Nitrogen‐Doped Carbon Networks for High Energy Density Supercapacitors Derived from Polyaniline Coated Bacterial Cellulose

Bacterial cellulose (BC) is used as both template and precursor for the synthesis of nitrogen‐doped carbon networks through the carbonization of polyaniline (PANI) coated BC. The as‐obtained carbon networks can act not only as support for obtaining high capacitance electrode materials such as activated carbon (AC) and carbon/MnO₂ hybrid material, but also as conductive networks to integrate active electrode materials. As a result, the as‐assembled AC//carbon‐MnO₂ asymmetric supercapacitor exhibits a considerably high energy density of 63 Wh kg^?1 in 1.0 m Na₂SO₄ aqueous solution, higher than most reported AC//MnO₂ asymmetric supercapacitors. More importantly, this asymmetric supercapacitor also exhibits an excellent cycling performance with 92% specific capacitance retention after 5000 cycles. Those results offer a low‐cost, eco‐friendly design of electrode materials for high‐performance supercapacitors.     

All‐Solid‐State Asymmetric Supercapacitors with Metal Selenides Electrodes and Ionic Conductive Composites Electrolytes

All‐solid‐state flexible asymmetric supercapacitors (ASCs) are developed by utilization of graphene nanoribbon (GNR)/Co_0.85Se composites as the positive electrode, GNR/Bi₂Se₃ composites as the negative electrode, and polymer‐grafted‐graphene oxide membranes as solid‐state electrolytes. Both GNR/Co_0.85Se and GNR/Bi₂Se₃ composite electrodes are developed by a facile one‐step hydrothermal growth method from graphene oxide nanoribbons as the nucleation framework. The GNR/Co_0.85Se composite electrode exhibits a specific capacity of 76.4 mAh g^?1 at a current density of 1 A g^?1 and the GNR/Bi₂Se₃ composite electrode exhibits a specific capacity of 100.2 mAh g^?1 at a current density of 0.5 A g^?1. Moreover, the stretchable membrane solid‐state electrolytes exhibit superior ionic conductivity of 108.7 mS cm^?1. As a result, the flexible ASCs demonstrate an operating voltage of 1.6 V, an energy density of 30.9 Wh kg^?1 at the power density of 559 W kg^?1, and excellent cycling stability with 89% capacitance retention after 5000 cycles. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate high performance flexible all‐solid‐state ASCs for energy storage.     

Molecular Design of Mesoporous NiCo2O4 and NiCo2S4 with Sub‐Micrometer‐Polyhedron Architectures for Efficient Pseudocapacitive Energy Storage

Spinel‐type NiCo₂O₄ (NCO) and NiCo₂S₄ (NCS) polyhedron architectures with sizes of 500–600 nm and rich mesopores with diameters of 1–2 nm are prepared facilely by the molecular design of Ni and Co into polyhedron‐shaped zeolitic imidazolate frameworks as solid precursors. Both as‐prepared NCO and NCS nanostructures exhibit excellent pseudocapacitance and stability as electrodes in supercapacitors. In particular, the exchange of O^2? in the lattice of NCO with S^2? obviously improves the electrochemical performance. NCS shows a highly attractive capacitance of 1296 F g^?1 at a current density of 1 A g^?1, ultrahigh rate capability with 93.2% capacitance retention at 10 A g^?1, and excellent cycling stability with a capacitance retention of 94.5% after cycling at 1 A g^?1 for 6000 times. The asymmetric supercapacitor with an NCS negative electrode and an active carbon positive electrode delivers a very attractive energy density of 44.8 Wh kg^?1 at power density 794.5 W kg^?1, and a favorable energy density of 37.7 Wh kg^?1 is still achieved at a high power density of 7981.1 W kg^?1. The specific mesoporous polyhedron architecture contributes significantly to the outstanding electrochemical performances of both NCO and NCS for capacitive energy storage.     

Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni?Mo?S and Ni?Fe?S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni²⁺ is optimized to attain hierarchical Ni?Mo?S and Ni?Fe?S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni?Mo?S and Ni?Fe?S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g^?1 at 1 mA cm^?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm^?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni?Mo?S NS//Ni?Fe?S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm^?3, excellent energy density of ≈82.13 Wh kg^?1 at 0.561 kW kg^?1, exceptional power density (≈13.103 kW kg^?1 at 61.51 Wh kg^?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.     

Synthesis of 3D Mesoporous Wall-Like MnO<Subscript>2</Subscript> with Improved Electrochemical Performance

Manganese dioxide (MnO₂) with mesoporous framework self-assembled by ultrathin nanosheets was synthesized via a facile hydrothermal strategy without any binders and substrates. The wall-like structure of this electrode material for supercapacitors can provide more attaching points for active material and shorten the diffusion paths of electrons and ions, leading to a high specific capacitance (SC) of 400 F g^?1 at current density of 1 A g^?1 and the good cyclic stability up to 3000 cycles. Meanwhile, the relationships among structure, specific surface area, pore size and electrochemical properties have been discussed. It indicated that three-dimensional (3D) wall-like δ-MnO₂ is a promising electrochemical electrode candidate for supercapacitors.     

Hierarchical Ni?Mo?S and Ni?Fe?S Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni? Mo? S and Ni? Fe? S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni²⁺ is optimized to attain hierarchical Ni? Mo? S and Ni? Fe? S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni? Mo? S and Ni? Fe? S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g^?1 at 1 mA cm^?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm^?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni? Mo? S NS//Ni? Fe? S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm^?3, excellent energy density of ≈82.13 Wh kg^?1 at 0.561 kW kg^?1, exceptional power density (≈13.103 kW kg^?1 at 61.51 Wh kg^?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.     

High‐Performance Supercapacitor Applications of NiO‐Nanoparticle‐Decorated Millimeter‐Long Vertically Aligned Carbon Nanotube Arrays via an Effective Supercritical CO2‐Assisted Method

Nickel oxide (NiO) nanoparticles are distributed uniformly in the vertically aligned carbon nanotube arrays (VACNTs) with millimeter thickness by an effective supercritical carbon dioxide‐assisted method. The as‐prepared VACNT/NiO hybrid structures are used as electrodes without binders and conducting additives for supercapacitor applications. Due to the synergetic effects of NiO and VACNTs with nanoporous structures and parallel 1D conductive paths for electrons, the supercapacitors exhibit a high capacitance of 1088.44 F g^?1. Furthermore, an asymmetric supercapacitor is assembled using the as‐synthesized VACNTs/NiO hybrids as the positive electrode and the VACNTs as the negative electrode. Remarkably, the energy density of the asymmetric supercapacitor is as high as 90.9 Wh kg^?1 at 3.2 kW kg^?1 and the maximum power density reaches 25.6 kW kg^?1 at 24.9 Wh kg^?1, which are superior to those of the NiO or VACNTs‐based asymmetric supercapacitors. More importantly, the asymmetric supercapacitors exhibit capacitance retention of 87.1% after 2000 cycles at 5 A g^?1. The work provides a novel approach in decorating highly dense and long VACNTs with active materials, which are promising electrodes for supercapacitors with ultrahigh power density and energy density.     

