Sulfidation of NiMn‐Layered Double Hydroxides/Graphene Oxide Composites toward Supercapacitor Electrodes with Enhanced Performance

Supercapacitors can deliver high‐power density and long cycle stability, but the limited energy density due to poor electronic and ionic conductivity of the supercapacitor electrode has been a bottleneck in many applications. A strategy to prepare microflower‐like NiMn‐layered double hydroxides (LDH) with sulfidation is delineated to reduce the charge transfer resistance of supercapacitor electrode and realize faster reversible redox reactions with notably enhanced specific capacitance. The incorporation of graphite oxide (GO) in NiMn LDH during sulfidation leads to simultaneous reduction of GO with enhanced conductivity, lessened defects, and doping of S into the graphitic structure. Cycling stability of the sulfidized composite electrode is enhanced due to the alleviation of phase transformation during electrochemical cycling test. As a result, this sulfidation product of LDH/GO (or LDHGOS) can reach a high‐specific capacitance of 2246.63 F g^?1 at a current density of 1 A g^?1, and a capacitance of 1670.83 F g^?1 is retained at a high‐current density of 10 A g^?1, exhibiting an outstanding capacitance and rate performance. The cycling retention of the LDHGOS electrode is also extended to ≈ 67% after 1500 cycles compared to only ≈44% of the pristine NiMn LDH.     

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.     

3D Hierarchical Porous α‐Fe2O3 Nanosheets for High‐Performance Lithium‐Ion Batteries

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α‐Fe₂O₃ nanosheets are fabricated on copper foil and directly used as binder‐free anode for lithium‐ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g^?1 is maintained at 2 C (2.01 A g^?1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g^?1), a capacity of 433 mA h g^?1 is retained. The unique porous 3D hierarchical nanostructure improves electronic–ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder‐free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance.     

Phase Transformation Induced Capacitance Activation for 3D Graphene‐CoO Nanorod Pseudocapacitor

Development of a pseudocapacitor over the integration of metal oxide on carbonaceous materials is a promising step towards energy storage devices with high energy and power densities. Here, a self‐assembled cobalt oxide (CoO) nanorod cluster on three‐dimensional graphene (CoO‐3DG) is synthesized through a facile hydrothermal method followed by heat treatment. As an additive‐free electrode, CoO‐3DG exhibits good electrochemical performance. Compared with CoO nanorod clusters grown on Ni foam (i.e., CoO‐Ni, ≈680 F g^?1 at 1 A g^?1 and ≈400 F g^?1 at 20 A g^?1), CoO‐3DG achieves much higher capacitance (i.e., ≈980 F g^?1 at 1 A g^?1 and ≈600 F g^?1 at 20 A g^?1) with excellent cycling stability of 103% retention of specific capacitance after 10 000 cycles. Furthermore, it shows an interesting activation process and instability with a redox reaction for CoO. In addition, the phase transformation from CoO nanorods to Co₃O₄ nanostructures was observed and investigated after charge and discharge process, which suggests the activation kinetics and the phase transformable nature of CoO based nanostructure. These observations demonstrate phase transformation with morphological change induced capacitance increasement in the emergent class of metal oxide materials for electrochemical energy storage device.     

High Performance,Flexible, Solid‐State Supercapacitors Based on a Renewable and Biodegradable Mesoporous Cellulose Membrane

A flexible, transparent, and renewable mesoporous cellulose membrane (mCel‐membrane) featuring uniform mesopores of ≈24.7 nm and high porosity of 71.78% is prepared via a facile and scalable solution‐phase inversion process. KOH‐saturated mCel‐membrane as a polymer electrolyte demonstrates a high electrolyte retention of 451.2 wt%, a high ionic conductivity of 0.325 S cm^?1, and excellent mechanical flexibility and robustness. A solid‐state electric double layer capacitor (EDLC) using activated carbon as electrodes, the KOH‐saturated mCel‐membrane as a polymer electrolyte exhibits a high capacitance of 110 F g^?1 at 1.0 A g^?1, and long cycling life of 10 000 cycles with 84.7% capacitance retention. Moreover, a highly integrated planar‐type micro‐supercapacitor (MSC) can be facilely fabricated by directly depositing the electrode materials on the mCel‐membrane‐based polymer electrolyte without using complicated devices. The resulting MSC exhibits a high areal capacitance of 153.34 mF cm^?2 and volumetric capacitance of 191.66 F cm^?3 at 10 mV s^?1, representing one of the highest values among all carbon‐based MSC devices. These findings suggest that the developed renewable, flexible, mesoporous cellulose membrane holds great promise in the practical applications of flexible, solid‐state, portable energy storage devices that are not limited to supercapacitors.     

