Freeze-Tolerant Hydrogel Electrolyte with High Strength for Stable Operation of Flexible Zinc-Ion Hybrid Supercapacitors

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.

Fire-resistant and low-temperature self-healing bio-based hydrogel electrolytes based on peach gum polysaccharide/sisal nanofibers for flexible supercapacitors

The introduction of flame retardancy and low-temperature self-healing capacities in hydrogel electrolytes are crucial for promoting the cycle stability and durability of the flexible supercapacitors in extreme environments. Herein, biomass-based dual-network hydrogel electrolyte (named PSBGL), was synthesized with borax crosslinked peach gum polysaccharide/sisal nanofibers composite, and its application in flexible supercapacitors was also investigated in detail. The dynamic cross-linking of the dual-network endows the PSBGL with excellent self-healing performance, enabling ultrafast self-healing within seconds at both room temperature and extreme low temperatures. The PSBGL bio-based hydrogel electrolyte can maintain the integrity of the carbon layer structure with limiting oxygen index of 56 % after 60 s of combustion under a flame gun. Additionally, the PSBGL exhibits high ionic conductivity (30.12 mS cm-1), good tensile strength (1.78 MPa), and robust adhesion to electrodes (1.15 MPa). The assembled supercapacitors demonstrate a high specific capacitance of 187.8 F g-1 at 0.5 A g-1, with 95.9 % capacitance retention rate after 10,000 cycles at room temperature. Importantly, even under extreme temperatures of 60 °C and -35 °C, the supercapacitors can also maintain high capacitance retention rates of 90.1 % and 86.5 % after 10,000 cycles. This work fills the gap between biomaterial design and high-performance flexible supercapacitors.

Nanocomposite hydrogel for skin motion sensing - An antifreezing, nanoreinforced hydrogel with decorated AuNP as a multicrosslinker

In this study, we present a nanocomposite hydrogel designed for skin motion sensing. The hydrogel is based on poly(acrylamide) crosslinked with gold nanoparticles covalently bound to the polymer matrix, yielding a robust, highly elastic and conductive material. The choice of amino acid derivative - N,N'-diacryloylcystine salt (BISS) - as a crosslinker allows for the introduction of gold nanoparticles, due to the presence of sulfide groups in its structure. During the nanoparticle modification process, covalent bonds between gold and sulfur atoms are formed as the disulfide bond is cleaved. In result of this self-assembly process, a multifunctional Au-BISS crosslinker is formed, enhancing the material's mechanical properties and introducing electrical conductivity. To confer anti-freezing properties and limit water evaporation, a binary mixture of water and glycerol was used. The resultant hydrogel exhibits high elasticity, strain sensitivity across a wide strain range and various types of deformation (elongation, bending, compression) with exceptional response time (120 ms) and recovery time (90 ms). The material's cold-resistance, resilience, and conductivity make it well-suited for real-time monitoring of joint movements and speech recognition, with potential applications in electronic skin and healthcare monitoring devices.

Next-generation all-organic composites: A sustainable successor to organic-inorganic hybrid materials

This Review presents an overview of all-organic nanocomposites, a sustainable alternative to organic-inorganic hybrids. All-organic nanocomposites contain nanocellulose, nanochitin, and aramid nanofibers as highly rigid reinforcing fillers. They offer superior mechanical properties and lightweight characteristics suitable for diverse applications. The Review discusses various methods for preparing the organic nanofillers, including top-down and bottom-up approaches. It highlights in situ polymerization as the preferred method for incorporating these nanomaterials into polymer matrices to achieve homogeneous filler dispersion, a crucial factor for realizing desired performance. Furthermore, the Review explores several applications of all-organic nanocomposites in diverse fields including food packaging, performance-advantaged plastics, and electronic materials. Future research directions-developing sustainable production methods, expanding biomedical applications, and enhancing resistance against heat, chemicals, and radiation of all-organic nanocomposites to permit their use in extreme environments-are explored. This Review offers insights into the potential of all-organic nanocomposites to drive sustainable growth while meeting the demand for high-performance materials across various industries.

