Flexible transparent supercapacitors (FTSCs) have been rapidly developed for next-generation intelligent electronics. Nonetheless, it remains challenging to balance the optical transparency and the areal capacitance of FTSCs because they are often contradictory. Two-dimensional (2D) metal-organic frameworks (MOFs) have emerged as appealing electrode materials due to their ultrathin nanosheets and accessible active sites; however, the intrinsically poor electrical conductivity of 2D MOFs hinders their advances in FTSCs. Herein, a layer-by-layer assembly strategy is proposed to fabricate the transparent conductive electrode of MOFs/PEDOT/PSS hybrid films, by employing NiCo-BDC (BDC = 1,4-benzenedicarboxylate) nanosheets and conductive poly(3,4-ethylenedioxy-thiophene)-poly(styrenesulfonate) (PEDOT/PSS). NiCo-BDC/PEDOT/PSS can synergistically utilize abundant redox-active sites of 2D NiCo-BDC and high electrical conductivity of PEDOT/PSS, enabling fast charge transport and electrolyte ion diffusion. As a consequence, the NiCo-BDC/PEDOT/PSS FTSCs show a superior areal capacitance of 4.0 mFcm-2, a high optical transparency of 56%, an outstanding energy capacity of 110 μW h cm-2 at 0.13 mW cm-2, excellent mechanical flexibility, and cycle stability. This work opens a new avenue for the fabrication of transparent conductive electrodes and is promising for high-performance flexible transparent energy storage devices.

Flexible energy-storage devices are essential for emerging applications such as wearable electronics and soft integrated systems, where mechanical adaptability and long-term stability are required. In this work, a cost-effective brush-painted strategy is developed to fabricate a flexible symmetric supercapacitor based on a NiMoO4 nanowire/polyaniline/chitosan/reduced graphene oxide composite electrode. The incorporation of reduced graphene oxide significantly enhances the electrochemical performance by improving the electrical conductivity and interfacial charge transfer, leading to more efficient energy storage. The device operates stably within a voltage window of 0.8 V and delivers an areal capacitance of 125.85 mF/cm2 at a low scan rate. In addition, it exhibits excellent cycling durability with 94.5% capacitance retention after 10,000 cycles, as well as robust mechanical flexibility, maintaining stable performance under repeated bending conditions. These results demonstrate that the synergistic design of hybrid electrode materials combined with a simple fabrication approach provides an effective route toward high-performance flexible supercapacitors for next-generation wearable and portable electronics.

Green self-assembly of digestate-derived humic acid/sulfonated polyaniline nanocomposites for high-performance flexible supercapacitors.

Rechargeable zinc ion batteries and capacitors with hydrogel electrolytes as the core component have received widespread recognition, benefiting from their prominent safety, low manufacturing cost, abundant raw material stockpiles, and excellent environmental compatibility. However, during the charge and discharge cycle of the zinc anode of this type of device, which is prone to side reactions of zinc dendrites, corrosion, and hydrogen evolution, and the coupling between the three is intensified, seriously restricting the cyclic stability and charge-discharge efficiency of the device. This paper systematically summarizes the classifications, key properties, and recent advances of representative hydrogel electrolytes, including dynamically tunable self-healing hydrogels, extreme-environment-tolerant hydrogels, and multidimensional conductive network hydrogels. The mechanism of action (zinc deposition regulation, interface kinetic optimization, and water molecule activity inhibition) is then focused on improving the inherent defects of the zinc anode. At the same time, the major breakthroughs in zinc ion energy storage devices in the field of structural engineering in recent years have been sorted out, providing new ideas for promoting the development of flexible energy storage devices based on hydrogel electrolytes.

