A Flexible Film with SnS2 Nanoparticles Chemically Anchored on 3D‐Graphene Framework for High Areal Density and High Rate Sodium Storage

The design and construction of flexible electrodes that can function at high rates and high areal capacities are essential regarding the practical application of flexible sodium‐ion batteries (SIBs) and other energy storage devices, which remains significantly challenging by far. Herein, a flexible and 3D porous graphene nanosheet/SnS₂ (3D‐GNS/SnS₂) film is reported as a high‐performance SIB electrode. In this hybrid film, the GNS/SnS₂ microblocks serve as pillars to assemble into a 3D porous and interconnected framework, enabling fast electron/ion transport; while the GNS bridges the GNS/SnS₂ microblocks into a flexible framework to provide satisfactorily mechanical strength and long‐range conductivity. Moreover, the SnS₂ nanocrystals, which chemically bond with GNS, provide sufficient active sites for Na storage and ensure the cycling stability. Consequently, this flexible 3D‐GNS/SnS₂ film exhibits excellent Na‐storage performances, especially in terms of high areal capacity (2.45 mAh cm^?2) and high rates with superior stability (385 mAh g^?1 at 1.0 A g^?1 over 1000 cycles with ≈100% retention). A flexible SIB full cell using this anode exhibits high and stable performance under various bending situations. Thus, this work provide a feasible route to prepare flexible electrodes with high practical viability for not only SIBs but also other energy storage devices.     

Controllable N‐Doped CuCo2O4@C Film as a Self‐Supported Anode for Ultrastable Sodium‐Ion Batteries

Rational synthesis of flexible electrodes is crucial to rapid growth of functional materials for energy‐storage systems. Herein, a controllable fabrication is reported for the self‐supported structure of CuCo₂O₄ nanodots (≈3 nm) delicately inserted into N‐doped carbon nanofibers (named as 3‐CCO@C); this composite is first used as binder‐free anode for sodium‐ion batteries (SIBs). Benefiting from the synergetic effect of ultrasmall CuCo₂O₄ nanoparticles and a tailored N‐doped carbon matrix, the 3‐CCO@C composite exhibits high cycling stability (capacity of 314 mA h g^?1 at 1000 mA g^?1 after 1000 cycles) and high rate capability (296 mA h g^?1, even at 5000 mA g^?1). Significantly, the Na storage mechanism is systematically explored, demonstrating that the irreversible reaction of CuCo₂O₄, which decomposes to Cu and Co, happens in the first discharge process, and then a reversible reaction between metallic Cu/Co and CuO/Co₃O₄ occurrs during the following cycles. This result is conducive to a mechanistic study of highly promising bimetallic‐oxide anodes for rechargeable SIBs.     

Flexible and Binder‐Free Electrodes of Sb/rGO and Na3V2(PO4)3/rGO Nanocomposites for Sodium‐Ion Batteries

Flexible power sources have shown great promise in next‐generation bendable, implantable, and wearable electronic systems. Here, flexible and binder‐free electrodes of Na₃V₂(PO₄)₃/reduced graphene oxide (NVP/rGO) and Sb/rGO nanocomposites for sodium‐ion batteries are reported. The Sb/rGO and NVP/rGO paper electrodes with high flexibility and tailorability can be easily fabricated. Sb and NVP nanoparticles are embedded homogenously in the interconnected framework of rGO nanosheets, which provides structurally stable hosts for Na‐ion intercalation and deintercalation. The NVP/rGO paper‐like cathode delivers a reversible capacity of 113 mAh g^?1 at 100 mA g^?1 and high capacity retention of ≈96.6% after 120 cycles. The Sb/rGO paper‐like anode gives a highly reversible capacity of 612 mAh g^?1 at 100 mA g^?1, an excellent rate capacity up to 30 C, and a good cycle performance. Moreover, the sodium‐ion full cell of NVP/rGO//Sb/rGO has been fabricated, delivering a highly reversible capacity of ≈400 mAh g^?1 at a current density of 100 mA g^?1 after 100 charge/discharge cycles. This work may provide promising electrode candidates for developing next‐generation energy‐storage devices with high capacity and long cycle life.     

