A bright future of hydrogels in flexible batteries and Supercapacitors storage systems: A review

Abstract

Summary The next generation of IoT, IoMT, and wearable bioelectronics demands the development of a novel form of thin‐film and flexible energy storage devices that offer high energy and power densities, mechanical reliability, and biocompatibility. Hydrogels are a class of materials that can be engineered with a range of desired properties, including stretchability, ionic conductivity, biocompatibility, adhesiveness, and mechanical match with organs, as they can be designed with Young's modulus in the range of the human skin. This review covers different types of hydrogels, including biopolymer hydrogels, carbon‐based hydrogels, and self‐healing hydrogels, and presents their use in the components of supercapacitors and batteries such as electrolyte; electrode, binder, separating membrane, and current collector. We also explain how these hydrogels contribute to improved properties of the energy storage devices and include cases in which the hydrogel is used for several functions in the same device. The contribution of hydrogels in the development of flexible energy storage devices and their impact on electrochemical performance are also discussed.

Flexible Polymer Hydrogels for Wearable Energy Storage Applications

“…The redox reactions on the interface of electrodes and the electrolyte continue to take place until no more substances are required for the reaction and the battery is discharged completely. [59] The porosity of polymer hydrogels is a key advantage in improving the kinetics of the redox reactions at the interface of electrodes and the electrolyte. [59] Moreover, the overheating issue of metal-ion batteries, which is a well-known safety concern of these rechargeable batteries, can be addressed by using polymer hydrogel electrolytes.…”

“…[59] The porosity of polymer hydrogels is a key advantage in improving the kinetics of the redox reactions at the interface of electrodes and the electrolyte. [59] Moreover, the overheating issue of metal-ion batteries, which is a well-known safety concern of these rechargeable batteries, can be addressed by using polymer hydrogel electrolytes. The overheating in metal-ion batteries usually occurs as a result of overcharging, abuse, internal short circuit, manufacturing defects, physical damage, or other failure mechanisms.…”

“…[ 58 ] However, high electrical/thermal conductivity can be introduced to the structure of polymer hydrogels by using conductive polymers as building units or by incorporating conductive nanomaterials in the structure of polymer hydrogels. [ 59 ]…”

“…The flexibility of polymer hydrogels is a key factor in wearable electronic and thermal energy storage applications. [ 7b,12,59 ] Structural parameters such as the chemical nature of the solid backbone (both polymer and cross‐linker), the state of crystallinity, and the degree of cross‐linking/polymerization affect the flexibility of polymer hydrogels. [ 133 ] Chemically cross‐linked hydrogels, such as copolymer hydrogels, [ 88 ] and hydrogels with chemical cross‐links between polymeric chains [ 134 ] can present high mechanical stability for wearable energy storage applications.…”

Triple crosslinking conductive hydrogels with digitally printable and outstanding mechanical stability for high-resolution conformable bioelectronics

“…Hydrogels, as soft materials with three-dimensional (3D) structures, are typically composed of crosslinked polymer networks that present the unique characteristics of viscoelasticity, and hydrophilicity. [1][2][3] They are rapidly finding their way into bioelectronics applications for skin-mounted sensors such as electromyography (EMG), electrocardiography (ECG), electroencephalography (EEG), or wearable mechanosensing. [4][5][6] Among functional bio-inspired materials, sodium alginate (SA)-acrylamide (AAm)-based hydrogels have been employed in a huge range of bioengineering applications owing to their inherent nature of SA and AAm.…”