Conductive Hydrogel‐Based Electrodes and Electrolytes for Stretchable and Self‐Healable Supercapacitors

Abstract

Stretchable self‐healing supercapacitors (SCs) can operate under extreme deformation and restore their initial properties after damage with considerably improved durability and reliability, expanding their opportunities in numerous applications, including smart wearable electronics, bioinspired devices, human–machine interactions, etc. It is challenging, however, to achieve mechanical stretchability and self‐healability in energy storage technologies, wherein the key issue lies in the exploitation of ideal electrode and electrolyte materials with exceptional mechanical stretchability and self‐healing ability besides conductivity. Conductive hydrogels (CHs) possess unique hierarchical porous structure, high electrical/ionic conductivity, broadly tunable physical and chemical properties through molecular design and structure regulation, holding tremendous promise for stretchable self‐healing SCs. Hence, this review is innovatively constructed with a focus on stretchable and self‐healing CH based electrodes and electrolytes for SCs. First, the common synthetic approaches of CHs are introduced; then the stretching and self‐healing strategies involved in CHs are systematically elaborated; followed by an explanation of the conductive mechanism of CHs; then focusing on CH‐based electrodes and electrolytes for stretchable self‐healing SCs; subsequently, application of stretchable and self‐healing SCs in wearable electronics are discussed; finally, a conclusion is drawn along with views on the challenges and future research directions regarding the field of CHs for SCs.

Recent Progress on Self‐Healable Conducting Polymers

“…[128][129][130] PEDOT-based hydrogels can be obtained by gelation of aqueous suspensions of the conducting polymer with nonvolatile compounds, such as agarose, lignin, alginates, guar gums or cellulose. These hydrogels typically show low Young's modulus, high electrical conductivity, excellent electrochemical properties [131][132][133] and self-healing properties, due to the presence of non-covalent and dynamic covalent bonds. [134][135][136] A nanocomposite hydrogel with porous structure and high swelling ability (≈700% weight increase in water) was obtained from a mixture of PEDOT:PSS and agarose, which acted as the backbone.…”

A durable high-energy implantable energy storage system with binder-free electrodes useable in body fluids

“…The skin-patchable method requires a wire connected to the implantable medical device from the outside of the body to supply power. 58–60 At this time, biological toxicity such as inflammatory reactions or rejection of the skin may occur due to the conductive wire penetrating the skin. In view of the problem of skin patchable energy harvesting devices, using a wireless charging system without the risk of secondary infection by wires is a progressive and innovative energy harvesting method for supplying power to IEMDs.…”

Ultra‐robust stretchable electrode for e‐skin: In situ assembly using a nanofiber scaffold and liquid metal to mimic water‐to‐net interaction

“…Robust and stable soft conductors are highly desirable for precise electric signal transmission as well as long-term dynamic services in smart wearable electronics, such as epidermal electronics, [1][2][3][4] implantable sensors, 5,6 optoelectronics devices, 7,8 neuroprosthetics, 9 energy-storage devices, 10 and soft robotics. 11 Furthermore, in epidermal electronic systems, stretchable electrodes are of paramount significance for the stable collection of human electrophysiological signals, for example, electrocardiography (ECG), 12 electromyography, 13 and electroencephalogram.…”