A Flexible Porous Carbon Nanofibers‐Selenium Cathode with Superior Electrochemical Performance for Both Li‐Se and Na‐Se Batteries

A flexible and free‐standing porous carbon nanofibers/selenium composite electrode (Se@PCNFs) is prepared by infiltrating Se into mesoporous carbon nanofibers (PCNFs). The porous carbon with optimized mesopores for accommodating Se can synergistically suppress the active material dissolution and provide mechanical stability needed for the film. The Se@PCNFs electrode exhibits exceptional electrochemical performance for both Li‐ion and Na‐ion storage. In the case of Li‐ion storage, it delivers a reversible capacity of 516 mAh g^?1 after 900 cycles without any capacity loss at 0.5 A g^?1. Se@PCNFs still delivers a reversible capacity of 306 mAh g^?1 at 4 A g^?1. While being used in Na‐Se batteries, the composite electrode maintains a reversible capacity of 520 mAh g^?1 after 80 cycles at 0.05 A g^?1 and a rate capability of 230 mAh g^?1 at 1 A g^?1. The high capacity, good cyclability, and rate capability are attributed to synergistic effects of the uniform distribution of Se in PCNFs and the 3D interconnected PCNFs framework, which could alleviate the shuttle reaction of polyselenides intermediates during cycling and maintain the perfect electrical conductivity throughout the electrode. By rational and delicate design, this type of self‐supported electrodes may hold great promise for the development of Li‐Se and Na‐Se batteries with high power and energy densities.     

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.     

Carbon‐Sheathed MoS2 Nanothorns Epitaxially Grown on CNTs: Electrochemical Application for Highly Stable and Ultrafast Lithium Storage

Molybdenum disulfide (MoS₂), which possesses a layered structure and exhibits a high theoretical capacity, is currently under intensive research as an anode candidate for next generation of Li‐ion batteries. However, unmodified MoS₂ suffers from a poor cycling stability and an inferior rate capability upon charge/discharge processes. Herein, a unique nanocomposite comprising MoS₂ nanothorns epitaxially grown on the backbone of carbon nanotubes (CNTs) and coated by a layer of amorphous carbon is synthesized via a simple method. The epitaxial growth of MoS₂ on CNTs results in a strong chemical coupling between active nanothorns and carbon substrate via C? S bond, providing a high stability as well as a high‐efficiency electron‐conduction/ion‐transportation system on cycling. The outer carbon layer can well‐accommodate the structural strain in the electrode upon lithium‐ion insertion/extraction. When employed as an anode for lithium storage, the prepared material exhibits remarkable electrochemical properties with a high specific capacity of 982 mA h g^?1 at 0.1 A g^?1, as well as excellent long‐cycling stability (905 mA h g^?1 at 1 A g^?1 after 500 cycles) and superior rate capability, confirming its potential application in high‐performance Li‐ion batteries.     

Chemically Exfoliating Biomass into a Graphene‐like Porous Active Carbon with Rational Pore Structure,Good Conductivity,and Large Surface Area for High‐Performance Supercapacitors

Active carbons have unique physicochemical properties, but their conductivities and surface to weight ratios are much poorer than graphene. A unique and facile method is innovated to chemically process biomass by “drilling” holes with H₂O₂ and exfoliating into graphene‐like nanosheets with HAc, followed by carbonization at a high temperature for highly graphitized activated carbon with greatly enhanced porosity, unique pore structure, high conductivity, and large surface area. This graphene‐like carbon exhibits extremely high specific capacitance (340 F g^?1 at 0.5 A g^?1) and high specific energy density (23.33 to 16.67 W h kg^?1) with excellent rate capability and long cycling stability (remains 98% after 10 000 cycles), which is much superior to all reported carbons including graphene. Synthesis mechanism for deriving biomass into porous graphene‐like carbons is discussed in detail. The enhancement mechanism for the porous graphene‐like carbon electrode reveals that rationally designed meso‐ and macropores are very critical in porous electrode performance, which can network micropores for diffusion freeways, high conductivity, and high utilization. This work has universal significance in producing highly porous and conductive carbons from biomass including biowastes for various energy storage/conversion applications.     

