A highly compressible hydrogel electrolyte for flexible Zn-MnO2 battery

Interpenetrating Composite Hydrogel Electrolyte with Organic/Inorganic Polar Groups for Stable Zinc Metal Anode

Hydrogel electrolytes have been widely explored in flexible zinc batteries owing to their considerable mechanical strain and water-retaining properties. However, it is difficult to balance the contradiction between the ionic conductivity and the mechanical strength due to the deterioration of structural stability with the addition of electrolyte salts. To address this, we designed a coassembling organic-inorganic hydrogel (P-P/M) based on poly(vinyl alcohol)-polyacrylamide (P-P) interpenetrating matrix decorated with Zn-based montmorillonite (Zn-MMT). The Zn-MMT with overall negative potential can attract and regulate the transport of Zn2+, while the Brønsted/Lewis acid sites with positive polarizations offer anchoring sites for anions, which increases the cation transference number and reduces byproduct formation. Moreover, the formation of hydrogen bonds in the hydrogel can weaken the contact between free water molecules and the zinc cations, which effectively suppresses the corrosion of zinc foil. Consequently, the Zn//Zn cell with P-P/M electrolyte delivers a long cycle life of 2400 h at 0.5 mA cm-2. The good mechanical properties of the P-P/M hydrogel boost its application in flexible pouch cells even under bending and cutting conditions. This study provides an effective approach to designing organic-inorganic hydrogel electrolytes for long-life flexible zinc batteries.

Gels/Hydrogels in Different Devices/Instruments-A Review

Owing to their physical and chemical properties and stimuli-responsive nature, gels and hydrogels play vital roles in diverse application fields. The three-dimensional polymeric network structure of hydrogels is considered an alternative to many materials, such as conductors, ordinary films, constituent components of machines and robots, etc. The most recent applications of gels are in different devices like sensors, actuators, flexible screens, touch panels, flexible storage, solar cells, batteries, and electronic skin. This review article addresses the devices where gels are used, the progress of research, the working mechanisms of hydrogels in those devices, and future prospects. Preparation methods are also important for obtaining a suitable hydrogel. This review discusses different methods of hydrogel preparation from the respective raw materials. Moreover, the mechanism by which gels act as a part of electronic devices is described.

Hydrogel Electrolyte Enabled High-Performance Flexible Aqueous Zinc Ion Energy Storage Systems toward Wearable Electronics

To cater to the swift advance of flexible wearable electronics, there is growing demand for flexible energy storage system (ESS). Aqueous zinc ion energy storage systems (AZIESSs), characterizing safety and low cost, are competitive candidates for flexible energy storage. Hydrogels, as quasi-solid substances, are the appropriate and burgeoning electrolytes that enable high-performance flexible AZIESSs. However, challenges still remain in designing suitable and comprehensive hydrogel electrolyte, which provides flexible AZIESSs with high reversibility and versatility. Hence, the application of hydrogel electrolyte-based AZIESSs in wearable electronics is restricted. A thorough review is required for hydrogel electrolyte design to pave the way for high-performance flexible AZIESSs. This review delves into the engineering of desirable hydrogel electrolytes for flexible AZIESSs from the perspective of electrolyte designers. Detailed descriptions of hydrogel electrolytes in basic characteristics, Zn anode, and cathode stabilization effects as well as their functional properties are provided. Moreover, the application of hydrogel electrolyte-based flexible AZIESSs in wearable electronics is discussed, expecting to accelerate their strides toward lives. Finally, the corresponding challenges and future development trends are also presented, with the hope of inspiring readers.

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Integrated supercapacitor with self-healing, arbitrary deformability and anti-freezing based on gradient interface structure from electrode to electrolyte