Recent Advances in Biopolymer-Based Hydrogel Electrolytes for Flexible Supercapacitors

Growing concern regarding the impact of fossil fuels has led to demands for the development of green and renewable materials for advanced electrochemical energy storage devices. Biopolymers with unique hierarchical structures and physicochemical properties, serving as an appealing platform for the advancement of sustainable energy, have found widespread application in the gel electrolytes of supercapacitors. In this Review, we outline the structure and characteristics of various biopolymers, discuss the proposed mechanisms and assess the evaluation metrics of gel electrolytes in supercapacitor devices, and further analyze the roles of biopolymer materials in this context. The state-of-the-art electrochemical performance of biopolymer-based hydrogel electrolytes for supercapacitors and their multiple functionalities are summarized, while underscoring the current technical challenges and potential solutions. This Review is intended to offer a thorough overview of recent developments in biopolymer-based hydrogel electrolytes, highlighting research concerning green and sustainable energy storage devices and potential avenues for further development.

Self-adhesive, freeze-tolerant, and strong hydrogel electrolyte containing xanthan gum enables the high-performance of zinc-ion hybrid supercapacitors

Hydrogel electrolyte is an ideal candidate material for flexible energy storage devices due to its excellent softness and conductivity properties. However, challenges such as the inherent mechanical weakness, the susceptibility to be frozen in low-temperature environments, and the insufficiency of hydrogel-electrode contact persist. Herein, a "Multi in One" strategy is employed to effectively conquer these difficulties by endowing hydrogels with high strength, freeze-resistance, and self-adhesive ability. Multiple hydrogen bond networks and ion crosslinking networks are constructed within the hydrogel electrolyte (PVA/PAAc/XG) containing polyvinyl alcohol (PVA), acrylic acid (AAc), and xanthan gum (XG), promoting the enhanced mechanical property, and the adhesion to electrode materials is also improved through abundant active groups. The introduction of zinc ions provides the material with superior frost resistance while also promoting electrical conductivity. Leveraging its multifunction of superior mechanical strength, anti-freeze property, and self-adhesive characteristic, the PVA/PAAc/XG hydrogel electrolyte is employed to fabricate zinc ion hybrid supercapacitors (ZHS). Remarkably, ZHS exhibits outstanding electrochemical performance and cycle stability. A remarkable capacity retention rate of 83.86 % after 10,000 charge-discharge cycles can be achieved at high current densities, even when the operational temperature decreases to -60 °C, showing great potential in the field of flexible energy storage devices.

Strong and tough poly(vinyl alcohol)/xanthan gum-based ionic conducting hydrogel enabled through the synergistic effect of ion cross-linking and salting out

The mechanical properties of ionic conductive hydrogels (ICHs) are generally inadequate, leading to their susceptibility to breakage under external forces and consequently resulting in the failure of flexible electronic devices. In this work, a simple and convenient strategy was proposed based on the synergistic effect of ion cross-linking and salting out, in which the hydrogels consisting of polyvinyl alcohol (PVA) and xanthan gum (XG) were immersed in zinc sulfate (ZnSO4) solution to obtain ICHs with exceptional mechanical properties. The salt-out effects between PVA chains and SO42- ions along with the cross-linked network of XG chains and Zn2+ ions contribute to the desirable mechanical properties of ICHs. Notably, the mechanical properties of ICHs can be adjusted by changing the concentration of ZnSO4 solution. Consequently, the optimum fracture stress and the fracture energy can reach 3.38 MPa and 12.13 KJ m-2, respectively. Moreover, the ICHs demonstrated a favorable sensitivity (up to 2.05) when utilized as a strain sensor, exhibiting an accurate detection of human body movements across various amplitudes.