Dual Support System Ensuring Porous Co–Al Hydroxide Nanosheets with Ultrahigh Rate Performance and High Energy Density for Supercapacitors

Layered double hydroxides (LDHs) are promising supercapacitor electrode materials due to their high specific capacitances. However, their electrochemical performances such as rate performance and energy density at a high current density, are rather poor. Accordingly, a facile strategy is demonstrated for the synthesis of the integrated porous Co–Al hydroxide nanosheets (named as GSP‐LDH) with dual support system using dodecyl sulfate anions and graphene sheets as structural and conductive supports, respectively. Owing to fast ion/electron transport, porous and integrated structure, the GSP‐LDH electrode exhibits remarkably improved electrochemical characteristics such as high specific capacitance (1043 F g^?1 at 1 A g^?1) and ultra‐high rate performance capability (912 F g^?1 at 20 A g^?1). Moreover, the assembled sandwiched graphene/porous carbon (SGC)//GSP‐LDH asymmetric supercapacitor delivers a high energy density up to 20.4 Wh kg^?1 at a very high power density of 9.3 kW kg^?1, higher than those of previously reported asymmetric supercapacitors. The strategy provides a facile and effective method to achieve high rate performance LDH based electrode materials for supercapacitors.     

Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density,Excellent Rate Capability,and Long Cycle Life

The utilization of Ni(OH)₂ as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)₂ deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)₂ is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g^?1 at 5 mV s^?1 and excellent rate capability (71.9% capacitance retention at 100 mV s^?1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)₂ nanomaterials. Using the ternary Ni(OH)₂ hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg^?1 at the power density of 780 W kg^?1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)₂ can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.     

Facile Synthesis of Hematite Quantum‐Dot/Functionalized Graphene‐Sheet Composites as Advanced Anode Materials for Asymmetric Supercapacitors

For building high‐energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe₂O₃ has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe₂O₃‐based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe₂O₃ quantum dots (QDs, ≈2 nm) decorated on functionalized graphene‐sheets (FGS) is prepared by a facile and scalable method. The Fe₂O₃ QDs/FGS composites exhibit a large specific capacitance up to 347 F g^?1 in 1 m Na₂SO₄ between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe₂O₃/FGS as anode and MnO₂/FGS as cathode in 1 m Na₂SO₄ aqueous electrolyte. The Fe₂O₃/FGS//MnO₂/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg^?1 at a power density of 100 W kg^?1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe₂O₃ QDs/FGS composites make them promising as anode materials for high‐performance asymmetric supercapacitors.     

Novel Core–Shell FeOF/Ni(OH)2 Hierarchical Nanostructure for All‐Solid‐State Flexible Supercapacitors with Enhanced Performance

Well‐controlled core–shell hierarchical nanostructures based on oxyfluoride and hydroxide are for the first time rationally designed and synthesized via a simple solvothermal and chemical precipitation route, in which FeOF nanorod acts as core and porous Ni(OH)₂ nanosheets as shell. When evaluated as electrodes for supercapacitors, a high specific capacitance of 1452 F g^?1 can be obtained at a current density of 1 A g^?1. Even as the current density increases to 10 A g^?1, the core–shell hybrid still reserves a noticeable capacitance of 1060 F g^?1, showing an excellent rate capacity. Furthermore, all‐solid‐state flexible asymmetric supercapacitor based on the FeOF/Ni(OH)₂ hybrid as a positive electrode and activated carbon as a negative electrode shows high power density, high energy density, and long cycling lifespan. The excellent electrochemical performance of the FeOF/Ni(OH)₂ core–shell hybrid is ascribed to the unique microstructure and synergistic effects. FeOF nanorod from FeF₃ by partial substitution of fluorine with oxygen behaves as a low intrinsic resistance, thus facilitating charge transfer processes. While the hierarchical Ni(OH)₂ nanosheets with large surface area provide enough active sites for redox chemical reactions, leading to greatly enhanced electrochemical activity. The well‐controllable oxyfluoride/hydroxide hybrid is inspiring, opening up a new way to design new electrodes for next‐generation all‐solid‐state supercapacitors.     

