Polysaccharide hydrogel electrolytes with robust interfacial contact to electrodes for quasi-solid state flexible aqueous zinc ion batteries with efficient suppressing of dendrite growth

Fe3+ intercalated hierarchical structured hydrated vanadate cathode for flexible iron ion hybrid supercapacitor

Energy storage devices are the core hub in constructing the modern energy system and have become an indispensable factor in driving the development of new electronic devices. In this work, we synthesized a flexible cathode of Fe3+ intercalated V2O5·3H2O (VOH) on carbon cloth (FeVOH@CC) and explored an advanced iron ion hybrid supercapacitor (IIHS). The presence of V4+/V5+ electrons in FeVOH@CC enhances the material's conductivity, while Fe3+ acts as a stabilizing pillar to accommodate structural expansion and contraction, thereby ensuring improved ion diffusion dynamics and cycling stability. Additionally, the growth of the material directly on the carbon cloth, eliminates the negative effects of conductive agents, binders, and other additives, and the prepared FeVOH@CC maintains structural flexibility, which is crucial for the effective insertion/extraction of Fe2+. As a result, the aqueous IIHS exhibits excellent areal capacitance (882.4 mF cm-2 at 1 mA cm-2) and energy density (176.5 μWh·cm-2 at 606.4 μW·cm-2). After 20,000 cycles, it retains 85.7 % of its capacity, significantly outperforming VOH. Meanwhile, we have developed a polyacrylamide/sodium alginate/glycerol-Fe2+ gel electrolyte for flexible IIHS, and the device exhibits outstanding performance by retaining 85.9 % of its capacity after 5,000 cycles. Therefore, FeVOH@CC cathode based flexible IIHS opens up new exploratory possibilities for next-generation energy storage devices.

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.

All-Cellulose-based flexible Zinc-Ion battery enabled by waste pomelo peel

Aqueous zinc-ion batteries are attracting extensive attention due to the long-term service life and credible safety as well as the superior price performance between the low cost of manufacture and high energy density. The fabrication of inexpensive, high-performance flexible solid-state zinc-ion batteries, thus, are urgently need for the blooming wearable electronics. Herein, as a proof-of-concept study of waste into wealth, cellulose flakes derived from waste pomelo peel are utilized as the substrate for electrodes and hydrogel electrolytes into a flexible rocking-chair zinc-ion battery. The unique sandwich-type structure holding the flake-like cellulose substrate and linear carbon nanotubes endows the flexible cathode and anode with fast ion and electron transportation. The obtained cellulose-based hydrogel electrolytes on account of special affinity with aqueous ZnSO4 electrolyte output an excellent ionic conductivity. The assembled flexible rocking-chair zinc-ion battery benefitting from the synergistic effect of sandwich-type electrodes and cellulose-based hydrogel electrolytes demonstrates outstanding electrochemical performance and mechanical properties. This work not only puts up an effective roadmap for flexible battery devices, but also reveals the great potential of waste biomass materials in energy storage applications.

Biomimetic multiscale structure with hierarchically entangled topologies of cellulose-based hydrogel sensors for human-computer interaction

The development of high-performance cellulose-based sensors with superior interfacial compatibility, flexibility, and strength has always been challenging. Drawing inspiration from the intricate multiscale hierarchy found in resilient natural materials, the incorporation of this structure into cellulose-based hydrogels using biomimetic strategies is anticipated to enhance their properties. Therefore, the cellulose/polyacrylamide (PAM) hybrid hydrogels are fabricated using the aqueous AlCl3/ZnCl2 system through an all-green one-pot method at room temperature, achieving efficient dissolution of cellulose at multiple scales and in-situ polymerization of polyacrylamide. The multiscale cellulose/PAM hydrogels achieve good interfacial compatibility, with the reinforcing mechanism being confirmed through a combination of experimental validation and atomic simulations. The findings underscore the key elements that drive the multiscale behavior of hydrogels, encompassing a range of factors such as multiple interfacial interactions, hierarchical molecular entanglements, and microskeleton reinforcement. The hydrogels exhibit satisfactory stretchability (412 %), compressive strength (1.2 MPa), conductivity (1.65 S m-1), and ultralong circulability (> 12,000 cycles), rendering them suitable for various scenarios of human-computer interaction. This work establishes a comprehensive interpretation of the strengthening mechanism in cellulose-based multiscale hierarchical structures, thereby providing novel insights for the advanced design strategies of other promising hierarchical materials.