Flexible supercapacitors have attracted more and more attention because of their promising applications in wearable electronics, however, it is still important to harmonize their mechanical and electrochemical properties for practical applications. In the present work, a seamless transition between polyaniline (PANI) electrode and NH₄VO₃_FeSO₄ dual redox-mediated gel polymer electrolyte (GPE) is presented through in situ formation of gradient interface structure. Multiple physical interactions make the GPE excellent mechanical and self-healing properties. Meanwhile, double role functions of Fe²⁺ ions greatly relieve the traditional contradiction between mechanical and electrochemical properties of GPE. Moreover, benefiting from the structure and reversible redox reactions of VO^3- and Fe²⁺, the integrated supercapacitor delivers an exceptional specific capacitance of 441.8 mF/cm², a high energy density of 63.1 μWh/cm², remarkable cyclic stability. Simultaneously, the gradient structure from PANI electrode to GPE greatly improves the electrode/electrolyte interface compatibility and ion transport, which endows the supercapacitor with stable electrochemical performance. Furthermore, the supercapacitor well-maintains the specific capacitance even at -20 °C with over 89.19 % retention after 6 cutting/healing cycles. The gradient interface structure design will promote the development of high-performance supercapacitor.

Tailoring the Electrochemical Deposition of Zn by Tuning the Viscosity of the Liquid Electrolyte

The issues during Zn deposition in rechargeable Zn-based batteries greatly hinder cycling stability. In this work, a simple and inexpensive approach to tailor the Zn electrodeposition is proposed by tuning the viscosity of the liquid electrolyte (LE). First, the growth mechanisms of Zn deposition under different electrolyte properties are investigated by numerical simulation, from which the bottom deposition tends to fuse with each other when there are more deposition sites, and the mass-transfer coefficient is lower, thus achieving uniform deposition. Besides, the whole process of Zn deposition in charging-discharging cycling is in situ observed by an optical microscope. It is found that the cause of the poor stability in the LE is due to the uneven Zn deposition, resulting in weak bonding between the deposition and the electrode surface, which is also the reason for the formation of dead Zn. In contrast, when an appropriate amount of the polymer is added to the LE to increase the viscosity, an appropriate overpotential can be created, generating more deposition sites. In addition, the viscosity reduces the mass-transfer coefficient, making the distance from the ion to the deposition sites the main controlling factor. The Zn ions are more inclined to move in the direction of electric field lines, which results in a uniform and dense deposition layer. Furthermore, the effectiveness of this method is demonstrated in a Zn-LiFePO₄ battery, from which the battery with the modified electrolyte condition still works properly even in the Zn utilization of 100% and shows a capacity retention rate (35%) of nearly twice that in the original LE condition (18%) after 10 cycles. This work provides a theoretical basis for Zn deposition and provides ideas for the future development of high-performance Zn-based batteries.

Bio-Inspired Instant Underwater Adhesive Hydrogel Sensors

Underwater adhesion plays an essential role in soft electronics for the underwater interface. Although hydrogel-based electronics are of great interest, because of their versatility, water molecules prevent hydrogels from adhering to substrates, thus bottlenecking further applications. Herein, inspired by the barnacle proteins, MXene/PHMP hydrogels with strong repeatable underwater adhesion are developed through the random copolymerization of 2-phenoxyethyl acrylate, 2-methoxyethyl acrylate, and N-(2-hydroxyethyl) acrylamide with the presence of MXene nanosheets. The hydrogels are mechanically tough (elastic modulus of 32 kPa, fracture stress of 0.11 MPa), and 2-phenoxyethyl acrylate (PEA) with aromatic groups endows the hydrogel with nonswelling property and prevents water molecules from invading the adhesive interface, rendering the hydrogels an outstanding adhesive behavior toward various substrates (including glass, iron, polyethylene terephthalate (PET), porcine). Besides, dynamic physical interactions allow for instant and repeatable underwater adhesion. Furthermore, the MXene/PHMP hydrogels exhibit a high conductivity (0.016 S/m), fast responsiveness, and superior sensitivity as a strain sensor (gauge factor = 7.17 at 200%-500% strain) and pressure sensor (0.63 kPa^-1 at 0-70 kPa). The underwater applications of bionic hydrogel-based sensors have been demonstrated, such as human motion, pressure sensing, and holding objects. It is anticipated that the instant and repeatable underwater adhesive hydrogel-based sensors extend the underwater applications of hydrogel electronics.

A flexible self-healing Zn3V2O7(OH)2·2H2O-based Zn-ion battery under continuous folding and twisting

Engineering flexible and self-healing batteries is significant for wearable electronics. Here, we develop a flexible self-healing Zn-ion battery with a three-dimensional Zn3V2O7(OH)2·2H2O cathode working with polyvinyl alcohol and Zn2+/Mn2+ ions-based...