Tough, Anti‐Fatigue, Self‐Adhesive, and Anti‐Freezing Hydrogel Electrolytes for Dendrite‐Free Flexible Zinc Ion Batteries and Strain Sensors

Hydrogel‐based flexible solid‐state supercapacitors (SSCs) hold great promise for wearable electronics, yet significant challenges persist in simultaneously achieving excellent mechanical properties, high ionic conductivity, outstanding electrochemical properties, and wide operating temperature ranges. Here, this study presents a straightforward method for synthesizing dual crosslinked polyvinyl alcohol‐polyimide (PVA‐PI) organohydrogels via a simple one‐pot synthesis followed by a freezing‐thawing process. The controlled dual crosslinked networks with significanonetly different crosslinking densities and robust intermolecular hydrogen bonding interactions facilitated by the macromolecular crosslinker of PI, endow the organohydrogels with both high mechanical properties and ionic conductivity. Furthermore, SSCs based on PVA‐PI organohydrogels are fabricated, which can exhibit outstanding electrochemical performance at temperatures ranging from −40 to 80 °C. Specifically, the energy density reaches 16.7 µWh cm−2 even at −40 °C under a power density of 410.0 µW cm−2. These SSCs also show excellent performance stability under various deformations, such as bending and compression, alongside exceptional long‐term cycling stability (over 10 000 cycles) with high capacitance retention from −40 to 50 °C. The synthesis strategy, along with a robust mechanism for enhancing mechanical properties of hydrogels, demonstrated in this study offers insights for the development of strong hydrogels/organohydrogels with broad temperature adaptability for soft electronic applications.

Mechanically Strong and Tough Organohydrogels for Wide Temperature Tolerant, Flexible Solid‐State Supercapacitors

Zhou,

Griffin,

Qian

et al. 2024

Hierarchically‐Structured and Mechanically‐Robust Hydrogel Electrolytes for Flexible Zinc‐Iodine Batteries

Tan,

Liao,

et al. 2024

Hydrogel electrolytes have been widely explored in aqueous zinc‐iodine batteries (AZIBs), in light of their intrinsic strong water‐retention capability and superior flexibility of hydrogel network. However, hydrogel‐based AZIBs are still facing challenges due to the inferior ionic conductivity, dendrite formation, and corresponding fatigue‐induced damage. Herein, a hydrogel electrolyte is designed and engineered with preferentially aligned porous structures, where Zn2+ can promptly transport along the pores. AZIBs fabricated from the hydrogel electrolyte exhibited distinct cycling stability over 1,000 h (500 cycles) at 0.5 mA cm−2. Moreover, in light of the substantially improved mechanical robustness, the hydrogel electrolyte network remained intact over a 27,000‐cycle charging/discharging test at 5 A g−1, with a slight change in capacity, surpassing most previously reported AZIBs. Such kind of hydrogel electrolyte‐based AZIBs can be further explored as the flexible power system for wearable devices, enabling significantly accelerated wound healing through electrical stimulation over the epidermal wounds. This work sheds light on hydrogel electrolytes design for long‐life aqueous zinc‐based batteries, with great potential as power systems for wearable and implantable devices.

Cellulose‐Based Dual‐Network Conductive Hydrogel with Exceptional Adhesion

Shi,

Huo,

Yang

et al. 2024

Cellulose consists of a natural, rigid polymer that is widely used to improve the mechanical and water‐holding properties of hydrogels. However, its abundant hydroxyl groups make it highly absorbent to free water, leading to swelling behavior. This increased free water content will also decrease mechanical and adhesive performance. In this study, cellulose is successfully hydrophobically modified to reduce its absorption of free water. Gelatin is then cross‐linked with cellulose through a Schiff‐base reaction, resulting in increased bound water content. This significantly enhances resistance to swelling and permeability, and improves the freeze–thaw stability of the hydrogel. Due to its internal hydrophobicity, water molecules can quickly penetrate into the interior, reducing their residence time on the hydrogel surface. This allows the hydrogel to maintain high adhesion in natural environments, achieving an adhesion strength of up to 3.0 MPa on wood and bamboo‐based materials. The hydrogel can retain its adhesive properties even after prolonged exposure to a humid environment. Additionally, Na+ ions enhance the electrical conductivity and sensitivity of the hydrogel (gauge factor (GF) = 1.51), demonstrating its potential applications in flexible sensing.