Flexible Cellulose Paper‐based Asymmetrical Thin Film Supercapacitors with High‐Performance for Electrochemical Energy Storage

Cellulose paper (CP)‐based asymmetrical thin film supercapacitors (ATFSCs) have been considered to be a novel platform for inexpensive and portable devices as the CP is low‐cost, lightweight, and can be rolled or folded into 3D configurations. However, the low energy density and poor cycle stability are serious bottlenecks for the development of CP‐based ATFSCs. Here, sandwich‐structured graphite/Ni/Co₂NiO₄‐CP is developed as positive electrode and the graphite/Ni/AC‐CP as negative electrode for flexible and high‐performance ATFSCs. The fabricated graphite/Ni/Co₂NiO₄‐CP positive electrode shows a superior areal capacitance (734 mF/cm² at 5 mV/s) and excellent cycling performance with ≈97.6% C_sp retention after 15 000 cycles. The fabricated graphite/Ni/AC‐CP negative electrode also exhibits large areal capacitance (180 mF/cm² at 5 mV/s) and excellent cycling performance with ≈98% C_sp retention after 15 000 cycles. The assembled ATFSCs based on the sandwich‐structured graphite/Ni/Co₂NiO₄‐CP as positive electrode and graphite/Ni/AC‐CP as negative electrode exhibit large volumetric C_sp (7.6 F/cm³ at 5 mV/s), high volumetric energy density (2.48 mWh/cm³, 80 Wh/kg), high volumetric power density (0.79 W/cm³, 25.6 kW/kg) and excellent cycle stability (less 4% C_sp loss after 20 000 cycles). This study shows an important breakthrough in the design and fabrication of high‐performance and flexible CP‐based electrodes and ATFSCs.     

Enhancing the Capacitive Storage Performance of Carbon Fiber Textile by Surface and Structural Modulation for Advanced Flexible Asymmetric Supercapacitors

The exploration of high‐energy anodes with good mechanical properties is highly attractive for flexible asymmetric supercapacitors (ASCs) but challenging. Owing to the excellent conductivity and superior mechanical flexibility, carbon fiber textile (CFT) holds great promise as a substrate/current‐collector for fabricating flexible electrodes. Yet, it is rarely used as a flexible active electrode in terms of its low electrochemical reactivity and small accessible area. In this work, an effective surface and structural modulation strategy is developed to directly tune CFT into a highly active anode for flexible ASCs by creating hierarchical pores and numerous pseudocapacitive oxygenic groups. Arising from large surface and increased active sites, the as‐prepared activated porous CFT (APCFT) electrode not only achieves a large capacitance (1.2 F cm^?2 at 4 mA cm^?2) and fast kinetics but also shows satisfying cycling durability (no capacitance decay after 25 000 cycles). More importantly, an advanced flexible ASC device with an impressive energy density of 4.70 mWh cm^?3 is successfully assembled by employing this APCFT as an anode, outperforming most recently reported ASC devices. This dual modification strategy may throw light on the rational design of new generation advanced carbon electrodes for high‐performance flexible supercapacitors.     

Multicomponent Hierarchical Cu‐Doped NiCo‐LDH/CuO Double Arrays for Ultralong‐Life Hybrid Fiber Supercapacitor

Fiber supercapacitors have aroused great interest in the field of portable and wearable electronic devices. However, the restrained surface area of fibers and limited reaction kinetics of active materials are unfavorable for performance enhancement. Herein, an efficient multicomponent hierarchical structure is constructed by integrating the Cu‐doped cobalt copper carbonate hydroxide@nickel cobalt layered double hydroxide (CCCH@NiCo‐LDH) core–shell nanowire arrays (NWAs) on Cu fibers with highly conductive Au‐modified CuO nanosheets (CCCH@NiCo‐LDH NWAs@Au–CuO/Cu) via a novel in situ corrosion growth method. This multicomponent hierarchical structure contributes to a large accessible surface area, which results in sufficient permeation of the electrolyte. The Cu dopant could reduce the work function and facilitate fast charge transfer kinetics. Therefore, the effective ion diffusion and electron conduction will facilitate the electrochemical reaction kinetics of the electrode. Benefiting from this unique structure, the electrode delivers a high specific capacitance (1.97 F cm^?2/1237 F g^?1/193.3 mAh g^?1) and cycling stability (90.8% after 30 000 cycles), exhibiting superb performance compared with most oxide‐based fiber electrodes. Furthermore, the hybrid fiber supercapacitor of CCCH@NiCo‐LDH NWAs@Au–CuO/Cu//VN/carbon fibers is fabricated, providing a remarkable maximal energy density of 34.97 Wh kg^?1 and a power density of 13.86 kW kg^?1, exhibiting a great potential in high‐performance fiber‐shape energy‐related systems.     

