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.     

A High Performance Stretchable Asymmetric Fiber‐Shaped Supercapacitor with a Core‐Sheath Helical Structure

The emerging fiber‐shaped supercapacitors (FSSs) have motivated tremendous research interest in energy storage devices. However, challenges still exist in the pursuit of combination of excellent electrochemical performance and mechanical stretchability. Here, a core‐sheath asymmetric FSS is first made by wrapping gel electrolyte coated carbon nanotube (CNT)@MnO₂ core fiber with CNT@PPy composite film. Then a stretchable helical structure is formed by over‐twisting the FSS. The resulted stretchable asymmetric FSS exhibits a specific capacitance of 60.435 mF cm^?2 at the scan rate of 10 mV s^?1 and the capacitance performance is well maintained during repeated stretching to 20% strain. Furthermore, a high energy density of 18.88 μW h cm^?2 is achieved for the stretchable FSS due to its high specific capacitance and extended potential window of 1.5 V.     

Revealing Pseudocapacitive Mechanisms of Metal Dichalcogenide SnS2/Graphene‐CNT Aerogels for High‐Energy Na Hybrid Capacitors

SnS₂ nanoplatelet electrodes can offer an exceptionally high pseudocapacitance in an organic Na⁺ ion electrolyte system, but their underlying mechanisms are still largely unexplored, hindering the practical applications of pseudocapacitive SnS₂ anodes in Na‐ion batteries (SIBs) and Na hybrid capacitors (SHCs). Herein, SnS₂ nanoplatelets are grown directly on SnO₂/C composites to synthesize SnS₂/graphene‐carbon nanotube aerogel (SnS₂/GCA) by pressurized sulfidation where the original morphology of carbon framework is preserved. The composite electrode possessing a large surface area delivers a remarkable specific capacity of 600.3 mA h g^?1 at 0.2 A g^?1 and 304.8 mA h g^?1 at an ultrahigh current density of 10 A g^?1 in SIBs. SHCs comprising a SnS₂/GCA composite anode and an activated carbon cathode present exceptional energy densities of 108.3 and 26.9 W h kg^?1 at power densities of 130 and 6053 W kg^?1, respectively. The in situ transmission electron microscopy and the density functional theory calculations reveal that the excellent pseudocapacitance originates from the combination of Na adsorption on the surface/Sn edge of SnS₂ nanoplatelets and ultrafast Na⁺ ion intercalation into the SnS₂ layers.     

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.     

A High‐Power Na3V2(PO4)3‐Bi Sodium‐Ion Full Battery in a Wide Temperature Range

Sodium‐ion batteries (SIBs) that operate in a wide temperature range are in high demand for practical large‐scale electric energy storage. Herein, a novel full SIB is composed of a bulk Bi anode, a Na₃V₂(PO₄)₃/carbon nanotubes composite (NVP‐CNTs) cathode and a NaPF₆‐diglyme electrolyte. The Bi anode gradually evolves into a porous network in the ether‐based electrolyte during initial cycles, and in the NVP‐CNTs cathode the NVP is cross linked by CNTs to show large exchange current density. These unique features merit the full SIB of Bi//NVP‐CNTs with high Na⁺ diffusion coefficient and low reaction activation energy, and hence fast Na⁺ transport and facile redox reaction kinetics. The resultant full SIB presents high power density of 2354.6 W kg^?1 and energy density of 150 Wh kg^?1 and superior cycling stability in a wide temperature range from ?15 to 45 °C. This will shed light on battery design, and promote their development for practical applications in various weather conditions.     

