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An elastic and safe electrolyte is demanded for flexible batteries. Herein, a stretchable solid electrolyte comprised of crosslinked elastic polymer matrix, poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP), and flameproof triethyl phosphate (TEP) is fabricated, which exhibits ultrahigh elongation of 450%, nonflammability and ionic conductivity above 1 mS cm−1. In addition, in order to improve the interface compatibility between the electrolyte and Li anode and stabilize the solid‐electrolyte interphase (SEI), a protecting layer containing poly(ethylene oxide) (PEO) is designed to effectively prevent the anode from reacting with TEP and optimize the chemical composition in SEI, leading to a tougher and more stable SEI on the anode. The LiFePO4/Li cells employing this double‐layer electrolyte exhibit an 85.0% capacity retention after 300 cycles at 1 C. Moreover, a flexible battery based on this solid electrolyte is fabricated, which can work in stretched, folded, and twisted conditions. This design of a stretchable double‐layer solid electrolyte provides a new concept for safe and flexible solid‐state batteries. A stretchable polymer electrolyte is fabricated based on resilient copolymer and poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP) with ultrahigh elasticity, nonflammability, and good ionic conductivity. A protective layer containing poly(ethylene oxide) (PEO) is designed to protect the electrolyte against the anode and stabilize the solid‐electrolyte interphase (SEI) during cycling. A flexible solid‐state battery is prepared using this double‐layer electrolyte, which can light a light emitting diode (LED) bulb under different deformed conditions.

Stretchable lithium batteries have attracted considerable attention as components in future electronic devices, such as wearable devices, sensors, and body‐attachment healthcare devices. However, several challenges still exist in the bid to obtain excellent electrochemical properties for stretchable batteries. Here, a unique stretchable lithium full‐cell battery is designed using 1D nanofiber active materials, stretchable gel polymer electrolyte, and wrinkle structure electrodes. A SnO2/C nanofiber anode and a LiFePO4/C nanofiber cathode introduce meso‐ and micropores for lithium‐ion diffusion and electrolyte penetration. The stretchable full‐cell consists of an elastic poly(dimethylsiloxane) (PDMS) wrapping film, SnO2/C and LiFePO4/C nanofiber electrodes with a wrinkle structure fixed on the PDMS wrapping film by an adhesive polymer, and a gel polymer electrolyte. The specific capacity of the stretchable full‐battery is maintained at 128.3 mAh g−1 (capacity retention of 92%) even after a 30% strain, as compared with 136.8 mAh g−1 before strain. The energy densities are 458.8 Wh kg−1 in the released state and 423.4 Wh kg−1 in the stretched state (based on the electrode), respectively. The high capacity and stability in the stretched state demonstrate the potential of the stretchable battery to overcome its limitations. A novel approach toward high‐performance stretchable batteries that applies 1D nanofiber active materials, stretchable gel polymer electrolyte, and an electrode with wrinkled structure is successfully demonstrated. The stretchable full‐battery exhibits high capacity, high energy density, and notable stability even in the stretched states.

Thermo‐electrochemical cells (TECs) provide a new potential for self‐powered devices by converting heat energy into electricity. However, challenges still remain in the fabrication of flexible and tough gel electrolytes and their compatibility with redox actives; otherwise, contact problems exist between electrolytes and electrodes during stretching or twisting. Here, a novel robust and neutral hydrogel with outstanding stretchability was developed via double‐network of crosslinked carboxymethyl chitosan and polyacrylamide, which accommodated both n‐type (Fe2+/Fe3+) and p‐type ([Fe(CN)6]3−/[Fe(CN)6]4−) redox couples and maintained stretchability (>300%) and recoverability (95% compression). Moreover, poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) textile electrodes with porous structure are integrated into gel electrolytes that avoid contact issues and effectively boost the Pmax of n‐ and p‐type thermocell by 76% and 26%, respectively. The optimized thermocell exhibits a quick current density response and is continually fully operational under deformations, which satisfies the working conditions of wearable devices. Multiple thermocells (four pairs) are effectively connected in alternating single n‐ and p‐type cells in series and outputted nearly 74.3 mV at ΔT = 10°C. The wearable device is manufactured into a soft‐pack thermocells to successfully harvest human body heat and illuminate an LED, demonstrating the potential of the actual application of the thermocell devices. This work designs the stretchable gel electrolytes via the double crosslinking. Moreover, the porous textile electrodes are encapsulated by gel electrolytes to avoid issue of contact and boost the Pmax of thermocell because of the larger active electrochemical surface. Finally, a wearable soft‐packing thermocell array can power an LED by harvesting human body heat, demonstrating the potential for actual application.

