A Mechanically Robust and Versatile Liquid-Free Ionic Conductive Elastomer
TL;DR: In this article, Li et al. proposed liquid-free ionic conductive elastomers (ICEs), which are copolymer networks hosting lithium cations and associated anions via lithium bonds and hydrogen bonds.
Abstract: Soft ionic conductors, such as hydrogels and ionogels, have enabled stretchable and transparent ionotronics, but they suffer from key limitations inherent to the liquid components, which may leak and evaporate. Here, novel liquid-free ionic conductive elastomers (ICE) that are copolymer networks hosting lithium cations and associated anions via lithium bonds and hydrogen bonds are demonstrated, such that they are intrinsically immune from leakage and evaporation. The ICEs show extraordinary mechanical versatility including excellent stretchability, high strength and toughness, self-healing, quick self-recovery, and 3D-printability. More intriguingly, the ICEs can defeat the conflict of strength versus toughness-a compromise well recognized in mechanics and material science-and simultaneously overcome the conflict between ionic conductivity and mechanical properties, which is common for ionogels. Several liquid-free ionotronics based on the ICE are further developed, including resistive force sensors, multifunctional ionic skins, and triboelectric nanogenerators (TENGs), which are not subject to limitations of previous gel-based devices, such as leakage, evaporation, and weak hydrogel-elastomer interfaces. Also, the 3D printability of the ICEs is demonstrated by printing a series of structures with fine features. The findings offer promise for a variety of ionotronics requiring environmental stability and durability.
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TL;DR: In this paper, the authors demonstrate a robust proton-conductive ionic skin design via introducing an entropy-driven supramolecular zwitterionic reorganizable network to the hydrogen-bonded polycarboxylic acid network.
Abstract: Stretchable ionic skins are intriguing in mimicking the versatile sensations of natural skins. However, for their applications in advanced electronics, good elastic recovery, self-healing, and more importantly, skin-like nonlinear mechanoresponse (strain-stiffening) are essential but can be rarely met in one material. Here we demonstrate a robust proton-conductive ionic skin design via introducing an entropy-driven supramolecular zwitterionic reorganizable network to the hydrogen-bonded polycarboxylic acid network. The design allows two dynamic networks with distinct interacting strength to sequentially debond with stretch, and the conflict among elasticity, self-healing, and strain-stiffening can be thus defeated. The representative polyacrylic acid/betaine elastomer exhibits high stretchability (1600% elongation), immense strain-stiffening (24-fold modulus enhancement), ~100% self-healing, excellent elasticity (97.9 ± 1.1% recovery ratio, <14% hysteresis), high transparency (99.7 ± 0.1%), moisture-preserving, anti-freezing (elastic at −40 °C), water reprocessibility, as well as easy-to-peel adhesion. The combined advantages make the present ionic elastomer very promising in wearable iontronic sensors for human-machine interfacing. Ionic skins are of interest for a range of electronic, sensing and interfacing applications but often have trade-offs in properties. Here, the authors report on the creation of a dual network ionic skin using a supramolecular zwitterionic competing network to produce a strain-stiffening, self-healing adhesive sensor.
143 citations
TL;DR: Li et al. as discussed by the authors proposed a dry ion-conducting elastomer with dynamic crosslinking structures, which achieved high ionic conductivity (2.04 × 10-4 S cm-1 at 25 °C).
Abstract: Soft ionic conductors show great promise in multifunctional iontronic devices, but currently utilized gel materials suffer from liquid leakage or evaporation issues. Here, a dry ion-conducting elastomer with dynamic crosslinking structures is reported. The dynamic crosslinking structures endow it with combined advantageous properties simultaneously, including high ionic conductivity (2.04 × 10-4 S cm-1 at 25 °C), self-healing capability (96% healing efficiency), stretchability (563%), and transparency (78%). With this ionic conductor as the electrode, two soft iontronic devices (electroluminescent devices and triboelectric nanogenerator tactile sensors) are realized with entirely self-healing and stretchable capabilities. Due to the absence of liquid materials, the dry ion-conducting elastomer shows wide operational temperature range, and the iontronic devices achieve excellent stability. These findings provide a promising strategy to achieve highly conductive and multifunctional soft dry ionic conductors, and demonstrate their great potential in soft iontronics or electronics.