Production of AgCu:NiO/Ni foam electrode with high charge accumulation and long cycling stability

Nickel oxide is a promising material for electrochemical energy storage devices due to its high specific surface area, rapid redox reactions, and short diffusion path in the solid electrode. It has been known that the loading of metallic elements into the NiO matrix enhances these superior properties. NiO material is electrochemically deposited on Ni foam, and then, Ag and Cu thin layers are coated on NiO by thermal evaporation. The produced NiO/Ni foam and AgCu:NiO/Ni foam electrodes are annealed at 400 °C for 1 h. Those are utilized as anode for high-performance energy storage electrode in an alkaline solution. The former has an energy density of 56.9 Wh kg^?1 at 3155.5 W kg^?1, while the latter has a high energy density of 107.6 Wh kg^?1 at the corresponding power density of 2957.7 W kg^?1. Although specific capacitance of the former decreases to 46.2% of its original capacitance at 10 A g^?1 after 5000 cycles, the latter exhibits higher cycling stability with 71.0% retention after 5000 charge–discharge cycles owing to the loading of Ag and Cu into NiO matrix. Charge transfer resistance of NiO/Ni foam, which is inversely proportional to electroactive surface area, reduces from 19.4 to 0.28 Ω after the incorporation of Ag and Cu. Compared to NiO/Ni foam, AgCu:NiO/Ni foam with a higher electroactive surface area is more appropriate for charge accumulation. As mention above, the features of AgCu:NiO/Ni foam indicate that it is a promising material as an effective start-of-art energy storage device.

     

An Ultrastable and High‐Performance Flexible Fiber‐Shaped Ni–Zn Battery based on a Ni–NiO Heterostructured Nanosheet Cathode

Currently, the main bottleneck for the widespread application of Ni–Zn batteries is their poor cycling stability as a result of the irreversibility of the Ni‐based cathode and dendrite formation of the Zn anode during the charging–discharging processes. Herein, a highly rechargeable, flexible, fiber‐shaped Ni–Zn battery with impressive electrochemical performance is rationally demonstrated by employing Ni–NiO heterostructured nanosheets as the cathode. Benefiting from the improved conductivity and enhanced electroactivity of the Ni–NiO heterojunction nanosheet cathode, the as‐fabricated fiber‐shaped Ni–NiO//Zn battery displays high capacity and admirable rate capability. More importantly, this Ni–NiO//Zn battery shows unprecedented cyclic durability both in aqueous (96.6% capacity retention after 10 000 cycles) and polymer (almost no capacity attenuation after 10 000 cycles at 22.2 A g^?1) electrolytes. Moreover, a peak energy density of 6.6 µWh cm^?2, together with a remarkable power density of 20.2 mW cm^?2, is achieved by the flexible quasi‐solid‐state fiber‐shaped Ni–NiO//Zn battery, outperforming most reported fiber‐shaped energy‐storage devices. Such a novel concept of a fiber‐shaped Ni–Zn battery with impressive stability will greatly enrich the flexible energy‐storage technologies for future portable/wearable electronic applications.     

Efficient Supercapacitor Energy Storage Using Conjugated Microporous Polymer Networks Synthesized from Buchwald–Hartwig Coupling

