All-solid-state Supercapacitors Research Articles

Rational design of MXene/MWCNT/TOCNF film for flexible supercapacitor

Two-dimensional (2D) MXenes are widely acknowledged as highly adaptable materials for flexible supercapacitors due to their high electronic conductivity, tunable surface chemistry, structural adaptability, and excellent mechanical strength. However, pure MXene nanosheets have a tendency to stack together, which decreases the mechanical and electrochemical properties for flexible devices. Herein, inspired by the structure of modern architecture, MXene/MWCNT/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical-mediated oxidized cellulose nanofibers (TOCNFs) (MMT) composite film (MMT-X, the content of MWCNT and TOCNFs is X% of the total weight of the film) is manufactured using a simple vacuum filtration method. In MMT, two-dimensional (2D) MXene is severed as nanometer “bricks”, one-dimensional (1D) TOCNFs is used as a nanometer “mortar” between MWCNTs and MXene based on synergistic electrostatic forces and hydrogen bonding to build a three-dimensional (3D) composite structures with excellent mechanical strength. The flexible MMT-8 film is used as a supercapacitor electrode with specific capacity 856 F cm−3. Furthermore, at a volume power density of 335.5 W L−1, the assembled flexible all-solid-state supercapacitor (ASSC) could provide a volumetric energy density of 11.64 Wh L−1 with good cycle stability.

In Situ Fabrication of Graphdiyne Nanoisland Anchored Ti3C2Tx Film to Accelerate Intercalation Pseudocapacitance Kinetics

AbstractA key challenge in flexible supercapacitor is balancing the trade‐off between high capacity and fast charging ability caused by dense structure‐induced sluggish ionic diffusion and storage dynamics. Herein, a hydrogen‐rich graphdiyne (GDY)–Ti3C2Tx electrode is reported with tunable interlayer spacing, abundant active sites, and extensive charge storage nanochannels. In particular, the GDY–Ti3C2Tx (12.6 wt.%) electrode has a remarkable volumetric capacitance (2296 F cm−3 at 1 A cm−3) and fast charging behavior (1262 F cm−3 at 50 A cm−3) resulting from the shortened transport pathways, enhanced ionic diffusion rate, and facilitated electrolyte mass transport. Moreover, an all‐solid‐state supercapacitor (ASSC) delivers a high volumetric energy density of 65.6 mWh cm−3, as well as long‐term deformable cyclic stability and high capacitance retention properties under harsh conditions. Density functional theory calculations and molecular dynamic simulation demonstrate the fast electronic responsiveness of the GDY–Ti3C2Tx heterostructure owning to the stronger H+ electrostatic attraction, lower migration resistance, and accelerated intercalation pseudocapacitance kinetics. In situ X‐ray diffraction reveals that a stable Ti─O─C bond bridged organic–inorganic heterostructure can tolerate the repeated high‐current charge/discharge cycling process. The state‐of‐the‐art ASSC delivers multiple functional outputs and shows great potential for efficient energy supply in practical applications.

All-Solid-State Supercapacitors Based on Cobalt Magnesium Telluride Microtubes Decorated with Tellurium Nanotubes.

Magnesium (Mg) has received very little exploration on its importance in the realm of battery-type energy storage technologies. They are abundantly present in seawater, and if successfully extracted and utilized in energy storage systems, it could lead to the long-term advancement of human civilization. Here, we fabricated an all-solid-state supercapacitor (ASSSC) using tellurium nanotubes decorated cobalt magnesium telluride microtubes (Te NTs@CoMgTe MTs) clad on nickel foam (NF). Owing to the unique mixed phase hierarchical structure, Te NTs@CoMgTe MTs showcases some advancement in energy storage performance. When tested in a three-electrode system, multiphasic hybrid of elemental Te and metal tellurides, Te NTs@CoMgTe MTs outperforms the monometallic telluride owing to the strong synergistic interaction effect triggered from conductive three components and delivers a long-life span performance up to 15,000 cycles. The fabricated Te NT@CoMgTe MT//AC solid-state device exhibits a maximum areal capacity of 59.2 μAh cm-2 (56.3 mAh g-1) at a current density of 6 mA cm-2 with a maximum energy density of 42.2 Wh kg-1 (46.5 μWh cm-2) at a power density of 6857.1 W kg-1 (7574.6 μW cm-2). The performance of the device is rigid even at different bending angles (0 to 180°) which validates the extensibility of the process for future applications.