Highly Stable Supercapacitors with Conducting Polymer Core‐Shell Electrodes for Energy Storage Applications

Conducting polymers such as polyaniline (PAni) show a great potential as pseudocapacitor materials for electrochemical energy storage applications. Yet, the cycling instability of PAni resulting from structural alteration is a major hurdle to its commercial application. Here, the development of nanostructured PAni–RuO₂ core–shell arrays as electrodes for highly stable pseudocapacitors with excellent energy storage performance is reported. A thin layer of RuO₂ grown by atomic layer deposition (ALD) on PAni nanofibers plays a crucial role in stabilizing the PAni pseudocapacitors and improving their energy density. The pseudocapacitors, which are based on optimized PAni–RuO₂ core–shell nanostructured electrodes, exhibit very high specific capacitance (710 F g^?1 at 5 mV s^?1) and power density (42.2 kW kg^?1) at an energy density of 10 Wh kg^?1. Furthermore, they exhibit remarkable capacitance retention of ≈88% after 10 000 cycles at very high current density of 20 A g^?1, superior to that of pristine PAni‐based pseudocapacitors. This prominently enhanced electrochemical stability successfully demonstrates the buffering effect of ALD coating on PAni, which provides a new approach for the preparation of metal‐oxide/conducting polymer hybrid electrodes with excellent electrochemical performance.     

A Novel High‐Energy Hybrid Supercapacitor with an Anatase TiO2–Reduced Graphene Oxide Anode and an Activated Carbon Cathode

A hybrid supercapacitor with high energy and power densities is reported. It comprises a composite anode of anatase TiO₂ and reduced graphene oxide and an activated carbon cathode in a non‐aqueous electrolyte. While intercalation compounds can provide high energy typically at the expense of power, the anatase TiO₂ nanoparticles are able to sustain both high energy and power in the hybrid supercapacitor. At a voltage range from 1.0 to 3.0 V, 42 W h kg^?1 of energy is achieved at 800 W kg^?1. Even at a 4‐s charge/discharge rate, an energy density as high as 8.9 W h kg^?1 can be retained. The high energy and power of this hybrid supercapacitor bridges the gap between conventional batteries with high energy and low power and supercapacitors with high power and low energy.     

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

The fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO₂) nanoparticles on Ti₃C₂T_x MXene nanosheets. The resulting RuO₂@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO₂ nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO₂@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm^?3 at 1 mV s^?1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm^?3 at 2000 mV s^?1), outstanding flexibility, remarkable energy (13.5 mWh cm^?3) and power density (48.5 W cm^?3).     

A Pair of NiCo2O4 and V2O5 Nanowires Directly Grown on Carbon Fabric for Highly Bendable Lithium‐Ion Batteries

Mechanically bendable and flexible functionalities are urgently required for next‐generation battery systems that will be included in soft and wearable electronics, active sportswear, and origami‐based deployable space structures. However, it is very difficult to synthesize anode and cathode electrodes that have high energy density and structural reliability under large bending deformation. Here, vanadium oxide (V₂O₅) and nickel cobalt oxide (NiCo₂O₄) nanowire‐carbon fabric electrodes for highly flexible and bendable lithium ion batteries are reported. The vanadium oxide and nickel cobalt oxide nanowires were directly grown on plasma‐treated carbon fabric and were used as cathode and anode electrodes in a full cell lithium ion battery. Most importantly, a pre‐lithiation process was added to the nickel cobalt oxide nanowire anode to facilitate the construction of a full cell using symmetrically‐architectured nanowire‐carbon fabric electrodes. The highly bendable full cell based on poly(ethylene oxide) polymer electrolyte and room temperature ionic liquid shows high energy density of 364.2 Wh kg^?1 at power density of 240 W kg^?1, without significant performance degradation even under large bending deformations. These results show that vanadium oxide and lithiated nickel cobalt oxide nanowire‐carbon fabrics are a good combination for binder‐free electrodes in highly flexible lithium‐ion batteries.     

Hollow NiCo2S4 Nanospheres Hybridized with 3D Hierarchical Porous rGO/Fe2O3 Composites toward High‐Performance Energy Storage Device

