Hydrogel Electrolyte Research Articles

Synergy between gelatin hydrogels and electrodes for adjustable and thermally stable ionic thermoelectric supercapacitors

Gelatin-based ionic hydrogels are flexible, bio-compatible, and abundant materials, showing immense potential as quasi-solid-state electrolytes in energy conversion and storage applications. Recent studies highlighted the critical synergy between hydrogel electrolytes and electrodes on the thermopower and energy density in emerging ionic thermoelectric (i-TE) devices. In this work, the significant impact from electrodes to the thermoelectric response of gelatin hydrogels is explored and explained at the molecular level. A universal negative offset in the thermopower is observed when substituting the conventional Cu foil by carbon-based paper (CBP) electrodes. This is attributed to the electrolyte infiltration and strong cation restriction on the CBP electrodes, which facilitates anion thermodiffusion. The thermopowers of Gelatin-CsCl change from p- (0.1–0.5 mV K−1) to n-type (up to −2.89 ± 0.34 mV K−1) and remain thermally stable at a large temperature difference of −36.8 K. The power factor and average power density in the ionic thermoelectric supercapacitors (ITESCs) made from Gelatin-0.02 M CsCl and CBP electrodes reach 2.13 ± 0.50 μW m−1 K−2 and 145.37 μW m−2 at a small temperature difference of −7.7 K. Furthermore, the highest normalized instantaneous power density achieved during the quasi-continuous charge–discharge cycles is 39.42 μW m−2 K−2, among the best ITESCs. This work provides fundamental insights into the previously overlooked synergy between gelatin hydrogels and electrodes for adjustable and thermally stable i-TE conversion and energy storage devices.

Dendrite-free, long cycle life Zn–MnO2 battery based on a polyanionic hydrogel electrolyte by constructing transfer channels and regulating solvation structure

Aqueous zinc ion batteries (AZIBs) are highly regarded as new generation of energy storage devices because of low cost and environmental friendliness. Particularly, flexible AZIBs with hydrogel electrolytes are suitable candidates for wearable electronics. However, continuous water-induced side reactions, uncontrolled dendrites and trade-off of electrochemical performances with mechanical strength are still obstacles for high-performance AZIBs. To address these issues, we designed a polyanionic hydrogel electrolyte (PAPHE) with sulfonate monomers and polyethylene glycol diacrylate (PEGDA) as crosslinker. Due to the electrostatic interactions between Zn2+ and sulfonate ions, Zn2+ can migrate along polyanionic chains. Meanwhile, electronegative oxygen atoms in PEGDA also interact with Zn2+ and weaken electrostatic interactions. The transfer channels are formed with “wall” of polyanion chains and PEGDA. Moreover, both sulfonate ions and ether bonds on the “wall” can regulate the solvation structure to reduce the activity of water, inhibiting side reactions, corrosion or by-products. Therefore, the PAPHE shows satisfying conductivity of 16.38 mS cm−1, stable Zn plating/stripping over 1600 h, flexibility and high compressive resistance (0.501 MPa at strain of 50 %). The Zn||PAPHE||MnO2 cells deliver good specific capacity of 274.5 mAh g−1 and can cycle over 1800 times. The pouch-cell can also work stably under various deformations.

Mussel-inspired, hydrophobic association-regulated hydrogel electrolytes with super-adhesive and self-healing properties for durable and flexible zinc-ion batteries

Quasi-solid-state gel polymer electrolytes (GPEs) can overcome the limitations of aqueous electrolytes and offer unparalleled adaptability which is critical to flexible aqueous Zn-ion batteries (AZIBs) for wearable electronics. However, the notorious Zn dendrites and inevitable interface delamination between electrodes and GPEs under mechanical deformation cause serious capacity fading or failure in AZIBs. Herein, highly adherable, strong, and self-healable GPEs constructed with physically crosslinked dopamine grafted sodium alginate and hydrophobic association network are designed to suppress Zn dendrite formation, reduce interfacial detachment, and maintain the electrochemical performance of flexible AZIBs during serious mechanical manipulations. The resulting GPE demonstrates outstanding attributes including high mechanical strength (382 kPa), good interfacial adhesion (80 kPa), exceptional ionic conductivity (32.3 mS cm−1), and desired self-healing efficiency (72.4 % after 5th breaking-healing cycle). Consequently, the assembled Zn//Zn cells achieve an improved cycling lifespan of over 2000 h at 2.0 mA cm−2. The assembled Zn//MnO2 batteries exhibit a high specific capacity of 290 mA h g−1 at 0.2 A g−1 and ultrahigh capacity retention of 91 % after 4000 cycles at 4 A g−1. Moreover, these flexible batteries maintain excellent performance under dynamic bending, twisting, and compressing, as well as remarkable reliability and self-healing ability, which are imperatively significant for practical applications.