Supercapacitors have received increasing interest as energy storage devices due to their rapid charge–discharge rates, high power densities, and high durability. In this work, novel conjugated microporous polymer (CMP) networks are presented for supercapacitor energy storage, namely 3D polyaminoanthraquinone (PAQ) networks synthesized via Buchwald–Hartwig coupling between 2,6‐diaminoanthraquinone and aryl bromides. PAQs exhibit surface areas up to 600 m² g^?1, good dispersibility in polar solvents, and can be processed to flexible electrodes. The PAQs exhibit a three‐electrode specific capacitance of 576 F g^?1 in 0.5 m H₂SO₄ at a current of 1 A g^?1 retaining 80–85% capacitances and nearly 100% Coulombic efficiencies (95–98%) upon 6000 cycles at a current density of 2 A g^?1. Asymmetric two‐electrode supercapacitors assembled by PAQs show a capacitance of 168 F g^?1 of total electrode materials, an energy density of 60 Wh kg^?1 at a power density of 1300 W kg^?1, and a wide working potential window (0–1.6 V). The asymmetric supercapacitors show Coulombic efficiencies up to 97% and can retain 95.5% of initial capacitance undergo 2000 cycles. This work thus presents novel promising CMP networks for charge energy storage.     

Interlayer Hydrogen‐Bonded Metal Porphyrin Frameworks/MXene Hybrid Film with High Capacitance for Flexible All‐Solid‐State Supercapacitors

2D metal‐porphyrin frameworks (MPFs) are attractive for advanced energy storage devices. However, the inferior conductivity and low structural stability of MPFs seriously limit their application as flexible free‐standing electrodes with high performance. Here, for the first time, an interlayer hydrogen‐bonded MXene/MPFs film is proposed to overcome these disadvantages by intercalation of highly conductive MXene nanosheets into MPFs nanosheets via a vacuum‐assisted filtration technology. The alternant insertion of MXene and MPFs affords 3D interconnected “MPFs‐to‐MXene‐to‐MPFs” conductive networks to accelerate the ionic/electronic transport rates. Meanwhile, the interlayer hydrogen bonds (F···H? O and O···H? O) contribute a high chemical stability due to a favorable tolerance to volume change caused by phase separation and structural collapse during the charge/discharge process. The synergistic effect makes MXene/MPFs film deliver a capacitance of 326.1 F g^?1 at 0.1 A g^?1, 1.64 F cm^?2 at 1 mA cm^?2, 694.2 F cm^?3 at 1 mA cm^?3 and a durability of about 30 000 cycles. The flexible symmetric supercapacitor shows an areal capacitance of 408 mF cm^?2, areal energy density of 20.4 µW h cm^?2, and capacitance retention of 95.9% after 7000 cycles. This work paves an avenue for the further exploration of 2D MOFs in flexible energy storage devices.     

Vertically Aligned Graphene–Carbon Fiber Hybrid Electrodes with Superlong Cycling Stability for Flexible Supercapacitors

Graphene electrode–based supercapacitors are in high demand due to their superior electrochemical characteristics. A major bottleneck of using the supercapacitors for commercial applications lies in their inferior electrode cycle life. Herein, a simple and facile method to fabricate highly efficient supercapacitor electrodes using pristine graphene sheets vertically stacked and electrically connected to the carbon fibers which can result in vertically aligned graphene–carbon fiber nanostructure is developed. The vertically aligned graphene–carbon fiber electrode prepared by electrophoretic deposition possesses a mesoporous 3D architecture which enabled faster and efficient electrolyte‐ion diffusion with a gravimetric capacitance of 333.3 F g^?1 and an areal capacitance of 166 mF cm^?2. The electrodes displayed superlong electrochemical cycling stability of more than 100 000 cycles with 100% capacitance retention hence promising for long‐lasting supercapacitors. Apart from the electrochemical double layer charge storage, the oxygen‐containing surface moieties and α‐Ni(OH)₂ present on the graphene sheets enhance the charge storage by faradaic reactions. This enables the assembled device to provide an excellent gravimetric energy density of 76 W h kg^?1 with a 100% capacitance retention even after 1000 bending cycles. This study opens the door for developing high‐performing flexible graphene electrodes for wearable energy storage applications.     

