Highly‐Safe and Ultra‐Stable All‐Flexible Gel Polymer Lithium Ion Batteries Aiming for Scalable Applications

With the development of flexible electronics, flexible lithium ion batteries (LIBs) have received great attention. Previously, almost all reported flexible components had shortcomings related to poor mechanical flexibility, low energy density, and poor safety, which led to the failure of scalable applications. This study demonstrates a fully flexible lithium ion battery using LiCoO₂ as the cathode, Li₄Ti₅O₁₂ as the anode, and graphene film as the flexible current collector. The graphene oxide modified gel polymer electrolyte exhibits higher ionic conductivity than a conventional liquid electrolyte and improves the safety of the flexible battery. The optimum design of the flexible graphene battery exhibits super electrochemical performance, with a 2.3 V output voltage plateau and a satisfactory capacity of 143.0 mAh g^?1 at 1 C. The mass energy density and power density are both ≈1.4 times higher than a standard electrode using metal foils as current collectors. No capacity loss is observed after 100 thousand cycles of mechanical bending. More importantly, even in the clipping state, this flexible gel polymer battery can still demonstrate a stable and safe electrochemical performance. This work may lead to a promising strategy of high‐performance scalable LIBs for the next‐generation flexible electronics.     

Integrated Conductive Hybrid Architecture of Metal–Organic Framework Nanowire Array on Polypyrrole Membrane for All‐Solid‐State Flexible Supercapacitors

Metal–organic frameworks (MOFs) with intrinsically porous structures are promising candidates for energy storage, however, their low electrical conductivity limits their electrochemical energy storage applications. Herein, the hybrid architecture of intrinsically conductive Cu‐MOF nanowire arrays on self‐supported polypyrrole (PPy) membrane is reported for integrated flexible supercapacitor (SC) electrodes without any inactive additives, binders, or substrates involved. The conductive Cu‐MOFs nanowire arrays afford high conductivity and a sufficiently active surface area for the accessibility of electrolyte, whereas the PPy membrane provides decent mechanical flexibility, efficient charge transfer skeleton, and extra capacitance. The all‐solid‐state flexible SC using integrated hybrid electrode demonstrates an exceptional areal capacitance of 252.1 mF cm^?2, an energy density of 22.4 µWh cm^?2, and a power density of 1.1 mW cm^?2, accompanied by an excellent cycle capability and mechanical flexibility over a wide range of working temperatures. This work not only presents a robust and flexible electrode for wide temperature range operating SC but also offers valuable concepts with regards to designing MOF‐based hybrid materials for energy storage and conversion systems.     

All‐Printed MnHCF‐MnOx‐Based High‐Performance Flexible Supercapacitors

Here, a simple active materials synthesis method is presented that boosts electrode performance and utilizes a facile screen‐printing technique to prepare scalable patterned flexible supercapacitors based on manganese hexacyanoferrate‐manganese oxide and electrochemically reduced graphene oxide electrode materials (MnHCF‐MnO_x/ErGO). A very simple in situ self‐reaction method is developed to introduce MnO_x pseudocapacitor material into the MnHCF system by using NH₄F. This MnHCF‐MnO_x electrode materials can deliver excellent capacitance of 467 F g^?1 at a current density of 1 A g^?1, which is a 2.4 times capacitance increase compared to MnHCF. In addition a printed, patterned, flexible MnHCF‐MnO_x/ErGO supercapacitor is fabricated, showing a remarkable areal capacitance of 16.8 mF cm^?2 and considerable energy and power density of 0.5 mWh cm^?2 and 0.0023 mW cm^?2, respectively. Furthermore, the printed patterned flexible supercapacitors also exhibit exceptional flexibility, and the capacitance remains stable, even while bending to various angles (60°, 90°, and 180°) and for 100 cycles. The flexible supercapacitor arrays integrated by multiple prepared single supercapacitors can power various LEDs even in the bent states. This approach offers promising opportunities for the development of printable energy storage materials and devices with high energy density, large scalability, and excellent flexibility.     

