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Potassium‐ion hybrid capacitors (PIHCs) overcome the limitations of potassium‐ion batteries (PIBs) and supercapacitors (SCs) and integrate the advantages of both, including high energy density, high power density, low cost, long cycle life, and stable electrochemical performance. However, the development of PIHCs is hindered by thermodynamic instability and kinetic hysteresis. Additionally, the dynamic mismatch between anode and cathode materials poses an urgent challenge. To this end, many research works related to material development have been dedicated to overcoming the drawbacks. In this review, the energy storage mechanism of PIHCs is briefly introduced. Moreover, the research progress and achievements of anode and cathode materials in recent years are reviewed, including carbon‐based materials, MXenes, transition metal materials, Prussian blue and its analogues. Finally, the challenges and prospects of PIHCs are proposed, together with guiding significant research directions in the future. [ABSTRACT FROM AUTHOR]

Metal–oxygen batteries have been growing rapidly as an energy storage technology in light of their high specific energy density. However, waste metal–oxygen batteries will raise many environmental issues; therefore, the recycling and reusing of the spent metal–oxygen batteries has attracted great attention. Herein, we report the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese–oxygen battery (MOB). Trace amounts of PTIO result in the discharge capacity of MOB increase to 2588 mAh g−1 and enhance the formation of manganese dioxide (MnO2) with toroidal appearance and high crystallinity on the cathode. After being used, the dismantled MnO2/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled free-standing MnO2/CNT electrode demonstrates an exceptional specific capacitance (253.86 F g−1) at a current density of 0.5 A g−1 in a 0.5 M Na2SO4 electrolyte. Moreover, we prepare an asymmetric supercapacitor fabricated with the recycled MnO2/CNT electrode and activated carbon (AC), which exhibits excellent energy density (32.00 Wh kg−1 at 413.70 W kg−1) with 78.26% retention over 6000 cycles. This work provides a promising strategy to derive high-quality and high-value MnO2/CNT electrode materials from the spent MOBs. It's the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese-oxygen battery (MOB). The recycled manganese dioxide (MnO2)/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled MnO2/CNT electrode shows the toroidal appearance and high crystallinity. Furthermore, the asymmetric supercapacitor fabricated with the MnO2/CNT free-standing electrode displays high specific capacitance, superior energy density, and good cyclic ability. [ABSTRACT FROM AUTHOR]

Silicon-based materials, as the most promising candidates for high-performance lithium-ion batteries (LIBs), have been widely researched. However, the construction of stable electrode structure is still a challenge due to the enormous volume variation. Herein, we developed a three-dimensional (3D) binder network, polydopamine grafted cross-linked polyacrylamide (PDA-c-PAM), to build a durable anode for LIBs. The flexible PDA side chain in PDA-c-PAM offers the superior adhesion with constitutes of the electrode. And the 3D cross-linked PAM main chain endows PDA-c-PAM high stretchability to accommodate the volume variation of active material and maintain the structural integrity of electrode. As a binder for SiO/graphite (SiO/C), the fabricated SiO/C@PDA-c-PAM anode delivers an initial discharge capacity of 1350 mAh g−1 at 0.1 A g−1. At a high current density of 1 A g−1, it maintains 591 mAh g−1 after 300 cycles with a 94% capacity retention of initial capacity after activation. Coupled with commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode, the full cell exhibits a high-energy density of 406 Wh kg−1 at 1 C as well as excellent stability. Thus, it is believed that designing 3D network binder is an effective approach to achieve superior cycle performance of SiO/C electrodes. We successfully synthesized a polydopamine grafted cross-linked polyacrylamide (PDA-c-PAM) polymer as binder for SiO/C anode to maintain the structural integrity and improve the cycling stability of electrode. The flexible PDA side chain in PDA-c-PAM offers the binder superior adhesion. And the 3D cross-linked PAM main chain endows the binder high stretchability. The fabricated SiO/C@PDA-c-PAM anode delivers a capacity of 591 mAh g−1 after 300 cycles at 1 A g−1. Thus, it is believed that designing 3D network binder is an effective approach to achieve superior cycle performance of SiO/C electrodes. [ABSTRACT FROM AUTHOR]