Lithium Titanate Cuboid Arrays Grown on Carbon Fiber Cloth for High‐Rate Flexible Lithium‐Ion Batteries

High‐rate performance flexible lithium‐ion batteries are desirable for the realization of wearable electronics. The flexibility of the electrode in the battery is a key requirement for this technology. In the present work, spinel lithium titanate (Li₄Ti₅O₁₂, LTO) cuboid arrays are grown on flexible carbon fiber cloth (CFC) to fabricate a binder‐free composite electrode (LTO@CFC) for flexible lithium‐ion batteries. Experimental results show that the LTO@CFC electrode exhibits a remarkably high‐rate performance with a capacity of 105.8 mAh g^?1 at 50C and an excellent electrochemical stability against cycling (only 2.2% capacity loss after 1000 cycles at 10C). A flexible full cell fabricated with the LTO@CFC as the anode and LiNi_0.5Mn_1.5O₄ coated on Al foil as the cathode displays a reversible capacity of 109.1 mAh g^?1 at 10C, an excellent stability against cycling and a great mechanical stability against bending. The observed high‐rate performance of the LTO@CFC electrode is due to its unique corn‐like architecture with LTO cuboid arrays (corn kernels) grown on CFC (corn cob). This work presents a new approach to preparing LTO‐based composite electrodes with an architecture favorable for ion and electron transport for flexible energy storage devices.     

Waterproof,Ultrahigh Areal‐Capacitance,Wearable Supercapacitor Fabrics

High‐performance supercapacitors (SCs) are promising energy storage devices to meet the pressing demand for future wearable applications. Because the surface area of a human body is limited to 2 m², the key challenge in this field is how to realize a high areal capacitance for SCs, while achieving rapid charging, good capacitive retention, flexibility, and waterproofing. To address this challenge, low‐cost materials are used including multiwall carbon nanotube (MWCNT), reduced graphene oxide (RGO), and metallic textiles to fabricate composite fabric electrodes, in which MWCNT and RGO are alternatively vacuum‐filtrated directly onto Ni‐coated cotton fabrics. The composite fabric electrodes display typical electrical double layer capacitor behavior, and reach an ultrahigh areal capacitance up to 6.2 F cm^?2 at a high areal current density of 20 mA cm^?2. All‐solid‐state fabric‐type SC devices made with the composite fabric electrodes and water‐repellent treatment can reach record‐breaking performance of 2.7 F cm^?2 at 20 mA cm^?2 at the first charge–discharge cycle, 3.2 F cm^?2 after 10 000 charge–discharge cycles, zero capacitive decay after 10 000 bending tests, and 10 h continuous underwater operation. The SC devices are easy to assemble into tandem structures and integrate into garments by simple sewing.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Interface‐Engineered Nickel Cobaltite Nanowires through NiO Atomic Layer Deposition and Nitrogen Plasma for High‐Energy,Long‐Cycle‐Life Foldable All‐Solid‐State Supercapacitors

The large‐scale application of supercapacitors (SCs) for portable electronics is restricted by low energy density and cycling stability. To alleviate the limitations, a unique interface engineering strategy is suggested through atomic layer deposition (ALD) and nitrogen plasma. First, commercial carbon cloth (CC) is treated with nitrogen plasma and later inorganic NiCo₂O₄ (NCO)/NiO core–shell nanowire arrays are deposited on nitrogen plasma–treated CC (NCC) to fabricate the ultrahigh stable SC. An ultrathin layer of NiO deposited on the NCO nanowire arrays via conformal ALD plays a vital role in stabilizing the NCO nanowires for thousands of electrochemical cycles. The optimized NCC/NCO/NiO core–shell electrode exhibits a high specific capacitance of 2439 F g^?1 with a remarkable cycling stability (94.2% over 20 000 cycles). Benefiting from these integrated merits, the foldable solid‐state SCs are fabricated with excellent NCC/NCO/NiO core–shell nanowire array electrodes. The fabricated SC device delivers a high energy density of 72.32 Wh kg^?1 at a specific capacitance of 578 F g^?1, with ultrasmall capacitance decline rate of 0.0003% per cycle over 10 000 charge–discharge cycles. Overall, this strategy offers a new avenue for developing a new‐generation high‐energy, ultrahigh stable supercapacitor for real‐life applications.     