Structural Engineering of Hierarchical Micro‐nanostructured Ge–C Framework by Controlling the Nucleation for Ultralong‐Life Li Storage

The rational design of a proper electrode structure with high energy and power densities, long cycling lifespan, and low cost still remains a significant challenge for developing advanced energy storage systems. Germanium is a highly promising anode material for high‐performance lithium ion batteries due to its large specific capacity and remarkable rate capability. Nevertheless, poor cycling stability and high price significantly limit its practical application. Herein, a facile and scalable structural engineering strategy is proposed by controlling the nucleation to fabricate a unique hierarchical micro‐nanostructured Ge–C framework, featuring high tap density, reduced Ge content, superb structural stability, and a 3D conductive network. The constructed architecture has demonstrated outstanding reversible capacity of 1541.1 mA h g^?1 after 3000 cycles at 1000 mA g^?1 (with 99.6% capacity retention), markedly exceeding all the reported Ge–C electrodes regarding long cycling stability. Notably, the assembled full cell exhibits superior performance as well. The work paves the way to constructing novel metal–carbon materials with high performance and low cost for energy‐related applications.     

A Novel Sustainable Flour Derived Hierarchical Nitrogen‐Doped Porous Carbon/Polyaniline Electrode for Advanced Asymmetric Supercapacitors

Hierarchically porous nitrogen‐doped carbon (HPC)/polyaniline (PANI) nanowire arrays nanocomposites are synthesized by a facile in situ polymerization. 3D interconnected honeycomb‐like HPC was prepared by a cost‐effective route via one‐step carbonization using urea and alkali‐treated wheat flour as carbon precursor with a high specific surface area (1294 m² g^?1). The specific capacitances of HPC and HPC/PANI (with a surface area of 923 m² g^?1) electrode are 383 and 1080 F g^?1 in 1 m H₂SO₄, respectively. Furthermore, an asymmetric supercapacitor based on HPC/PANI as positive electrode and HPC as negative electrode is successfully assembled with a voltage window of 0–1.8 V in 1 m Na₂SO₄ aqueous electrolyte, exhibiting high specific capacitance (134 F g^?1), high energy density (60.3 Wh kg^?1) and power density (18 kW kg^?1), and excellent cycling stability (91.6% capacitance retention after 5000 cycles).     

Construction of CoP/NiCoP Nanotadpoles Heterojunction Interface for Wide pH Hydrogen Evolution Electrocatalysis and Supercapacitor

Constructing well defined nanostructures is promising but still challenging for high‐efficiency catalysts for hydrogen evolution reaction (HER) and energy storage. Herein, utilizing the differences in surface energies between (111) facets of CoP and NiCoP, a novel CoP/NiCoP heterojunction is designed and synthesized with a nanotadpoles (NTs)‐like morphology via a solid‐state phase transformation strategy. By effective interface construction, the disorder in terms of electronic structure and coordination environment at the interface in CoP/NiCoP NTs is created, which leads to dramatically elevated HER performance within a wide pH range. Theoretical calculations prove that an optimized proton chemisorption and H₂O dissociation are achieved by an optimized phosphide polymorph at the interface, accelerating the HER reaction. The CoP/NiCoP NTs are also proved to be excellent candidates for use in supercapacitors (SCs) with a high specific capacitance (1106.2 F g^?1 at 1 A g^?1) and good cycling stability (nearly 100% initial capacity retention after 1000 cycles). An asymmetric supercapacitor shows a high energy density (145 F g^?1 at 1 A g^?1) and good cycling stability (capacitance retention is 95% after 3200 cycles). This work provides new insights into the catalyst design for electrocatalytic and energy storage applications.     

