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or woven fabrics. This difference presents special challenges to the field of e-textiles, distinguishing it conceptually from elastomer-based stretchable electronics. A fundamental step toward sophisticated e-textiles involves endowing textiles with electrical conductivity, which forms the basis of two design concepts: The first concept uses conductive wiring integrated in the textile to form a power bus and data network to connect multiple, separate devices, effectively decoupling device fabrication from the textile and enabling the distribution of high-performance devices over different locations in clothing. [4] The second concept seeks more intimate merging of devices with textiles by using a conductive textile as a base on which to build up layers of functional materials to form highly integrated, imperceptible devices. [5] Both approaches require highly conductive textiles with stable conductivity under strain for consistent performance, as well as stretchability and flexibility.Knitted or woven textiles present a unique challenge owing to their complex, porous 3D structure, which consists of an interconnected network of fiber bundles (yarns) separated by a network of voids. These voids are key to the flexibility and stretchability of the fabric by providing space for the yarns to move and slip in response to stress. Creating conductive pathways by filling these voids with conductive inks or pastes, such as conductive polymers, [6] or composites of polymers with graphene, [7] carbon nanotubes, [8] silver nanoparticles, [9] or silver flakes, [10] forms a conductive composite; however, this approach restricts the movement of yarns and stiffens the textile. Such composites are also vulnerable to cracking under strain. [7] Weaving, [11] knitting [12] or embroidering [13] metal wires or conductive threads into the fabric is one way to add conductivity while maintaining the void network, although this approach can be laborious, and breakage of metal wires during the manufacturing process is a concern. [14] Another tactic has been to develop methods that coat only the individual yarns or fibers of fabric with conductive materials, which leaves the void network unchanged to retain stretchability. For example, Jin et al. developed specialized conductive ink formulations to control the permeation of the ink in the textile and maintain the voids. [15] Other approaches use in situ polymerization of conductive polymers [16] in the textile or carbonization [17] of textiles through thermal treatment; however, The vision for wearable electronics involves creating an imperceptible boundary between humans and devices. Integrating electronic devices into clothing represents an important path to this vision; however, combining conductive materials with textiles is challenging due to the porous structure of knitted textiles. Stretchability depends on maintaining the void structure between the yarns of the fabric; filling these voids with conductive materials stiffens the textile and can lead to detrimental cracking. The auth...

Conspectus Electronics worn on the body have the potential to improve human health and the quality of life by monitoring vital signs and movements, displaying information, providing self-illumination for safety, and even providing new routes for personal expression through fashion. Textiles are a part of daily life in clothing, making them an ideal platform for wearable electronics. The acceptance of wearable e-textiles hinges on maintaining the properties of textiles that make them compatible with the human body. Beneficial properties such as softness, stretchability, drapability, and breathability come from the 3D fibrous structures of knitted and woven textiles. However, these structures also present considerable challenges for the fabrication of wearable e-textiles. Fabrication methods used for modern electronic devices are designed for 2D planar substrates and are mostly unsuitable for the complex 3D structures of textiles. There is thus an urgent need to develop fabrication methods specifically for e-textiles to advance wearable electronics. Solution-based fabrication methods are a promising approach to fabricating wearable e-textiles, especially considering that textiles have been successfully modified using pigmented dyes in dyebaths and printing inks for thousands of years. In this Account, we discuss our research on the solution-based electroless metallization of textiles to fabricate conductive e-textiles that are building blocks for e-textile devices. Electroless metallization solutions fully permeate textile structures to deposit metallic coatings on the surfaces of individual textile fibers, maintaining the inherent textile structures and wearability. The resulting e-textiles are highly conductive, soft, and stretchable. We furthermore discuss ways to turn the challenges related to textile structures into new opportunities by strategically using the structural features of textiles for e-textile device design. We demonstrate this textile-centric approach to designing e-textile devices using two examples. We discuss how the structure of an ultrasheer knitted textile forms a useful framework for new e-textile transparent conductive electrodes and describe the implementation of these electrodes to form highly stretchable light-emitting e-textiles. We also show how the structural features of velour fabrics form the basis for an innovative “island-bridge” strain-engineering structure that enables the integration of brittle electroactive materials and protects them from strain-induced damage, leading to the fabrication of stretchable textile-based lithium-ion battery electrodes. With the vast variety of textile structures available, we highlight the opportunities associated with this textile-centric design approach to advance textile-based wearable electronics. Such advances depend on a deep understanding of the relationship between the textile structure and the device requirements, which may potentially lead to the development of new textile structures customized to support specific devices. We conclude w...

Stretchable electronic devices rely on stretchable conductors to form device interconnects and electrodes that maintain electrical performance during deformation. Although the high conductivity of metals makes them desirable materials for these applications, the lack of intrinsic stretchability of metals is a fundamental problem in stretchable electronics. Research efforts to impart stretchability to metal films on elastomers have involved configuring the films into wavy features that unbend with strain or using high surface roughness to engineer how cracks form in metal films under strain. However, the topographies used in these approaches cause problems with integrating these metal films as electrodes in thin-film devices. This paper presents a new, simple, and low-cost strategy for the fabrication of stretchable gold films with planar topography that remain highly conductive to 95% elongation. Using solution-based electroless plating to deposit gold films on the elastomer poly(dimethylsiloxane) results in a heterogeneous crystalline surface texture with misoriented grains that are strong barriers to dislocation movement. Under strain, the misoriented grains cause the formation of a unique nanoscale cracking pattern that is remarkably effective at preserving conductivity. We demonstrate that this performance, coupled with the planar topography of these gold films, makes them suitable as electrodes in intrinsically stretchable light-emitting devices.

The advancement of wearable electronics depends on the seamless integration of lightweight and stretchable energy storage devices with textiles. Integrating brittle energy storage materials with soft and stretchable textiles, however, presents a challenging mechanical mismatch. It is critical to protect brittle energy storage materials from strain-induced damage and at the same time preserve the softness and stretchability of the functionalized e-textile. Here, we demonstrate the strategic use of a warp-knitted velour fabric in an “island-bridge” architectural strain-engineering design to prepare stretchable textile-based lithium-ion battery (LIB) electrodes. The velour fabric consists of a warp-knitted framework and a cut pile. We integrate the LIB electrode into this fabric by solution-based metallization to create the warp-knitted framework current collector “bridges” followed by selective deposition of the brittle electroactive material CuS on the cut pile “islands”. As the textile electrode is stretched, the warp-knitted framework current collector elongates, while the electroactive cut pile fibers simply ride along at their anchor points on the framework, protecting the brittle CuS coating from strain and subsequent damage. The textile-based stretchable LIB electrode exhibited excellent electrical and electrochemical performance with a current collector sheet resistance of 0.85 ± 0.06 Ω/sq and a specific capacity of 400 mAh/g at 0.5 C for 300 charging–discharging cycles as well as outstanding rate capability. The electrical performance and charge–discharge cycling stability of the electrode persisted even after 1000 repetitive stretching–releasing cycles, demonstrating the protective functionality of the textile-based island-bridge architectural strain-engineering design.