Coupling PEDOT on Mesoporous Vanadium Nitride Arrays for Advanced Flexible All‐Solid‐State Supercapacitors

Tailored construction of advanced flexible supercapacitors (SCs) is of great importance to the development of high‐performance wearable modern electronics. Herein, a facile combined wet chemical method to fabricate novel mesoporous vanadium nitride (VN) composite arrays coupled with poly(3,4‐ethylenedioxythiophene) (PEDOT) as flexible electrodes for all‐solid‐state SCs is reported. The mesoporous VN nanosheets arrays prepared by the hydrothermal–nitridation method are composed of cross‐linked nanoparticles of 10–50 nm. To enhance electrochemical stability, the VN is further coupled with electrodeposited PEDOT shell to form high‐quality VN/PEDOT flexible arrays. Benefiting from high intrinsic reactivity and enhanced structural stability, the designed VN/PEDOT flexible arrays exhibit a high specific capacitance of 226.2 F g^?1 at 1 A g^?1 and an excellent cycle stability with 91.5% capacity retention after 5000 cycles at 10 A g^?1. In addition, high energy/power density (48.36 Wh kg^?1 at 2 A g^?1 and 4 kW kg^?1 at 5 A g^?1) and notable cycling life (91.6% retention over 10 000 cycles) are also achieved in the assembled asymmetric flexible supercapacitor cell with commercial nickel–cobalt–aluminum ternary oxides cathode and VN/PEDOT anode. This research opens up a way for construction of advanced hybrid organic–inorganic electrodes for flexible energy storage.     

Rational Design of a Flexible CNTs@PDMS Film Patterned by Bio‐Inspired Templates as a Strain Sensor and Supercapacitor

Flexible devices integrated with sensing and energy storage functions are highly desirable due to their potential application in wearable electronics and human motion detection. Here, a flexible film is designed in a facile and low‐cost leaf templating process, comprising wrinkled carbon nanotubes (CNTs) as the conductive layer and patterned polydimethylsiloxane (PDMS) with bio‐inspired microstructure as a soft substrate. Assembled from wrinkled CNTs on patterned PDMS film, a strain sensor is realized to possess sensitive resistance response against various deformations, producing a resistance response of 0.34%, 0.14%, and 9.1% under bending, pressing, and 20% strain, respectively. Besides, the strain sensor can reach a resistance response of 3.01 when stretched to 44%. Furthermore, through the electro‐deposition of polyaniline, the CNTs film is developed into a supercapacitor, which exhibits a specific capacitance of 176 F g^?1 at 1 A g^?1 and a capacitance retention of 88% after 10 000 cycles. In addition, the fabricated supercapacitor shows super flexibility, delivering a capacitance retention of 98% after 180° bending for 100 cycles, 95% after 45° twisting for 100 cycles, and 98% after 100% stretching for 400 cycles. The superior capacitance stability demonstrates that the design of wrinkled CNTs‐based electrodes fixed by microstructures is beneficial to the excellent electrochemical performance.     

High-yield synthesis of carbon nanotube–porous nickel oxide nanosheet hybrid and its electrochemical capacitance performance

This study reports an easy chemical conversion route toward large-scale fabrication of carbon nanotube (CNT)–porous nickel oxide (NiO) hybrid nanocomposites as supercapacitor electrode materials. The electrocapacitive performance of CNT–porous NiO hybrids is evaluated by cyclic voltammetry and galvanostatic charge–discharge measurements. The synthesized CNT–NiO hybrid nanocomposite electrode presents a high specific capacitance of 759 F g⁻¹ at 0.5 A g⁻¹ in 6 M KOH aqueous electrolyte, which is almost twice that of pure NiO nanoparticle (388 F g⁻¹) electrodes and nine times of that of commercial NiO particle (88.4 F g⁻¹) electrodes. Furthermore, good capacitance retention is achieved after 1000 cycles of galvanostatic charge–discharge. The synergistic effects from the pseudocapacitance of porous NiO particles, good electrical conductivity, and open tip CNTs attribute to the high capacitance performance.     