Proton‐conducting hydrogel electrolytes with tight contact to binder‐free MXene electrodes for high‐performance thermally chargeable supercapacitor

AbstractThermally chargeable supercapacitors (TCSCs) have offered exceptional energy‐converting efficiency for absorbing human epidermal heat and generating and storing electrical energy, which then realize continuous power supply to electronic devices, such as sensors and wearable electronic products, in a wide range of practical significance. Here, we proposed a flexible TCSC by attaching binder‐free Ti3C2Tx MXene@PPy electrodes on both ends of the H3PO4@P(AM‐co‐AA‐co‐AYP K+) hydrogel electrolyte, which exhibits a large thermal power of 35.2 mV K−1 at 50% relative humidity and maximum figure of merit of 2.1. The high performances of the fabricated devices can be attributed to the tunable electrical, thermodynamic, thermoelectric, and mechanical properties of the hydrogel electrolyte by adjusting the acid content and the proportion of zwitterionic compound AYP K+ in the hydrogel, and the high photothermal conversion efficiency and electrochemical performance of the electrodes. Moreover, the stable and outstanding thermofvoltage output (∼200 mV) under different time scenarios of the TCSC makes it possible to drive a strain sensor, accomplishing the objectives of a human activity monitor.

Entanglement Added to Cross-Linked Chains Enables Tough Gelatin-Based Hydrogel for Zn Metal Batteries.

Currently, it is still challenging to develop a hydrogel electrolyte matrix that can successfully achieve a harmonious combination of mechanical strength, ionic conductivity, and interfacial adaptability. Herein, a multi-networked hydrogel electrolyte with a high entanglement effect based on gelatin/oxidized dextran/methacrylic anhydride, denoted as ODGelMA is constructed. Attribute to the Schiff base network formulation of ─RC═N─, oxidized dextran integrated gelatin chains induce a dense hydrophilic conformation group. Furthermore, addition of methacrylic anhydride through a grafting process, the entangled hydrogel achieves impressive mechanical features (6.8MPa tensile strength) and high ionic conductivity (3.68mScm-1 at 20°C). The ODGelMA electrolyte regulates the zinc electrode by circumventing dendrite growth, and showcases an adaptable framework reservoir to accelerate the Zn2+ desolvation process. Benefiting from the entanglement effect, the Zn anode achieves an outstanding average Coulombic efficiency (CE) of 99.8% over 500 cycles and cycling stability of 900h at 5mAcm-2 and 2.5mAhcm-2. The Zn||I2 full cell yields an ultra-long cycling stability of 10000 cycles with a capacity retention of 92.4% at 5C. Furthermore, a 60mAh single-layer pouch cell maintains a stable work of 350 cycles.

Aqueous AlCl3/ZnCl2 solution room-induced the self-growing strategy of expanded topological network for cellulose/polyacrylamide-based solid-state electrolytes

The green synthesis strategy for cellulose-containing hydrogel electrolytes is significant for effectively managing resources, energy, and environmental concerns in the contemporary world. Herein, we propose an all-green strategy using AlCl3/ZnCl2/H2O solvent to create cellulose/polyacrylamide-based hydrogel (AZ-Cel/PAM) with expanded hierarchical topologies. The aqueous AlCl3/ZnCl2 facilitates the efficient dissolution of cellulose at room temperature, and the dispersed Al3+-Zn2+ ions autocatalytic system catalyzes in-situ polymerization of acrylamide (AM) monomer. This expands the AM network within the cellulose framework, forming multiple bonding interactions and stable ion channels. The resulting hybrid hydrogel exhibits improved mechanical properties (tensile strength of 56.54 kPa and compressive strength of 359.43 kPa) and enhanced ionic conductivity (1.99 S/m). Furthermore, it also demonstrates excellent adhesion, freeze resistance (−45 °C), and water retention capabilities. Quantum simulations further clarify the mechanical composition and ion transport mechanism of AZ-Cel/PAM hydrogels. The assembled supercapacitor with the hydrogel electrolyte, demonstrates an ideal area-specific capacitance of 203.80 mF/cm2. This all-green strategy presents a novel approach to developing sustainable energy storage devices.