Rational Design of Nickel Hydroxide‐Based Nanocrystals on Graphene for Ultrafast Energy Storage

Compact, light, and powerful energy storage devices are urgently needed for many emerging applications; however, the development of advanced power sources relies heavily on advances in materials innovation. Here, the findings in rational design, one‐pot synthesis, and characterization of a series of Ni hydroxide‐based electrode materials in alkaline media for fast energy storage are reported. Under the guidance of density functional theory calculations and experimental investigations, a composite electrode composed of Co‐/Mn‐substituted Ni hydroxides grown on reduced graphene oxide (rGO) is designed and prepared, demonstrating capacities of 665 and 427 C g^?1 at current densities of 2 and 20 A g^?1, respectively. The superior performance is attributed mainly to the low deprotonation energy and the facile electron transport, as elaborated by theoretical calculations. When coupled with an electrode based on organic molecular‐modified rGO, the resulting hybrid device demonstrates an energy density of 74.7 W h kg^?1 at a power density of 1.68 kW kg^?1 while maintaining capacity retention of 91% after 10,000 cycles (20 A g^?1). The findings not only provide a promising electrode material for high‐performance hybrid capacitors but also open a new avenue toward knowledge‐based design of efficient electrode materials for other energy storage applications.     

Lignin Laser Lithography: A Direct‐Write Method for Fabricating 3D Graphene Electrodes for Microsupercapacitors

In this work, a simple lignin‐based laser lithography technique is developed and used to fabricate on‐chip microsupercapacitors (MSCs) using 3D graphene electrodes. Specifically, lignin films are transformed directly into 3D laser‐scribed graphene (LSG) electrodes by a simple one‐step CO₂ laser irradiation. This step is followed by a water lift‐off process to remove unexposed lignin, resulting in 3D graphene with the designed electrode patterns. The resulting LSG electrodes are hierarchically porous, electrically conductive (conductivity is up to 66.2 S cm^?1), and have a high specific surface area (338.3 m² g^?1). These characteristics mean that such electrodes can be used directly as MSC electrodes without the need for binders and current collectors. The MSCs fabricated using lignin laser lithography exhibit good electrochemical performances, namely, high areal capacitance (25.1 mF cm^?2), high volumetric energy density (≈1 mWh cm^?3), and high volumetric power density (≈2 W cm^?3). The versatility of lignin laser lithography opens up the opportunity in applications such as on‐chip microsupercapacitors, sensors, and flexible electronics at large‐scale production.     

Highly Stable Transparent Conductive Silver Grid/PEDOT:PSS Electrodes for Integrated Bifunctional Flexible Electrochromic Supercapacitors

Silver grids are attractive for replacing indium tin oxide as flexible transparent conductors. This work aims to improve the electrochemical stability of silver‐based transparent conductors. A silver grid/PEDOT:PSS hybrid film with high conductivity and excellent stability is successfully fabricated. Its functionality for flexible electrochromic applications is demonstrated by coating one layer of WO₃ nanoparticles on the silver grid/PEDOT:PSS hybrid film. This hybrid structure presents a large optical modulation of 81.9% at 633 nm, fast switching, and high coloration efficiency (124.5 cm² C^?1). More importantly, an excellent electrochemical cycling stability (sustaining 79.1% of their initial transmittance modulation after 1000 cycles) and remarkable mechanical flexibility (optical modulation decay of only 7.5% after 1200 compressive bending cycles) is achieved. A novel smart supercapacitor is presented that functions as a regular energy‐storage device and simultaneously monitors the level of stored energy by a rapid and reversible color variation even at high current charge/discharge conditions. The film sustains an optical modulation of 87.7% and a specific capacitance of 67.2% at 10 A g^?1 compared to their initial value at a current density of 1 A g^?1. The high‐performance silver grid/PEDOT:PSS hybrid transparent films exhibit promising features for various emerging flexible electronics and optoelectronic devices.     