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.     

Promoting Highly Reversible Sodium Storage of Iron Sulfide Hollow Polyhedrons via Cobalt Incorporation and Graphene Wrapping

Sodium ion batteries (SIBs) have drawn significant attention owing to their low cost and inherent safety. However, the absence of suitable anode materials with high rate capability and long cycling stability is the major challenge for the practical application of SIBs. Herein, an efficient anode material consisting of uniform hollow iron sulfide polyhedrons with cobalt doping and graphene wrapping (named as CoFeS@rGO) is developed for high‐rate and long‐life SIBs. The graphene‐encapsulated hollow composite assures fast and continuous electron transportation, high Na⁺ ion accessibility, and strong structural integrity, showing an extremely small volume expansion of only 14.9% upon sodiation and negligible volume contraction during the desodiation. The CoFeS@rGO electrode exhibits high specific capacity (661.9 mAh g^?1 at 100 mA g^?1), excellent rate capability (449.4 mAh g^?1 at 5000 mA g^?1), and long cycle life (84.8% capacity retention after 1500 cycles at 1000 mA g^?1). In situ X‐ray diffraction and selected‐area electron diffraction patterns show that this novel CoFeS@rGO electrode is based on a reversible conversion reaction. More importantly, when coupled with a Na₃V₂(PO₄)₃/C cathode, the sodium ion full battery delivers a superexcellent rate capability (496.8 mAh g^?1 at 2000 mA g^?1) and ≈96.5% capacity retention over 200 cycles at 500 mA g^?1 in the 1.0–3.5 V window. This work indicates that the rationally designed anode material is highly applicable for the next generation SIBs with high‐rate capability and long‐term cyclability.     

Carbonized Chicken Eggshell Membranes with 3D Architectures as High‐Performance Electrode Materials for Supercapacitors

Supercapacitor electrode materials are synthesized by carbonizing a common livestock biowaste in the form of chicken eggshell membranes. The carbonized eggshell membrane (CESM) is a three‐dimensional macroporous carbon film composed of interwoven connected carbon fibers containing around 10 wt% oxygen and 8 wt% nitrogen. Despite a relatively low surface area of 221 m² g^?1, exceptional specific capacitances of 297 F g^?1 and 284 F g^?1 are achieved in basic and acidic electrolytes, respectively, in a 3‐electrode system. Furthermore, the electrodes demonstrate excellent cycling stability: only 3% capacitance fading is observed after 10 000 cycles at a current density of 4 A g^?1. These very attractive electrochemical properties are discussed in the context of the unique structure and chemistry of the material.     

Confined Fe2VO4⊂Nitrogen‐Doped Carbon Nanowires with Internal Void Space for High‐Rate and Ultrastable Potassium‐Ion Storage

Developing low‐cost, high‐capacity, high‐rate, and robust earth‐abundant electrode materials for energy storage is critical for the practical and scalable application of advanced battery technologies. Herein, the first example of synthesizing 1D peapod‐like bimetallic Fe₂VO₄ nanorods confined in N‐doped carbon porous nanowires with internal void space (Fe₂VO₄?NC nanopeapods) as a high‐capacity and stable anode material for potassium‐ion batteries (KIBs) is reported. The peapod‐like Fe₂VO₄?NC nanopeapod heterostructures with interior void space and external carbon shell efficiently prevent the aggregation of the active materials, facilitate fast transportation of electrons and ions, and accommodate volume variation during the cycling process, which substantially boosts the rate and cycling performance of Fe₂VO₄. The Fe₂VO₄?NC electrode exhibits high reversible specific depotassiation capacity of 380 mAh g^?1 at 100 mA g^?1 after 60 cycles and remarkable rate capability as well as long cycling stability with a high capacity of 196 mAh g^?1 at 4 A g^?1 after 2300 cycles. The first‐principles calculations reveal that Fe₂VO₄?NC nanopeapods have high ionic/electronic conductivity characteristics and low diffusion barriers for K⁺‐intercalation. This study opens up new way for investigating high‐capacity metal oxide as high‐rate and robust electrode materials for KIBs.     

