Insights on Flexible Zinc-Ion Batteries from Lab Research to Commercialization

Bio-derived chitosan additive enables anion anchoring and Zn(002) deposition for high-performance Zn anodes

Bio-derived quaternary-ammonium-functionalized chitosan (HACC) was investigated as an electrolyte additive for Zn anode stabilization, for the first time to the best of our knowledge. Due to its special structure, including abundant hydrophilic functional groups and positive charge, HACC can inhibit the hydrogen evolution reaction, promote Zn2+ transport, and induce the deposition of Zn(002). Consequently, the electrolyte with HACC exhibits improved electrochemical performance.

3D Printed Flexible Zinc-Ion Battery for Real-Time Health Monitoring Devices

The growing need for multifunctional wearable electronics for mobile applications has triggered the demand for flexible and reliable energy storage devices. 3D printing technology has emerged as a promising and attractive method for manufacturing these devices. This study presents the design and fabrication of a flexible quasi-solid-state Zn-ion battery using the direct-writing 3D printing technique. A conductive silver paste with high conductivity was printed onto a PET substrate to serve as the current collector. The cathode was fabricated from carbon-coated MnO2 nanorods produced using hydrothermal methods, while the anode consisted of commercial zinc powder. The cathode and anode slurries exhibiting excellent viscoelasticity were 3D printed on the current collector. To complete the flexible quasi-solid-state zinc-ion battery, a PVA gel electrolyte was printed onto the PET substrate. This battery delivered an initial capacity of 267.3 mAh g-1 and maintained a capacity of 189.7 mAh g-1 after 500 cycles at a current density of 0.2 A g-1. Furthermore, the 3D printed battery successfully powered a portable human heart rate sensor, showcasing the potential of 3D printing technology as an environmentally friendly, cost-effective, and scalable solution for wearable energy storage devices.

Unidirectional Ion Sieve Enabling High-Flux and Reversible Zinc Anodes

The longevity of aqueous batteries after scaling up is largely restricted by metal anodes (Zn, Al, and Mg). Parasitic reactions and uncontrolled dendrites dominate failure modes, especially at high current densities. To fully improve its reversibility, tailored surface chemistry and well-designed ion transport channels are simultaneously demanded. Here, inspired by the reticulated structure of the sea urchin shell, an aligned porous coating assembled from graphene oxide and sodium alginate is anchored on zinc anodes, termed a unidirectional ion sieve. As revealed by multiscale modeling and tests, this biomimetic layer produces a high surface area, creating low-tortuosity channels that greatly enhance transport kinetics and uniform distribution of ions. The introduction of an ion-conductive natural polymer enables a well-tuned hydration structure and ion selectivity, greatly alleviating aqueous side reactions. With the structural-functional integrity design, the decorated symmetrical cell presents reversible cycling for 1600 h, with a greatly reduced nucleation potential of 21 mV and high Coulombic efficiency. Aided by the Distribution of Relaxation Time tool, different electrochemical processes are deconvoluted to understand respective mechanisms, thereby providing a referable strategy for product scaling. In the end, a 7Ah Zn||VO2 pouch cell demonstrates stable cycling for over 500 cycles at 1 A·g-1, with the capacity retention over 90%.

The Design of Chemically Self-Charging Aqueous Batteries

The chemically self-charging aqueous batteries are regarded as potential candidates for off-grid energy storage devices due to their environmental independence and simple construction. Although tremendous research efforts have been recently made to design chemically self-charging aqueous batteries, a comprehensive review about them is still absent. This review describes the design principles of chemically self-charging aqueous batteries and their self-charging mechanism. The advances in their cathode materials mainly include transition-metal oxides or sulfides, Prussian blue analogues, and organic compounds. Subsequently, the strategies of enhancing chemically self-charging kinetics are highlighted, including the design of materials, selection of oxidants, and the introduction of catalysts. In addition, various applications of chemically self-charging batteries are also discussed in wearable electronic devices, low temperatures, and all-pH scenarios. In the final section, the challenges and future perspectives are presented for designing high-performance chemically self-charging aqueous batteries. It will shed light on the R&D of chemically self-charging aqueous batteries.

Progress in Developing Polymer Electrolytes for Advanced Zn Batteries

Aqueous Zn batteries (ZBs) are promising candidates for large-scale energy storage, considering their intrinsically safe features, competitive cost, and environmental friendliness. However, the fascinating metallic Zn anode is subjected to severe issues, such as dendrite growth, hydrogen evolution, and corrosion. Additionally, traditional aqueous electrolytes' narrow electrochemical windows and temperature ranges further hinder the practical application of ZBs. Solid-state electrolytes, including solid polymer electrolytes and hydrogel electrolytes, offer distinct paths to mitigate these issues and simultaneously endow the ZBs with customizable functions such as flexibility, self-healing, anti-freezing, and regulated Zn deposition, etc, due to their tuneable structures. This review summarizes the latest progress in developing polymer electrolytes for ZBs, focusing on modifying the ionic conductivity, interfacial compatibility, Zn anode stability, electrochemical stability windows, and improving the environmental adaptability under harsh conditions. Although some achievements are obtained, many critical challenges still exist, and it is hoped to offer guidance for future research, accelerating the development and application of polymer electrolytes.

Multiple Charge Carriers Manipulation Toward Semiconductive Ceramic Nanocomposites for Corrosion-Resistant Electromagnetic Wave Absorption

The modulation of transport properties in ceramic-based semiconductors can be used to optimize the electromagnetic response mechanism and performance. A semiconductor ceramic foam interlayer wall (SCFW) is designed by a physical vapor deposition method. The interlayer structural SCFW is composed of semiconductor-insulator-semiconductor layers, incorporating a composite system of SiC, Al4.8Si1.2O9.6, and Al2O3. Moreover, the hierarchical network structure of the foam interlayer wall is controlled by the pyrolysis-deposition kinetic process. Electrons and holes are transported through the heterojunctions between SiC and Al4.8Si1.2O9.6, achieving effective charge relaxation. The Al2O3 matrix provides lightweight properties (density of 0.967 g cm-3), while the hierarchical network structure determines the excellent electromagnetic wave (EMW) absorption performance of the SCFW, with an effective bandwidth up to 14.8 GHz under electromagnetic response (minimum reflection loss RLmin = -50.6 dB). the SCFW has been proven to exhibit corrosion resistance and thermal insulation properties, with a thermal conductivity up to 0.025 W m-1 K-1. This study provides valuable insights into the structural design and dielectric property optimization of ceramic-based semiconductor nanocomposites, which leads to strong polarization loss, opening new avenues for the application of EMW absorbers, and the EMW absorption mechanism of ceramics.

Stacking Pressure Modulated Deposition and Dissolution of Zinc Anode

Aqueous zinc-ion batteries (ZIBs) are emerging as a promising candidate for large-scale energy storage, offering enhanced safety and low costs. Nevertheless, the disordered growth of zinc dendrites has resulted in low coulombic efficiency and the dangers of short circuits, limiting the commercialization of ZIBs. In this study, a planar growth of zinc along the (002) direction is achieved by regulating the moderate initial stacking pressure during cell cycling and facilitating a larger zinc deposition particle size. The pivotal role of stacking pressure on the zinc nucleation, growth, and dissolution processes is elucidated with in situ pressure X-ray diffraction (XRD), time of flight secondary ion mass spectrometry (TOF-SIMs), and scanning electronic microscopy (SEM). By adjusting the staking pressure from 20 to 300 kPa, the battery cycle time increased 5 times. This work highlights the opportunity to precisely manipulate metal deposition/dissolution with stacking pressure for long-cycle life batteries.