Natural Leaf Made Triboelectric Nanogenerator for Harvesting Environmental Mechanical Energy

Distributed environmental mechanical energy is rarely collected due to its fluctuating amplitudes and low frequency, which is usually attributed as “random” energy. Considering the rapid development of the Internet of things (IoT), there is a great need for a large number of distributed and sustainable power sources. Here, a natural leaf assembled triboelectric nanogenerator (Leaf‐TENG) is designed by utilizing the green leaf as an electrification layer and electrode to effectively harvest environmental mechanical energy. The Leaf‐TENG with good adaptability has the maximum output power of ≈45 mW m^?2, which is capable of driving advertising LEDs and commercial electronic temperature sensors. Besides, a tree‐shaped energy harvester is integrated with natural Leaf‐TENG to harvest large‐area environmental mechanical energy. This work provides a new prospect for distributed and environmental‐friendly power sources and has potential applications in the IoT and self‐powered systems.     

Monolithic Integration of All‐in‐One Supercapacitor for 3D Electronics

A supercapacitor is usually stacked in the configuration of a layered sandwiched architecture, and has been adopted as discrete energy storage device or circuit component. However, this stacked structure decreases mechanical integrity, leads to low specific capacity, and prevents high‐density monolithic integration. Here all‐in‐one supercapacitors are fabricated by integrating cathode, anode, current collector, and separator into one monolithic glass fiber (GF) substrate together with other circuit components through matured and scalable fabrication techniques, the all‐in‐one supercapacitor is embedded as a component for 3D electronics. This all‐in‐one architecture demonstrates its effectiveness in the prevention of the delamination of the sandwiched supercapacitor and the minimization of the proportion of inactive materials. The supercapacitor delivers high power density (320 mW cm^?3) and energy density (2.12 mWh cm^?3), and exhibits a capacitance retention of 100% even after a continuous cycling of 431 h. Furthermore, a 3D polydimethylsiloxane/GF architecture is constructed for driving a flash light emitting diode system, where the all‐in‐one supercapacitor is monolithically integrated in the 3D system, and each layer is connected via vertical through‐holes. This all‐in‐one device can be constructed with a macroscopically available membrane and readily integrated into 3D systems without secondary packaging, providing the potential for high‐density heterogeneous 3D electronics.     

Low Current Density Driving Leads to Efficient,Bright and Stable Green Electroluminescence

Electroluminescent devices have the potential to reshape lighting and display technologies by providing low‐energy consuming solutions with great aesthetic features, such as flexibility and transparency. In particular, light‐emitting electrochemical cells (LECs) are among the simplest electroluminescent devices. The device operates with air‐stable materials and the active layer can be resumed to an ionic phosphorescent emitter. As a consequence, LECs can be assembled using solution‐process technologies, which could allow for low‐cost and large‐area lighting applications in the future. High efficiencies have been reported at rather low luminances (<50 cd m^?2) and at very low current densities. Moreover, these efficiencies could be sustained for a brief moment only during operation time. Here, we demonstrate that a pulsed driving mode at low current densities leads to unequalled overall performances with excellent efficiencies throughout the lifetime of the device. The lifetime of the LECs is defined as the time it takes to reach 50% of the peak luminance. Upon optimization of various parameters (frequency, duty cycle and average current density), the green LEC reaches efficacies and power efficiencies of 28.2 cd A^?1 and 17.1 lm W^?1, respectively, at a luminance above 750 cd m^?2 and 98 hours lifetime. The present work also rationalizes why high efficiencies have been obtained only at low current densities so far.     

An Aqueous Zn‐Ion Hybrid Supercapacitor with High Energy Density and Ultrastability up to 80 000 Cycles

Integrating a battery‐type electrode to build a hybrid supercapacitor is a promising approach to improve the overall energy density of a supercapacitor‐type energy storage device without sacrificing its power output. However, this strategy is usually achieved at the expense of cycling lifespan. In this work, a hybrid supercapacitor comprising Zn foil and porous carbon derived from chemical activated graphene (aMEGO) is developed, and the trade‐off between energy density and cycling life is well‐balanced by the utilization of 3 m Zn(CF₃SO₃)₂ electrolyte with high Zn stripping/plating efficiency. Such a hybrid supercapacitor demonstrates an energy density of 106.3 Wh kg^?1 and a power density of 31.4 kW kg^?1, and significantly a wide operation voltage of 1.9 V is achieved in aqueous electrolyte. Benefitting from the high Zn stripping/plating efficiency, the Zn‐aMEGO hybrid‐supercapacitor also exhibits an ultralong cycling life up to 80 000 cycles with capacity retention of 93%, which is comparable to that of conventional electrochemical double‐layer capacitors.     