Research and development of double layer P-doped laser induced graphene thin film electrode for flexible micro-supercapacitor applications

Laser-induced graphene (LIG) has garnered significant attention for its cost-effectiveness and high efficiency in fabricating flexible micro-energy storage devices. In this study, we devised a simple method to fabricate double layer P-doped LIG electrodes through repetitive laser induction technology for high-performance flexible energy storage applications. Instead of utilizing commercial polyimide (PI) thin film, we optimized the formation process of P-doped PI thin film and achieved a highly flexible double layer P-doped LIG thin film electrode with a uniformly porous structure and the high porosity through repeated laser induction processes. Experimental results demonstrated that the developed double layer P-doped LIG thin film electrode exhibits high porosity, high specific areal capacitance of 180 mF cm−2, and high energy density of 0.025 mWh cm−2. Furthermore, an all-solid-state micro-supercapacitor utilizing hydrogel electrolyte was assembled, demonstrating a high areal capacitance of 62 mF cm−2 and excellent cycling stability with 95% capacitance retention after 6000 charging/discharging cycles. Moreover, the developed all-solid-state micro-supercapacitor successfully powered a light-emitting diode, showcasing its significant potential for practical energy storage applications.

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.

Strategies of regulating Zn2+ solvation structures toward advanced aqueous zinc-based batteries

Rechargeable aqueous zinc-based batteries not only pave the way for environmentally friendly and safe energy storage devices but also hold great promise for reducing the manufacturing costs of next-generation batteries, positioning them as the most promising energy storage system to replace lithium-ion batteries. However, the commercial application of aqueous zinc-based batteries (AZBs) is severely constrained by issues such as zinc dendrites, hydrogen evolution reaction (HER), and electrode corrosion. While significant efforts have been devoted to exploring electrode materials and their storage mechanisms in this system in recent years, research on the nature of Zn2+ solvation in electrolytes remains insufficient. Therefore, this review primarily provides a comprehensive and in-depth elucidation of the existing issues such as dendrite formation, hydrogen/oxygen evolution, electrode corrosion and passivation interactions. Additionally, from the perspective of electrolyte optimization, this review emphasizes existing strategies to address Zn2+ solvation, including adjusting electrolyte concentration, incorporating functional additives or co-solvents, utilizing ionic liquids, and developing hydrogel electrolytes, and summarizes approaches and mechanisms for improving their relevant performance. Finally, prospects for electrolyte modification and innovation directions of AZBs are proposed, providing guidance for future AZB studies.

Synergistic effects of dimethyl sulfoxide-treatment and aramid nanofiber addition on performance enhancement of the PEDOT: PSS-based supercapacitor

Charge storage performance of the poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS, PH1000)-based supercapacitor is greatly enhanced by dimethyl sulfoxide (DMSO)-treatment and addition of aramid nanofibers (ANFs), but the underlying mechanism is unclear. To reveal it, we synthesized the films of PH1000, DMSO-treated PH1000 (D-P) and DMSO-treated PH1000-20 wt%ANF (D-PA) to construct the in-plane supercapacitors. A comparative study of electrochemical performance was firstly conducted to identify the specific contribution of DMSO-treatment and ANF components. Electrochemical impedance spectroscopy (EIS) was then analyzed, and the results demonstrated that the reduction of the ohmic resistance of the device was mainly attributed to the DMSO-treatment, while the addition of ANFs was found to contribute more to the decrease of Warburg resistance. The effects of DMSO-treatment and ANF components on the electrical propertíe and microstructure of PH1000 film were analyzed based on the square resistance results and AFM/SEM images, respectively. Dynamic permeation processes of the hydrogel electrolyte on the films were further recorded, vividly showing that the electrolyte permeability is highly dependent on the microstructure of the film. Through these analyses, a deep insight into the synergistic effects of DMSO-treatment and ANF addition on the electrochemical performance of the PH1000-based supercapacitor has been reached.