High-Performance Fatigue-Resistant Dual- Polyrotaxane Hydrogel Electrolytes for Flexible Aqueous Zinc-Ion Batteries

This study presents a novel anti-fatigue hydrogel electrolyte with a slip-ring structure for next-generation flexible wearable energy storage systems. Conventional quasi-solid aqueous zinc-ion batteries (ZIBs) with hydrogel electrolytes often suffer from mechanical degradation under repeated stress, limiting practical use. To overcome this, a dual-Polyrotaxane (DPR)-polyacrylic acid (PAA) hydrogel with a unique slip-ring architecture is synthesized, that enhances mechanical durability, self-healing, and adhesion. The interwoven DPR and PAA networks distribute stress evenly, ensuring high ionic conductivity while preventing zinc dendrites and parasitic reactions for uniform zinc deposition during cycling.When applied to a flexible quasi-solid-state Zn-MnO₂ battery, this hydrogel achieves a specific capacity of 295 mAh g⁻¹ MnO₂ at 0.5C, retains 147 mAh g⁻¹ at 5C, and shows 81.52% capacity retention after 1000 cycles. The battery also demonstrates exceptional stability, with zinc pairs lasting over 1750 h at 5 mA cm⁻2. Furthermore, it maintains reliable operation under mechanical stresses like pressing, folding, and twisting, making it ideal for wearable applications. This work advances hydrogel electrolyte design, offering a durable, high-performance solution for flexible energy storage systems.

Phase Transition Driven Zn-Ion Battery With Laser-Processed V2C/V2O5 Electrodes for Wearable Temperature Monitoring

Flexible power supply devices present significant potential for wearable bioelectronics within the Internet of Things. Aqueous zinc-ion batteries have emerged as a viable and safe alternative for power supply in flexible electronics. Nevertheless, typical battery behaviors are generally detrimental with unfavorable phase transition of electrodes, which invariably lead to rapid performance degradation. Here, extraordinary capacity enhancement of 150% is presented, sustained over 60 000 cycles, attained using vanadium carbide MXene (V2C)/vanadium pentoxide (V2O5) heterostructure as cathode. The unique cathode material is created through the rational engineering of MAX (V2AlC), employing a single-step laser writing process. The ultrastable Zn ion battery stands in stark contrast to all previously reported counterparts, which typically exhibit capacity degradation within a few hundred/thousand cycles. The primary mechanisms driving this enhancement include the delamination of V2C MXene and an unexpected favorable phase transition during cycling. Additionally, a wearable power supply is constructed using a series configuration and is integrated with a commercial temperature sensor for wireless, real-time body temperature monitoring. This study highlights the critical role of electrode design for advanced wearable bioelectronics.

Ultralight flexible 3D nickel micromesh decorated with NiCoP for high stability alkaline zinc batteries

Rechargeable alkaline zinc batteries are emerging as promising candidates for next-generation energy storage systems, owing to their affordability, eco-friendliness and high energy density. However, their widespread application is hindered by stability challenges, particularly in alkaline environments, due to cathode corrosion and deformation, as well as dendrite formation and unwanted side reactions at the Zn anode. To address these issues, we successfully developed a 3D nickel micromesh-supported NiCoP (3D NM@NiCoP) electrode. This unique structure integrates an ultrathin (4 μm), flexible and conductive nickel micromesh (NM) with a high-capacity bimetallic phosphide, NiCoP, fabricated through a combination of photolithography, chemical etching, and electro-deposition processes. The resulting electrode achieves an impressive capacitance of 26.1 μA h cm-2 at a current density of 4 mA cm-2 in a 2 M KOH electrolyte. When assembled with a superhydrophilic Zn@Al2O3@TiO2 anode, the device (3D NM@NiCoP//Zn@Al2O3@TiO2) exhibits outstanding stability, retaining 91% of its initial capacity after 11 000 cycles at 3 mA cm-2 in a 2 M KOH electrolyte. This novel configuration, with potential for scalable fabrication, provides valuable insights into the development of high-capacity and durable electrodes for alkaline zinc batteries.

The Effect of Sodium Dodecyl Sulphate Additives on the Electrochemical Performance of Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries are considered one of the most promising energy storage devices due to their high safety, low cost, and ease of fabrication. However, the growth of anode dendrites and continuous side reactions during cycling limit the practical application of zinc ion batteries. In this paper, sodium dodecyl sulfate (SDS) was used as an aqueous electrolyte additive to improve the surface deposition of Zn2+. The experimental results show that the SDS electrolyte additive forms a protective layer on the anode surface through electrostatic action and inhibits the growth of dendritic protruding dendrites by increasing the zinc deposition overpotential, as well as by limiting the two-dimensional diffusion of Zn2+ on the negative electrode surface of the aqueous zinc ion battery. As a result, adding SDS improves the discharge specific capacity of NVP/Zn batteries at high voltages and results in improved capacity retention. The cycling stability of NVP/Zn batteries was greatly enhanced by using a battery containing 1% SDS that still had a discharge specific capacity of 71 mAh/g after 100 cycles at a charging current density of 1 C, with a capacity retention rate of 89%. This work provides a simple and feasible solution to the anode problem of aqueous zinc ion batteries.

Rational design of epoxy functionalized ionic liquids electrolyte additive for hydrogen-free and dendrite-free aqueous zinc batteries

Despite the high safety and low cost associated with aqueous Zn-ion batteries (ZIBs), uncontrolled Zn dendrite growth and parasitic reactions induced by water significantly diminish their stability. Herein, a new epoxy functionalized ionic liquid, 4-methyl-4-glycidylmorpholin bis[(trifluoromethyl)sulfonyl]imide (MGM[TFSI]), has been developed to mitigate water reactivity for stable ZIBs. It was found that the MGM+ cation disrupts the hydrogen bond network of water, hindering its adsorption on Zn anodes, thereby suppressing water decomposition and enhancing anode stability. Additionally, preferential adsorption of MGM+ cations on the Zn anode surface mitigates tip effects, suppresses dendrite growth, and promotes the formation of a ZnF2 solid electrolyte interphase layer, effectively isolating the anode from the bulk electrolyte. As a result, benefiting from the well-designed MGM+-based electrolyte, Zn//Zn cells achieve significantly enhanced cycling stability, lasting over 2000 h at 1 mA cm-2 with 1 mAh cm-2. Furthermore, Zn//MnO2 full cells deliver remarkable stability, retaining approximately 89 % of their initial capacity after 3000 cycles at 5 A/g. This work proposes that the MGM[TFSI] additive can effectively regulate the interfacial chemistry of the Zn anode, providing an opportunity to design advanced electrolytes for highly reversible ZIBs and beyond.