Carbon materials are widely used as anodes of supercapacitors due to the long cycling stability, but the low capacitance results in low energy density of the supercapacitor device in aqueous solution, greatly limiting the application field of the supercapacitor. Here, the spiral low-crystalline Ni(OH)2 supported on self-standing layered film structure of N-doped graphene/carbon nanotubes film (NCF) is reported. The prepared flexible film electrode of low-crystalline Ni(OH)2/NCF is functioned as cathode directly, presenting high gravimetric capacitance (GC) and areal capacitance of 2130 F g − 1 (2 A g − 1 ) and 2.88 F cm − 2 (1 A g − 1 ). Also, this self-standing electrode film shows ultra-long cycle life, retaining 111.4% of initial capacitance after 30 000 circles at large current densities (20 A g − 1 ) and almost 0% fade before 10 000 circles. Moreover, Ni(OH)2/NCF and activated polyaniline derived carbon (APDC) have been assembled into an asymmetric supercapacitor, exhibiting a high gravimetric energy density of 60 Wh kg − 1 at 800 W kg − 1 , suggesting that the obtained electrode has a good prospect application in long cycling stability with high energy density of supercapacitor devices. Low-crystalline flower-like Ni(OH)2 nanosheets have been prepared on N-doped graphene/carbon nanotubes film (NCF) by hydrothermal process. The CF with oxygen-containing functional groups can absorb positively-charged Ni2+ through mutual electrostatic interactions. In addition, the introduction of nitrogen can enhance the coupling and electrostatic interaction between Ni(OH)2 and NCF. Therefore, Ni2+ could be easily adsorbed onto the surface of the NCF. The as-synthesized Ni(OH)2/NCF samples exhibited ultra-long cycle life and high specific capacitance. [ABSTRACT FROM AUTHOR]

Abstract: Highly conductive metal selenides are gaining prominence as promising electrode materials in electrochemical energy‐storage fields. However, phase‐pure bimetallic selenides are scarcely retrieved, and their underlying charge‐storage mechanisms are still far from clear. Here, first a solvothermal strategy is devised to purposefully fabricate monodisperse hollow NiCoSe2 (H‐NiCoSe2) sub‐microspheres. Inherent formation of metallic H‐NiCoSe2 is tentatively put forward with comparative structure‐evolution investigations. Interestingly, the fresh H‐NiCoSe2 does not demonstrate striking supercapacitive behaviors when evaluated for electrochemical supercapacitors (ESs). But it exhibits competitive pseudocapacitance of ≈750 F g−1 at a rate of 3 A g−1 with a high loading of 7 mg cm−2 after ≈100 cyclic voltammetry (CV) cycles. With systematic physicochemical/electrochemical analyses, intrinsic energy‐storage mechanism of the H‐NiCoSe2 is convincingly revealed that the electrooxidation‐generated biactive CoOOH/NiOOH phases in aqueous KOH over CV scanning, rather than the H‐NiCoSe2 itself, account for the remarkable pesudocapacitance observed after cycling. An assembled H‐NiCoSe2‐based asymmetric device has delivered an energy density of ≈25.5 Wh kg−1 with a power rate of ≈3.75 kW kg−1, and long‐span cycle life. More significantly, the electrode design and new perspectives here hold profound promise in enriching material synthesis methodologies and in‐depth understanding of the complex charge‐storage process of newly emerging pseudocapacitive materials for next‐generation ESs. [ABSTRACT FROM AUTHOR]

Abstract: Although two‐dimensional (2D) carbon materials are widely investigated, a well‐defined 2D carbon nanosheet with an ordered mesostructure has rarely been realized. Monolayer‐ordered mesoporous carbon nanosheets (OMCNS) were prepared through confinement assembly of resol and F127 in the interlayer of montmorillonite (MONT). The nanoscale distance of the interlayer space of MONT only allow the assembly of resol and F127 in the same plane, leading to ordered mesopores perpendicular to carbon nanosheets, and favor the formation of sp2 carbon, resulting in a high degree of graphitization. The mesopores on the carbon nanosheets provide efficient ion diffusion, and the high degree of graphitization provides a fast electron‐transport route, enabling OMCNS as excellent electrode materials for electric double layer capacitors. [ABSTRACT FROM AUTHOR]