Flexible Supercapacitor with Wide Electrochemical Stable Window Based on Hydrogel Electrolyte

Hydrogel electrolyte can endow supercapacitors with excellent flexibility, which has developed rapidly in recent years. However, the water-rich structures of hydrogel electrolyte are easy to freeze at subfreezing and dry at high temperatures, which will affect its energy storage characteristics. The low energy density of micro supercapacitors also hinders their development. Herein, a strategy is proposed to reduce the free water activity in the hydrogel to improve the operating voltage and the energy density of the device, which is achieved through the synergistic effect of the hydrogel skeleton, N, N'-dimethylformamide (DMF), NaClO4 and water. High concentrations of DMF and NaClO4 are introduced into sodium alginate/polyacrylamide (SA/PAAM) hydrogel through solvent exchange to obtain SA/PAAM/DMF/NaClO4 hydrogel electrolyte, which exhibited a high ionic conductivity of 82.1 mS cm-1, a high breaking strength of 563.2 kPa, and a wide voltage stability window of 3.5 V. The supercapacitor devices are assembled by the process of direct adhesion of the hydrogel electrolyte and  laser induced graphene (LIG). The micro-supercapacitor exhibited an operating voltage of 2.0 V, with a specific capacitance of 2.41 mF cm-2 and a high energy density of 1.34 µWh cm-2, and it also exhibit a high cycle stability, good flexibility, and integration performance.

Construction methods and biomedical applications of PVA-based hydrogels

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.

Tough, Antifreezing, and Piezoelectric Organohydrogel as a Flexible Wearable Sensor for Human-Machine Interaction

Piezoelectric hydrogel sensors are becoming increasingly popular for wearable sensing applications due to their high sensitivity, self-powered performance, and simple preparation process. However, conventional piezoelectric hydrogels lack antifreezing properties and are thus confronted with the liability of rupture in low temperatures owing to the use of water as the dispersion medium. Herein, a kind of piezoelectric organohydrogel that integrates piezoelectricity, low-temperature tolerance, mechanical robustness, and stable electrical performance is reported by using poly(vinylidene fluoride) (PVDF), acrylonitrile (AN), acrylamide (AAm), p-styrenesulfonate (NaSS), glycerol, and zinc chloride. In detail, the dipolar interaction of the PVDF chain with the PAN chain facilitates the crystal phase transition of PVDF from the α to β phase, which endows the organohydrogels with a high piezoelectric constant d33 of 35 pC/N. In addition, the organohydrogels are highly ductile and can withstand significant tensile and compressive forces through the synergy of the dipolar interaction and amide hydrogen bonding. Besides, by incorporating glycerol and zinc chloride, the growth of ice crystals is inhibited, allowing the organohydrogels to maintain stable flexibility and sensitivity even at -20 °C. The real-time monitoring of the pulse signal for up to 2 min indicates that the gel sensor has stable sensitivity. It is believed that our organohydrogels will have good prospects in future wearable electronics.

Ultrahigh-Ionic-Conductivity, Antifreezing Poly(amidoxime)-Grafted Polyzwitterion Hydrogel for Facile Integrated into High-Performance Stretchable Flexible Supercapacitor

Developing wearable supercapacitors (SCs) with high stretchability, arbitrary deformability, and antifreezing ability is still a challenge. In the present work, an ultrahigh-ionic-conductivity, antifreezing poly(amidoxime)-graft-polyzwitterion (PAO-g-PSBMA) hydrogel electrolyte is fabricated by grafting PSBMA in PAO. Owing to the abundant hydrophilic and high ionic adsorption capacity of amidoxime groups in PAO and zwitterion groups in PSBMA, the as-prepared PAO-g-PSBMA hydrogel can facilitate the dissociation of lithium salt and exhibit an ultrahigh ionic conductivity of 29.8 S m-1 at 25 °C and 3.4 S m-1 even at -30 °C. Employing mATi3C2Tx and mSTi3C2Tx, which contain small amounts of PAO-AGE and PAO-g-PSBMA dispersions, respectively, coated onto both sides of the PAO-g-PSBMA hydrogel, we followed a thermal treatment to facilely form integrated stretchable flexible SCs. The as-prepared SCs show an outstanding recoverable tensile stain of 80% and an excellent electrochemical stability under many types and times of arbitrary deformation. More importantly, as-prepared mATi3C2Tx- and mSTi3C2Tx-based SCs present fantastic antifreezing ability and excellent stability with 74.6 and 78.3% retention of the initial capacitance, respectively, even after 1000 times of stretching to 60% at -30 °C. This work offers a new strategy of using PAO-grafted polyzwitterion for obtaining an antifreezing stretchable SC, which shows a high potential for application in next-generation integrated stretchable devices in various fields.