Advancing Anode Performance in Aqueous Zinc-Ion Batteries: A Review of Metal-Organic Framework-Based Strategies

Aqueous zinc-ion batteries (AZIBs) are garnering substantial research interest in electric vehicles, energy storage systems, and portable electronics, primarily for the reason that the inexpensive cost, high theoretical specific capacity, and environmental sustainability of zinc metal anodes, which are an essential component to their design. Nonetheless, the progress of AZIBs is hindered by significant obstacles, such as the occurrence of anodic side reactions (SR) and the formation of zinc dendrites. Metal-organic framework (MOF)-based materials are being explored as promising alternatives owing to homogeneous porous structure and large specific surface areas. There has been a rare overview and discussion on strategies for protecting anodes using MOF-based materials. This review specifically aims to investigate cutting-edge strategies for the design of highly stable MOF-based anodes in AZIBs. Firstly, the mechanisms of dendrites and SR are summarized. Secondly, the recent advances in MOF-based anodic protection including those of pristine MOFs, MOF composites, and MOF derivatives are reviewed. Furthermore, the strategies involving MOF-based materials for zinc anode stabilization are presented, including the engineering of surface coatings, three-dimensional zinc structures, artificial solid electrolyte interfaces, separators, and electrolytes. Finally, the ongoing challenges and prospective directions for further enhancement of MOF-based anodic protection technologies in AZIBs are highlighted.

Interfacial modulation of nicotinamide additive enables 9700 h Zn metal batteries

Aqueous zinc-ion batteries (AZIBs) have recently been paid great attention due to their robust safety features, high theoretical capacity, and eco-friendliness, yet their practical application is hindered by the serious dendrite formation and side reactions of Zn metal anode during cycling. Herein, a low-cost small molecule, nicotinamide (NIC), is proposed as an electrolyte additive to effectively regulate the Zn interface, achieving a highly reversible and stable zinc anode without dendrites. NIC molecules not only modify the Zn2+ solvation structure but also preferentially adsorb on the Zn surface than solvated H2O to protect the Zn anode and provide numerous nucleation sites for Zn2+ to homogenize Zn deposition. Consequently, the addition of 1 wt% NIC enables Zn||Zn symmetric cells an ultra-long lifespan of over 9700 h at 1 mA cm-2, which expands nearly 808 times compared to that without NIC. The advantages of NIC additives are further demonstrated in NaVO||Zn full cells, which exhibit exceptional capacity retention of 90.3 % after 1000 cycles with a high Coulombic efficiency of 99.9 % at 1 A/g, while the cell operates for only 42 cycles without NIC additive. This strategy presents a promising approach to solving the anode problem, fostering advancements in practical AZIBs.

Iodine/Chlorine Multi-Electron Conversion Realizes High Energy Density Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are promising energy storage devices; however, the conventional single-electron reaction potential and energy density of iodine cathode are inadequate for practical applications. Activation of high-valence iodine cathode reactions has evoked a compelling direction to developing high-voltage zinc-iodine batteries. Herein, ethylene glycol (EG) is proposed as a co-solvent in a water-in-deep eutectic solvent (WiDES) electrolyte, enabling significant utilization of two-electron-transfer I+/I0/I- reactions and facilitating an additional reversibility of Cl0/Cl- redox reaction. Spectroscopic characterizations and calculations analyses reveal that EG integrates into the Zn2+ solvation structure as a hydrogen-bond donor, competitively binding O atoms in H2O, which triggers a transition from water-rich to water-poor clusters of Zn2+, effectively disrupting the H2O hydrogen-bond network. Consequently, the aqueous Zn-I2 cell achieves an exceptional capacity of 987 mAh gI2 -1 with an energy density of 1278 Wh kgI2 -1, marking an enhancement of ≈300 mAh g-1 compared to electrolyte devoid of EG, and enhancing the Coulombic efficiency (CE) from 68.2% to 98.7%. Moreover, the pouch cell exhibits 3.72 mAh cm-2 capacity with an energy density of 4.52 mWh cm-2, exhibiting robust cycling stability. Overall, this work contributes to the further development of high-valence and high-capacity aqueous Zn-I2 batteries.

Stable Zinc Metal Battery Development: Using Fibrous Zirconia for Rapid Surface Conduction of Zinc Ions With Modified Water Solvation Structure

The two most critical technical issues in Zn-based batteries, dendrite formation, and hydrogen evolution reaction, can be simultaneously addressed by introducing negatively charged fibrous ZrO2 as a separator. Electron redistribution between ZrO2 and Zn2+ ions renders the ZrO2 surface a preferred adsorption site for Zn2+ ions, making surface conduction the primary ion-transport mode. Surface conduction enables fibrous ZrO2 to exhibit a 6.54 times higher single-Zn-ion conductivity than that of conventional glass fiber, minimizing the concentration gradient of Zn2+ and suppressing dendrite formation. Additionally, strong Zr─O─Zn bonding stabilizes the Zn2+ ions with fewer solvated H2O molecules (≈2), preventing water molecules from approaching the electrode surface, as evidenced by a 58.8% decrease in the hydrogen evolution rate. Consequently, the cycling stability of a fibrous-ZrO2-based Zn/Zn symmetric cell (3000 h at 1 mAh cm-2 and 5 mA cm-2) is approximately ten times greater than that of the conventional variant. Furthermore, a fibrous-ZrO2-based Zn-I2 full cell exhibits a notably high energy density (271.4 Wh kg-1) as well as a long lifespan (≈5000 cycles) at an ultrahigh current density (4 A g-1).

Low-Concentration Redox-Electrolytes for High-Rate and Long-Life Zinc Metal Batteries

The uncontrolled zinc electrodeposition and side reactions severely limit the power density and lifespan of Zn metal batteries. Herein, the multi-level interface adjustment effect is realized with low-concentration redox-electrolytes (0.2 m KI) additives. The iodide ions adsorbed on the zinc surface significantly suppress water-induced side reactions and by-product formation and enhance the kinetics of zinc deposition. The distribution of relaxation times results reveal that iodide ions can reduce the desolvation energy of hydrated zinc ions and guide the deposition of zinc ions due to their strong nucleophilicity. As a consequence, the Zn||Zn symmetric cell achieves superior cycling stability (>3000 h at 1 mA cm-2, 1 mAh cm-2) accompanied by a uniform deposition and a fast reaction kinetics with a low voltage hysteresis (<30 mV). Additionally, coupled with an activated carbon (AC) cathode, the assembled Zn||AC cell delivers a high-capacity retention of 81.64% after 2000 cycles at 4 A g-1. More importantly, the operando electrochemical UV-vis spectroscopies show that a small number of I3 - can spontaneously react with the dead zinc as well as basic zinc saltsand regenerate iodide ions and zinc ions; thus, the Coulombic efficiency of each charge-discharge process is close to 100%.

A New High-Performance Porous Carbon-Coated Mn3O4/Na2CO3 Cathode for Suppressing Mn2+Dissolution in Aqueous Zinc Ion Batteries

Manganous-manganic oxide (Mn3O4), akin to other manganese-based oxides, faces several critical challenges such as substantial capacity fading and limited rate performance due to its inferior electrical conductivity, in addition to the inevitable dissociation of Mn2+. To address these issues, we introduce for the first time a novel carbon-coated Mn3O4/Na2CO3 (Mn3O4/Na2CO3/C) composite material. Comprehensive characterizations indicate that Na2CO3 effectively curtails Mn2+dissolution, enhances carbon encapsulation throughout charging/discharging cycles, and exposes additional active sites on the Mn3O4/Na2CO3/C composite. Electrochemical assessments confirm that the Mn3O4/Na2CO3/C-2 cathode exhibits exceptional electrochemical performance, outperforming other cathodes in the ZnSO4 system. Moreover, the Mn3O4/Na2CO3/C-2 cathode delivers a high specific capacity of ~550 mAh gM-1 at 0.1 A g-1 and maintains a significant capacity of ~230 mAh g-1 after 360 cycles at 1.0 A g-1 within the 2.0 M ZnSO4+0.2 M MnSO4 electrolyte system, demonstrating its potential as a high-performance cathode material for aqueous zinc-ion batteries.

