Spider-Silk-Inspired Tough, Self-Healing, and Melt-Spinnable Ionogels

Empowering soft conductive elastomers with self-reinforcement and remarkable resilience via phase-locking ions

Endowing soft and long-range stretchable elastomers with exceptional strength, resilience, and ion-conductivity is crucial for high-performance flexible sensors. However, achieving this entails significant challenges due to intrinsic yet mutually exclusive structural factors. In this work, a series of self-reinforcing ion-conductive elastomers (SRICEs) is thus designed to meet the advanced but challenging requirements. The SRICEs behave like a soft/hard dual-phase separated micro-structure, which is optimized through a straightforward preferential assembly strategy (PAS) to ensure that the subsequently introduced ions are locked in the soft phase. Meanwhile, the interaction between ions and soft segments is meticulously tailored to achieve self-reinforcement through strain-induced crystallization. Consequently, an outstanding ultimate strength of approximately ∼51.0 MPa and an exceptional instant resilient efficiency of ∼92.9% are attained. To the best knowledge of the authors, these are the record-high values achieved simultaneously in one ion-conductive elastomer. Furthermore, the resultant toughness of ∼202.4 MJ m-3 is significantly higher, while the modulus of ∼5.0 MPa is lower than that of most reported robust ion-conductive elastomers. This unique combination of properties makes it suitable for advanced flexible applications, e.g. grid-free position recognition sensors. This work provides guidance for designing soft yet robust ion-conductive elastomers and optimizing their mechanical properties.

A Recyclable Ionogel with High Mechanical Robustness Based on Covalent Adaptable Networks

Ionogels are an emerging class of soft materials for flexible electronics, with high ionic conductivity, low volatility, and mechanical stretchability. Recyclable ionogels are recently developed to address the sustainability crisis of current electronics, through the introduction of non-covalent bonds. However, this strategy sacrifices mechanical robustness and chemical stability, severely diminishing the potential for practical application. Here, covalent adaptable networks (CANs) are incorporated into ionogels, where dynamic covalent crosslinks endow high strength (11.3 MPa tensile strength), stretchability (2396% elongation at break), elasticity (energy loss coefficient of 0.055 at 100% strain), and durability (5000 cycles of 150% strain). The reversible nature of CANs allows the ionogel to be closed-loop recyclable for up to ten times. Additionally, the ionogel is toughened by physical crosslinks between conducting ions and polymer networks, breaking the common dilemma in enhancing mechanical properties and electrical conductivity. The ionogel demonstrates robust strain sensing performance under harsh mechanical treatments and is applied for reconfigurable multimodal sensing based on its recyclability. This study provides insights into improving the mechanical and electrical properties of ionogels toward functionally reliable and environmentally sustainable bioelectronics.

Sea Cucumber-Inspired Polyurethane Demonstrating Record-Breaking Mechanical Properties in Room-Temperature Self-Healing Ionogels

Practical applications of existing self-healing ionogels are often hindered by the trade-off between their mechanical robustness, ionic conductivity, and temperature requirements for their self-healing ability. Herein, this challenge is addressed by drawing inspiration from sea cucumber. A polyurethane containing multiple hydrogen-bond donors and acceptors is synthesized and used to fabricate room-temperature self-healing ionogels with excellent mechanical properties, high ionic conductivity, puncture resistance, and impact resistance. The hard segments of polyurethane, driven by multiple hydrogen bonds, coalesce into hard phase regions, which can efficiently dissipate energy through the reversible disruption and reformation of multiple hydrogen bonds. Consequently, the resulting ionogels exhibit record-high tensile strength and toughness compared to other room-temperature self-healing ionogels. Furthermore, the inherent reversibility of multiple hydrogen bonds within the hard phase regions allows the ionogels to spontaneously and efficiently self-heal damaged mechanical properties and ionic conductivity multiple times at room temperature. To underscore their application potential, these ionogels are employed as electrolytes in the fabrication of electrochromic devices, which exhibit excellent and stable electrochromic performance, repeatable healing ability, and satisfactory impact resistance. This study presents a novel strategy for the fabrication of ionogels with exceptional mechanical properties and room-temperature self-healing capability.

Self-Healing Ionogel-Enabled Self-Healing and Wide-Temperature Flexible Zinc-Air Batteries with Ultra-Long Cycling Lives

Hydrogel-based zinc-air batteries (ZABs) are promising flexible rechargeable batteries. However, the practical application of hydrogel-based ZABs is limited by their short service life, narrow operating temperature range, and repair difficulty. Herein, a self-healing ionogel is synthesized by the photopolymerization of acrylamide and poly(ethylene glycol) monomethyl ether acrylate in 1-ethyl-3-methylimidazolium dicyanamide with zinc acetate dihydrate and first used as an electrolyte to fabricate self-healing ZABs. The obtained self-healing ionogel has a wide operating temperature range, good environmental and electrochemical stability, high ionic conductivity, satisfactory mechanical strength, repeatable and efficient self-healing properties enabled by the reversibility of hydrogen bonding, and the ability to inhibit the production of dendrites and by-products. Notably, the self-healing ionogel has the highest ionic conductivity and toughness compared to other reported self-healing ionogels. The prepared self-healing ionogel is used to assemble self-healing flexible ZABs with a wide operating temperature range. These ZABs have ultra-long cycling lives and excellent stability under harsh conditions. After being damaged, the ZABs can repeatedly self-heal to recover their battery performance, providing a long-lasting and reliable power supply for wearable devices. This work opens new opportunities for the development of electrolytes for ZABs.

Continuous Melt Spinning of Adaptable Covalently Cross-Linked Self-Healing Ionogel Fibers for Multi-Functional Ionotronics

Stretchable conductive fibers play key roles in electronic textiles, which have substantial improvements in terms of flexibility, breathability, and comfort. Compared to most existing electron-conductive fibers, ion-conductive fibers are usually soft, stretchable, and transparent, leading to increasing attention. However, the integration of desirable functions including high transparency, stretchability, conductivity, solvent resistance, self-healing ability, processability, and recyclability remains a challenge to be addressed. Herein, a new molecular strategy based on dynamic covalent cross-linking networks is developed to enable continuous melt spinning of the ionogel fiber with the aforementioned properties. As a proof of concept, adaptable covalently cross-linked ionogel fibers based on dimethylglyoximeurethane (DOU) groups (DOU-IG fiber) are prepared. The resultant DOU-IG fiber exhibited high transparency (>93%), tensile strength (0.76 MPa), stretchability (784%), and solvent resistance. Owing to the dynamic of DOU groups, the DOU-IG fiber shows high healing performance using near-infrared light. Taking advantage of DOU-IG fibers, multifunctional ionotronics with the integration of several desirable functionalities including sensor, triboelectric nanogenerator, and electroluminescent display are fabricated and used for motion monitoring, energy harvesting, and human-machine interaction. It is believed that these DOU-IG fibers are promising for fabricating the next generation of electronic textiles and other wearable electronics.