Key to High Performance Ion Hybrid Capacitor: Weakly Solvated Zinc Cations

Zinc ion hybrid capacitors suffer from lack of reversibility and dendrite formation. An electrolyte, based on a solution of a zinc salt in acetonitrile and tetramethylene sulfone, allows smooth zinc deposition with high coulombic efficiency in a Zn||stainless steel cell (99.6% for 2880 cycles at 1.0 mA cm-2 , 1.0 mAh cm-2 ). A Zn||Zn cell operates stably for at least 7940 h at 1.0 mA cm-2 with an area capacity of 10 mAh cm-2 , or 648 h at 90% depth of discharge and 1 mA cm-2 , 9.0 mAh cm-2 . Molecular dynamics simulations reveal the reason for the excellent reversibility: The zinc cation is only weakly solvated than in pure tetramethylene sulfone with the closest atoms at 3.3 to 3.8 Å. With this electrolyte, a zinc||activated-carbon hybrid capacitor exhibits an operating voltage of 2.0 to 2.5 V, an energy-density of 135 Wh kg-1 and a power-density of 613 W kg-1 at 0.5 A g-1 . At the very high current-density of 15 A g-1 , 29.3 Wh kg-1 and 14 250 W kg-1 are achieved with 81.2% capacity retention over 9000 cycles.

Stable zinc anode interface and environmentally adaptable hydrogel electrolytes for stable operation of zinc-ion hybrid supercapacitors

Hydrogel-based zinc ion hybrid supercapacitors (ZIHS) have stood out from many energy storage device candidates due to their battery-level energy density, inherent flexibility, and safety. Nevertheless, the inevitable dendrite growth of Zn anodes and sharp capacity degradation at low-temperature seriously hinder their practical application. Herein, a dense ZnF2 solid electrolyte interface protective layer was constructed in situ on the Zn electrode surface by a simple chemical deposition method, effectively isolating the water molecules and alleviating the water-induced dendrite growth and parasitic reaction. To achieve the flexible ZIHS with environmental adaptability, a self-adhesion and anti-freezing zwitterionic hydrogel electrolyte was fabricated to afford superior ionic conductivity (97.1 mS cm-1), excellent anti-drying ability, and robust interfacial adhesion. Benefitting from the integrated merits of the as-designed electrolyte and electrode, the ZIHS delivered excellent mechanical adaptability, favorable energy density (103.9 Wh kg-1 at 270.1 W kg-1), broad operating temperature range (-40 to 40 °C), along with long-term cycling stability (12,000 cycles) with 90.3 % capacity retention at -25 °C. Notably, the unencapsulated ZIHS achieved exceptional electrochemical stability in an open environment. This finding provides valuable insights for constructing durable, flexible, and environmentally adaptable zinc-based energy storage systems.

Amorphous carbon nanosheets suitable for deep eutectic solvent electrolyte toward cryogenic energy storage

The emerging deep eutectic solvent (DES) electrolyte has great potential in realizing commercial-scale application of electric double-layer capacitors (EDLCs) served in low temperature environment. That goal, however, rests with how to design the interface structure of electrode materials for well-matching with DES electrolyte. Herein, porous carbon nanosheets (PCNs) were obtained from coal tar pitch through Friedel-Crafts acylation reaction and melting salt intercalation process. The morphology, specific surface area and porosity of porous carbon nanosheets were regulated by tailoring the abundance of the dangling-bonds grafted on the CTP molecules. Profiting from the large specific surface area, suitable pore structure and good two-dimensional structure to provide more active sites and enhance ion transport capacity, the PCNs-0.10 delivers a maximal specific capacitance of 504F g-1 at 0.1 A g-1, which is overmatch than most of previously reported for other carbon materials. As-assembled symmetrical EDLCs using K+ DES electrolyte, can be assembled to work at -40 °C to 75 °C and exhibit satisfactory energy density. The strategy proposed here has opened a new way for exploring the large-scale preparation of electrode materials suitable for ultra-low temperature capacitors.