Exploring the Potential of MBenes Supercapacitors: Fluorine-Free Synthesized MoAl1-xB with Ultrahigh Conductivity and Open Space.

The present study describes the synthesis of multilayered MBenes MoAl1-xB with different degrees of Al deintercalation using a mild, fluorine-free approach of dilute alkali to remove Al from MoAlB. We propose an etching route and compare it to conventional fluoride etching products. Additionally, the study explores the possible application and energy storage mechanism of MBenes in supercapacitors, marking the first investigation of its kind. At room temperature, 1/24-MoAl1-xB with terminal groups -OH exhibits ∼25% Al removal in 1 wt % NaOH for 24 h, outperforming traditional etching technology. Increasing the Al removal exposed more open space, resulting in a higher capacitance. Compared to LiF/HCl-MoAl1-xB (etched by LiF + HCl), 1/24-MoAl1-xB has a higher energy storage capability. The multilayered 1/24-MoAl1-xB film electrode exhibits ultrahigh conductivity with a rapid relaxation time of 0.97 s and high areal capacitance (2006.60 mF cm-2) while maintaining 80.2% capacitance after 5000 cycles. The MoAl1-xB all-solid-state supercapacitor (ASSS) delivers a high capacitance of 741.6 mF cm-2 at 1 mV s-1 for a single electrode and exhibits stable capacitance even at a 90° bending angle, highlighting its potential practical use. Our research represents an important step in the synthesis of MBenes and highlights their potential applications in supercapacitors.

Improving Interfaces in All-Solid-State Supercapacitors Using Polymer-Added Activated Carbon Electrodes

Solvent-free all-solid-state supercapacitors have recently received attention. Despite their highly specific capacitance, they suffer issues related to the solid–solid interface that degrade their performance during prolonged cycling. Here, we propose a novel strategy for improving the electrode–electrolyte interface by introducing a small amount of polymer into the activated carbon-based electrode. An electrode composition of 80AC:8SA:7AB:5[PEO0.95 (LiClO4)0.05]—where AC, SA, and AB stand for activated carbon, sodium alginate binder, and acetylene black, respectively—is optimized. A composite membrane—viz., PEO-LiClO4 reinforced with 38 wt% NASICON structured nano crystallites of Li1.3Al0.3Ti1.7(PO4)3—is used as a solid electrolyte. Incorporating a small amount of salt-in-polymer (95PEO-5 LiClO4) in the electrode matrix leads to a smooth interface formation, thereby improving the performance parameters of the all-solid-state supercapacitors (ASSCs). A typical supercapacitor with a polymer-incorporated electrode exhibits a specific capacitance of ~102 Fg−1 at a discharge current of 1.5 Ag−1 and an operating voltage of 2 V near room temperature. These ASSCs also exhibit relatively better galvanostatic charge–discharge cycling, coulombic efficiency, specific energy, and power in comparison to those based on conventional activated carbon.

Solid polymer electrolytes reinforced with porous polypropylene separators for all-solid-state supercapacitors.

Solid polymer electrolytes (SPEs) encounter the challenge of balancing high ionic conductivity and mechanical strength. Ionic liquids, which are among the contenders to be used in high-performance supercapacitors, have difficulty infiltrating commercial polyolefin separators for combined applications. In this study, a novel SPE involving uniform infiltration in the micropores of commercial polyolefin separators with polyethylene oxide (PEO), lithium salt, and different proportions of added ionic liquid was developed. The composite membranes combining ionic liquid-filled SPE with polypropylene (PP) microporous separators simultaneously achieve excellent mechanical strength and high-ionic conductivity. The low wettability of pure ionic liquids and commercial polyolefin-based separators is addressed. The 70 wt% IL-filled solid electrolyte composite membrane (PLI(70)@PP) exhibits a high ionic conductivity (2.9 × 10-3 S cm-1), low resistance at the electrolyte-electrode interface and excellent mechanical strength (128 MPa) at 25 °C. The all-solid-state supercapacitor using PLI(70)@PP exhibits a specific capacitance of 158 F g-1 at 0.1 A g-1 and stable cycle performance. The proposed method can be performed via high-volume roll-to-roll processing to obtain high-performance all-solid-state supercapacitors (ASSCs) for engineering applications.