A multifunctional quasi-solid-state polymer electrolyte with highly selective ion highways for practical zinc ion batteries

The uncontrolled dendrite growth and detrimental parasitic reactions of Zn anodes currently impede the large-scale implementation of aqueous zinc ion batteries. Here, we design a versatile quasi-solid-state polymer electrolyte with highly selective ion transport channels via molecular crosslinking of sodium polyacrylate, lithium magnesium silicate and cellulose nanofiber. The abundant negatively charged ionic channels modulate Zn2+ desolvation process and facilitate ion transport. Moreover, an in-situ formed Zn-Mg-Si medium-entropy alloy on Zn anode allows for an improved Zn nucleation kinetics and homogeneous Zn deposition. These combined advantages of the polymer electrolyte enable Zn anodes to achieve an average Coulombic efficiency of 99.7 % over 2400 cycles and highly reversible cycling up to 600 h with large depth of discharge of 85.6%. The resultant Zn | |V2O5 offers a stable long-term cycling performance and its pouch cell achieves a cycling capacity of 1.13 Ah at industrial-level loading mass of 31.3 mg.

Development of flexible Zn/MnO2 secondary batteries using a fumed silica-doped hydrogel electrolyte

Hydrogel electrolytes have received tremendous research interest in designing flexible zinc-ion secondary batteries, making them highly promising for flexible energy storage and wearable electronic devices. Herein, we report a composite hydrogel electrolyte (CHE) prepared using a fumed silica-doped gelatin hydrogel. This electrolyte is specifically designed for use in rechargeable aqueous Zn/MnO2 batteries (ReAZMBs). Experimental results showed that after fumed silica was added, the porosity and ionic conductivity of the gelatin hydrogel electrolyte increased. Meanwhile, adding fumed silica to the hydrogel electrolyte contributed to reducing self-corrosion and promoting rapid and uniform deposition of zinc ions. When the addition of fumed silica to gelatin was 10 wt%, ReAZMBs with this CHE exhibited a superior rate and cycling performance. More specifically, ReAZMBs with this CHE achieved an initial specific capacity of 150 mA h g-1 at a current density of 1.5 A g-1 and a capacity retention rate of 67% after 1000 cycles, which was much higher than that of the battery with the pure gelatin hydrogel electrolyte (33%). This was because of the improved interface stability between the zinc anode and electrolyte and the reduced formation of by-products (3Zn(OH)2·ZnSO4·3H2O and 3Zn(OH)2·ZnSO4·5H2O), according to the results of the charge-discharge test of Zn//Zn symmetric batteries and SEM and XRD characterizations of post-run zinc anodes. In addition, the ReAZMBs with the CHE demonstrated good flexibility and could supply power reliably even when bent.

Advanced electrolytes for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have garnered significant attention in the realm of large-scale and sustainable energy storage, primarily owing to their high safety, low cost, and eco-friendliness. Aqueous electrolytes, serving as an indispensable constituent, exert a direct influence on the electrochemical performance and longevity of AZIBs. Nonetheless, conventional aqueous electrolytes often encounter formidable challenges in AZIB applications, such as the limited electrochemical stability window and the zinc dendrite growth. In response to these hurdles, a series of advanced aqueous electrolytes have been proposed, such as "water-in-salt" electrolytes, aqueous eutectic electrolytes, molecular crowding electrolytes, and hydrogel electrolytes. This comprehensive review commences by presenting an in-depth overview of the fundamental compositions, principles, and distinctive characteristics of various advanced aqueous electrolytes for AZIBs. Subsequently, we systematically scrutinizes the recent research progress achieved with these advanced aqueous electrolytes. Furthermore, we summarizes the challenges and bottlenecks associated with these advanced aqueous electrolytes, along with offering recommendations. Based on the optimization of advanced aqueous electrolytes, this review outlines future directions and potential strategies for the development of high-performance AZIBs. This review is anticipated to provide valuable insights into the development of advanced electrolyte systems for the next generation of stable and sustainable multi-valent secondary batteries.

Zn Anode Surviving Extremely Corrosive Polybromide Environment with Alginate-Graphene Oxide Hydrogel Coating

Zinc-bromine (Zn-Br) redox provides a high energy density and low-cost option for next-generation energy storage systems, and polybromide diffusion remains a major issue leading to Zn anode corrosion, dendrite growth, battery self-discharge and limited electrochemical performance. A dual-functional Alginate-Graphene Oxide (AGO) hydrogel coating is proposed to prevent polybromide corrosion and suppress dendrite growth in Zn-Br batteries through negatively charged carboxyl groups and enhanced mechanical properties. The battery with anode of plain zinc coated with AGO (Zn]AGO) survives a severely corrosive environment with higher polybromide concentration than usual without a membrane, and achieves 80 cycles with 100% Coulombic and 80.65% energy efficiencies, four times compared to plain Zn anode. The promising performance is comparable to typical Zn-Br batteries using physical membranes, and the AGO coating concept can be well adapted to various Zn-Br systems to promote their applications.