An Ion-Pumping Quasi-Solid Electrolyte Enabled by Electrokinetic Effects for Stable Aqueous Zinc Metal Batteries

The practical application of aqueous zinc (Zn) metal batteries (ZMBs) is hindered by the complicated hydrogen evolution, passivation reactions, and dendrite growth of Zn metal anodes. Here, an ion-pumping quasi-solid electrolyte (IPQSE) with high Zn2+ transport kinetics enabled by the electrokinetic phenomena to realize high-performance quasi-solid state Zn metal batteries (QSSZMBs) is reported. The IPQSE is prepared through the in situ ring-opening polymerization of tetramethylolmethane-tri-β-aziridinylpropionate in the aqueous electrolyte. The porous polymer framework with high zeta potential provides the IPQSE with an electrokinetic ion-pumping feature enabled by the electrokinetic effects (electro-osmosis and electrokinetic surface conduction), which significantly accelerates the Zn2+ transport, reduces the concentration polarization and overcomes the diffusion-limited current. Moreover, the Zn2+ affinity of the polymer and hydrogen bonding interactions in the IPQSE changes the Zn2+ coordination environment and reduces the amount of free H2O, which lowers the H2O activity and inhibits H2O-induced side reactions. Consequently, the highly reversible and stable Zn metal anodes are achieved. The assembled QSSZMBs based on the IPQSE display excellent cycling stability with high capacity retention and Coulombic efficiency. The high-performance quasi-solid state Zn metal pouch cells are demonstrated, showing great promise for the practical application of the IPQSE.

Molecular Bridging Induced Anti-Salting-Out Effect Enabling High Ionic Conductive ZnSO4-Based Hydrogel for Quasi-Solid-State Zinc Ion Batteries

Hydrogel electrolytes (HEs) hold great promise in tackling severe issues emerging in aqueous zinc-ion batteries, but the prevalent salting-out effect of kosmotropic salt causes low ionic conductivity and electrochemical instability. Herein, a subtle molecular bridging strategy is proposed to enhance the compatibility between PVA and ZnSO4 from the perspective of hydrogen-bonding microenvironment re-construction. By introducing urea containing both an H-bond acceptor and donor, the broken H-bonds between PVA and H2O, initiated by the SO4 2--driven H2O polarization, could be re-united via intense intermolecular hydrogen bonds, thus leading to greatly increased carrying capacity of ZnSO4. The urea-modified PVA-ZnSO4 HEs featuring a high ionic conductivity up to 31.2 mS cm-1 successfully solves the sluggish ionic transport dilemma at the solid-solid interface. Moreover, an organic solid-electrolyte-interphase can be derived from the in situ electro-polymerization of urea to prohibit H2O-involved side reactions, thereby prominently improving the reversibility of Zn chemistry. Consequently, Zn anodes witness an impressive lifespan extension from 50 h to 2200 h at 0.1 mA cm-2 while the Zn-I2 full battery maintains a remarkable Coulombic efficiency (>99.7 %) even after 8000 cycles. The anti-salting-out strategy proposed in this work provides an insightful concept for addressing the phase separation issue of functional HEs.

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.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Ion-Sieving Separator Functionalized by Natural Mineral Coating toward Ultrastable Zn Metal Anodes

Aqueous zinc-ion batteries (AZIBs) exhibit promising prospects in becoming large-scale energy storage systems due to environmental friendliness, high security, and low cost. However, the growth of Zn dendrites and side reactions remain heady obstacles for the practical application of AZIBs. To solve these challenges, a functionalized Janus separator is successfully constructed by coating halloysite nanotubes (HNTs) on glass fiber (GF). Impressively, the different electronegativity on the inner and outer surfaces of HNTs endows the HNT-GF separator with ion-sieving property, leading to a significantly high transference number of Zn2+ (tZn2+ = 0.71). Meanwhile, the HNT-GF separator works as an interfacial ion comb to regular Zn2+ flux and realizes multisite progressive nucleation, bringing decreased nucleation overpotential and uniform Zn2+ deposition. Consequently, the HNT-GF separator enables the Zn anode to display an ultralong plating/stripping life of 3000 h and high rate tolerance with a stable long cycle life even under a density of 50 mA cm-2. Moreover, the Z n ∥ H N T - G F ∥ M n O 2 full cell represents an ultrastable cycling stability with a high capacity retention of 93.4% even after 1000 cycles at a current density of 2 A g-1. This work provides a convenient method for the separator modification of AZIBs.

Facile Formation of Multifunctional Biomimetic Hydrogel Fibers for Sensing Applications

To face the challenges in preparing hydrogel fibers with complex structures and functions, this study utilized a microfluidic coaxial co-extrusion technique to successfully form functional hydrogel fibers through rapid ionic crosslinking. Functional hydrogel fibers with complex structures, including linear fibers, core-shell structure fibers, embedded helical channels, hollow tubes, and necklaces, were generated by adjusting the composition of internal and external phases. The characteristic parameters of the hydrogel fibers (inner and outer diameter, helix generation position, pitch, etc.) were achieved by adjusting the flow rate of the internal and external phases. As biocompatible materials, hydrogel fibers were endowed with electrical conductivity, temperature sensitivity, mechanical enhancement, and freeze resistance, allowing for their use as temperature sensors for human respiratory monitoring and other biomimetic application developments. The hydrogel fibers had a conductivity of up to 22.71 S/m, a response time to respiration of 37 ms, a recovery time of 1.956 s, and could improve the strength of respiration; the tensile strength at break up to 8.081 MPa, elongation at break up to 159%, and temperature coefficient of resistance (TCR) up to -13.080% °C-1 were better than the existing related research.

Recent Advancements in Gel Polymer Electrolytes for Flexible Energy Storage Applications

Since the last decade, the need for deformable electronics exponentially increased, requiring adaptive energy storage systems, especially batteries and supercapacitors. Thus, the conception and elaboration of new deformable electrolytes becomes more crucial than ever. Among diverse materials, gel polymer electrolytes (hydrogels, organogels, and ionogels) remain the most studied thanks to the ability to tune the physicochemical and mechanical properties by changing the nature of the precursors, the type of interactions, and the formulation. Nevertheless, the exploitation of this category of electrolyte as a possible commercial product is still restrained, due to different issues related to the nature of the gels (ionic conductivity, evaporation of filling solvent, toxicity, etc.). Therefore, this review aims to resume different strategies to tailor the properties of the gel polymer electrolytes as well as to provide recent advancements in the field toward the elaboration of deformable batteries and supercapacitors.