Biomechanical Energy‐Driven Hybridized Generator as a Universal Portable Power Source for Smart/Wearable Electronics

The fast growth of smart electronics requires novel solutions to power them sustainably. Portable power sources capable of harvesting biomechanical energy are a promising modern approach to reduce battery dependency. Herein, a novel elastic impact‐based nonresonant hybridized generator (EINR‐HG) is reported to effectively harvest biomechanical energy from diverse human activities outdoors. Through the rational integration of a nonlinear electromagnetic generator with two contact‐mode triboelectric nanogenerators, the proposed EINR‐HG generates hybrid electrical output simultaneously under the same mechanical excitations. By introducing a flux‐concentrator with a nanowire‐nanofiber surface modification, significant improvement in the energy harvesting efficiency of the EINR‐HG is achieved. After optimizing using simulations and vibration tests, the as‐fabricated EINR‐HG delivers an outstanding normalized power density of 3.13 mW cm^?3 g^?2 across a matching resistance of 1.5 kΩ at 6 Hz under 1 g acceleration. Under human motion testing, the EINR‐HG generates an optimal output power of 131.4 mW with horizontal handshaking. With a customized power management circuit, the EINR‐HG serves as a universal power source that successfully drives commercial smart electronics, including smart bands and smartphones. This work shows the massive potential of biomechanical energy‐driven hybridized generators for powering personal electronics and portable healthcare monitoring devices.     

Flexible Asymmetric Micro‐Supercapacitors Based on Bi2O3 and MnO2 Nanoflowers: Larger Areal Mass Promises Higher Energy Density

A flexible asymmetric supercapacitor (ASC) with high energy density is designed and fabricated using flower‐like Bi₂O₃ and MnO₂ grown on carbon nanofiber (CNF) paper as the negative and positive electrodes, respectively. The lightweight (1.6 mg cm^?2), porous, conductive, and flexible features make the CNF paper an ideal support for guest active materials, which permit a large areal mass of 9 mg cm^?2 for Bi₂O₃ (≈85 wt% of the entire electrode). Thus, the optimal device with an operation voltage of 1.8 V can deliver a high energy density of 43.4 μWh cm^?2 (11.3 W h kg^?1, based on the total electrodes) and a maximum power density of 12.9 mW cm^?2 (3370 W kg^?1). This work provides an example of large areal mass and flexible electrode for ASCs with high areal capacitance and high energy density, holding great promise for future flexible electronic devices.     

2D Metal Zn Nanostructure Electrodes for High‐Performance Zn Ion Supercapacitors

Recent supercapacitors show a high power density with long‐term cycle life time in energy‐powering applications. A supercapacitor based on a single metal electrode accompanying multivalent cations, multiple charging/discharging kinetics, and high electrical conductivity is a promising energy‐storing system that replaces conventionally used oxide and sulfide materials. Here, a hierarchically nanostructured 2D‐Zn metal electrode‐ion supercapacitor (ZIC) is reported which significantly enhances the ion diffusion ability and overall energy storage performance. Those nanostructures can also be successfully plated on various flat‐type and fiber‐type current collectors by a controlled electroplating method. The ZIC exhibits excellent pseudocapacitive performance with a high energy density of 208 W h kg^?1 and a power density from 500 W kg^?1, which are significantly higher than those of previously reported supercapacitors with oxide and sulfide materials. Furthermore, the fiber‐type ZIC also shows high energy‐storing performance, outstanding mechanical flexibility, and waterproof characteristics, without any significant capacitance degradation during bending tests. These results highlight the promising possibility of nanostructured 2D Zn metal electrodes with the controlled electroplating method for future energy storage applications.     