Hierarchical hollow NiCo₂S₄ microspheres with a tunable interior architecture are synthesized by a facile and cost‐effective hydrothermal method, and used as a cathode material. A three‐dimensional (3D) porous reduced graphene oxide/Fe₂O₃ composite (rGO/Fe₂O₃) with precisely controlled particle size and morphology is successfully prepared through a scalable facile approach, with well‐dispersed Fe₂O₃ nanoparticles decorating the surface of rGO sheets. The fixed Fe₂O₃ nanoparticles in graphene efficiently prevent the intermediates during the redox reaction from dissolving into the electrolyte, resulting in long cycle life. KOH activation of the rGO/Fe₂O₃ composite is conducted for the preparation of an activated carbon material–based hybrid to transform into a 3D porous carbon material–based hybrid. An energy storage device consisting of hollow NiCo₂S₄ microspheres as the positive electrode, the 3D porous rGO/Fe₂O₃ composite as the negative electrode, and KOH solution as the electrolyte with a maximum energy density of 61.7 W h kg^?1 is achieved owing to its wide operating voltage range of 0–1.75 V and the designed 3D structure. Moreover, the device exhibits a high power density of 22 kW kg^?1 and a long cycle life with 90% retention after 1000 cycles at the current density of 1 A g^?1.     

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).     

High Energy Density Supercapacitor Based on a Hybrid Carbon Nanotube–Reduced Graphite Oxide Architecture

A high energy density supercapacitor device is reported that utilizes hybrid carbon electrodes and the ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF₄) as an electrolyte. The hybrid electrodes are prepared from reduced graphite oxide (rGO) and purified single‐walled carbon nanotubes (SWCNTs). A simple casting technique gives the hybrid structure with optimum porosity and functionality that provides high energy and power densities. The combination of SWCNTs and rGO in a weight ratio of 1:1 is found to afford a specific capacitance of 222 F g^?1 and an energy density of 94 Wh kg^?1 at room temperature.     

3D‐Printed Stretchable Micro‐Supercapacitor with Remarkable Areal Performance

While stretchable micro‐supercapacitors (MSCs) have been realized, they have suffered from limited areal electrochemical performance, thus greatly restricting their practical electronic application. Herein, a facile strategy of 3D printing and unidirectional freezing of a pseudoplastic nanocomposite gel composed of Ti₃C₂T_x MXene nanosheets, manganese dioxide nanowire, silver nanowires, and fullerene to construct intrinsically stretchable MSCs with thick and honeycomb‐like porous interdigitated electrodes is introduced. The unique architecture utilizes thick electrodes and a 3D porous conductive scaffold in conjunction with interacting material properties to achieve higher loading of active materials, larger interfacial area, and faster ion transport for significantly improved areal energy and power density. Moreover, the oriented cellular scaffold with fullerene‐induced slippage cell wall structure prompts the printed electrode to withstand large deformations without breaking or exhibiting obvious performance degradation. When imbued with a polymer gel electrolyte, the 3D‐printed MSC achieves an unprecedented areal capacitance of 216.2 mF cm^?2 at a scan rate of 10 mV s^?1, and remains stable when stretched up to 50% and after 1000 stretch/release cycles. This intrinsically stretchable MSC also exhibits high rate capability and outstanding areal energy density of 19.2 µWh cm^?2 and power density of 58.3 mW cm^?2, outperforming all reported stretchable MSCs.     

Toward High Energy Density All Solid‐State Sodium Batteries with Excellent Flexibility

All solid‐state sodium batteries (ASSBs) have attracted considerable attention due to their enhanced safety, long lifespan, and high energy density. However, several challenges have plagued the development of ASSBs, especially the relatively low ionic conductivity of solid‐state electrolytes (SSEs), large interfacial resistance, and low stability/compatibility between SSEs and electrodes. Here, a high‐performance all solid‐state sodium battery (NVP@C|PEGDMA‐NaFSI‐SPE|Na) is designed by employing carbon coated Na₃V₂(PO₄)₃ composite nanosheets (NVP@C) as the cathode, solvent‐free solid polymer electrolyte (PEGDMA‐NaFSI‐SPE) as the electrolyte and metallic sodium as the anode. The integrated electrolyte and cathode system prepared by the in situ polymerization process exhibits high ionic conductivity (≈10^?4 S cm^?1 at room temperature) and an outstanding electrolyte/electrode interface. Benefiting from these merits, the soft‐pack ASSB (NVP@C|PEGDMA‐NaFSI‐SPE|Na) delivers excellent cycling life over 740 cycles (capacity decay of only 0.007% per cycle) and maintains 95% of the initial reversible capacity with almost no self‐discharge even after resting for 3 months. Moreover, the bendable ASSB exhibits a high capacity of 106 mAh g^?1 (corresponds to energy density of ≈355 Wh kg^?1) at 0.5 C despite undergoing repeated bending for 535 cycles. This work offers a new strategy to fabricate high‐performance flexible ASSBs with a long lifespan and excellent flexibility.     