MXenes for Zinc-Based Electrochemical Energy Storage Devices

As an economical and safer alternative to lithium, zinc (Zn) is promising for realizing new high-performance electrochemical energy storage devices, such as Zn-ion batteries, Zn-ion hybrid capacitors, and Zn-air batteries. Well-designed electrodes are needed to enable efficient Zn electrochemistry for energy storage. Two-dimensional transition metal carbides and nitrides (MXenes) are emerging materials with unique electrical, mechanical, and electrochemical properties and versatile surface chemistry. They are potential material candidates for constructing high-performance electrodes of Zn-based energy storage devices. This review first briefly introduces the working mechanisms of the three Zn-based energy storage devices. Then, the recent progress on the synthesis, chemical functionalization, and structural design of MXene-based electrodes is summarized. Their performance in Zn-based devices is analyzed to establish relations between material properties, electrode structures, and device performance. Last, several research topics are proposed to be addressed for developing practical MXene-based electrodes for Zn-based energy storage devices to enable their commercialization and broad adoption in the near future.

Upgrading Gel Electrolytes Through Electrostatic-Induced Dual-Salt Paradigm for Superior Zn-Ion Battery Performance

Gel electrolytes are gaining attention for rechargeable Zn-ion batteries because of their high safety, high flexibility, and excellent comprehensive electrochemical performances. However, current gel electrolytes still perform at mediocre levels due to incomplete Zn salts dissociation and side reactions. Herein, an electrostatic-induced dual-salt strategy is proposed to upgrade gel electrolytes to tackle intrinsic issues of Zn metal anodes. The competitive coordination mechanism driven by electrostatic repulsion and steric hindrance of dual anions promotes zinc salt dissociation at low lithium salt addition levels, improving ion transport and mechanical properties of gel electrolytes. Li+ ions and gel components coordinate with H2O, reducing active H2O molecules and inhibiting associated side reactions. The dual-salt gel electrolyte enables excellent reversibility of Zn anodes at both room and low temperatures. Zn||Polyaniline cells using the dual-salt gel electrolyte exhibit a high discharge capacity of 180 mAh g-1 and long-term cycling stability over 180 cycles at -20 °C. The dual-salt strategy offers a cost-effective approach to improving gel electrolytes for high-performance flexible Zn-ion batteries.

Improvements and Challenges of Hydrogel Polymer Electrolytes for Advanced Zinc Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are widely regarded as desirable energy storage devices due to their inherent safety and low cost. Hydrogel polymer electrolytes (HPEs) are cross-linked polymers filled with water and zinc salts. They are not only widely used in flexible batteries but also represent an ideal electrolyte candidate for addressing the issues associated with the Zn anode, including dendrite formation and side reactions. In HPEs, an abundance of hydrophilic groups can form strong hydrogen bonds with water molecules, reducing water activity and inhibiting water decomposition. At the same time, special Zn2+ transport channels can be constructed in HPEs to homogenize the Zn2+ flux and promote uniform Zn deposition. However, HPEs still face issues in practical applications, including poor ionic conductivity, low mechanical strength, poor interface stability, and narrow electrochemical stability windows. This Review discusses the issues associated with HPEs for advanced AZIBs, and the recent progresses are summarized. Finally, the Review outlines the opportunities and challenges for achieving high performance HPEs, facilitating the utilization of HPEs in AZIBs.

Implantable Zinc Ion Battery and Osteogenesis-Immunoregulation Bifunction of Its Catabolite

Biocompatible batteries can power implantable electronic devices and have broad applications in medicine. However, the controlled degradation of implantable batteries, the impact of battery catabolites on surrounding tissues, and wireless charging designs are often overlooked. Here, we designed an implantable zinc ion battery (ZIB) using a gelatin/polycaprolactone-based composite gel electrolyte. The prepared ZIBs deliver a high specific capacity of 244.0 mA h g-1 (0.5C) and long cycling stability of 300 cycles (4C). ZIBs were completely degraded within 8 weeks in rats and 30 days in a phosphate-buffered saline lipase solution, demonstrating good biocompatibility and degradability. ZIBs catabolites induced macrophage M2 polarization and exhibited anti-inflammatory properties, with mRNA levels of the M2 markers Arg-1 and CD206 up-regulated 15.8-fold and 13.4-fold, respectively, compared to the blank control group. Meanwhile, the expressions of two typical osteogenic markers, osteopontin and osteocalcin, were up-regulated by 3.6-fold and 5.6-fold, respectively, demonstrating that designed ZIBs promoted osteogenic differentiation of bone marrow mesenchymal stem cells. Additionally, a wireless energy transmission module was designed using 3D printing technology to realize real-time charging of the ZIB in rats. The designed ZIB is a promising power source for implantable medical electronic devices and also serves as a functional material to accelerate bone repair.

Switching Hydrophobic Interface with Ionic Valves for Reversible Zinc Batteries

Developing hydrophobic interface has proven effective in addressing dendrite growth and side reactions during zinc (Zn) plating in aqueous Zn batteries. However, this solution inadvertently impedes the solvation of Zn2+ with H2O and subsequent ionic transport during Zn stripping, leading to insufficient reversibility. Herein, an adaptive hydrophobic interface that can be switched "on" and "off" by ionic valves to accommodate the varying demands for interfacial H2O during both the Zn plating and stripping processes, is proposed. This concept is validated using octyltrimethyl ammonium bromide (C8TAB) as the ionic valve, which can initiatively establish and remove a hydrophobic interface in response to distinct electric-field directions during Zn plating and stripping, respectively. Consequently, the Zn anode exhibits an extended cycling life of over 2500 h with a high Coulombic efficiency of ≈99.8%. The full cells also show impressive capacity retention of over 85% after 1 000 cycles at 5 A g-1. These findings provide a new insight into interface design for aqueous metal batteries.

Flexible electrochemical energy storage devices and related applications: recent progress and challenges

Given the escalating demand for wearable electronics, there is an urgent need to explore cost-effective and environmentally friendly flexible energy storage devices with exceptional electrochemical properties. However, the existing types of flexible energy storage devices encounter challenges in effectively integrating mechanical and electrochemical performances. This review is intended to provide strategies for the design of components in flexible energy storage devices (electrode materials, gel electrolytes, and separators) with the aim of developing energy storage systems with excellent performance and deformability. Firstly, a concise overview is provided on the structural characteristics and properties of carbon-based materials and conductive polymer materials utilized in flexible energy storage devices. Secondly, the fabrication process and strategies for optimizing their structures are summarized. Subsequently, a comprehensive review is presented regarding the applications of carbon-based materials and conductive polymer materials in various fields of flexible energy storage, such as supercapacitors, lithium-ion batteries, and zinc-ion batteries. Finally, the challenges and future directions for next-generation flexible energy storage systems are proposed.

Biomass Solid-State Electrolyte with Abundant Ion and Water Channels for Flexible Zinc-Air Batteries

Flexible zinc-air batteries are the leading candidates as the next-generation power source for flexible/wearable electronics. However, constructing safe and high-performance solid-state electrolytes (SSEs) with intrinsic hydroxide ion (OH-) conduction remains a fundamental challenge. Herein, by adopting the natural and robust cellulose nanofibers (CNFs) as building blocks, the biomass SSEs with penetrating ion and water channels are constructed by knitting the OH--conductive CNFs and water-retentive CNFs together via an energy-efficient tape casting. Benefiting from the abundant ion and water channels with interconnected hydrated OH- wires for fast OH- conduction under a nanoconfined environment, the biomass SSEs reveal the high water-uptake, impressive OH- conductivity of 175 mS cm-1 and mechanical robustness simultaneously, which overcomes the commonly existed dilemma between ion conductivity and mechanical property. Remarkably, the flexible zinc-air batteries assemble with biomass SSEs deliver an exceptional cycle lifespan of 310 h and power density of 126 mW cm-2. The design methodology for water and ion channels opens a new avenue to design high-performance SSEs for batteries.