Biomass‐Derived Nitrogen‐Doped Carbon Nanofiber Network: A Facile Template for Decoration of Ultrathin Nickel‐Cobalt Layered Double Hydroxide Nanosheets as High‐Performance Asymmetric Supercapacitor Electrode

The development of biomass‐based energy storage devices is an emerging trend to reduce the ever‐increasing consumption of non‐renewable resources. Here, nitrogen‐doped carbonized bacterial cellulose (CBC‐N) nanofibers are obtained by one‐step carbonization of polyaniline coated bacterial cellulose (BC) nanofibers, which not only display excellent capacitive performance as the supercapacitor electrode, but also act as 3D bio‐template for further deposition of ultrathin nickel‐cobalt layered double hydroxide (Ni‐Co LDH) nanosheets. The as‐obtained CBC‐N@LDH composite electrodes exhibit significantly enhanced specific capacitance (1949.5 F g^?1 at a discharge current density of 1 A g^?1, based on active materials), high capacitance retention of 54.7% even at a high discharge current density of 10 A g^?1 and excellent cycling stability of 74.4% retention after 5000 cycles. Furthermore, asymmetric supercapacitors (ASCs) are constructed using CBC‐N@LDH composites as positive electrode materials and CBC‐N nanofibers as negative electrode materials. By virtue of the intrinsic pseudocapacitive characteristics of CBC‐N@LDH composites and 3D nitrogen‐doped carbon nanofiber networks, the developed ASC exhibits high energy density of 36.3 Wh kg^?1 at the power density of 800.2 W kg^?1. Therefore, this work presents a novel protocol for the large‐scale production of biomass‐derived high‐performance electrode materials in practical supercapacitor applications.     

Inkjet‐Printed Lithium–Sulfur Microcathodes for All‐Printed,Integrated Nanomanufacturing

Improved thin‐film microbatteries are needed to provide appropriate energy‐storage options to power the multitude of devices that will bring the proposed “Internet of Things” network to fruition (e.g., active radio‐frequency identification tags and microcontrollers for wearable and implantable devices). Although impressive efforts have been made to improve the energy density of 3D microbatteries, they have all used low energy‐density lithium‐ion chemistries, which present a fundamental barrier to miniaturization. In addition, they require complicated microfabrication processes that hinder cost‐competitiveness. Here, inkjet‐printed lithium–sulfur (Li–S) cathodes for integrated nanomanufacturing are reported. Single‐wall carbon nanotubes infused with electronically conductive straight‐chain sulfur (S@SWNT) are adopted as an integrated current‐collector/active‐material composite, and inkjet printing as a top‐down approach to achieve thin‐film shape control over printed electrode dimensions is used. The novel Li–S cathodes may be directly printed on traditional microelectronic semicoductor substrates (e.g., SiO₂) or on flexible aluminum foil. Profilometry indicates that these microelectrodes are less than 10 µm thick, while cyclic voltammetry analyses show that the S@SWNT possesses pseudocapacitive characteristics and corroborates a previous study suggesting the S@SWNT discharge via a purely solid‐state mechanism. The printed electrodes produce ≈800 mAh g^?1 S initially and ≈700 mAh g^?1 after 100 charge/discharge cycles at C/2 rate.     