A Novel Graphene Oxide Wrapped Na2Fe2(SO4)3/C Cathode Composite for Long Life and High Energy Density Sodium‐Ion Batteries

The cathode materials in the Na‐ion battery system are always the key issue obstructing wider application because of their relatively low specific capacity and low energy density. A graphene oxide (GO) wrapped composite, Na₂Fe₂(SO₄)₃@C@GO, is fabricated via a simple freeze‐drying method. The as‐prepared material can deliver a 3.8 V platform with discharge capacity of 107.9 mAh g^?1 at 0.1 C (1 C = 120 mA g^?1) as well as offering capacity retention above 90% at a discharge rate of 0.2 C after 300 cycles. The well‐constructed carbon network provides fast electron transfer rates, and thus, higher power density also can be achieved (75.1 mAh g^?1 at 10 C). The interface contribution of GO and Na₂Fe₂(SO₄)₃ is recognized and studied via density function theory calculation. The Na storage mechanism is also investigated through in situ synchrotron X‐ray diffraction, and pseudocapacitance contributions are also demonstrated. The diffusion coefficient of Na⁺ ions is around 10^?12–10^?10.8 cm² s^?1 during cycling. The higher working voltage of this composite is mainly ascribed to the larger electronegativity of the element S. The research indicates that this well‐constructed composite would be a competitive candidate as a cathode material for Na‐ion batteries.     

Paper‐Based Energy‐Storage Devices Comprising Carbon Fiber‐Reinforced Polypyrrole‐Cladophora Nanocellulose Composite Electrodes

Composites of polypyrrole (PPy) and Cladophora nanocellulose, reinforced with 8 μm‐thick chopped carbon filaments, can be used as electrode materials to obtain paper‐based energy‐storage devices with unprecedented performance at high charge and discharge rates. Charge capacities of more than 200 C g^?1 (PPy) are obtained for paper‐based electrodes at potential scan rates as high as 500 mV s^?1, whereas cell capacitances of ～60–70 F g^?1 (PPy) are reached for symmetric supercapacitor cells with capacitances up to 3.0 F (i.e.,0.48 F cm^?2) when charged to 0.6 V using current densities as high as 31 A g^?1 based on the PPy weight (i.e., 99 mA cm^?2). Energy and power densities of 1.75 Wh kg^?1 and 2.7 kW kg^?1, respectively, are obtained when normalized with respect to twice the PPy weight of the smaller electrode. No loss in cell capacitance is seen during charging/discharging at 7.7 A g^?1 (PPy) over 1500 cycles. It is proposed that the nonelectroactive carbon filaments decrease the contact resistances and the resistance of the reduced PPy composite. The present straightforward approach represents significant progress in the development of low‐cost and environmentally friendly paper‐based energy‐storage devices for high‐power applications.     

Boron Element Nanowires Electrode for Supercapacitors

The pursuit of new categories of active materials as electrodes of supercapacitors remains a great challenge. Herein, for the first time, elemental boron as a superior electrode material of supercapacitors is reported, which exhibits significantly high capacitances and excellent rate performance in all alkaline, neutral, and acidic electrolytes. Notably, boron nanowire‐carbon fiber cloth (BNWs‐CFC) electrodes achieve a capacitance up to 42.8 mF cm^?2 at a scan rate of 5 mV s^?1 and 60.2 mF cm^?2 at a current density of 0.2 mA cm^?2 in the acidic electrolyte. Moreover, in all these three kinds of electrolytes, BNWs‐CFC electrodes demonstrate a decent cycling stability with >80% capacitance retention after 8000 charging/discharging cycles. The Dominating energy storage mechanism of BNWs in the different electrolytes is analyzed by looking into the kinetics of the electrochemical process. Subsequently, the BNWs‐CFC electrode is used to fabricate a flexible solid‐state supercapacitor, which reveals a specific capacitance up to 22.73 mF cm^?2 and good mechanical performance after 1000 bending cycles. This study opens a new avenue to explore elemental boron‐based new nanomaterials for the application of energy storage with superior electrochemical performance.     