Advances of Nanomaterials for High-Efficiency Zn Metal Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have emerged as one of the most promising candidates for next-generation energy storage devices due to their outstanding safety, cost-effectiveness, and environmental friendliness. However, the practical application of zinc metal anodes (ZMAs) faces significant challenges, such as dendrite growth, hydrogen evolution reaction, corrosion, and passivation. Fortunately, the rapid rise of nanomaterials has inspired solutions for addressing these issues associated with ZMAs. Nanomaterials with unique structural features and multifunctionality can be employed to modify ZMAs, effectively enhancing their interfacial stability and cycling reversibility. Herein, an overview of the failure mechanisms of ZMAs is presented, and the latest research progress of nanomaterials in protecting ZMAs is comprehensively summarized, including electrode structures, interfacial layers, electrolytes, and separators. Finally, a brief summary and optimistic perspective are given on the development of nanomaterials for ZMAs. This review provides a valuable reference for the rational design of efficient ZMAs and the promotion of large-scale application of AZIBs.

Blocking Interfacial Proton Transport via Self-Assembled Monolayer for Hydrogen Evolution-Free Zinc Batteries

Aqueous Zn-ion batteries (ZIBs) are promising next-generation energy storage devices, yet suffer from the issues of hydrogen evolution reaction (HER) and intricate side reactions on the Zn anode surface. The hydrogen (H)-bond networks play a critical role in interfacial proton transport that may closely relate to HER but are rarely investigated. Herein, we report a self-assembled monolayer (SAM) strategy which is constructed by anchoring ionic liquid cations on Ti3C2Tx substrate for HER-free Zn anode. Molecule dynamics simulations reveal that the rationally designed SAM with a high coordination number of water molecules (25-27, 4-6 for Zn2+) largely reduces the interfacial densities of H2O molecules, therefore breaking the connectivity of H-bond networks and blocking proton transport on the interface, by which the HER is suppressed. Then, a series of in situ characterizations demonstrate that negligible amounts of H2 gas are collected from the Zn@SAM-MXene anode. Consequently, the symmetric cell enables a long-cycling life of 3000 h at 1 mA cm-2 and 1000 h at 5 mA cm-2. More significantly, the stable Zn@SAM-MXene films are successfully used for coin full cells showing high-capacity retention of over 94 % after 1000 cycles and large-area (10×5 cm2) pouch cells with desired performance.

An Ionic Liquid Supramolecular Gel Electrolyte with Unique Wide Operating Temperature Range Properties for Zinc-Ion Batteries

Zinc-ion batteries are promising candidates for large-scale energy storage. The side reactions of the hydrogen evolution reaction (HER) and zinc dendrite growth are major challenges for developing high-performance zinc-ion batteries. In this paper, a supramolecular gel electrolyte (BLO-ILZE) was self-assembled in an ionic liquid (EMIMBF4) with zinc tetrafluoroborate (Zn(BF4)2) on the separator in situ to obtain a gel electrolyte used in zinc-ion batteries. BLO-ILZE is demonstrated to significantly enhance conductivity over a broad temperature range between -70 and 100 °C. Interestingly, through testing and fitting, it is found that the supramolecular gel electrolyte satisfies the liquid state law over a wide temperature range, and even achieves high conductivity (2.12 mS cm-1) at -40 °C. It is equivalent to the conductivity of aqueous zinc-ion batteries (ZnSO4/H2O) at -10 °C, which is 2.33 mS cm-1. Moreover, the supramolecular gel electrolyte can effectively inhibit the HER, thus exhibiting a longer lifetime in Zn/Zn cells for 3470 h at 1 mA cm-2 compared to the aqueous zinc-ion batteries with the Zn(BF4)2 aqueous electrolyte (400 h at 1 mA cm-2). The assembled V2O5/BLO-ILZE/Zn full cells also showed cycling performance, with 5000 cycles at 0.5 mA g-1 at room temperature, a capacity of 98%, and a coulombic efficiency of about 100%.

High-Entropy Polymer Electrolytes Derived from Multivalent Polymeric Ligands for Solid-State Lithium Metal Batteries with Accelerated Li+ Transport

Solid-state polymer-based electrolytes (SSPEs) exhibit great possibilities in realizing high-energy-density solid-state lithium metal batteries (SSLMBs). However, current SSPEs suffer from low ionic conductivity and unsatisfactory interfacial compatibility with metallic Li because of the high crystallinity of polymers and sluggish Li+ movement in SSPEs. Herein, differing from common strategies of copolymerization, a new strategy of constructing a high-entropy SSPE from multivariant polymeric ligands is proposed. As a protocol, poly(vinylidene fluoride-co-hexafluoropropylene) (PH) chains are grafted to the demoed polyethylene imine (PEI) with abundant -NH2 groups via a click-like reaction (HE-PEIgPHE). Compared to a PH-based SSPE, our HE-PEIgPHE shows a higher modulus (6.75 vs 5.18 MPa), a higher ionic conductivity (2.14 × 10-4 vs 1.03 × 10-4 S cm-1), and a higher Li+ transference number (0.55 vs 0.42). A Li|HE-PEIgPHE|Li cell exhibits a long lifetime (1500 h), and a Li|HE-PEIgPHE|LiFePO4 cell delivers an initial capacity of 160 mAh g-1 and a capacity retention of 98.7%, demonstrating the potential of our HE-PEIgPHE for the SSLMBs.

Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li-ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake-like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.

Lamellar Nanoporous Metal/Intermetallic Compound Heterostructure Regulating Dendrite-Free Zinc Electrodeposition for Wide-Temperature Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries are attractive post-lithium battery technologies for grid-scale energy storage because of their inherent safety, low cost and high theoretical capacity. However, their practical implementation in wide-temperature surroundings persistently confronts irregular zinc electrodeposits and parasitic side reactions on metal anode, which leads to poor rechargeability, low Coulombic efficiency and short lifespan. Here, this work reports lamellar nanoporous Cu/Al2Cu heterostructure electrode as a promising anode host material to regulate high-efficiency and dendrite-free zinc electrodeposition and stripping for wide-temperatures aqueous zinc-ion batteries. In this unique electrode, the interconnective Cu/Al2Cu heterostructure ligaments not only facilitate fast electron transfer but work as highly zincophilic sites for zinc nucleation and deposition by virtue of local galvanic couples while the interpenetrative lamellar channels serving as mass transport pathways. As a result, it exhibits exceptional zinc plating/stripping behaviors in aqueous hybrid electrolyte of diethylene glycol dimethyl ether and zinc trifluoromethanesulfonate at wide temperatures ranging from 25 to -30 °C, with ultralow voltage polarizations at various current densities and ultralong lifespan of >4000 h. The outstanding electrochemical properties enlist full cell of zinc-ion batteries constructed with nanoporous Cu/Al2Cu and ZnxV2O5/C to maintain high capacity and excellent stability for >5000 cycles at 25 and -30 °C.