HighlightsFacile fabrication of high-transconductance (>10 mS) and highly elastic all-polymer organic electrochemical transistors was presented using gelatin-based electrolyte supporting printed PEDOT:PSS/LiTFSI microstructures.PEDOT:PSS/LiTFSI wrinkled microelectrodes and imprinted 3D-microstructured channel/electrolyte interface allowed biaxial stretchability of 100% strain and performance preservation after 1000 cycles of 80% strain.The glycerol-soaked elastic gelatin electrolyte also permitted long-term environmental stability for months and enabled readily recyclable device, paving the way to wide applications spanning from artificial synapses to wearable sensing.Organic electrochemical transistors (OECTs) have emerged as versatile platforms for broad applications spanning from flexible and wearable integrated circuits to biomedical monitoring to neuromorphic computing. A variety of materials and tailored micro/nanostructures have recently been developed to realized stretchable OECTs, however, a solid-state OECT with high elasticity has not been demonstrated to date. Herein, we present a general platform developed for the facile generation of highly elastic all-polymer OECTs with high transconductance (up to 12.7 mS), long-term mechanical and environmental durability, and sustainability. Rapid prototyping of these devices was achieved simply by transfer printing lithium bis(trifluoromethane)sulfonimide doped poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS/LiTFSI) microstructures onto a resilient gelatin-based gel electrolyte, in which both depletion-mode and enhancement-mode OECTs were produced using various active channels. Remarkably, the elaborate 3D architectures of the PEDOT:PSS were engineered, and an imprinted 3D-microstructured channel/electrolyte interface combined with wrinkled electrodes provided performance that was retained (> 70%) through biaxial stretching of 100% strain and after 1000 repeated cycles of 80% strain. Furthermore, the anti-drying and degradable gelatin and the self-crosslinked PEDOT:PSS/LiTFSI jointly enabled stability during > 4 months of storage and on-demand disposal and recycling. This work thus represents a straightforward approach towards high-performance stretchable organic electronics for wearable/implantable/neuromorphic/sustainable applications.

Stretchable energy storage devices, maintaining the capability of steady operation under large mechanical strain, have become increasing more important with the development of stretchable electronic devices. Stretchable supercapacitors (SSCs), with high power density, modest energy density, and superior mechanical properties are regarded as one of the most promising power supplies to stretchable electronic devices. Conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh) and poly(3,4-ehtylenedioxythiophene) (PEDOT), are among the well-studied electroactive materials for the construction of SSCs because of their high specific theoretical capacity, excellent electrochemical activity, light weight, and high flexibility. Much effort has been devoted to developing stretchable, conductive polymer-based SSCs with different device structures, such as sandwich-type and fiber-shaped type SSCs. This review summarizes the material and structural design for conductive polymer-based SSCs and discusses the challenge and important directions in this emerging field.

Sensing technology is under intense development to enable the Internet of everything and everyone in new and useful ways. Here we demonstrate a method of stretchable and self-powered temperature sensing. The basic sensing element consists of three layers: an electrolyte, a dielectric, and an electrode. The electrolyte/dielectric interface accumulates ions, and the dielectric/electrode interface accumulates electrons (in either excess or deficiency). The ions and electrons at the two interfaces are usually not charge-neutral, and this charge imbalance sets up an ionic cloud in the electrolyte. The design functions as a charged temperature-sensitive capacitor. When temperature changes, the ionic cloud changes thickness, and the electrode changes open-circuit voltage. We demonstrate high sensitivity (∼1 mV/K) and fast response (∼10 ms). Such temperature sensors can be made small, stable, and transparent. Depending on the arrangement of the electrolyte, dielectric, and electrode, we develop four designs for the temperature sensor. In addition, the temperature sensor has good linearity in the range of tens of Kelvin. We further show that the temperature sensors can be integrated into stretchable electronics and soft robots.

Intrinsically stretchable organic electrochemical transistors (OECTs) are being pursued as the next‐generation tissue‐like bioelectronic technologies to improve the interfacing with the soft human body. However, the performance of current intrinsically stretchable OECTs is far inferior to their rigid counterparts. In this work, for the first time, the authors report intrinsically stretchable OECTs with overall performance benchmarkable to conventional rigid devices. In particular, oxygen level in the stretchable substrate is revealed to have a significant impact on the on/off ratio. By employing stretchable substrates with low oxygen permeabilities, the on/off ratio is elevated from ≈10 to a record‐high value of ≈104, which is on par with a rigid OECT. The device remained functional after cyclic stretching tests. This work demonstrates that intrinsically stretchable OECTs have the potential to serve as a new building block for emerging soft bioelectronic applications such as electronic skin, soft implantables, and soft neuromorphic computing. It is observed that the poor electrical performance of stretchable organic electrochemical transistors (OECTs) can be significantly improved by controlling the oxygen permeability of the elastic substrate. The overall performance of the optimized device is verified benchmarkable to a conventional rigid OECT.