Flexible and Stretchable Biobatteries: Monolithic Integration of Membrane‐Free Microbial Fuel Cells in a Single Textile Layer

The fabrication and performance of a flexible and stretchable microbial fuel cell (MFC) monolithically integrated into a single sheet of textile substrate are reported. The single‐layer textile MFC uses Pseudomonas aeruginosa (PAO1) as a biocatalyst to produce a maximum power of 6.4 µW cm^?2 and current density of 52 µA cm^?2, which are substantially higher than previous textile‐MFCs and are similar to other flexible paper‐based MFCs. The textile MFC demonstrates a stable performance with repeated stretching and twisting cycles. The membrane‐less single‐chamber configuration drastically simplifies the fabrication and improves the performance of the MFC. A conductive and hydrophilic anode in a 3D fabric microchamber maximizes bacterial electricity generation from a liquid environment and a silver oxide/silver solid‐state cathode reduces cathodic overpotential for fast catalytic reaction. A simple batch fabrication approach simultaneously constructs 35 individual devices, which will revolutionize the mass production of textile MFCs. This stretchable and twistable power device printed directly onto a single textile substrate can establish a standardized platform for textile‐based biobatteries and will be potentially integrated into wearable electronics in the future.     

Flexible Supercapacitors Based on Bacterial Cellulose Paper Electrodes

Supercapacitors based on freestanding and flexible electrodes that can be fabricated with bacterial cellulose (BC), multiwalled carbon nanotubes (MWCNTs), and polyaniline (PANI) are reported. Due to the porous structure and electrolyte absorption properties of the BC paper, the flexible BC‐MWCNTs‐PANI hybrid electrode exhibits appreciable specific capacitance (656 F g^?1 at a discharge current density of 1 A g^?1) and remarkable cycling stability with capacitance degradation less than 0.5% after 1000 charge–discharge cycles at a current density of 10 A g^?1. The facile and low‐cost of this binder‐free paper electrode may have great potential in development of flexible energy‐storage devices.     

Ultrafast All‐Solid‐State Coaxial Asymmetric Fiber Supercapacitors with a High Volumetric Energy Density

Fiber‐supercapacitors (FSCs) are promising energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. Currently, a major challenge for FSCs is achieving ultrahigh volumetric energy and power densities simultaneously, especially when the charge/discharge rates exceed 1 V s^?1. Herein, an Au‐nanoparticle‐doped‐MnO_x@CoNi‐alloy@carbon‐nanotube (Au–MnO_x@CoNi@CNT) core/shell nanocomposite fiber electrode is designed, aiming to boost its charge/discharge rate by taking advantage of the superconductive CoNi alloy network and the greatly enhanced conductivity of the Au doped MnO_x active materials. An all‐solid‐state coaxial asymmetric FSC (CAFSC) prototype device made by wrapping this fiber with a holey graphene paper (HGP) exhibits excellent performance at rates up to 10 V s^?1, which is the highest charge rate demonstrated so far for FSCs based on pseudocapacitive materials. Furthermore, our fully packaged CAFSC delivers a volumetric energy density of ≈15.1 mW h cm^?3, while simultaneously maintaining a high power density of 7.28 W cm^?3 as well as a long cycle life (90% retention after 10 000 cycles). This value is the highest among all reported FSCs, even better than that of a typical 4 V/500 µA h thin‐film lithium battery.     

3D Architecture Materials Made of NiCoAl‐LDH Nanoplates Coupled with NiCo‐Carbonate Hydroxide Nanowires Grown on Flexible Graphite Paper for Asymmetric Supercapacitors