Amphiphilic ionic liquid hydrogel electrolytes with high ionic conductivity towards dendrite-free ultra-stable aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) are highly promising as large-scale energy storage devices with high capacity, safety, and low cost. However, the parasitic reaction on the of Zn anode and the growth of Zn dendrites greatly prevent the practical application of AZIBs. Here, we propose an effective strategy with hydrogel electrolytes by adding dual amphiphilic ionic liquids into acrylamide, allowing for the occurrence of the following phenomena related to the Zn anode: 1) Zn2+ preferential adsorption by the amphiphilic ionic groups to regulate the electrodeposition behavior of Zn2+ on the Zn(002) crystal surface and inhibit the growth of Zn dendrites; 2) water removal from the Zn2+ solvation sheath, reducing water activity and inhibiting side reactions; 3) improved environmental adaptability of the hydrogel electrolyte through enhancing its mechanical properties and adhesion. The obtained hydrogel electrolyte has a high ionic conductivity of 41.47 mS/cm, a highly reversible Zn plating/stripping cycle of 1400 h in Zn||Zn symmetric batteries and an enhanced electrochemical performance in Zn||NVO full batteries (94 % capacity retention at 5.0 A g−1/3000 cycles). Even under harsh conditions (10 mA cm−2/10 mAh cm−2), these cells maintained excellent cycling stability. This study provides new ideas for the practical applications of AZIBs.

Activating the Intrinsic Zincophilicity of PAM Hydrogel to Stabilize the Metal-Electrolyte Dynamic Interface for Stable and Long-Life Zinc Metal Batteries.

As a potential material to solve rampant dendrites and hydrogen evolution reaction (HER) problem of aqueous zinc metal batteries (AZMB), hydrogel electrolytes usually require additional additives or multi-molecular network strategies to solve existing problems of ionic conductivity, mechanical properties and interface stability. However, the intrinsic zincophilic properties of the gel itself are widely neglected leading to the addition of additional molecules and the complexity of the preparation process. In this work, we innovatively utilize the characteristics of acrylamide's high zincophilic group density, activating the intrinsic zincophilic properties of PAM gel through a simple concentration control strategy which reconstructs a novel zinc-electrolyte interface different from conventional PAM electrolyte. The activated novel gel electrolyte with intrinsic zincophilic properties has high ionic conductivity and effectively suppresses water activity, thereby inhibiting HER corrosion. Meanwhile, it induces uniform deposition of (002) crystal planes, leading to excellent deposition kinetics and long cycle life, thereby ensuring high interfacial stability. Compared with conventional PAM gel electrolytes, the activated zincophilic group-rich hydrogel maintained excellent cycling stability (1 mA/cm2, 1 mAh/cm2) over 2250 hours; The Zn//MnO₂ coin cell using novel zincophilic group -rich hydrogel still retains a high specific capacity of more than 170 mAh/g at 0.5 A/g after 1000 cycles.

Hydrated Calcium Vanadate Nanoribbons with a Stable Structure and Fast Ion Diffusion as a Cathode for Quasi-Solid-State Zinc-Ion Batteries.

We demonstrated the use of hydrated calcium vanadate (CaV6O16·3H2O, denoted as CaVO-2) as a cathode for aqueous zinc-ion batteries (AZIBs). Nanoribbons of hydrated calcium vanadate facilitated shortening of the Zn2+ transport distance and accelerated zinc-ion insertion. The introduction of interlayer structure water increased the interlayer spacing of calcium vanadate and as a "lubricant". Ca2+ insertion also expanded the interlayer spacing and further stabilized the interlayer structure of vanadium-based oxide. The density functional theory results showed that the introduction of Ca2+ and structured water could effectively improve the diffusion kinetics, resulting in the rapid transport of zinc ions. As a result, AZIBs based on the CaVO-2 cathode offered high specific capacity (329.6 mAh g-1 at 200 mA g-1) and fast charge/discharge capability (147 mAh g-1 at 10 A g-1). Impressively, quasi-solid-state zinc-ion batteries based on the CaVO-2 cathode and polyacrylamide-cellulose nanofiber hydrogel electrolytes maintained an outstanding specific capacity and long cycle life (162 mAh g-1 over 10 000 cycles at 5 A g-1). This study provided a reliable strategy for metal-ion insertion and the structural water introduction of oxides to produce a high-quality cathode for ZIBs. Meanwhile, it provides ideas for the combination of vanadium-based materials and gel electrolytes to construct solid-state zinc-ion batteries.

Multifunctional Zincophilic Hydrogel Electrolyte with Abundant Hydrogen Bonds for Zinc-Ion Capacitors and Supercapacitors.