An efficient anion-exchange protocol was investigated for the controllable fabrication of hollow NiCo2S4 nanoboxes (NBs) from mesocrystalline nickel cobalt carbonate nanocubes as promising pseudocapacitive materials for electrochemical capacitors. The underlying processes of the formation of the hollow architecture were systematically investigated. Originating from the unique structural and compositional advantages, the resultant hollow NiCo2S4 NB electrode with a loading of 5 mg cm2 delivered a large specific capacitance of 777 F g−1 at a high rate of 4 A g−1 in a three-electrode configuration with 6 m KOH as electrolyte. Furthermore, an asymmetric device constructed with the hollow NBs and activated carbon (AC) as positive and negative electrodes, respectively, showed extraordinary supercapacitance within an electrochemically operating voltage window from 0.0 to 1.5 V. The unique AC//NiCo2S4 NB hybrid capacitor exhibited a large specific energy density (active mass normalized) of approximately 17.1 W h kg−1 at a high power density of 2250 W kg−1, and desirable cycling durability with approximately 75 % specific capacitance retention after 5000 consecutive cycles at a current rate of 2 A g−1. These electrochemical investigations strongly indicated that the as-fabricated hollow NiCo2S4 NBs can be elegantly utilized as powerful candidates for advanced electrode platforms. [ABSTRACT FROM AUTHOR]

In this work, ternary metal nitrides are proposed as novel electrode materials for supercapacitors. We selectively fabricate ternary vanadium titanium nitride/carbon (VTiN/C) nanofibers through a facile electrospinning strategy and investigate their electrochemical performance for the first time. The obtained well-interconnected VTiN/C nanofibers with VTiN nanoparticles embedded into carbon ensure rapid electron/ion transfer and offer a highly ion-accessible surface. Appealingly, the VTiN-4/C nanofibers exhibit a greatly improved performance, with a high specific capacitance (430.7 F g−1, 0.5 A g−1) and a good rate capability. Furthermore, the performance of the VTiN/C nanofibers is found to be controllable by adjusting the V/Ti atomic ratio. The encouraging electrochemical performance suggests that ternary VTiN could be a promising electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfides. Here, the rational design and fabrication of NiCo2S4 nanosheets supported on nitrogen-doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two-step method is developed for growth of NiCo2S4 nanosheets on NCF with robust adhesion, involving the growth of Ni-Co precursor and subsequent conversion into NiCo2S4 nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo2S4/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g−1 at 20 A g−1) and excellent cycling stability. Moreover, a binder-free asymmetric supercapacitor device is also fabricated by using NiCo2S4/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg−1 at 512 W kg−1). [ABSTRACT FROM AUTHOR]

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co3O4 hollow nanoparticles (NPs) and are directly applied as self-supported electrodes for high-performance electrochemical capacitors. Uniform Co3O4 hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co3O4-CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder-free Co3O4 hollow NPs/CNF hybrid film electrodes exhibit high specific capacitance (SC), excellent rate capability and cycling stability. As an example, the flexible hybrid film with loading of 35.9 wt% Co3O4 delivers a SC of 556 F g−1 at a current density of 1 A g−1, and 403 F g−1 even at a very high current density of 12 A g−1. Remarkably, almost no decay in SC is found after continuous charge/discharge cycling for 2000 cycles at 4 A g−1. This exceptional electrochemical performance makes such novel self-supported Co3O4-CNFs hybrid films attractive for high-performance electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Nanostructured CoNi-Al layered triple hydroxides (CoNi-Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of CoNi-Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge-discharge techniques. Electrochemical data demonstrated that the CoNi-Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g at a current density of 0.5 A g and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge-discharge cycles at a current density of 2 A g. [ABSTRACT FROM AUTHOR]

Abstract: A simple hydrothermal treatment was developed to synthesize Co3O4 powders with different morphologies in mass production by using hexamethylenetetramine (HMT, C6H12N4) as a precipitator. By changing the initial HMT concentrations, the prepared Co3O4 powders were readily regulated in its morphologies, which varied from microsphere to urchin-like hollow microsphere, and finally to collapsed porous structure. Moreover, the four Co3O4 powders with different HMT concentrations had been applied in the negative electrode materials for lithium ion batteries, which exhibited different electrochemical properties. The present research demonstrated that morphology was one of the crucial factors that affected the electrochemical properties of electrodes. The capacity retention of sample with an original Co(NO3)2:HMT mole ratio of 1:1 is almost above 94% from the 5th cycle at different current densities of 40 and 60mAg−1, exhibiting the better long-life stability and favorable electrochemical behaviors due to its higher specific surface area (97.1m2 g−1) and the uniform urchin-like hollow structure. [Copyright &y& Elsevier]