Multi-Physically Cross-Linked Hydrogels for Flexible Sensors with High Strength and Self-Healing Properties

Excellent mechanical properties and self-healing properties are very important for the practical application of hydrogel flexible sensors. In this study, acrylic acid and stearyl methyl acrylate were selected as monomers to synthesize hydrophobic association hydrogels, and multi-physically cross-linked hydrogels were synthesized by adding ferric chloride and polyvinyl alcohol to introduce ion interaction and a hydrogen bond cross-linking network. The hydrogels were characterized by FTIR, XRD and SEM, and the mechanical properties and self-healing properties were tested using a universal testing machine. It was confirmed that the strength of the hydrogel was significantly improved with the addition of ferric chloride and polyvinyl alcohol, and the hydrogel still showed good self-healing properties. Further testing of its application as a conductive sensor has demonstrated sensitive and stable motion sensing capabilities. This provides an important reference for high-performance hydrogel sensors with both high strength and self-healing properties.

Anti-Fatigue Hydrogel Electrolyte for All-Flexible Zn-Ion Batteries

Hydrogel electrolytes are widely explored in Zn metal batteries for application in wearable electronics. While extensive studies have been conducted on optimizing the chemical structure and boosting the tensile elasticity, the mechanical stability of the hydrogel under repeated deformation is largely overlooked, leading to unsatisfactory performance at large cycling capacity. This work systematically analyzes the compressive fatigue-resistance properties of the hydrogel electrolyte, revealing the critical roles of the salt and copolymer matrix on crack initiation and propagation. It shows that, on the premise of homogeneous Zn deposition, an improved anti-fatigue property is essential to achieve high-capacity Zn metal anodes. The optimal Zn(ClO4 )2 -polyacrylamide/chitosan hydrogel electrolyte (C-PAMCS) exhibits an unprecedented lifespan of 1500 h for Zn//Zn cells at a current density of 10 mA cm-2 and a high areal capacity of 10 mAh cm-2 . The potential application of C-PAMCS is exemplified in all-flexible Zn-ion batteries enabled by a flexible current collector consisting of a Ag nanowires embedded elastomer. This study provides the rationale under hydrogel electrolyte engineering toward advanced Zn-ion battereis and the application in flexible devices.

Recent progress in structural modification of polymer gel electrolytes for use in solid-state zinc-ion batteries

Zinc-ion batteries are one of the promising energy storage devices, which have the advantages of environmental friendliness, high safety and low price and are expected to be used in large-scale battery application fields. However, four prominent water-induced adverse reactions, including zinc dendrite formation, zinc corrosion, passivation and the hydrogen evolution reaction in aqueous systems, seriously shorten the cycling life of zinc-ion batteries and greatly hinder their development. Based on this, polymer gel electrolytes have been developed to alleviate these issues due to their unique network structure, which can reduce water activity and suppress water-induced side reactions. Based on the challenges of polymer gel electrolytes, this review systematically summarizes the latest research progress in the use of additives in them and explores new perspectives in response to the existing problems with polymer electrolytes. In order to expand the performance of polymer gel electrolytes in zinc-ion batteries, a range of different types of additives are added via physical/chemical crosslinking, such as organic or inorganic substances, natural plants, etc. In addition, different types of additives and polymerization crosslinking from different angles essentially improve the ionic conductivity of the gel electrolyte, inhibit the growth of zinc dendrites, and reduce hydrogen evolution and oxygen-absorbed corrosion. After these modifications of polymer gel electrolytes, a more stable and superior electrochemical performance of zinc-ion batteries can be obtained, which provides some strategies for solid-state zinc-ion batteries.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