Preparation of strong, tough and conductive soy protein isolate/poly(vinyl alcohol)-based hydrogel via the synergy of biomineralization and salting out

Conductive hydrogels have shown a great potential in the field of flexible electronic devices. However, conductive hydrogels prepare by traditional methods are difficult to combine high strength and toughness, which limits their application in various fields. In this study, a strategy for preparing conductive hydrogels with high strength and toughness by using the synergistic effect of biomineralization and salting-out was pioneered. In simple terms, by immersing the CaCl2 doped soy protein isolate/poly(vinyl alcohol)/dimethyl sulfoxide (SPI/PVA/DMSO) hydrogel in Na2CO3 and Na3Cit complex solution, the biomineralization aroused by Ca2+ and CO32-, and the salting-out effect of both NaCl and Na3Cit would enhance the mechanical properties of SPI/PVA/DMSO hydrogel. Meanwhile, the ionic conductivity of the hydrogel would also increase due the introduction of cation and anion. The mechanical and electrical properties of SPI/PVA/DMSO/CaCO3/Na3Cit hydrogels were significantly enhanced by the synergistic effect of biomineralization and salting-out. The optimum tensile strength, toughness, Young's modulus and ionic conductivity of the hydrogel were 1.4 ± 0.08 MPa, 0.51 ± 0.04 MPa and 1.46 ± 0.01 S/m, respectively. The SPI/PVA/DMSO/CaCO3/Na3Cit hydrogel was assembled into a strain sensor. The strain sensor had good sensitivity (GF = 3.18, strain in 20 %-500 %) and could be used to accurately detect various human movements.

Ultra-thin amphiphilic hydrogel electrolyte for flexible zinc-ion paper batteries

The paper-like ZIBs can be folded and unfolded using the Miura folding technique, enhancing the areal energy density by a factor of 18.

Designing of zwitterionic proline hydrogel electrolytes for anti-freezing supercapacitors

Hydrogel electrolytes containing a large amount of freezable water tend to freeze at subzero temperatures, which catastrophically reduces their ionic conductivity and thus limits their practical applications. In this work, we propose a new type anti-freezing hydrogel electrolyte based on an additive of zwitterionic proline, which can maintain high ionic conductivities of hydrogel electrolytes at subzero temperatures. The unique zwitterionic structure leads to several interesting characters like strong hydration, strong ionic interactions and low self-associations, which is proved to be the keys for the high performance of hydrogel electrolytes under low temperatures. As a result, the proline hydrogel electrolytes show a high ionic conductivity of 4.2 mS cm-1 even at -40 °C. The activated carbon electrode of supercapacitors based on proline hydrogel electrolytes delivers high specific capacitances of 145.8 (at 0.5 A g-1) and 116.1 F g-1 (at 0.5 A g-1) at 25 and -30 °C, respectively. Furthermore, the specific capacitance still shows a high retention of 71% after 12,000 charge/discharge cycles at -30 °C, confirming the good low-temperature adaptability. Such anti-freezing electrolytes with high ionic conductivity will open up a new avenue for anti-freezing energy storage devices, not limited to supercapacitors.

A Minireview of the Solid-State Electrolytes for Zinc Batteries

Aqueous zinc-ion batteries (ZIBs) have gained significant recognition as highly promising rechargeable batteries for the future due to their exceptional safety, low operating costs, and environmental advantages. Nevertheless, the widespread utilization of ZIBs for energy storage has been hindered by inherent challenges associated with aqueous electrolytes, including water decomposition reactions, evaporation, and liquid leakage. Fortunately, recent advances in solid-state electrolyte research have demonstrated great potential in resolving these challenges. Moreover, the flexibility and new chemistry of solid-state electrolytes offer further opportunities for their applications in wearable electronic devices and multifunctional settings. Nonetheless, despite the growing popularity of solid-state electrolyte-based-ZIBs in recent years, the development of solid-state electrolytes is still in its early stages. Bridging the substantial gap that exists is crucial before solid-state ZIBs become a practical reality. This review presents the advancements in various types of solid-state electrolytes for ZIBs, including film separators, inorganic additives, and organic polymers. Furthermore, it discusses the performance and impact of solid-state electrolytes. Finally, it outlines future directions for the development of solid-state ZIBs.