Abstract: Polypyrrole (PPy) nanotubes were synthesized by using the complex of methyl orange (MO)/FeCl3 as a template. Then the core–shell polypyrrole/polyaniline (PPy/PANI) composite was prepared by in situ chemical oxidation polymerization of aniline on the surface of PPy nanotubes. The morphology and molecular structure were characterized by transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). TEM images confirmed that the composite was core–shell nanotubes. The electrochemical properties of the PPy/PANI composite electrode were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The electrochemical experiments showed that the specific capacitance of the PPy/PANI composite was 416Fg−1 in 1M H2SO4 electrolyte and 291Fg−1 in 1M KCl electrolyte. Furthermore, the composite electrode exhibited a good rate capability and maintained 91% of initial capacity at a current density of 15mAcm−2 in 1M H2SO4 electrolyte. [Copyright &y& Elsevier]

[Display omitted] • A flexible infrared electrochromic film based on oxygen-deficient W 18 O 49 nanowires was reported. • The mechanism of the impressive infrared electrochromic performance of W 18 O 49 nanowires was revealed in detail. • A multi-band transparent conducting electrode based on MXene nanosheets was constructed. • A flexible infrared electrochromic device with high infrared emissivity modulation and long cycle life was presented. Electrochromism with tunable infrared (IR) responses has emerged as an intriguing technology for adaptive IR camouflage and radiative thermal management. Its current development is however hindered by low IR emissivity modulation and unsatisfactory cycle life. Herein, a flexible IR electrochromic device with large IR emissivity modulation and high stability is fabricated by combining an oxygen-deficient W 18 O 49 nanowire cathode and a MXene-based IR transparent conducting electrode. The nanowire structure and abundant oxygen vacancies of W 18 O 49 works in synergy with the high IR transparence of the MXene conducing electrode, to provide the IR emissivity to vary from 0.8 to 0.4 within 3–5 μm (△ε = 0.4), and from 0.77 to 0.3 within 8–14 μm (△ε = 0.47). A long cycle life of more than 2000 cycles was also verified, which could be attributed to the high stability of W 18 O 49 and no material phase transition during cycling. This work demonstrates a viable pathway to design and build high performance flexible IR electrochromic devices for adaptive thermal management. [ABSTRACT FROM AUTHOR]

Li 4 Ti 5 O 12 with long cycling life has been deemed to be one of the most promising anode materials for lithium ion battery. Nevertheless, poor electronic conductivity impedes its application for energy storage. Meanwhile MXene possesses high electrical conductivity and moderate electrochemical energy storage. Herein, we develop a novel strategy for the in-situ synthesis of layered-stacked Li 4 Ti 5 O 12 -MXene composite. The synergistic effect of Li 4 Ti 5 O 12 and MXene greatly improved the electrochemical properties of Li 4 Ti 5 O 12 -MXene composite. At a high current density of 10 A g − 1 , a high discharge capacity of 116 mAh g − 1 can be achieved. Moreover, a high discharge capacity of 178 mAh g − 1 after 500 cycles can be maintained at a current density of 5 A g − 1 . This work demonstrates a scalable route to assemble MXene-derived Ti-based materials for high-performance electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]

• The synergistic effect exists in V s -NiCo 2 S 4 @NiCoS 2 core-shell electrode materials with interfacial sulfur vacancy modification. • The V s -NiCo 2 S 4 @NiCoS 2 provides a capacitance of 3200 f g −1 with the 1 + 1>2 effect compared to V s -NiCo 2 S 4 and NiCoS 2. • The V s -NiCo 2 S 4 @NiCoS 2 @AC devices deliver up to 46.3 Wh kg−1 energy density at 799.8 W kg−1 power density. Nickel-cobalt based bimetallic sulfide has attracted much attention as positive electrode materials for supercapacitors due to its microstructure designability. However, charge storage occurs mostly on the surface of the material, which limits the full utilization of the active material inside. Here, rich sulfur vacancies modified NiCo 2 S 4 @NiCoS 2 (V s -NiCo 2 S 4 @NiCoS 2) core-shell structures are grown tightly on a nickel foam substrate and prepared as positive material for supercapacitors. The rich sulfur vacancies in the V s -NiCo 2 S 4 "core" increase the electrochemical active sites and electron transport rates, while the amorphous NiCoS 2 "shell" facilitates the rapid diffusion of ions. The results show that V s -NiCo 2 S 4 @NiCoS 2 core-shell structure has a specific capacitance of 3200 F g −1, achieving the effect of "1 + 1>2". The excellent electrochemical performance is attributed to the surface/interface modification of rich sulfur vacancies and the synergistic effect induced by heterogeneous core-shell boundaries. Moreover, the asymmetric supercapacitor V s -NiCo 2 S 4 @NiCoS 2 //AC exhibits an energy density of 46.3 Wh kg−1 and a power density of 799.8 W kg−1, as well as excellent cyclic stability (nearly 80% capacity retention after 10,000 cycles). This work provides a new idea and strategy for core-shell structure design of nickel-cobalt sulfide electrode materials combined with surface/interface modification. Sulfur vacancy modified V s -NiCo 2 S 4 @NiCoS 2 core-shell structure electrode material has been synthesized by hydrothermal, chemical reduction and electrochemical deposition. [Display omitted] [ABSTRACT FROM AUTHOR]