Achieving High Ionic Conductivity and Mechanical Strength by a Leather Gel Electrolyte for Flexible Zinc-Ion Batteries

The continuous advancement in the field of flexible and wearable electronics has led to increased research interest in safe, low-cost, and flexible zinc-ion batteries, particularly with a focus on flexible electrolytes. In this study, we present a leather gel electrolyte (LGE) that offers robust mechanical properties and an excellent electrochemical performance. LGE exhibits an ionic conductivity of 1.36 × 10-2 S cm-1 and achieves a capacity of 303.7 mAh g-1 in flexible zinc-manganese dioxide batteries. Even after 1000 cycles, the capacity retention remains above 90%, demonstrating outstanding performance in protecting the zinc anode. Furthermore, such a flexible battery shows good resistance to damage due to the strong mechanical strength originating from leather. Notably, LGE utilizes green and sustainable leather as a raw material, making it a promising option for sustainable flexible devices.

Wood-inspired anisotropic hydrogel electrolyte with large modulus and low tortuosity realizing durable dendrite-free zinc-ion batteries

While aqueous zinc-ion batteries exhibit great potential, their performance is impeded by zinc dendrites. Existing literature has proposed the use of hydrogel electrolytes to ameliorate this issue. Nevertheless, the mechanical attributes of hydrogel electrolytes, particularly their modulus, are suboptimal, primarily ascribed to the substantial water content. This drawback would severely restrict the dendrite-inhibiting efficacy, especially under large mass loadings of active materials. Inspired by the structural characteristics of wood, this study endeavors to fabricate the anisotropic carboxymethyl cellulose hydrogel electrolyte through directional freezing, salting-out effect, and compression reinforcement, aiming to maximize the modulus along the direction perpendicular to the electrode surface. The heightened modulus concurrently serves to suppress the vertical deposition of the intermediate product at the cathode. Meanwhile, the oriented channels with low tortuosity enabled by the anisotropic structure are beneficial to the ionic transport between the anode and cathode. Comparative analysis with an isotropic hydrogel sample reveals a marked enhancement in both modulus and ionic conductivity in the anisotropic hydrogel. This enhancement contributes to significantly improved zinc stripping/plating reversibility and mitigated electrochemical polarization. Additionally, a durable quasi-solid-state Zn//MnO2 battery with noteworthy volumetric energy density is realized. This study offers unique perspectives for designing hydrogel electrolytes and augmenting battery performance.

Rational Design of an In-Situ Polymer-Inorganic Hybrid Solid Electrolyte Interphase for Realising Stable Zn Metal Anode under Harsh Conditions

The in-depth understanding of the composition-property-performance relationship of solid electrolyte interphase (SEI) is the basis of developing a reliable SEI to stablize the Zn anode-electrolyte interface, but it remains unclear in rechargeable aqueous zinc ion batteries. Herein, a well-designed electrolyte based on 2 M Zn(CF3SO3)2-0.2 M acrylamide-0.2 M ZnSO4 is proposed. A robust polymer (polyacrylamide)-inorganic (Zn4SO4(OH)6.xH2O) hybrid SEI is in situ constructed on Zn anodes through controllable polymerization of acrylamide and coprecipitation of SO4 2- with Zn2+ and OH-. For the first time, the underlying SEI composition-property-performance relationship is systematically investigated and correlated. The results showed that the polymer-inorganic hybrid SEI, which integrates the high modulus of the inorganic component with the high toughness of the polymer ingredient, can realize high reversibility and long-term interfacial stability, even under ultrahigh areal current density and capacity (30 mA cm-2~30 mAh cm-2). The resultant Zn||NH4V4O10 cell also exhibits excellent cycling stability. This work will provide a guidance for the rational design of SEI layers in rechargeable aqueous zinc ion batteries.

Multiple Cations Nanoconfinement in Ultrathin V2O5 Nanosheets Enables Ultrafast Ion Diffusion Kinetics Toward High-performance Zinc Ion Battery

Nanoconfinement of cations in layered oxide cathode is an important approach to realize advanced zinc ion storage performance. However, thus far, the conventional hydrothermal/solvothermal route for this nanoconfinement has been restricted to its uncontrollable phase structure and the difficulty on the multiple cation co-confinement simultaneously. Herein, this work reports a general, supramolecular self-assembly of ultrathin V2O5 nanosheets using various unitary cations including Na+, K+, Mg2+, Ca2+, Zn2+, Al3+, NH4 +, and multiple cations (NH4 + + Na+, NH4 + + Na+ + Ca2+, NH4 + + Na+ + Ca2+ +Mg2+). The unitary cation confinement results in a remarkable increase in the specific capacity and Zn-ion diffusion kinetics, and the multiple cation confinement gives rise to superior structural and cycling stability by multiple cation synergetic pillaring effect. The optimized diffusion coefficient of Zn-ion (7.5 × 10-8 cm2 s-1) in this assembly series surpasses most of the V-based cathodes reported up to date. The work develops a novel multiple-cations nanoconfinement strategy toward high-performance cathode for aqueous battery. It also provides new insights into the guest cation regulation of zinc-ion diffusion kinetics through a general, supramolecular assembly pathway.

Molecular Engineering Enables Hydrogel Electrolyte with Ionic Hopping Migration and Self-Healability toward Dendrite-Free Zinc-Metal Anodes

Hydrogel electrolytes (HEs), characterized by intrinsic safety, mechanical stability, and biocompatibility, can promote the development of flexible aqueous zinc-ion batteries (FAZIBs). However, current FAZIB technology is severely restricted by the uncontrollable dendrite growth arising from undesirable reactions between the HEs with sluggish ionic conductivity and Zn metal. To overcome this challenge, this work proposes a molecular engineering strategy, which involves the introduction of oxygen-rich poly(urea-urethane) (OR-PUU) into polyacrylamide (PAM)-based HEs. The OR-PUU/PAM HEs facilitate rapid ion transfer through their ionic hopping migration mechanism, resulting in uniform and orderly Zn2+ deposition. The abundant polar groups on the OR-PUU molecules in OR-PUU/PAM HEs break the inherent H-bond network, tune the solvation structure of hydrated Zn2+, and inhibit the occurrence of side reactions. Moreover, the interaction of hierarchical H-bonds in the OR-PUU/PAM HEs endows them with self-healability, enabling in situ repair of cracks induced by plating/stripping. Consequently, Zn symmetric cells incorporating the novel OR-PUU/PAM HEs exhibit a long cycling life of 2000 h. The resulting Zn-MnO2 battery displays a low capacity decay rate of 0.009% over 2000 cycles at 2000 mA g-1. Overall, this work provides valuable insights to facilitate the realization of dendrite-free Zn-metal anodes through the molecular engineering of HEs.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Water and Salt Concentration-Dependent Electrochemical Performance of Hydrogel Electrolytes in Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) are promising energy storage devices with safe, nonflammable electrolytes and abundant, low-cost electrode materials. Their practical applications are hampered by various water-related undesirable reactions, such as the hydrogen evolution reaction (HER), corrosion of zinc metal, and water-induced decay of cathode materials. Polymer hydrogel electrolytes were used to control these reactions. However, salt, water, and polymeric backbones intervene in polymer hydrogels, and currently, there are no systematic studies on how salt and water concentrations synergistically affect polymer hydrogels' electrochemical performance. Here, we used an in situ polymerization method to synthesize polyacrylamide (PAM) hydrogels with varied Zn(ClO4)2 (0.5 to 2.0 mol kg-1) and water (40 to 90 wt %) concentrations. Their electrochemical performances in Zn||Ti half-cells, Zn||Zn symmetrical cells, and Zn||V2O5 full cells have been comprehensively evaluated. Although the ionic conductivity of electrolytes increases with the salt concentration, a high salt concentration of 2.0 mol kg-1 with more Zn2+ solvated H2O would induce more severe HER and Zn corrosion at the electrolyte/electrode interfaces. A narrow window of the water concentration at 70-80 wt % is optimal to balance needs for achieving a high ionic conductivity and restricting water-related undesirable reactions. The chemically more active water counts roughly 64.1-73.1 wt % of the total water in electrolytes. PAM hydrogel electrolyte with 1.0 mol kg-1 Zn(ClO4)2 and 80 wt % water enables 1200 h of stable cycling in a Zn||Zn symmetric cell and 99.24% of Coulombic efficiency in a Zn||Ti half-cell. Due to the water-induced decay of V2O5, the electrolyte with 70 wt % water delivers the best performance in a Zn||V2O5 full cell, which can retain 73.7% of its initial capacity after 400 charge/discharge cycles. Our results show that achieving precise control of salt and water concentrations of hydrogel electrolytes in their optimal windows to reduce the fraction of chemically more active water while retaining high ionic conductivity is essential to enabling high-performance ZIBs.

