth by traditional textile forming processes [75]. [PERSON] et al. fabricated textile-based supercapacitors (TSCs) on different types of textile fabrics using additive functionalization and embroidery manufacturing (AFEM) [75]. High areal energy storage and power capabilities of TSCs were demonstrated with various electrode materials, device structures, pattern designs, and array connections during the AFEM process [75]. The AFEM-fabricated TSCs show high potential for mass production in the near future [75]. Cloths protect human skin from the external environment and absorb solar energy. Fiber-shaped and fabric-based solar cells, another important energy-harvesting device for wearables, have recently been demonstrated: organic solar cells [76], dye-sensitized solar cells [77; 78], and perovskite photovoltaics [79; 80] based on coaxial and twisted fiber struc  
Figure 7: **(a)** Schematic of the double-layer-encapsulated Zn-ion battery fiber. **(b)** A thermometer powered by two air-rechargeable VCF/Zn battery fibers connected in series, shown in exhausted (left) and air-recharged (right) states, respectively. **(c)** The air-rechargeable VCF/Zn battery fiber presents stable voltage output under various environmental disturbances. **(d)** Left: schematic illustration of a strain sensor fiber powered by VCF/Zn battery fibers integrated in a flexible fingertip. Right: current-time curve of the strain sensor fiber upon the increasing bending cycle. **(a–d)** Reproduced with permission Ref. [69]. Copyright 2021, Royal Society of Chemistry. **(e)** Schematics of the fabrication process of the fiber TENG and its uses in collecting ambient energy and self-powered sensing. **(f)** Schematic illustration of the working mechanism for collecting energy from human motion. **(g)** Stress-strain curve of the fiber TENG. **(h)** Left: photograph of the fiber TENG as a self-powered finger-motion sensor. Right: real-time outputs when a finger is bent at different angles. **(e–h)** Reproduced with permission Ref. [73]. Copyright 2021, Wiley-VCH. tures. Many efforts have been made to demonstrate fiber solar cells that are lightweight, soft, flexible, portable, and mechanically robust. Fiber-shaped solar cells in woven structures could improve overall power output. We expect future garments to be made from energy-harvesting and storage textiles that will be used as primary power sources for wearable devices in daily life, although that could require a technical revolution.