Bacterial cellulose (BC), a typical biomass prepared from the microbial fermentation process, has been proved that it can be an ideal platform for design of three-dimensional (3D) multifunctional nanomaterials in energy storage and conversion field. Here we developed a simple and general silica-assisted strategy for fabrication of interconnected 3D meso-microporous carbon nanofiber networks by confine nanospace pyrolysis of sustainable BC, which can be used as binder-free electrodes for high-performance supercapacitors. The synthesized carbon nanofibers exhibited the features of interconnected 3D networks architecture, large surface area (624 m 2 g −1 ), mesopores-dominated hierarchical porosity, and high graphitization degree. The as-prepared electrode (CN-BC) displayed a maximum specific capacitance of 302 F g −1 at a current density of 0.5 A g −1 , high-rate capability and good cyclicity in 6 M KOH electrolyte. This work, together with cost-effective preparation strategy to make high-value utilization of cheap biomass, should have significant implications in the green and mass-producible energy storage. [ABSTRACT FROM AUTHOR]

High energy density batteries and high power density supercapacitors have attracted much attention because they are crucial to the power supply of future portable electronic devices, electric automobiles, unmanned aerial vehicles, etc. The electrode materials are key components for batteries and supercapacitors, which influence the practical energy and power density. Metal-organic frameworks possessing unique morphology, high specific surface area, functional linkers, and metal sites are excellent electrode materials for electrochemical energy storage devices. Herein, we review and comment on recent progress in metal-organic framework-based lithium-ion batteries, sodium-ion batteries, lithium-air batteries, lithium-sulfur/selenium batteries, and supercapacitors. Future perspectives and directions of metal-organic framework-based electrochemical energy storage devices are put forward on the basis of theoretical knowledge from the reported literature and our experimental experience. [ABSTRACT FROM AUTHOR]

The manufacturing processes of electrodes have a prominent influence on the cost and performance of lithium-ion capacitors (LICs), which are limited by the conventional wet-coated method due to the usage of solvent. Herein, the solvent-free Li 4 Ti 5 O 12 (LTO) electrodes are prepared with electrostatic spraying deposition using for LICs. Owing to the solvent being avoided during the manufacturing, the dry-sprayed electrode exhibits a higher porosity (∼40%) than that of the wet-coated electrode (∼30%), together with a larger electrochemically active surface area. The optimized microstructure improves electrolyte infiltration and offers effective Li-ion transport paths, which reduces the electrochemical polarization and boosts the specific capacity of the dry-sprayed electrode. When the current density increases from 0.5 C to 10 C, the reversible capacity retention of the dry-sprayed electrode is 74%, which is higher than that of the wet-coated electrode (56%). In addition, the powder resistivity of the dry-sprayed electrode decreases sharply by introducing two-dimension (2D) graphene nanoplate (GN) as the conductive agent, thus side effects have been effectively suppressed during the spraying process. As a result, the assembled LICs using the dry-sprayed LTO electrodes show superior energy density and excellent cycling performance, demonstrating this novel fabrication method has practical application prospects. [Display omitted] • Solvent-free Li 4 Ti 5 O 12 electrodes are prepared by electrostatic spraying. • The differences between dry-sprayed and wet-coated electrodes are explored. • The optimization of electrode microstructure helps properties improve. • Adopting graphene nanoplates as conductive agents perfects spraying results. • Li-ion capacitors with solvent-free electrodes exhibit better performance. [ABSTRACT FROM AUTHOR]