MoS2 nanosheets on plasma-nitrogen-doped carbon cloth for high-performance flexible supercapacitors

With the surging demand for flexible and portable electronic devices featuring high energy and power density, the development of next-generation lightweight, flexible energy storage devices is crucial. However, achieving the expected energy and power density of supercapacitors remains a great challenge. This work reports a facile plasma-enabled method for preparing supercapacitor electrodes made of MoS2 nanosheets grown on flexible and lightweight N-doped carbon cloth (NCC). The MoS2/NCC presents an outstanding specific capacitance of 3834.28 mF/cm2 at 1 mA/cm2 and energy density of 260.94 µWh/cm2 at a power density of 354.48 µW/cm2. An aqueous symmetric supercapacitor fitted with two MoS2/NCC electrodes achieved the maximum energy density of 138.12 µWh/cm2 and the highest power density of 7,417.33 µW/cm2, along with the excellent cycling stability of 83.3 % retention over 10,000 cycles. The high-performance energy storage ASSSs (all-solid-state supercapacitors) are demonstrated to power devices in both rigid and flexible operation modes. This work provides a new perspective for fabricating high-performance all-solid-state flexible supercapacitors for clean energy storage.

Strong Magnetic-Field-Engineered Porous Template for Fabricating Hierarchical Porous Ni-Co-Zn-P Nanoplate Arrays as Battery-Type Electrodes of Advanced All-Solid-State Supercapacitors.

The sluggish charge transport kinetics that exist in the energy storage process of all-solid-state supercapacitors (ASSSCs) can be improved by designing open hierarchical porous structures for binder-free electrodes. Herein, a template-directed strategy is developed to fabricate open hierarchical porous Ni-Co-Zn-P nanoplate arrays (NCZP6T) through phosphating the electrodeposited NiCo-LDH nanosheets loaded on a template. At first, porous conductive NiZn alloy nanoplate arrays are rationally devised as the template by a strong magnetic field (SMF)-assisted electrodeposition. The Lorentz force caused by coupling the SMF with the electrical current induces a magnetohydrodynamic (MHD) flow (including the micro-MHD flow), which homogenizes the deposition coating, tunes the nucleation and growth of the NiZn alloy, and produces pores in the nanoplates. The open hierarchical porous structure offers a larger specific surface area and pore volume for accelerating charge transport and gives a synergistic effect between the inner porous conductive NiZn array template and the outer electrochemical active phosphides for high-performance hybrid ASSSCs. Accordingly, the battery-type electrode of NCZP6T shows a much higher specific capacitance of 3.81 F cm-2 at 1 mA cm-2, enhanced rate capability, and remarkable cycling stability at progressively varying current densities. Finally, the NCZP6T//FeS ASSSC delivers a high energy density of 77 μW h cm-2 at a large power density of 12 mW cm-2, outperforming most state-of-the-art supercapacitors.

Spinel-MgMn2O4 nanofibers: An attractive material for high performance aqueous symmetric supercapacitor

It is a known fact that morphology greatly influences the energy storage performance of a material. In this work, spinel magnesium manganese oxide (MgMn2O4) having nanofibric morphology has successfully been prepared for the first time using a versatile and cost-effective electrospinning technique. The morphology and the pore size are altered and optimized by varying the process parameters in the electrospinning process, and their corresponding effect on supercapacitive properties are also studied thoroughly. The aligned, mesoporous, and high aspect ratio of spinel-MgMn2O4 nanofiber exhibit the specific capacitance of ∼345 Fg−1 at 1 Ag−1 and 250 Fg−1 at 4 Ag−1 as well as demonstrate an outstanding rate capability and good capacity retention (∼90%) after 10,000 successive cycles at 4 Ag−1 in a three-electrode configuration. The improved energy storage performance of MgMn2O4 active material on graphite substrate is ascribed to its nanofibric morphology with interconnected particles having pores/voids in between, which impart a higher diffusion coefficient (D= 3.226 × 10−10 cm2s−1) and a small relaxation time constant (τ = 0.1 s). The quantitative capacitive contribution generating from EDLC and/or the surface pseudocapacitance reactions and the contribution from diffusion-controlled redox reactions to the total current have also been determined. The assembled symmetric all-solid-state supercapacitor (ASSSC) shows the high specific energy of ∼30 W h kg−1 at the specific power of ∼510 W kg−1 in the potential window of 0.0 V to 2 V with PVA-H2SO4 gel electrolyte. This performance is superior to that exhibited by many ASSSC reported recently. Two ASSSC devices connected in series can light up parallelly connected 55 red LEDs for more than 3 min, indicating practical applicability of our designed symmetric supercapacitor in electronics appliances. The outstanding electrochemical performance of the MgMn2O4 nanofiber reveals its potential to be a promising electrode material for supercapacitors.