Conventional flexible MXene films are predominantly fabricated via vacuum filtration, which inevitably suffers from concentration polarization, strict size limitations, and structural brittleness at high mass loadings. To address this issue, we introduced carbon nanotubes (CNTs) as interlayer spacers, leveraging their high conductivity and mechanical strength. The flexible and self-supporting composite films Nb2CTx/CNTs with layered porous structures were prepared by roller wetting method and freeze-drying techniques. The porous architecture effectively inhibited the restacking of Nb2CTxnanosheets and provided numerous active sites. Furthermore, a Co2+-intercalated composite (Co@Nb2CTx/CNTs) was fabricated through electrostatic adsorption and thermal annealing. The resulting electrode material demonstrated a larger specific surface area, multiplied reactive sites, and a decreased charge transfer resistance. Owing to the synergistic effects, the Co@Nb2CTx/CNTs electrode achieved a marked enhancement in performance, exhibiting a high specific capacity (300.2 mAh g-1at 0.05 A g-1) coupled with robust cyclic stability (229.6 mAh g-1retained after 2000 cycles at 2 A g-1). In addition, its remarkable mechanical flexibility suggests potential applicability in flexible energy storage devices.

To address the global energy crisis, supercapacitors─as highly efficient energy storage devices─are emerging as a key technology for solving energy storage and rapid discharge challenges. Porous carbon materials, owing to their high specific surface area and excellent electrochemical stability, have become an ideal choice for supercapacitor electrode materials. However, traditional porous carbon materials are predominantly powder-based, limiting their application in flexible energy storage devices. To address this challenge, electrospinning technology was incorporated into the fabrication process of porous carbon materials. The fabrication process involved electrospinning a blend of polyacrylonitrile and hyper-cross-linked polymers (HCPs) with fiber structure, resulting in nanofiber membranes characterized by a continuous architecture. Following high-temperature carbonization, this nanofiber membrane developed a uniform porous structure and demonstrated outstanding electrochemical performance. Experimental results indicate that the porous carbon nanofiber membrane exhibits optimal specific capacitance performance when the HCPs content is 40 mg, achieving a specific capacitance of 311 F g-1 at a current density of 0.5 A g-1. Moreover, it retains 88.7% of its capacitance performance after 10,000 charge-discharge cycles. This porous carbon nanofiber membrane not only eliminates the need for binders required by traditional powder electrode materials but can also be directly used as a flexible electrode, demonstrating significant application potential in the field of flexible energy storage devices.

The rapid surge in energy demand and concerns over global warming have led to the use of nonconventional and green energy sources to replace conventional fossil fuels. Although the photovoltaic industry has experienced significant growth over the past two decades, a gap remains in optimising the utilisation of solar energy. This gap can be addressed by developing flexible photovoltaic devices (FPVDs). Among the various types of solar cells, kesterite‐based solar cells have proven to be an environmentally safe, inexpensive, and stable option. Flexible energy conversion and storage devices are widely preferred for the development of wearable electronic devices. Unlike rigid photovoltaic devices, fabricating flexible devices requires careful analysis and selection of the substrate, as well as control over absorber characteristics. Additionally, the method used to form the active layer and the stacking order of the functional layers in kesterite materials also influence device performance. The absence of a rigid substrate in flexible devices makes doping with alkali materials a crucial step to prevent detrimental defects and secondary phase formation. This review examines recent developments in kesterite‐based FPVD. It discusses various aspects, including substrate selection, defect origins, control of secondary phases, different doping strategies, and new techniques for active‐layer formation, such as adhesive‐bonding transfer, plasma‐jet utilisation, and monograin layer formation. Bending characteristics that significantly affect FPVD performance have also been discussed in detail.

Mechanically Strong, Antiswelling and Antifreezing PVA–PSS Hydrogels for Strain Sensing and Flexible Energy Storage Devices