Abstract: Graphene/MnO2 hybrid nanosheets were prepared by incorporating graphene and MnO2 nanosheets in ethylene glycol. Scanning electron microscopy and transmission electron microscopy analyses confirmed nanosheet morphology of the hybrid materials. Graphene/MnO2 hybrid nanosheets with different ratios were investigated as electrode materials for supercapacitors by cyclic voltammetry (CV) and galvanostatic charge–discharge in 1 M Na2SO4 electrolyte. We found that the graphene/MnO2 hybrid nanosheets with a weight ratio of 1:4 (graphene:MnO2) delivered the highest specific capacitance of 320 F g−1. Graphene/MnO2 hybrid nanosheets also exhibited good capacitance retention on 2000 cycles. [Copyright &y& Elsevier]

Abstract: We developed a direct carbonization strategy to efficiently fabricate mesoporous N-containing carbon nanosheets (N-CNSs) by using polyaniline nanosheets as a carbon precursor. Physicochemical characterizations revealed that the as-synthesized N-CNSs with 5.9wt.% N species possessed a well-developed mesoporous architecture with large specific surface area of 352m2 g−1, high mesoporous volume of 0.32cm3 g−1, and average pore size of ∼5.2nm. When further utilized as an electrode for electrochemical capacitors, the mesoporous N-CNSs delivered a large specific capacitance of 239Fg−1 at 0.5Ag−1, and even 197Fg−1 at a high current load of 8Ag−1, indicating its good rate behavior. Furthermore, the capacitance degradation of ∼4% over continuous 5000 charge–discharge cycles at 6Ag−1 further verified its good electrochemical stability at high rates for long-term electrochemical capacitors application. [Copyright &y& Elsevier]

Nickel cobalt sulfur is attracting more attention due to its great electrical conductivity and high specific capacitance for faraday pseudo-capacitors. Here, by evaporation-induced drying, heterostructure NiS 2 /NiCo 2 S 4 nanosheets on self-supporting substrate of nitrogen-doped single-walled carbon nanotubes sponge (NSCS) are obtained with the sponge volume significantly being reduced. With the electrode film thickness being 80 μm, the as-prepared heterostructure NiS 2 /NiCo 2 S 4 /NSCS electrode shows outstanding areal/gravimetric/volumetric capacitance of 10.5 F cm−2/2905 F g−1/1307.2 F cm−3 at 1 A g−1. With the increase of current density from 1 to 60 A g−1, the current retention rate maintains at 61%. When the active material loading is increased to 14 mg cm−2, the gravimetric capacitance can still maintain at 1725 F g−1, indicating the high ratio performance. After 10,000 cycles, the capacity retention still remains 83% at current density of 10 A g−1. In addition, an asymmetric supercapacitor (ASC) delivers have high gravimetric/volumetric energy density of 58.1 W h kg−1/52.3 W h L−1 with excellent cycle stability after 20,000 cycles. Therefore, the electrode material with high loading and high rate performance can be realized by this method. • By evaporation-induced drying, the volume of NiS 2 /NiCo 2 S 4 /NSCS shrinks obviously. • The electrode has high areal and volumetric capacitance with high loading. • Heterostructure material of NiS 2 /NiCo 2 S 4 greatly improves the electrochemical performance. • The asymmetric supercapacitor delivers high gravimetric/volumetric energy density. [ABSTRACT FROM AUTHOR]

Abstract: In the work, we develop a novel two-step strategy to synthesize self-supported hexagonal nickel oxide nanoplatelet arrays on Ni foam: precipitating hydroxides followed by calcinating process. These nanoplatelets are composed of a multilayer of ultrathin mesoporous NiO nanosheets. The unique Ni foam-supported mesoporous NiO nanoplatelet arrays electrode promises fast ion and electron transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with large specific capacitance in the range of 1124–864Fg−1 and excellent cycling stability up to 5000 cycles, suggesting their promising application for electrochemical capacitors. [Copyright &y& Elsevier]