Construction of Biomass-Derived Hybrid Organogel Electrodes with a Cross-Linking Conductive Network for High-Performance All-Solid-State Supercapacitors.

The biomass-based inter-transmission network architecture is expected to act on all-solid-state supercapacitors (ASSSCs) by building excellent conductive paths and achieving high ionic conductivity to promote their development as future electronic devices. Here, biomass-derived hybrid organogel electrodes constructed by incorporating polyaniline (PANI) into cellulose/dealkaline lignin (C/DL) film architectures exhibit an impressive specific capacitance (582 F g-1 at 1 A g-1) due to the effective dispersion and doping of PANI. Moreover, the specific capacitance of the best C/DL-PANI electrode is nearly 19 times higher than that of a cellulose-PANI electrode, which is attributed to the contribution of DL to the pseudocapacitance. ASSSCs assembled using the C/DL-PANI electrodes and the DL gel electrolyte exhibit excellent specific capacitance (344 F g-1 at 1 A g-1), Coulombic efficiency (∼100% for 5000 cycles), cycle stability (85.7% for 5000 cycles at 1 A g-1), and energy density (58.1 W h kg-1 at 0.5 kW kg-1). The ASSSCs showed a comparable or even higher electrochemical performance than the reported PANI-based or biomass-based ASSSCs, which can be due to the conductive network of the biomass-derived electrodes, the migration of ions between the electrodes through the gel electrolyte ion pathway, and the interfacial synergy. This innovative work paves the way for the development of ASSSC applications based on biomass materials.

Multi‐Foldable and Environmentally Stable All‐Solid‐State Supercapacitor Based on Hierarchical Nano‐Canyon Structured Ionic‐Gel Polymer Electrolyte

AbstractNew ionic‐gel polymer electrolytes (IGPEs) are designed for use as electrolytes for all‐solid‐state supercapacitors (ASSSs) with excellent deformability and stability. The combination of the photochemical reaction‐based polymer matrix, weak‐binding lithium salt with ionic liquid, and ion dissociating solvator is employed to construct the nano‐canyon structured IGPE with high ionic conductivity (σDC = 1.2 mS cm−1 at 25 °C), high dielectric constant (εs = 131), and even high mechanical robustness (bending deformation for 10 000 cycles with superior conductivity retention [≈91%]). This gives rise to ASSS with high compatibility and stability, which is compliant with foldable electronics. Consequently, this ASSS delivers remarkable electrochemical performance (specific capacitance of ≈105 F g−1 at 0.22 A g−1, maximum energy density and power density of 23 and 17.2 kW kg−1), long lifetime (≈93% retention after 30 days), wider operating temperature (≈0–120 °C), and mechanical stabilities with no significant capacitance reduction after mechanical bending and multiple folding, confirming the superior electrochemical durability under serious deformation states. Therefore, this ultra‐flexible and environmentally stable ASSS based on the IGPE having the nano‐canyon morphology can be a novel approach for powering up the ultra‐deformable and durable next‐generation wearable energy storage devices.