The new-generation flexible Zn-ion capacitors (ZICs) require multifunctionality and environmental adaptability for practical applications. This essentially means that hydrogel electrolytes are expected to possess superior mechanical properties, temperature resistance, and tunable interface properties to resist flexibility loss and performance degradation over a wide operating temperatures range. Herein, a multifunctional polyzwitterionic hydrogel electrolyte (PAM/LA/PSBMA) with wide operating temperatures, excellent tensile ability, high water retention, and self-adhesion is designed. Molecular dynamics simulations and experimental results show that polar functional groups (-COO-, -SO3-, -C═O, and -NHCO-) in the hydrogel can form abundant hydrogen bonds with water molecules, which can destroy the original hydrogen bonds (HBs) network between the water molecules and have a low freezing point. It can also form coordination with Zn2+, so that the deposition of Zn2+ electric field homogenization effectively alleviates the growth of Zn dendrites. On this basis, the constructed Zn//Zn cell can be stably cycled 290 h at 10 mA cm-2 (1 mA h cm-2). The constructed ZICs and supercapacitor have a high specific capacitance, excellent energy density, good ionic conductivity, and long cycling stability. This study provides guidance on molecular design for the development of integrated multifunctional smart electronic devices that are environmentally adaptable, resistant to drying, and highly flexible.

3D printed dual network Cross-Linked hydrogel electrolytes for high area capacity flexible zinc ion Micro-Batteries

Hydrogel electrolytes have wide applications in flexible zinc ion micro-batteries (FZIMBs) due to their excellent mechanical flexibility, biocompatibility, and ionic conductivity. However, traditional templating methods are limited to fabricating two-dimensional and simple three-dimensional structures, making them insufficient for preparing complex structures in FZIMBs. Here, we report a printable hydrogel electrolyte ink with excellent rheological properties. By utilizing 3D printing technology, we achieve the preparation of a custom-shaped, double-network crosslinked polyacrylamide-hydroxypropyl methylcellulose hydrogel electrolyte (PHHE). The PHHE exhibits high ionic conductivity (31.72 mS cm−1), good cycling stability, and mechanical flexibility. Furthermore, we constructed FZIMBs with high areal capacities (6.45 mAh cm−2 at 0.5 mA cm−2) and good mechanical flexibility by leveraging PHHE and 3D printing technology. Integrating FZIMBs with a pressure sensing component, we establish a sensing interaction system, demonstrating practical applications of flexible wearable devices. This work presents a novel method for the preparation of customized hydrogel electrolytes and highlights the significant potential of FZIMBs in practical applications.

Self-Powered Biomimetic Pressure Sensor Based on Mn-Ag Electrochemical Reaction for Monitoring Rehabilitation Training of Athletes.

Self-powered pressure detection using smart wearable devices is the subject of intense research attention, which is intended to address the critical need for prolonged and uninterrupted operations. Current piezoelectric and triboelectric sensors well respond to dynamic stimuli while overlooking static stimuli. This study proposes a dual-response potentiometric pressure sensor that responds to both dynamic and static stimuli. The proposed sensor utilizes interdigital electrodes with MnO2/carbon/polyvinyl alcohol (PVA) as the cathode and conductive silver paste as the anode. The electrolyte layer incorporates a mixed hydrogel of PVA and phosphoric acid. The optimized interdigital electrodes and sandpaper-like microstructured surface of the hydrogel electrolyte contribute to enhanced performance by facilitating an increased contact area between the electrolyte and electrodes. The sensor features an open-circuit voltage of 0.927V, a short-circuit current of 6µA, a higher sensitivity of 14mV/kPa, and outstanding cycling performance (>5000 cycles). It can accurately recognize letter writing and enable capacitor charging and LED lighting. Additionally, a data acquisition and display system employing the proposed sensor, which facilitates the monitoring of athletes' rehabilitation training, and machine learning algorithms that effectively guide rehabilitation actions are presented. This study offers novel solutions for the future development of smart wearable devices.

Lean-water hydrogel electrolyte with improved ion conductivity for dendrite-free zinc-Ion batteries

Although rechargeable aqueous zinc-ion batteries (ZIBs) are regarded as promising energy storage devices, the uncontrollable Zn dendrite and undesirable side reactions severely limit their practical applications. Herein, an anionic hydrogel electrolyte PAM/SA with 3D porous structures is developed by integrating sodium alginate (SA) and polyacrylamide (PAM) networks for highly reversible Zn plating/stripping. Mechanically enhanced and lean-water PAM/SA hydrogel with anionic chains for constructing ionic channels and molecular lubrication films, which facilitate Zn2+ migration for a high ionic conductivity (5.4 S m−1) and Zn2+ transference number (0.86) even under lean-water conditions (about 60%). Based on the experimental and theoretical analysis, the SA chain with strong coordination ability endows PAM/SA with improved desolvation kinetics and the ability to regulate the electric field intensity at the electrode/electrolyte interface, which is beneficial for suppressing side reactions and facilitating directional Zn deposition. Subsequently, the symmetric Zn//Zn cell based on PAM/SA hydrogel electrolyte delivers stable cycles for over 1800 h. The assembled Zn//V2O5 battery based on PAM/SA reveals a high specific capacity and a long cycle life. This work provides a new insight for developing hydrogel electrolytes with high ionic conductivity and lean-water properties toward stable Zn anode