Nickel–Cobalt Layered Double Hydroxide Nanosheets for High‐performance Supercapacitor Electrode Materials

A facile and novel one‐step method of growing nickel‐cobalt layered double hydroxide (Ni‐Co LDH) hybrid films with ultrathin nanosheets and porous nanostructures on nickel foam is presented using cetyltrimethylammonium bromide as nanostructure growth assisting agent but without any adscititious alkali sources and oxidants. As pseudocapacitors, the as‐obtained Ni‐Co LDH hybrid film‐based electrodes display a significantly enhanced specific capacitance (2682 F g^?1 at 3 A g^?1, based on active materials) and energy density (77.3 Wh kg^?1 at 623 W kg^?1), compared to most previously reported electrodes based on nickel‐cobalt oxides/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni‐Co LDH hybrid film as the positive electrode material and porous freeze‐dried reduced graphene oxide (RGO) as the negative electrode material, exhibits an ultrahigh energy density (188 Wh kg^?1) at an average power density of 1499 W kg^?1 based on the mass of active material, which greatly exceeds the energy densities of most previously reported nickel or cobalt oxide/hydroxide‐based asymmetric supercapacitors.     

Polyoxometalate‐coupled Graphene via Polymeric Ionic Liquid Linker for Supercapacitors

The integration of electrical double‐layer capacitive and pseudocapacitive materials into novel hybrid materials is crucial to realize supercapacitors with high energy and power densities. Here, high levels of energy and power densities are demonstrated in supercapacitors based on a new type of nanohybrid electrode consisting of polyoxometalate (POM)‐coupled graphene in which a polymeric ionic liquid (henceforth simply PIL) serves as an interfacial linker. The adoption of PIL in the construction of nanohybrids enables a uniform distribution of discrete POM molecules along with a large surface area of graphene sheets. When testing electrochemical characteristics under a two‐electrode system, as‐prepared supercapacitors exhibit a high specific capacitance (408 F g^?1 at 0.5 A g^?1), rapid rate capability (92% retention at 10 A g^?1), a long cycling life (98% retention during 2000 cycles), and high energy (56 Wh kg^?1) and power (52 kW kg^?1) densities. First‐principles calculations and impedance spectroscopy analysis reveal that the PILs enhance the redox reactions of POMs by providing efficient ion transfer channels and facilitating the charge transfer in the nanohybrids.     

A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

Alternative-Ultrathin Assembling of Exfoliated Manganese Dioxide and Nitrogen-Doped Carbon Layers for High-Mass-Loading Supercapacitors with Outstanding Capacitance and Impressive Rate Capability