High capacitance for asymmetric supercapacitors based on one-step synthetic nanoflowers/nanocones arrays as cathode and pomelo peel as anode

In this work, NiCoO2 nanoflowers and nanocones are synthesized by one-step hydrothermal method. A layer of NiCoO2 nanoflowers is initially grown on the surface of Ni foam, followed by subsequent growth of NiCoO2 nanocones in order to obtain hierarchical NiCoO2/NiCoO2 nanoflowers/nanocones arrays (NNFC arrays). Various characterization methods are used to ensure the structure, morphology and composition of the materials. The results confirm that the as-prepared sample exhibits high specific surface area and voidage, low electrode internal resistance (0.5Ω), extremely fast diffusion and migration, and high electrochemical performance (1215.2 ​F ​g−1 at 5 ​mA ​cm−2). Furthermore, an all-solid-state supercapacitor (ASC) using NNFC arrays as a cathode, pomelo peel carbon (PPC) as an anode, and polyvinyl alcohol/KOH as separator is assembled. The ASC exhibits excellent specific capacitance (318.7 ​F ​g−1 at 5 ​mA ​cm−2) and large energy density (113.3 ​Wh·kg−1 at 396 ​W ​kg−1). Two ASCs in series can illume a red LED of 1.8 ​V for 30 ​min. The present work provides an effective approach to hydrothermally prepare two different morphologies in one-step, offering a facile and cost-efficient route to design outstanding supercapacitors (SCs).

Chicken nuggets-like core/shell nanosheet arrays as high performance flexible all-solid-state supercapacitor cathode and buckwheat shell as anode

The energy density of a flexible all-solid-state supercapacitor (ASC) requires new electrode material with special structure and morphology as a prerequisite for its secured improvement. In this paper, a new morphological exploration of chicken nuggets-like core/shell NiCo2O4/MnO2 (NCM) nanosheet arrays on Ni foam was employed. The application of this special morphology aims to greatly improve the electrochemical performance of the cathode electrode. Additionally, Buckwheat Biochar (BBC) is utilized as the anode while the PVA/KOH thin film is prepared as the separator. The chicken nuggets-like core/shell NCM nanosheet arrays were obtained by a two-step hydrothermal method. A series of characterization methods were carried out to further support the core/shell's well-designed structure and precise composition. The tests exhibited excellent specific capacitance of 593.3 F g−1 at 5 mA cm−2 and outstanding cycling stability with a retention of 90% after 10000 cycles. Furthermore, the assembled NCM//BBC ASC device indicated a high specific capacitance (239 F g−1 at the current density of 5 mA cm−2), this is in due part of the unique architecture of NCM nanosheet arrays and interconnected special porous structure of the BBC and the thin film PVA/KOH. Hence, the assembled ASC device exhibited high energy density (an energy density of 58 Wh·kg−1 at 3263 W kg−1) and remarkable cycling stability.

Engineering Textile Electrode and Bacterial Cellulose Nanofiber Reinforced Hydrogel Electrolyte to Enable High‐Performance Flexible All‐Solid‐State Supercapacitors

AbstractThe fabrication of highly durable, flexible, all‐solid‐state supercapacitors (ASCs) remains challenging because of the unavoidable mechanical stress that such devices are subjected to in wearable applications. Natural/artificial fiber textiles are regarded as prospective materials for flexible ASCs due to their outstanding physicochemical properties. Here, a high‐performance ASC is designed by employing graphene‐encapsulated polyester fiber loaded with polyaniline as the flexible electrodes and bacterial cellulose (BC) nanofiber‐reinforced polyacrylamide as the hydrogel electrolyte. The ASC combines the textile electrode capable of arbitrary deformation with the BC‐reinforced hydrogel with high ionic conductivity (125 mS cm−1), high tensile strength (330 kPa), and superelasticity (stretchability up to ≈1300%), giving rise to a device with high stability/compatibility between the electrodes and electrolyte that is compliant with flexible electronics. As a result, this ASC delivers high areal capacitance of 564 mF cm−2, excellent rate capability, good energy/power densities, and more importantly, superior mechanical properties without significant capacitance degradation after repeated bending, confirming the functionality of the ASC under mechanical deformation. This work demonstrates an effective design for a sufficiently tough energy storage device, which shows great potential in truly wearable applications.