In-Situ Spontaneous Electropolymerization Enables Robust Hydrogel Electrolyte Interfaces in Aqueous Batteries.

Hydrogels hold great promise as electrolytes for emerging aqueous batteries, for which establishing a robust electrode-hydrogel interface is crucial for mitigating side reactions. Conventional hydrogel electrolytes fabricated by ex situ polymerization through either thermal stimulation or photo exposure cannot ensure complete interfacial contact with electrodes. Herein, we introduce an in situ electropolymerization approach for constructing hydrogel electrolytes. The hydrogel is spontaneously generated during the initial cycling of the battery, eliminating the need of additional initiators for polymerization. The involvement of electrodes during the hydrogel synthesis yields well-bonded and deep infiltrated electrode-electrolyte interfaces. As a case study, we attest that, the in situ-formed polyanionic hydrogel in Zn-MnO2 battery substantially improves the stability and kinetics of both Zn anode and porous MnO2 cathode owing to the robust interfaces. This research provides insight to the function of hydrogel electrolyte interfaces and constitutes a critical advancement in designing highly durable aqueous batteries.

In‐Situ Spontaneous Electropolymerization Enables Robust Hydrogel Electrolyte Interfaces in Aqueous Batteries

AbstractHydrogels hold great promise as electrolytes for emerging aqueous batteries, for which establishing a robust electrode‐hydrogel interface is crucial for mitigating side reactions. Conventional hydrogel electrolytes fabricated by ex situ polymerization through either thermal stimulation or photo exposure cannot ensure complete interfacial contact with electrodes. Herein, we introduce an in situ electropolymerization approach for constructing hydrogel electrolytes. The hydrogel is spontaneously generated during the initial cycling of the battery, eliminating the need of additional initiators for polymerization. The involvement of electrodes during the hydrogel synthesis yields well‐bonded and deep infiltrated electrode‐electrolyte interfaces. As a case study, we attest that, the in situ‐formed polyanionic hydrogel in Zn‐MnO2 battery substantially improves the stability and kinetics of both Zn anode and porous MnO2 cathode owing to the robust interfaces. This research provides insight to the function of hydrogel electrolyte interfaces and constitutes a critical advancement in designing highly durable aqueous batteries.

Distinguish MnO2/Mn2+ Conversion/ Zn2+ Intercalation/ H+ Conversion Chemistries at Different Potentials in Aqueous Zn||MnO2 Batteries

AbstractThe rechargeable aqueous Zn||MnO2 chemistry has been extensively explored, but its electrochemical reaction mechanisms, especially in the context of MnO2/Mn2+ conversion and Zn2+/H+ intercalation chemistry, remain not fully understood. Here, we designed an amphiphilic hydrogel electrolyte, which distinguished the MnO2/Mn2+ conversion, Zn2+ intercalation, and H+ intercalation and conversion processes at three distinct discharge plateaus of an aqueous Zn||MnO2 battery. The amphiphilic hydrogel electrolyte is featured with an extended electrochemical stability window up to 3.0 V, high ionic conductivity, Zn2+‐selective ion tunnels, and hydrophobic associations with cathode materials. This specifically designed electrolyte allows the MnO2/Mn2+ conversion reaction at a discharge plateau of 1.75 V. More interesting, the discharge plateaus of ~1.33 V, previously assigned as the co‐intercalation of Zn2+ and H+ ions in the MnO2 cathode, are specified as the exclusive intercalation of Zn2+ ions, leading to an ultra‐flat voltage plateau. Furthermore, with a distinct three‐step electrochemical energy storage process, a high areal capacity of 1.8 mAh cm−2 and high specific energy of 0.858 Wh cm−2, even at a low MnO2 loading mass of 0.5 mg cm−2 are achieved. To our knowledge, this is the first report to fully distinguish different mechanisms at different potentials in aqueous Zn||MnO2 batteries.