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TL;DR: This work focuses on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture.
Abstract: The attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues for stronger and harder materials, these have little to no use as bulk structural materials without appropriate fracture resistance. It is the lower-strength, and hence higher-toughness, materials that find use for most safety-critical applications where premature or, worse still, catastrophic fracture is unacceptable. For these reasons, the development of strong and tough (damage-tolerant) materials has traditionally been an exercise in compromise between hardness versus ductility. Drawing examples from metallic glasses, natural and biological materials, and structural and biomimetic ceramics, we examine some of the newer strategies in dealing with this conflict. Specifically, we focus on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture. We show how these new and natural materials can defeat the conflict of strength versus toughness and achieve unprecedented levels of damage tolerance within their respective material classes.
2,350 citations
TL;DR: A class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts are described.
Abstract: Existing stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.
1,331 citations
TL;DR: In this article, state-of-the-art polymer electrolytes are discussed with respect to their electrochemical and physical properties for their application in lithium polymer batteries, and the incorporation of inorganic fillers into GPEs to improve their mechanical strength as well as their transport properties and electrochemical properties is discussed.
Abstract: In this review, state-of-the-art polymer electrolytes are discussed with respect to their electrochemical and physical properties for their application in lithium polymer batteries. We divide polymer electrolytes into the two large categories of solid polymer electrolytes and gel polymer electrolytes (GPE). The performance requirements and ion transfer mechanisms of polymer electrolytes are presented at first. Then, solid polymer electrolyte systems, including dry solid polymer electrolytes, polymer-in-salt systems (rubbery electrolytes), and single-ion conducting polymer electrolytes, are described systematically. Solid polymer electrolytes still suffer from poor ionic conductivity, which is lower than 10−5 S cm−1. In order to further improve the ionic conductivity, numerous new types of lithium salt have been studied and inorganic fillers have been incorporated into solid polymer electrolytes. In the section on gel polymer electrolytes, the types of plasticizer and preparation methods of GPEs are summarized. Although the ionic conductivity of GPEs can reach 10−3 S cm−1, their low mechanical strength and poor interfacial properties are obstacles to their practical application. Significant attention is paid to the incorporation of inorganic fillers into GPEs to improve their mechanical strength as well as their transport properties and electrochemical properties.
969 citations
TL;DR: A soft skin-like triboelectric nanogenerator that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively is reported, providing new opportunities for multifunctional power sources and potential applications in soft/wearable electronics.
Abstract: Rapid advancements in stretchable and multifunctional electronics impose the challenge on corresponding power devices that they should have comparable stretchability and functionality We report a soft skin-like triboelectric nanogenerator (STENG) that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively For the first time, ultrahigh stretchability (uniaxial strain, 1160%) and transparency (average transmittance, 962% for visible light) are achieved simultaneously for an energy-harvesting device The soft TENG is capable of outputting alternative electricity with an instantaneous peak power density of 35 mW m −2 and driving wearable electronics (for example, an electronic watch) with energy converted from human motions, whereas the STENG is pressure-sensitive, enabling its application as artificial electronic skin for touch/pressure perception Our work provides new opportunities for multifunctional power sources and potential applications in soft/wearable electronics
852 citations
TL;DR: An ionic touch panel based on a polyacrylamide hydrogel containing lithium chloride salts is demonstrated, which can be operated under more than 1000% areal strain without sacrificing its functionalities.
Abstract: Because human-computer interactions are increasingly important, touch panels may require stretchability and biocompatibility in order to allow integration with the human body. However, most touch panels have been developed based on stiff and brittle electrodes. We demonstrate an ionic touch panel based on a polyacrylamide hydrogel containing lithium chloride salts. The panel is soft and stretchable, so it can sustain a large deformation. The panel can freely transmit light information because the hydrogel is transparent, with 98% transmittance for visible light. A surface-capacitive touch system was adopted to sense a touched position. The panel can be operated under more than 1000% areal strain without sacrificing its functionalities. Epidermal touch panel use on skin was demonstrated by writing words, playing a piano, and playing games.
749 citations