Interconnected Frameworks with a Sandwiched Porous Carbon Layer/Graphene Hybrids for Supercapacitors with High Gravimetric and Volumetric Performances

A facile approach to synthesize porous disordered carbon layers as energy storage units coating on graphene sheets to form interconnected frameworks by one‐step pyrolysis of the mixture of graphene oxide/polyaniline and KOH is presented. As effective energy storage units, these porous carbon layers play an important role in enhancing the electrochemical performances. The obtained porous carbon material exhibits a high specific surface area (2927 m² g^?1), hierarchical interconnected pores, moderate pore volume (1.78 cm³ g^?1), short ion diffusion paths, and a high nitrogen level (6 at%). It displays both unparalleled gravimetric (481 F g^?1) and outstanding volumetric capacitance (212 F cm^?3) in an aqueous electrolyte. More importantly, the assembled symmetrical supercapacitor delivers not only high gravimetric (25.7 Wh kg^?1 based on total mass of electroactive materials) but also high volumetric energy densities (11.3 Wh L^?1) in an aqueous electrolyte. Furthermore, the assembled asymmetric supercapacitor yields a maximum energy density up to 88 Wh kg^?1, which is, to the best of our knowledge, the highest value so far reported for carbon//MnO₂ asymmetric supercapacitors in aqueous electrolytes. Therefore, this novel carbon material holds great promise for potential applications in energy‐related technological fields.     

Nature of FeSe2/N‐C Anode for High Performance Potassium Ion Hybrid Capacitor

Potassium ion hybrid capacitors have great potential for large‐scale energy devices, because of the high power density and low cost. However, their practical applications are hindered by their low energy density, as well as electrolyte decomposition and collector corrosion at high potential in potassium bis(fluoro‐sulfonyl)imide‐based electrolyte. Therefore, anode materials with high capacity, a suitable voltage platform, and stability become a key factor. Here, N‐doping carbon‐coated FeSe₂ clusters are demonstrated as the anode material for a hybrid capacitor, delivering a reversible capacity of 295 mAh g^?1 at 100 mA g^?1 over 100 cycles and a high rate capability of 158 mAh g^?1 at 2000 mA g^?1 over 2000 cycles. Meanwhile, through density functional theory calculations, in situ X‐ray diffraction, and ex situ transmission electron microscopy, the evolution of FeSe₂ to Fe₃Se₄ for the electrochemical reaction mechanism is successfully revealed. The battery‐supercapacitor hybrid using commercial activated carbon as the cathode and FeSe₂/N‐C as the anode is obtained. It delivers a high energy density of 230 Wh kg^?1 and a power density of 920 W kg^?1 (the energy density and power density are calculated based on the total mass of active materials in the anode and cathode).     

A Layered–Tunnel Intergrowth Structure for High‐Performance Sodium‐Ion Oxide Cathode

Delivery of high‐energy density with long cycle life is facing a severe challenge in developing cathode materials for rechargeable sodium‐ion batteries (SIBs). Here a composite Na_0.6MnO₂ with layered–tunnel structure combining intergrowth morphology of nanoplates and nanorods for SIBs, which is clearly confirmed by micro scanning electron microscopy, high‐resolution transmission electron microscopy as well as scanning transmission electron microscopy with atomic resolution is presented. Owing to the integrated advantages of P2 layered structure with high capacity and that of the tunnel structure with excellent cycling stability and superior rate performance, the composite electrode delivers a reversible discharge capacity of 198.2 mAh g^?1 at 0.2C rate, leading to a high‐energy density of 520.4 Wh kg^?1. This intergrowth integration engineering strategy may modulate the physical and chemical properties in oxide cathodes and provide new perspectives on the optimal design of high‐energy density and high‐stable materials for SIBs.