Rational design of dense microporous carbon derived from coal tar pitch towards high mass loading supercapacitors

The compact carbon materials with huge specific surface area (SSA) and proper pore structure are highly desirable towards high-performance supercapacitors at the cell level. However, to well balance of porosity and density is still an on-going task. Herein, a universal and facile strategy of pre-oxidation-carbonization-activation is employed to prepare the dense microporous carbons from coal tar pitch. The optimized sample POCA800 not only possesses a well-developed porous structure with the SSA of 2142 m² g^-1 and total pore volume (V_t) of 1.540 cm³ g^-1, but also exhibits a high packing density of 0.58 g cm^-3 and proper graphitization. Owing to these advantages, POCA800 electrode at areal mass loading of 10 mg cm^-2 shows a high specific capacitance of 300.8 F g^-1 (174.5 F cm^-3) at 0.5 A g^-1 and good rate performance. The POCA800 based symmetrical supercapacitor with a total mass loading of 20 mg cm^-2 displays a large energy density of 8.07 Wh kg^-1 at 125 W kg^-1 and remarkable cycling durability. It is revealed that the prepared density microporous carbons are promising for practical applications.

Facile fabrication of strong and conductive cellulose hydrogels with wide temperature tolerance for flexible sensors

Cellulose-based ionic conductive hydrogels (ICHs) have found extensive applications in flexible electronics and multifunctional sensors. However, simultaneous realization of sufficient conductivity, superior mechanical property and extreme environment tolerance for ICHs remains to be a huge challenge. In this work, a facile one-pot approach was developed to fabricate ICHs by directly dissolving cotton linter cellulose and polyvinyl alcohol (PVA) in a concentrated ZnCl₂ solution. By regulating the content of PVA in ICHs, the optimal hydrogel (Gel-5) exhibits a tensile strength of 0.30 MPa, a compressive strength of 2.05 MPa and a conductivity of 8.16 S m^-1. Moreover, the resulting dual-network ICHs present high transparency, good thermal reversibility and desirable ionic conductivity. Due to the high concentration of inorganic salts in the porous dual-network structure, the ICH presents good anti-drying and anti-freezing (as low as -90 °C) properties. Such hydrogel can be assembled into multi-functional sensors for human motion and temperature monitoring, and they demonstrate durable sensitivity, cycling stability in a wide operating temperature. This work will shed light on the design of cellulose-based hydrogels with good ionic conductivity and mechanical performance under extreme conditions.

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors with high energy density and wide temperature range

All-solid-state Ti₃C₂T_x neutral symmetric fiber supercapacitors (PVA EGHG Ti₃C₂T_x FSCs) with high energy density and wide temperature range are constructed by using polyvinyl alcohol (PVA)-ethylene glycol hydrogel (EGHG)-sodium perchlorate (NaClO₄) as electrolyte and separator, and Ti₃C₂T_x fiber as electrodes. Ti₃C₂T_x fiber is prepared using 130 mg mL^-1 Ti₃C₂T_x nanosheet ink as an assembly unit in a coagulation bath of isopropyl alcohol (IPA) and distilled water with 5 wt% CaCl₂ by a wet spinning method. The prepared Ti₃C₂T_x fiber exhibits a specific capacity of 385 F cm^-3 and a capacitance retention of 94 % after 10,000 cycles in 1 M NaClO₄ electrolyte. The assembled PVA EGHG Ti₃C₂T_x FSCs deliver a specific capacitance of 41 F cm^-3, a volumetric energy density of 5 mWh cm^-3, and a capacitance retention of 92 % after 500 times continuous bending. Furthermore, it shows good flexibility and excellent capacitance over a wide temperature range of -40 to 40 °C and maintains its electrochemical performance under varying degrees of bending. This study provides a viable strategy for designing and assembling all-solid-state neutral symmetric fiber supercapacitors with high energy density and wide temperature range.

