A Mechanically Robust and Versatile Liquid‐Free Ionic Conductive Elastomer

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.

A Puncture‐Resistant and Self‐Healing Conductive Gel for Multifunctional Electronic Skin

“…In an ionic conductive polymer, the polymer acts as both an ion and a plasticizer, so the movement of the polymer backbone has a crucial influence on the conductivity. [28] As shown in Figure 4a, when the temperature increased, elevated temperature leads to greater segmental motion of polymer chains and facilitates the ion transport, [29] which is manifested as a decrease in impedance. For MASTA-PANI 5 , when the temperature increased from 10 to 80 °C, the impedance exhibited a linear decrease behavior (Figure 4b).…”

Skin-like hydrogel devices for wearable sensing, soft robotics and beyond

“…Ionogels keep most properties of ILs without the leakage and exhibit an elastomeric feature. Therefore, ionogels have been applied to construct lithium-ion batteries ( Wu et al., 2017 ), fuel cells ( Zhang et al., 2019 ), solar cells ( Le Bideau et al., 2011 ), electrochemical sensors ( Khodagholy et al., 2012 ), wearable sensors ( Yiming et al., 2021a ), actuators( Chen et al., 2014 ), ionic diodes ( Lee et al., 2018a ), and energy harvesters ( Yiming et al., 2021b ). For example, one IL–based ionogel was prepared by the thiol-ene click chemistry ( Ren et al., 2019 ), in which solution A [poly(ethylene glycol) diacrylate (PEGDA), pentaerythritol tetraacrylate (PETA; cross-linker for covalent network), and anionic benzene tetracarboxylic acid (BTCA; cross-linker for the ionic bond network) dissolved in methanol] was mixed with solution B [mixture containing PIL-BF 4 , triethylamine (TEA; a catalyst for the thiol-ene click reaction), and 1,2-ethanedithiol (ED) dissolved in methanol] at room temperature to form the gel; then the IL [i.e., 1-propyl-3-methylimidazolium fluoborate (IL-BF 4 )] was introduced into the prepared gel at 80°C under vacuum for 24 h. This ionogel exhibits excellent mechanical properties, high resilience after 10,000 fatigue cycles, high ionic conductivity, high transparency, and good nonflammability over a wide temperature range (−75° to 340°C).…”

Ionic conductive gels based on deep eutectic solvents

“…Ionogels are polymer networks infused by ionic liquids [10]. Unlike water, ionic liquids evaporate negligibly even at high temperature [11]. And it shows better anti-corrosion property to metals comparing to regular salt-containing hydrogels [12].…”