With the rapidly growing demand for flexible energy storage devices in wearable electronics, the development of electrode materials that combine high energy/power density with excellent flexibility has become critical. Inspired by the natural "spiderweb-mucilage" structure, we successfully prepared a lignin-based electrode material via electrospinning, carbonization, and hydrothermal processes. This material achieves efficient dual-mode energy storage by mimicking the synergistic roles of the spider web and mucilage. The material features an rGO-CNFs skeleton with high conductivity (4.02 S·cm-1) and flexibility, serving as a "conductive spider web", while NiCo-LDHs nanosheets are anchored as "mucilage" for rapid Faradaic reactions. The above components are tightly interconnected by stable M-O-C chemical bonds, endowing the composite structure with excellent mechanical robustness. This design yields exceptional performance: a specific capacitance of 1492.6 F·g-1 at 1 A·g-1, vastly surpassing pure CNFs (161.4 F·g-1) and rGO-CNFs (440.6 F·g-1). Such excellent electrochemical performance originates from the synergistic effect of dual-energy storage and the significantly enhanced electrolyte wettability of the electrode, whose contact angle with the electrolyte is reduced from 133.3° to 34.4°. The assembled flexible symmetric supercapacitor achieves an energy density of 82.67 Wh·kg-1 at 800 W·kg-1 and retains 94.5% capacitance after 2000 cycles, demonstrating excellent stability.

From biomass to supercapacitor electrode materials: bamboo derived carbon decorated with MnO2 used in flexible energy storage device

The excellent redox properties and high electrical conductivity of transition metal phosphates have shown exceptional contribution as electrochemical energy storage materials. In this study, nickel cobalt phosphate (NiCo(PO 4 ) 3 ) nanostructures were directly grown on flexible carbon cloth (CC) through a simple and cost-effective hydrothermal process, enabling the fabrication of a binder-free and mechanically robust electrode. The prepared NiCo(PO 4 ) 3 @CC electrode exhibits outstanding electrochemical performance in a three-electrode system using 1 M KOH, delivering a high specific capacity of 117 C/g at 0.4 A/g and an areal capacitance of 59.80 F/cm 2 at 10 mV/s. Notably, the asymmetric device (NiCo(PO 4 ) 3 @CC//AC), remained stable over a wide-operating potential of 1.5 V, delivering a maximum specific capacity of 96.16 C/g, and excellent cycling durability with 79.1% retention after 8000 cycles. This work highlights the synergistic integration of redox-active bimetallic phosphate with a conductive and flexible carbon cloth-based substrate, offering an effective pathway for high-performance, flexible, and wearable electrochemical energy storage devices. • NiCo(PO 4 ) 3 nanostructures were directly grown on flexible carbon cloth • Binder-free electrode fabricated through a simple hydrothermal method • High specific capacity of 215 F g -1 at 0.4 A g -1 in 1 M KOH electrolyte • Excellent cycling stability with 85 % retention after 8000 cycles • Promising flexible electrode for next-generation energy storage devices

Compatibility electrode-electrolyte interface through supramolecular gel polymer electrolyte for flexible energy storage

To meet the requirements of flexibility and high performance for energy storage devices in flexible wearable electronic equipment, the MnO2/acetylene black composite flexible cathodes is fabricated via 3D printing technology and the aqueous manganese-based zinc-ion flexible batteries are assembled. Based on bending and torsion mechanical tests, and the electrochemical tests, the optimal 3D printing electrode structure was determined. The micromorphology of the electrode after mechanical tests shows that when the printed lines of the upper and lower layers form a 30° angle, the electrode sheet exhibits the least damage. Electrochemical tests indicated that it had an ohmic resistance of 2.052 Ω, an interfacial charge transfer resistance of 141.1 Ω, a specific capacity of 103 mAh/g at 50 mA/g, and a specific capacity of 65 mAh/g at 500 mA/g. Compared with traditional coated electrodes, the 3D-printed electrode showed significantly improved diffusion coefficient, conductivity, and cycle stability. The assembled 3D-printed flexible battery could stably power a 1.5 V LED bulb under flat, bent, and twisted states. It provides a feasible solution for the development of high-performance flexible energy storage devices.