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

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

Multifunctional Quasi-Solid-State Zinc-Sulfur Battery

The introduction of structural energy storage devices into emerging markets, such as electric vehicles, is predominately hindered by weak energy density, safety concerns, and immaturity of the field in materials. Herein, fabrication and testing of a freeze-resistant, multifunctional quasi-solid-state zinc-sulfur battery (ZnS) are reported. To this end, an electrostatic spray coating technique was used to deposit a thin layer of sulfur on the highly porous, unidirectional activated carbon nanofibers (A-CNFs) as a load-bearing cathode. This technique could fill micro- and mesopores, and microsized channels with sulfur, achieving an extensive sulfur loading of 60 wt %. Several drawbacks of structural energy storage devices (applicability under varied climate conditions, poor electrochemical performance and mechanical properties) are addressed by initiating an antifreezing hydrogel electrolyte with a failure strain of over 200%. This electrolyte possesses ethylene glycol and an I2 additive as an antifreezing agent and redox mediator, respectively. The as-assembled ZnS battery offers a high energy density of 283 Wh/kg based on the CNF-S cathode (149 Wh/kg based on the ZnS cell) and mechanical properties beyond state-of-the-art structural energy storage devices with a tensile strength of 377 MPa, Young's modulus of 16.7 GPa, and energy-to-failure of 4.5 MJ/m3. The electrochemomechanical properties of the ZnS battery were also investigated to elucidate the effects of electrochemical energy storage on mechanical properties and vice versa. Overall, the ZnS battery outperforms state-of-the-art structural energy storage devices in terms of energy storage and load-bearing capabilities.

High-Rate, Large Capacity, and Long Life Dendrite-Free Zn Metal Anode Enabled by Trifunctional Electrolyte Additive with a Wide Temperature Range

Aqueous Zn-ion batteries (AZIBs) have been recognized as promising energy storage devices due to their high theoretical energy density and cost-effectiveness. However, side reactions and Zn dendrite generation during cycling limit their practical application. Herein, ammonium acetate (CH₃ COONH₄ ) is selected as a trifunctional electrolyte additive to enhance the electrochemical performance of AZIBs. Research findings show that NH₄ ⁺ (oxygen ligand) and CH₃ COO^- (hydrogenligand) with preferential adsorption on the Zn electrode surface can not only hinder Zn anode directly contact with active H₂ O, but also regulate the pH value of the electrolyte, thus suppressing the parasitic reactions. Additionally, the formed SEI is mainly consisted of Zn₅ (CO₃ )₂ (OH)₆ with a high Zn²⁺ transference number, which could achieve a dendrite-free Zn anode by homogenizing Zn deposition. Consequently, the Zn||Zn symmetric batteries with CH₃ COONH₄ -based electrolyte can operate steadily at an ultrahigh current density of 40 mA cm^-2 with a cumulative capacity of 6880 mAh cm^-2 , especially stable cycling at -10 °C. The assembled Zn||MnO₂ full cell and Zn||activated carbon capacitor also deliver prominent electrochemical reversibility. This work provides unique understanding of designing multi-functional electrolyte additive and promotes a long lifespan at ultrahigh current density for AZIBs.

Integratable photodetectors based on photopolymerized conductive polymer via femtosecond laser direct writing

Conductive polymers have attracted a great deal of attention due to their remarkable electrical conductivity. However, the low solubility and inability to meet the limit for the flexible patterning fabrication ability of conductive polymers hinders their applications in miniaturized and integrated electronic devices. Here, femtosecond laser direct writing (FsLDW) is employed to achieve the in situ fabrication of polypyrrole (PPy) with flexibility. Notably, high-precision flexible patterning with a minimum feature size of 5.2 µm and spatial control over the polymerization of PPy is achieved. Moreover, PPy microwires are constructed into a photodetector that exhibits a responsivity of 644 A/W at 0.1-V bias under ultraviolet (UV) irradiation. Ultimately, an image sensor is fabricated by integrating multiple photodetectors, demonstrating the application potential of FsLDW technology for developing miniaturized and integrated electronic devices based on conductive polymers.