Salting-Out Effect Realizing High-Strength and Dendrite-Inhibiting Cellulose Hydrogel Electrolyte for Durable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are limited by poor Zn stripping/plating reversibility. Not only can hydrogel electrolytes address this issue, but also they are suitable for constructing flexible batteries. However, there exists a contradiction between the mechanical strength and the ionic conductivity for hydrogel electrolytes. Herein, high-concentration kosmotropic ions are introduced into the cellulose hydrogel electrolyte to take advantage of the salting-out effect. This can significantly improve both the mechanical strength and ionic conductivity. Additionally, the obtained cellulose hydrogel electrolyte (denoted as Con-CMC) has strong adhesion, a wide electrochemical stability window, and good water retaining ability. The Con-CMC is also found to accelerate the desolvation process, improve Zn deposition kinetics, promote Zn deposition along the (002) plane, and suppress parasitic reactions. Accordingly, the Zn/Zn cell with Con-CMC demonstrates dendrite-free behavior with prolonged lifespan and can endure extremely large areal capacity of 25 mAh cm-2. The Con-CMC also enables a large average Coulombic efficiency of 99.54% over 500 cycles for the Zn/Cu cell. Furthermore, the assembled pouch-type Zn/polyaniline full battery provides great rate capability, superior cyclability (even with limited Zn anode excess), a slow self-discharge rate, and outstanding affordability to external forces. Overall, this work extends our knowledge of the rational design of hydrogel electrolytes.

Nanomicellar Electrolyte To Control Release Ions and Reconstruct Hydrogen Bonding Network for Ultrastable High-Energy-Density Zn-Mn Battery

Zn-Mn batteries with two-electron conversion reactions simultaneously on the cathode and anode harvest a high voltage plateau and high energy density. However, the zinc anode faces dendrite growth and parasitic side reactions while the Mn2+/MnO2 reaction on the cathode involves oxygen evolution and possesses poor reversibility. Herein, a novel nanomicellar electrolyte using methylurea (Mu) has been developed that can encapsulate ions in the nanodomain structure to guide the homogeneous deposition of Zn2+/Mn2+ in the form of controlled release under an external electric field. Consecutive hydrogen bonding network is broken and a favorable local hydrogen bonding system is established, thus inhibiting the water-splitting-derived side reactions. Concomitantly, the solid-electrolyte interface protective layer is in situ generated on the Zn anode, further circumventing the corrosion issue resulting from the penetration of water molecules. The reversibility of the Mn2+/MnO2 conversion reaction is also significantly enhanced by regulating interfacial wettability and improving nucleation kinetics. Accordingly, the modified electrolyte endows the symmetric Zn∥Zn cell with extended cyclic stability of 800 h with suppressed dendrites growth at an areal capacity of 1 mAh cm-2. The assembled Zn-Mn electrolytic battery also demonstrates an exceptional capacity retention of nearly 100% after 800 cycles and a superior energy density of 800 Wh kg-1 at an areal capacity of 0.5 mAh cm-2.

Ni-doped Bi2O2CO3 nanosheet with H+/Zn2+ co-insertion for "rocking chair" zinc-ion battery

Developing insertion-type anode is key to advancing "rocking chair" zinc-ion batteries, though there are few reported insertion-type anodes. Herein, the Bi₂O₂CO₃ is a high-potential anode, with a special layered structure. A one-step hydrothermal method was used to prepare Ni-doped Bi₂O₂CO₃ nanosheet, and also a free-standing electrode consisting of Ni-Bi₂O₂CO₃ and CNTs was designed. Both cross-linked CNTs conductive networks and Ni doping improve charge transfer. Ex situ tests (XRD, XPS, TEM, etc.) reveal the H⁺/Zn²⁺ co-insertion mechanism of Bi₂O₂CO₃ and that Ni doping improves its electrochemical reversibility and structural stability. Therefore, this optimized electrode offers a high specific capacity of 159 mAh g^-1 at 100 mA g^-1, a suitable average discharge voltage of ≈0.400 V, and a long-term cycling stability of 2200 cycles at 700 mA g^-1. Besides, the Ni-Bi₂O₂CO₃//MnO₂ "rocking chair" zinc-ion battery (based on the total mass of cathode and anode) delivers a high capacity of ≈100 mAh g^-1 at 50.0 mA g^-1. This work provides a reference for designing high-performance anode in zinc-ion batteries.