Flexible Graphene‐Wrapped Carbon Nanotube/Graphene@MnO2 3D Multilevel Porous Film for High‐Performance Lithium‐Ion Batteries

The ingenious design of a freestanding flexible electrode brings the possibility for power sources in emerging wearable electronic devices. Here, reduced graphene oxide (rGO) wraps carbon nanotubes (CNTs) and rGO tightly surrounded by MnO₂ nanosheets, forming a 3D multilevel porous conductive structure via vacuum freeze‐drying. The sandwich‐like architecture possesses multiple functions as a flexible anode for lithium‐ion batteries. Micrometer‐sized pores among the continuously waved rGO layers could extraordinarily improve ion diffusion. Nano‐sized pores among the MnO₂ nanosheets and CNT/rGO@MnO₂ particles could provide vast accessible active sites and alleviate volume change. The tight connection between MnO₂ and carbon skeleton could facilitate electron transportation and enhance structural stability. Due to the special structure, the rGO‐wrapped CNT/rGO@MnO₂ porous film as an anode shows a high capacity, excellent rate performance, and superior cycling stability (1344.2 mAh g⁻¹ over 630 cycles at 2 A g⁻¹, 608.5 mAh g⁻¹ over 1000 cycles at 7.5 A g⁻¹). Furthermore, the evolutions of microstructure and chemical valence occurring inside the electrode after cycling are investigated to illuminate the structural superiority for energy storage. The excellent electrochemical performance of this freestanding flexible electrode makes it an attractive candidate for practical application in flexible energy storage.     

Achieving Ultrahigh Energy Density and Long Durability in a Flexible Rechargeable Quasi‐Solid‐State Zn–MnO2 Battery

Advanced flexible batteries with high energy density and long cycle life are an important research target. Herein, the first paradigm of a high‐performance and stable flexible rechargeable quasi‐solid‐state Zn–MnO₂ battery is constructed by engineering MnO₂ electrodes and gel electrolyte. Benefiting from a poly(3,4‐ethylenedioxythiophene) (PEDOT) buffer layer and a Mn²⁺‐based neutral electrolyte, the fabricated Zn–MnO₂@PEDOT battery presents a remarkable capacity of 366.6 mA h g^?1 and good cycling performance (83.7% after 300 cycles) in aqueous electrolyte. More importantly, when using PVA/ZnCl₂/MnSO₄ gel as electrolyte, the as‐fabricated quasi‐solid‐state Zn–MnO₂@PEDOT battery remains highly rechargeable, maintaining more than 77.7% of its initial capacity and nearly 100% Coulombic efficiency after 300 cycles. Moreover, this flexible quasi‐solid‐state Zn–MnO₂ battery achieves an admirable energy density of 504.9 W h kg^?1 (33.95 mW h cm^?3), together with a peak power density of 8.6 kW kg^?1, substantially higher than most recently reported flexible energy‐storage devices. With the merits of impressive energy density and durability, this highly flexible rechargeable Zn–MnO₂ battery opens new opportunities for powering portable and wearable electronics.     

A Flexible Ionic Liquid Gelled PVA‐Li2SO4 Polymer Electrolyte for Semi‐Solid‐State Supercapacitors

A novel high‐performance flexible gel polymer electrolyte (FGPE) for supercapacitors is prepared by a freeze‐drying method. In the presence of 1‐butyl‐3‐methylimidazolium chloride (BMIMCl) ionic liquid, Li₂SO₄ can easily be added into poly(vinyl alcohol) (PVA) aqueous solution over a large concentration range. The resultant FGPE demonstrates considerably high ionic conductivity (37 mS cm⁻¹) and a high fracture strain at 100% elongation at the optimal weight ratio of PVA:BMIMCl:Li₂SO₄ = 1:3:2.2. The supercapacitor fabricated with the resultant FGPE and activated carbon electrodes shows an electrode‐specific capacitance of 136 F g⁻¹ with a stable operating voltage of 1.5 V, a maximum energy density of 10.6 Wh kg⁻¹, and a power density of 3400 W kg⁻¹. Double supercapacitors in series can efficiently drive a light emitting diode (LED) bulb for over 5 min and the retention of the specific capacitance reaches 90% even after 3000 charge–discharge cycles. The ionic conductivity and charge–discharge behaviors of the resultant FGPE are not affected by bending up to 180°. The flexible supercapacitor device shows only a small capacitance loss of 18% after 1000 cycles of 135° bending.