Benefiting from their outstanding porosity, considerable specific surface area, and natural flexibility, cellulose nanofibers (CNFs)/MOF materials have emerged as competitive candidates for advanced flexible energy storage devices. However, conventional CNFs/MOFs aerogels or films often suffer from poor recoverability under compression, bending, and folding, accompanied by severe plastic deformation that compromises the cycling and structural stability of devices. To address this issue, we report a rationally designed flexible PU/CNFs/ZIF-8/PANI composite foam with an interconnected micro-mesoporous structure. Using polyurethane foam as a soft substrate and CNFs/ZIF-8 as building blocks, the composite was fabricated through a combined strategy of impregnation, in situ ZIF-8 growth, hot-pressing, and in situ aniline polymerization with simultaneous etching of the ZIF-8. The incorporation of carboxylated CNFs enhances the hydrophilicity of the PU skeleton. This, in combination with the hot-pressed framework, establishes an interconnected 3D network, thereby effectively preventing the agglomeration of active materials. Meanwhile, the hierarchical pores derived from the sacrificial ZIF-8 template provide abundant electroactive sites, accelerate ion transport, and facilitate high PANI loading. By virtue of this synergistic architectural effect, the resultant electrode achieves a high specific capacitance of 449 F/g at 0.2 A/g, with 97% capacitance retention after 2000 cycles at 5 A/g. Furthermore, the composite foam demonstrates excellent mechanical flexibility, with a tensile strength of 0.87 MPa and an elongation at break of 230%. This work offers a feasible approach for developing high-performance flexible supercapacitors and provides novel perspectives for the rational design of portable energy storage devices.

With the increasingdemand for wearable and flexible energy storagedevices, there has been significant interest in developing safe andmechanically stable prototypes. For this, liquid electrolytes forbatteries and supercapacitors (SC) need to be replaced by self-chargedgel-type polyelectrolytes (SCGPE), which exhibit good ionic mobilityand offer the advantage of being incorporated into solid-state electronicdevices. Here, the SCGPE studied has been synthesized by a polyhydroxyalkylationreaction in a superacid medium of 4-acetylpyridine and the nonactivatedaromatic compounds para-terphenyl and biphenyl. Thereaction was carried out in a single step at room temperature, withoutthe use of metal catalysts, and yielded water as the only byproduct.Chemical modification reactions were then carried out by quaternizing4-acetylpyridine using a bromohexyltrimethylammonium salt, which incorporatedpositively charged elements onto the polymer backbone. The functionalizationdegree and viscosity of the gel polyelectrolyte were the two mainfactors affecting SC performance. These SCGPEs exhibit ionic conductivitywithout the need for doping with a conducting salt, ionic liquid,or acid, thereby ensuring that the PE maintains its mechanical stabilityand safety. Molecular dynamics simulations have confirmed the keyrole of the solvent in influencing the polymer conformation and iontransport. SCGPEs enable the sparing of dopants, such as ionic liquids,conducting salts, or acids, as the SCGPE exhibits good ionic conductivity(on the order of 10–4 S/cm) and high specific capacitance(up to 123 mF cm–2) when used in textile carbon-basedSCs. It also showed only slight differences with a well-known gelpolyelectrolyte (GPE), poly­(vinyl alcohol)-potassium hydroxide (PVA-KOH).GPEs used with textile carbon electrodes pave the way for developingall-solid-state wearable SCs without leaking or spilling of liquidelectrolytes.

Fiber-shaped supercapacitors (FSSCs) hold immense potential for wearable electronics, yet balancing electrochemical performance, mechanical flexibility, and sustainability remains a challenging. While lignin is a sustainable biomass precursor, conventional carbonization strategies inevitably compromise the intrinsic functional groups and mechanical integrity. Herein, we report a sustainable “supramolecular interaction–structural regulation” strategy to fabricate noncarbonized lignin-based fiber electrodes. Hierarchical porous polypyrrole (PPy)/poly(vinyl alcohol) (PVA)/alkali lignin (AL) fibers are fabricated via wet spinning, freeze-drying, and low-temperature in situ polymerization. The abundant hydroxyl (−OH) groups in the PVA/AL matrix enhance the fiber hydrophilicity and provide supramolecular anchoring sites. Combined with capillary effects from the hierarchical porous structure, these sites promote the uniform in situ polymerization of pyrrole (Py) and form a continuous 3D conductive network for efficient charge transfer. Furthermore, the hierarchical porosity reduces the ion diffusion resistance and facilitates rapid electrolyte transport while maintaining fiber flexibility. The optimized fibers deliver high conductivity (424.4 S/m), fast ion transport kinetics (relaxation time constant of 11.6 s), and a high volumetric capacitance (163.1 F/cm3), significantly outperforming the nonporous control (27.3 F/cm3). The assembled symmetric device delivers a high energy density of 9.3 mWh/cm3 and retains 94.2% of its capacitance under 180° bending, demonstrating a stable electrochemical performance under mechanical deformation. This work provides a feasible noncarbonized strategy for sustainable lignin-based flexible energy storage devices.