Given the rise in the popularity of wearable electronics that are able to deform into desirable configurations while maintaining electrochemical functionality, stretchable and flexible (hybrid) supercapacitors (SCs) have become increasingly of interest as innovative energy storage devices. Their outstanding power density, long lifetime with low capacitance loss, and appropriate energy density, in particular in hybrid cases make them ideal candidates for flexible electronics. The aim of this review paper is to provide an in‐depth discussion of these stretchable and flexible SCs ranging from fabrication to electro‐mechanical properties. This review paper begins with a short overview of the fundamentals of charge storage mechanisms and different types of multivalent metal‐ion hybrid SCs. The research methods leading up to the current state of these stretchable and flexible SCs are then presented. This is followed by an in‐depth presentation of the challenges associated with the fabrication methods for different configurations. Proposed novel strategies to maximize the elastic and electrochemical properties of stretchable/flexible or quasi‐solid‐state SCs are classified and the pros and cons associated with each are shown. The advances in mechanical properties and the expected advancements for the future of these SCs are discussed in the last section. The recent advancements and future potential application potential of flexible and stretchable supercapacitors (SCs) and hybrid SCs with different configurations have been studied. Mechanisms associated with energy storage, layouts, energy materials, different configurations, and their effects on mechanical and electrochemical properties are studied. Manufacturing methods associated with different device configurations and challenges are discussed.

Dynamic glucose monitoring is important to reduce the risk of metabolic diseases such as diabetes. Wearable biosensors based on organic electrochemical transistors (OECTs) have been developed due to their excellent signal amplification capabilities and biocompatibility. However, traditional wearable biosensors are fabricated on flat substrates with limited gas permeability, resulting in the inefficient evaporation of sweat, reduced wear comfort, and increased risk of inflammation. Here, we proposed breathable OECT-based glucose sensors by designing a porous structure to realize optimal breathable and stretchable properties. The gas permeability of the device and the relationship between electrical properties under different tensile strains were carefully investigated. The OECTs exhibit exceptional electrical properties (gm ~1.51 mS and Ion ~0.37 mA) and can retain up to about 44% of their initial performance even at 30% stretching. Furthermore, obvious responses to glucose have been demonstrated in a wide range of concentrations (10−7–10−4 M) even under 30% strain, where the normalized response to 10−4 M is 26% and 21% for the pristine sensor and under 30% strain, respectively. This work offers a new strategy for developing advanced breathable and wearable bioelectronics.

Wearable electronics have attracted extensive attentions over the past few years for their potential applications in health monitoring based on continuous data collection and real‐time wireless transmission, which highlights the importance of portable powering technologies. Batteries are the most used power source for wearable electronics, but unfortunately, they consist of hazardous materials and are bulky, which limit their incorporation into the state‐of‐art skin‐integrated electronics. Sweat‐activated biocompatible batteries offer a new powering strategy for skin‐like electronics. However, the capacity of the reported sweat‐activated batteries (SABs) cannot support real‐time data collection and wireless transmission. Focused on this issue, soft, biocompatible, SABs are developed that can be directly integrated on skin with a record high capacity of 42.5 mAh and power density of 7.46 mW cm−2 among the wearable sweat and body fluids activated batteries. The high performance SABs enable powering electronic devices for a long‐term duration, for instance, continuously lighting 120 lighting emitting diodes (LEDs) for over 5 h, and also offers the capability of powering Bluetooth wireless operation for real‐time recording of physiological signals for over 6 h. Demonstrations of the SABs for powering microfluidic system based sweat sensors are realized in this work, allowing real‐time monitoring of pH, glucose, and Na+ in sweat. A stretchable, conformable sweat‐activated battery (SAB) has been developed with high power density (7.46 mW cm−2) and energy capacity (42.5 mAh); it enables lighting 120 lighting emitting diodes (LEDs) for 5 h, and offers enough power to support Bluetooth wireless operation for real‐time recording of physiological signals in state‐of‐art wearable sensors for over 6 h. The SAB is also demonstrated in powering microfluidic system based sweat sensors for real‐time monitoring of pH, glucose, and Na+ in sweat.