A Hydrogel Electrolyte toward a Flexible Zinc-Ion Battery and Multifunctional Health Monitoring Electronics

The compact design of an environmentally adaptive battery and effectors forms the foundation for wearable electronics capable of time-resolved, long-term signal monitoring. Herein, we present a one-body strategy that utilizes a hydrogel as the ionic conductive medium for both flexible aqueous zinc-ion batteries and wearable strain sensors. The poly(vinyl alcohol) hydrogel network incorporates nano-SiO2 and cellulose nanofibers (referred to as PSC) in an ethylene glycol/water mixed solvent, balancing the mechanical properties (tensile strength of 6 MPa) and ionic diffusivity at -20 °C (2 orders of magnitude higher than 2 M ZnCl2 electrolyte). Meanwhile, cathode lattice breathing during the solvated Zn2+ intercalation and dendritic Zn protrusion at the anode interface are mitigated. Besides the robust cyclability of the Zn∥PSC∥V2O5 prototype within a wide temperature range (from -20 to 80 °C), this microdevice seamlessly integrates a zinc-ion battery with a strain sensor, enabling precise monitoring of the muscle response during dynamic body movement. By employing transmission-mode operando XRD, the self-powered sensor accurately documents the real-time phasic evolution of the layered cathode and synchronized strain change induced by Zn deposition, which presents a feasible solution of health monitoring by the miniaturized electronics.

Recent Advances on Stretchable Aqueous Zinc-Ion Batteries for Wearable Electronics

The rapid development of wearable electronics has stimulated the pursuit of advanced stretchable power sources. As a promising candidate, stretchable aqueous zinc-ion batteries (AZIBs), have attracted unprecedented attention owing to their intrinsic safety, low cost, environmental benignity, and high performance, and can be endowed with additional functionalities to broaden the applications of wearable electronics. Here, a comprehensive review on the latest advances of stretchable AZIBs is presented. The materials and methods for stretchable components in AZIBs are first summarized, covering current collectors, electrodes, electrolytes/separators, and encapsulating layers. Subsequently, the benefits of the coplanar, fiber-shaped, and sandwiched configurations for stretchable AZIBs are analyzed. Moreover, the additional features integrated into stretchable AZIBs are highlighted. Finally, the challenges and prospects of stretchable AZIBs for wearable applications in the future are proposed.

Three-dimensional Ordered Macroporous Flexible Electrode Design toward High-Performance Zinc-Ion Batteries

Flexible zinc-ion batteries (ZIBs) have been considered to have huge potential in portable and wearable electronics due to their high safety, cost efficiency, and considerable energy density. Therein, the design and construction of flexible electrodes significantly determine the performance and lifespan of flexible battery devices. In this work, an ultrathin flexible three-dimensional ordered macroporous (3DOM) Sn@Zn anode (60 μm in thickness) is presented to relieve dendrite growth and expand the lifespan of flexible ZIBs. The 3DOM structure can ensure uniform electric field distribution, guide oriented zinc plating/stripping, and extend the lifespan of anodes. The rich zincophilic Sn sites on the electrode surface significantly facilitate Zn nucleation. Accordingly, a lowered nucleation overpotential of 8.9 mV and an ultralong cycling performance of 2400 h at 0.1 mA cm-2 and 0.1 mAh cm-2 are achieved in symmetric cells, and the 3DOM Sn@Zn anode can also operate in deep cycling for over 200 h at 10 mA cm-2 and 5 mAh cm-2. A flexible 3DOM MnO2/Ni cathode with a high structural stability and a high mass-specific capacity is fabricated to match with the anode to form a flexible ZIB with a total thickness of 200 μm. The flexible device delivers a high volumetric energy density of 11.76 mWh cm-3 at 100 mA gMnO2-1 and a high average open-circuit voltage of 1.5 V and exhibits high-performance power supply under deformation in practical application scenarios. This work may shed some light on the design and fabrication of flexible energy-storage devices.

Electrochemical Hydrophobic Tri-layer Interface Rendered Mechanically Graded Solid Electrolyte Interface for Stable Zinc Metal Anode

The aqueous zinc-ion battery is promising as grid scale energy storage device, but hindered by the instable electrode/electrolyte interface. Herein, we report the lean-water ionic liquid electrolyte for aqueous zinc metal batteries. The lean-water ionic liquid electrolyte creates the hydrophobic tri-layer interface assembled by first two layers of hydrophobic OTF- and EMIM+ and third layer of loosely attached water, beyond the classical Gouy-Chapman-Stern theory based electrochemical double layer. By taking advantage of the hydrophobic tri-layer interface, the lean-water ionic liquid electrolyte enables a wide electrochemical working window (2.93 V) with relatively high zinc ion conductivity (17.3 mS/cm). Furthermore, the anion crowding interface facilitates the OTF- decomposition chemistry to create the mechanically graded solid electrolyte interface layer to simultaneously suppress the dendrite formation and maintain the mechanical stability. In this way, the lean-water based ionic liquid electrolyte realizes the ultralong cyclability of over 10000 cycles at 20 A/g and at practical condition of N/P ratio of 1.5, the cumulated areal capacity reach 1.8 Ah/cm2 , which outperforms the state-of-the-art zinc metal battery performance. Our work highlights the importance of the stable electrode/electrolyte interface stability, which would be practical for building high energy grid scale zinc-ion battery.

Thermally Healable Electrolyte-Electrode Interface for Sustainable Quasi-Solid Zinc-ion Batteries

Quasi-solid zinc-ion batteries using hydrogel electrolytes show great potential in energy storage devices owing to their intrinsic safety, fewer side reactions and wide electrochemical windows. However, the dendrite issues on the zinc anodes cannot be fundamentally eliminated and the intrinsic anode-electrolyte interfacial interspace is rarely investigated. Here, we design a dynamically healable gelatin-based hydrogel electrolyte with a highly reversible sol-gel transition, which can construct a conformal electrode-electrolyte interface and further evolve into a stable solid-solid interface by in situ solidification. The unique helical gelatin chain structure provides a uniform channel for zinc ion transport by the bridging effect of sulfate groups. As a consequence, the dynamically healable interface enables dendrite-free zinc anodes and repeatedly repairs the anode-electrolyte interfacial interspaces by the reversible sol-gel transition of gelatin electrolyte to retain long-lasting protection for sustainable zinc-ion batteries.