Abstract: A flexible graphene/multiwalled carbon nanotube (GN/MWCNT) film has been fabricated by flow-directed assembly from a complex dispersion of graphite oxide (GO) and pristine MWCNTs followed by the use of gas-based hydrazine to reduce the GO into GN sheets. The GN/MWCNT (16wt.% MWCNTs) film characterized by Fourier transformation infrared spectra, X-ray diffraction and scanning electron microscope has a layered structure with MWCNTs uniformly sandwiched between the GN sheets. The MWCNTs in the obtained composite film not only efficiently increase the basal spacing but also bridge the defects for electron transfer between GN sheets, increasing electrolyte/electrode contact area and facilitating transportation of electrolyte ion and electron into the inner region of electrode. Electrochemical data demonstrate that the GN/MWCNT film possesses a specific capacitance of 265Fg−1 at 0.1Ag−1 and a good rate capability (49% capacity retention at 50Ag−1), and displays an excellent specific capacitance retention of 97% after 2000 continuous charge/discharge cycles. The results of electrochemical measurements indicate that the freestanding GN/MWCNT film has a potential application in flexible energy storage devices. [Copyright &y& Elsevier]

Abstract: A loose whisker-like Co(OH)2 was synthesized by means of polyethylene glycol 4000 as soft template under ultrasonic condition, and investigated as an active electrode material for electrochemical capacitors. The composition and microstructure of the as-prepared Co(OH)2 were investigated by X-ray diffraction spectroscopy and transmission electron microscopy. The formation mechanism of the whisker-like Co(OH)2 was attentively proposed based on Fourier transform infrared spectroscopy analysis. Electrochemical studies revealed that the whisker-like Co(OH)2 delivered a specific capacitance of 325F/g at a current density of 20mA/cm2 (ca. 1.3A/g) and even 279F/g at 80mA/cm2 (ca. 5.3A/g) due to its special nanostructure, indicating its fast electrochemical response property. A capacitance attenuation of ca. 7% over 1000 cycles meant the good cyclic stability of the whisker-like Co(OH)2 for electrochemical capacitors application. [Copyright &y& Elsevier]

The commercial coating way of lithium-ion batteries has generally used wet coating technology so far. However, N-Methyl-2-pyrrolidone (NMP) is a toxic and expensive organic solvent using in this wet electrode manufacturing process, which is not environmentally friendly and greatly increases the cost of batteries. Herein, the solvent-free electrodes are prepared by electrostatic spraying without any solvent for lithium-ion batteries. The effects of different binder content on the mechanical, morphology and electrochemical performance are explored for solvent-free electrodes. When the contents of binder added are too much or little, the aggregates of binder and conductive agent more easily present uneven distribution in the whole electrodes. Moreover, the differences between the solvent-free electrodes and conventional wet electrodes are systematically compared. Notably, the binder and conductive agent are uniformly distributed with a point contact mode in the solvent-free electrode, which is conducive to rapid ions transfer and robust structural integrity, leading to a better rate capabilities and cycle performance. This work provides some reference value and guiding significance for the subsequent preparation and research of solvent-free electrodes. [Display omitted] ● Solvent-free Li-ion battery electrode is prepared by electrostatic spraying. ● The effects of binder content for solvent-free electrodes are explored. ● The solvent-free electrode and the conventional wet electrode are compared. ● The solvent-free electrodes have better cycling and rate capabilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • An eco-friendly yet facile approach is proposed to fabricate nano porous fibers. • The porous carbon fibers exhibit satisfactory electrochemical performance. • A high-performance supercapacitor is constructed. Recently, tremendous attention has been paid to carbon-based fibers, particularly porous carbon fibers (PCFs), because of their great potential as electrodes for advanced supercapacitors (SCs). However, the relatively complex preparation and monotonous pore structure are still the most important challenge that PCFs needs to counter. In this work, an eco-friendly yet facile approach has been applied to synthesis PCFs with tunable multi-level pores and satisfactory electrochemical performance. By using the combinations of electrospinning technology, hard-template method and carbonization process, nanofibers with interconnected multi-level pores can be achieved. It is demonstrated that the pore engineered PCF possesses enhanced electrochemical performance. For instance, the PCF electrode possesses a high capacitance of 211 F g−1 in 6 mol L−1 KOH at a density of 0.5 A g−1 together with excellent rate capability. Meanwhile, a high areal capacitance of 1.2 F cm−2 also can be achieved at a mass loading of 10 mg cm−2. Additionally, symmetrical supercapacitor assembled by PCF electrodes exhibits good capacitance of 101.9 F g−1 at the current density of 0.5 A g−1, such device also can deliver an energy density up to 60.1 Wh kg−1 with ionic liquid electrolyte. [ABSTRACT FROM AUTHOR]