A Layered Inorganic–Organic Open Framework Material as a 4 V Positive Electrode with High‐Rate Performance for K‐Ion Batteries

K‐ion batteries (KIBs) are promising for large‐scale energy storage owing to various advantages like the high abundance of potassium resources in the Earth's crust, high operational potentials, and high power due to fast diffusion of K⁺ ions. However, to realize the practical application of KIBs, electrode materials are needed with high operational voltage, good capacity, long cycle life, and low‐cost. This work reports a layered open framework material, K₂[(VOHPO₄)₂(C₂O₄)], composited with reduced graphene oxide (rGO) as a 4 V positive electrode material for KIBs. The material is prepared by a simple precipitation reaction at room temperature. The material demonstrates reversible K‐extraction/insertion with conventional carbonate ester KPF₆ solutions; however, with low specific capacity and low Coulombic efficiency. A high discharge capacity of >100 mAh g^?1 with good cycling stability and higher Coulombic efficiency is achieved in a highly concentrated electrolyte, 7 mol kg^?1 of potassium bis(fluorosulfonyl)amide (KFSA) in dimethoxyethane (DME) at 0.1 C rate. Due to the facile migration of K⁺ ions in the framework, the material exhibits excellent rate capability with a discharge capacity of 80 mAh g^?1 at 10 C rate, and a good capacity retention of 67% after 500 cycles at 2 C rate.     

Controlled Growth of NiMoO4 Nanosheet and Nanorod Arrays on Various Conductive Substrates as Advanced Electrodes for Asymmetric Supercapacitors

Hierarchical NiMoO₄ architectures assembled from well‐aligned uniform nanosheets or nanorods are successfully grown on various conductive substrates using a facile and effective general approach. Importantly, the nanostructures of NiMoO₄ can be easily controlled to be nanosheets or nanorods by using different solvents. By virtue of their intriguing structure features, NiMoO₄ nanosheets as integrated additive‐free electrodes for supercapacitors manifest higher Faradaic capacitance than NiMoO₄ nanorods. Moreover, an asymmetric supercapacitor (ASC) is constructed using the as‐prepared NiMoO₄ nanosheets as the positive electrode and activated carbon (AC) as the negative electrode. The optimized ASC with an extended operating voltage range of 0–1.7 V displays excellent electrochemical performance with a high energy density of 60.9 Wh kg^?1 at a power density of 850 W kg^?1 in addition to superior rate capability. Furthermore, the NiMoO₄//AC ASC device exhibits remarkable cycling stability with 85.7% specific capacitance retention after 10 000 cycles. The results show that these NiMoO₄‐based nanostructures are promising for high‐energy supercapacitors.     

Graphene‐Indanthrone Donor–π–Acceptor Heterojunctions for High‐Performance Flexible Supercapacitors

To overcome the low energy density bottleneck of graphene‐based supercapacitors and to organically endow them with high‐power density, ultralong‐life cycles, etc., one rational strategy that couple graphene sheets with multielectron, redox‐reversible, and structurally‐stable organic compounds. Herein, a graphene‐indanthrone (IDT) donor–π–acceptor heterojunction is conceptualized for efficient and smooth 6H⁺/6e^? transfers from pseudocapacitive IDT molecules to electrochemical double‐layer capacitive graphene scaffolds. To construct this, water‐processable graphene oxide (GO) is employed as a graphene precursor, and to in situ exfoliate IDT industrial dyestuff, followed by a hydrothermally‐induced reduction toward GO and self‐assembly between reduced GO (rGO) donors (D) and IDT acceptors (A), affording rGO‐π‐IDT D–A heterojunctions. Electrochemical tests indicate that rGO‐π‐IDT heterojunctions deliver a gravimetric capacitance of 535.5 F g^?1 and an amplified volumetric capacitance of 685.4 F cm^?3. The assembled flexible all‐solid‐state supercapacitor yields impressive volumetric energy densities of 31.3 and 25.1 W h L^?1, respectively, at low and high power densities of 767 and 38 554 W L^?1, while exhibiting an exceptional rate capability, cycling stability, and enduring mechanically‐challenging bending and distortions. The concept and methodology may open up opportunities for other two‐dimensional materials and other energy‐related devices.     

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.