The advancement of flexible energy storage devices relies critically on the development of a flexible cathode that combines high specific capacity with long-term cycling stability. Here, we report the rational design and fabrication of a freestanding flexible cathode material for Zn-ion batteries (ZIB), denoted as MD-VO2@CNF, through electrospinning and thermal conversion of vanadium-based metal–organic framework (V-MOF). The resulting architecture consists of MOF-derived VO2 nanoparticles uniformly anchored within a conductive carbon nanofiber (CNF) network. This hierarchical structure not only facilitates efficient exposure of active sites and accommodates volume variations during cycling, but also establishes abundant heterointerfaces between VO2 and CNF. Density functional theory (DFT) calculations reveal that a built-in electric field forms at the VO2/CNF interface, which significantly enhances the charge transfer kinetics and strengthens the adsorption of Zn ions. Benefiting from these synergistic effects, the MD-VO2@CNF cathode delivers a high specific capacity of 425.8 mAh g–1 at 0.2 A g–1 and exceptional cycling stability, retaining 236 mAh g–1 after 2000 cycles at 5 A g–1. When integrated into a quasi-solid-state flexible zinc-ion battery, the electrode maintains stable performance under mechanical deformation and achieves a high energy density of 248 Wh kg–1. This work offers a feasible strategy for designing high-performance flexible energy storage materials and provides fundamental insights into heterointerface engineering for metal oxide-carbon composite systems.

One-pot synthesis of strongly adhesive 3D printable gelatin/carrageenan conductive hydrogels for flexible sensors and supercapacitors.

ABSTRACT The development of flexible electronics is causing a high demand for energy storage devices that provide high energy density and reliable mechanical performance. This review summarizes recent progress in high‐energy‐density flexible batteries, focusing on the emerging material systems, including dynamic bonding network electrolytes, biomass‐derived electrodes, MOF‐confined active materials, and flexible substrates, along with structural designs such as self‐supporting electrode architectures, gradient buffering layers, and heterogeneous interface engineering. Particularly, it summarizes how machine learning‐assisted intelligent manufacturing enables precise optimization of green processes (screen printing, electrospinning) and facilitates new energy enhancement mechanisms (photoelectric collaborative catalysis, intelligent thermal management), toward the controllable fabrication of high‐performance flexible batteries. Moreover, this article also looks forward to the application prospects of flexible batteries in wearable devices, medical electronics, and special equipment, and points out the current technical challenges and future development directions, providing important references for promoting the practical application process of flexible energy storage devices.

Wearable and deformable electronics are becoming increasingly essential components of modern healthcare and daily life. To power such devices, flexible electrochemical energy storage (FEES) plays a critical role. The practical performance of FEES is dominated by charge and mass transfer at the electrode-electrolyte interface, similar to many rigid battery technologies. However, a unique challenge for FEES is the durability of this interface under deformation. Herein, we present the first comprehensive review of the interface physics, unveiling the crucial role of interface adhesion in the mechanical endurance of FEES. By bridging adhesion physics, material chemistry, and device mechanics, adhesion reinforcement strategies are comprehensively discussed and quantitatively compared, providing multi-scale mechanisms for optimizing FFES interface - from nanoscale bond engineering to microscale surface topology, mechanical interlocking, and macroscale device design. Further, inspired by the synergetic effect of adhesion mechanisms, we propose potential research directions for durable electrode-electrolyte interfaces under dynamic deformation. We also revisit the evaluation of flexibility and electrochemical performance, proposing an application-driven bending index for device assessment. These insights on electrode-electrolyte interface physics of FEES will facilitate the flourishing future of flexible devices.