Asymmetric supercapacitors featuring both high energy and power densities as well as a long lifespan are much sought after and may become a reality depending on the availability of cheap yet highly active electrode materials. Here, a novel flexible architecture electrode made of NiCoAl‐layered double hydroxide (NiCoAl‐LDH) nanoplates coupled with NiCo‐carbonate hydroxide (NiCo‐CH) nanowires, grown on graphite paper via an in situ, one‐step, hydrothermal method is reported. The nanowire‐like NiCo‐CH species in the nanoplate matrix function as a scaffold and support the dispersion of the NiCoAl‐LDH nanoplates, resulting in a relatively loose and open structure within the electrode matrix. Asymmetric supercapacitors fabricated using the nanohybrids as the positive electrode and a typical activated carbon (AC) as negative electrode show a high energy density of 58.9 Wh kg^?1 at a power density of 0.4 kW kg^?1, which is based on the total mass of active materials at a voltage of 1.6 V. An energy density of 14.9 Wh kg^?1 can be retained even at a high power density of 51.5 kW kg^?1. Our asymmetric supercapacitor also exhibits an excellent long cycle life, whereby a specific capacitance of 97% is retained even after 10 000 cycles.     

Nanostructured Ternary Electrodes for Energy‐Storage Applications

A three‐component, flexible electrode is developed for supercapacitors over graphitized carbon fabric, utilizing γ‐MnO₂ nanoflowers anchored onto carbon nanotubes (γ‐MnO₂/CNT) as spacers for graphene nanosheets (GNs). The three‐component, composite electrode doubles the specific capacitance with respect to GN‐only electrodes, giving the highest‐reported specific capacitance (308 F g^?1) for symmetric supercapacitors containing MnO₂ and GNs using a two‐electrode configuration, at a scan rate of 20 mV s^?1. A maximum energy density of 43 W h kg^?1 is obtained for our symmetric supercapacitors at a constant discharge‐current density of 2.5 A g^?1 using GN–(γ‐MnO₂/CNT)‐nanocomposite electrodes. The fabricated supercapacitor device exhibits an excellent cycle life by retaining ≈90% of the initial specific capacitance after 5000 cycles.     

Pore and Heteroatom Engineered Carbon Foams for Supercapacitors

Carbonaceous materials are attractive supercapacitor electrode materials due to their high electronic conductivity, large specific surface area, and low cost. Here, a unique hierarchical porous N,O,S‐enriched carbon foam (KNOSC) with high level of structural complexity for supercapacitors is reported. It is fabricated via a combination of a soft‐template method, freeze‐drying, and chemical etching. The carbon foam is a macroporous structure containing a network of mesoporous channels filled with micropores. It has an extremely large specific surface area of 2685 m² g^?1. The pore engineered carbon structure is also uniformly doped with N, O, and S. The KNOSC electrode achieves an outstanding capacitance of 402.5 F g^?1 at 1 A g^?1 and superior rate capability of 308.5 F g^?1 at 100 A g^?1. The KNOSC exhibits a Bode frequency at the phase angle of ?45° of 18.5 Hz, which corresponds to a time constant of 0.054 s only. A symmetric supercapacitor device using KNOSC as electrodes can be charged/discharged within 1.52 s to deliver a specific energy density of 15.2 W h kg^?1 at a power density of 36 kW kg^?1. These results suggest that the pore and heteroatom engineered structures are promising electrode materials for ultrafast charging.     

Graphene–Cellulose Paper Flexible Supercapacitors

A simple and scalable method to fabricate graphene‐cellulose paper (GCP) membranes is reported; these membranes exhibit great advantages as freestanding and binder‐free electrodes for flexible supercapacitors. The GCP electrode consists of a unique three‐dimensional interwoven structure of graphene nanosheets and cellulose fibers and has excellent mechanical flexibility, good specific capacitance and power performance, and excellent cyclic stability. The electrical conductivity of the GCP membrane shows high stability with a decrease of only 6% after being bent 1000 times. This flexible GCP electrode has a high capacitance per geometric area of 81 mF cm^?2, which is equivalent to a gravimetric capacitance of 120 F g^?1 of graphene, and retains >99% capacitance over 5000 cycles. Several types of flexible GCP‐based polymer supercapacitors with various architectures are assembled to meet the power‐energy requirements of typical flexible or printable electronics. Under highly flexible conditions, the supercapacitors show a high capacitance per geometric area of 46 mF cm^?2 for the complete devices. All the results demonstrate that polymer supercapacitors made using GCP membranes are versatile and may be used for flexible and portable micropower devices.