Manganese dioxide (MnO₂) materials have received much attention as promising pseudocapacitive materials owing to their high theoretical capacitance and natural abundance. Unfortunately, the charge storage performance of MnO₂ is usually limited to commercially available mass loading electrodes because of the significantly lower electron and ion migration kinetics in thick electrodes. Here, an alternatively assembled 2D layered material consisting of exfoliated MnO₂ nanosheets and nitrogen-doped carbon layers for ultrahigh-mass-loading supercapacitors without sacrificing energy storage performance is reported. Layered birnessite-type MnO₂ is efficiently exfoliated and intercalated by a carbon precursor of dopamine using a fluid dynamic-induced process, resulting in MnO₂/nitrogen-doped carbon (MnO₂/C) materials after self-polymerization and carbonization. The alternatively stacked and interlayer-expanded structure of MnO₂/C enables fast and efficient electron and ion transfer in a thick electrode. The resulting MnO₂/C electrode shows outstanding electrochemical performance at an ultrahigh mass loading of 19.7 mg cm⁻², high gravimetric and areal capacitances of 480.3 F g⁻¹ and 9.4 F cm⁻² at 0.5 mA cm⁻², and rapid charge/discharge capability of 70% capacitance retention at 40 mA cm⁻². Furthermore, asymmetric supercapacitor based on high-mass-loading MnO₂/C can deliver an extremely high energy of 64.2 Wh kg⁻¹ at a power density of 18.8 W kg⁻¹ in an aqueous electrolyte.     

Aqueous Ammonium-Ion Supercapacitors with Unprecedented Energy Density and Stability Enabled by Oxygen Vacancy-Enriched MoO3@C

The use of non-metal charge carriers such as ammonium (NH₄⁺) in electrochemical energy storage devices offers advantages in terms of weight, element abundance, and compatibility with aqueous electrolytes. However, the development of suitable electrodes for such carriers lags behind other technologies. Herein, we present a high-performance anode material for ammonium-ion supercapacitors based on a MoO₃/carbon (MoO₃@C) composite. The NH₄⁺ storage performance of such composites and their practical application prospects are evaluated both in a three-electrode configuration and as symmetric supercapacitors. The optimized material reaches an unprecedented specific capacitance of 473 F·g⁻¹ (158 mAh·g⁻¹; 1592 mF·cm⁻²) at a current density of 1 A·g⁻¹, and 92.7% capacitance retention after 5000 cycles in a three-electrode set-up. This outstanding performance is related to the presence of oxygen vacancies that enhance the composites’ ionic/electronic transportation and electrochemical reaction site, while at the same time facilitating the formation of hydrogen bonds between NH₄⁺ and the host material. Using the optimized composite, symmetric supercapacitors based on an (NH₄)₂SO₄ gel electrolyte are fabricated and demonstrated to provide unmatched energy densities above 78 Wh·kg⁻¹ at a power density of 929 W·kg⁻¹. Besides, such devices are characterized by extraordinary capacitance retention of 97.6% after 10,000 cycles.     

In‐Plane Assembled Orthorhombic Nb2O5 Nanorod Films with High‐Rate Li+ Intercalation for High‐Performance Flexible Li‐Ion Capacitors

Organic hybrid supercapacitors that consist of a battery electrode and a capacitive electrode show greatly improved energy density, but their power density is generally limited by the poor rate capability of battery‐type electrodes. In addition, flexible organic hybrid supercapacitors are rarely reported. To address the above issues, herein an in‐plane assembled orthorhombic Nb₂O₅ nanorod film anode with high‐rate Li⁺ intercalation to develop a flexible Li‐ion hybrid capacitor (LIC) is reported. The binder‐/additive‐free film exhibits excellent rate capability (≈73% capacity retention with the rate increased from 0.5 to 20 C) and good cycling stability (>2500 times). Kinetic analyses reveal that the high rate performance is mainly attributed to the excellent in‐plane assembly of interconnected single‐crystalline Nb₂O₅ nanorods on the current collector, ensuring fast electron transport, facile Li‐ion migration in the porous film, and greatly reduced ion‐diffusion length. Using such a Nb₂O₅ film as anode and commercial activated carbon as cathode, a flexible LIC is designed. It delivers both high gravimetric and high volumetric energy/power densities (≈95.55 Wh kg^?1/5350.9 W kg^?1; 6.7 mW h cm^?3/374.63 mW cm^?3), surpassing previous typical Li‐intercalation electrode‐based LICs. Furthermore, this LIC device still keeps good electrochemical attributes even under serious bending states (30°–180°).