Construction of MXene‐Coupled Nitrogen‐Doped Porous Carbon Hybrid from a Conjugated Microporous Polymer for High‐Performance Supercapacitors

MXene‐based organic material hybrids present huge potential for energy storage applications. However, the compatibility of hydrophilic MXenes with organic materials and their subsequent processing still remain elusive. Herein, a MXene‐based 2D sandwich‐like conjugated microporous polymer (MX‐CMP) manifesting high specific surface area and layered structure using a functionalized MXene as a 2D structure‐directing template is developed. The MX‐CMP is used as a robust organic precursor for preparing a MXene‐coupled nitrogen‐doped porous carbon (MX‐MC‐N) hybrid. The interconnected porous networks and large aspect ratio of MX‐MC‐N enhances the electrochemical active surface area and boosts the long‐distance charge transport. This leads to excellent performance for a three‐electrode, flexible all‐solid‐state supercapacitor (ASSC) and an asymmetric supercapacitor (ASC) with an expanded voltage window (1.6 V) and long‐term cyclability (>5000 cycles) compared to many state‐of‐the‐art analogous materials and hybrids. It is believed that the synthetic strategy presented for the MX‐MC‐N hybrid will indubitably pave a path for the development of novel MXenes and heteroatom‐doped porous hybrid materials for sustainable energy applications.

Large-area (64 cm2), semi-transparent, flexible all-solid-state supercapacitor using D-bar coating process

In this work, we report large-area, semi-transparent, and flexible all-solid-state supercapacitors (ASSCs) fabricated using scalable D-bar coating, which is compatible with roll-to-roll printing processes. The poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS)-based transparent conducting electrodes (TCEs) show optical transparencies of T550nm > 85% and conductivities of ~3645 S cm−1. An ASSC device (~1 cm2) consists of D-bar coated TCEs and PVA/LiCl gel-electrolyte and exhibits a high areal capacitance per electrode (Ca) of 4.7 mF cm−2, which is about 35% higher than that of ASSC devices containing spin coated TCEs. A PEDOT:PSS ASSCs with the transparency of T550nm > 65% presents stable capacitance up to 10,000 charge/discharge cycles and 5000 bending cycles at a bending radius of 2 mm, demonstrating excellent electrochemical robustness and flexibility. Moreover, the large-area (~64 cm2) ASSC fabricated with D-bar coating exhibited a Ca of 2.9 mF cm−2, a maximum energy density of 18 µWh cm−2 and a power density of 1600 µW cm−2, which outperforms state-of-the-art transparent and flexible ASSCs. The agglomerated PEDOT:PSS nanofibrils and dipper pore size on D-bar coated TCEs, enables efficient ion adsorption/desorption and charge intercalation, which leads to the high performance of the flexible ASSC.

Improved redox-active ionic liquid-based ionogel electrolyte by introducing carbon nanotubes for application in all-solid-state supercapacitors

More attention has been focused on the design of all-solid-state supercapacitors (ASSCs) due to that this kind of supercapacitors can avoid some problems such as electrolyte leakage occurring in liquid electrolyte-based supercapacitors. However, ASSCs present lower specific energy, which is generally in great relation with the very low ionic conductivity of utilized electrolyte. To achieve high-specific-energy ASSCs with superior performance, a redox-active ionic liquid-based ionogel electrolyte (IGE) consisting of 1-butyl-3-methylimidazolium iodide (BMIMI) IL, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and carbon nanotubes (CNTs) was prepared by a solution-casting method. By optimizing BMIMI/PVDF-HFP and CNTs/PVDF-HFP mass ratios, the obtained PVDF-HFP/BMIMI/CNTs IGE presents the maximum ionic conductivity as high as 17.6 mS cm−1. A sandwiched ASSC constructed by two identical activated carbon electrodes and an as-prepared PVDF-HFP/BMIMI/CNTs IGE possesses a high specific energy of 50.1 Wh kg−1 as a result of the extra pseudocapacitance contribution from the redox-reactions related to I-based ions happening at the interface between electrolyte and electrode and the increased ionic conductivity of IGE for the existence of CNTs network into the IGE providing fast ion transfer channel. The self-discharge behavior of this device is effectively weakened due to the addition of CNTs. Furthermore, the promising cyclic stability is achieved.

High areal capacitance of vanadium oxides intercalated Ti3C2 MXene for flexible supercapacitors with high mass loading

Flexible all-solid-state supercapacitors (ASSSs) have caught the scientific attention to meet the explosive demand for portable and wearable electronic devices. However, it is difficult for flexible electrode materials to obtain a high areal capacitance at a high mass loading, which limits their commercial applications. In this study, vanadium oxide (V2O5) nanoparticles are introduced into Ti3C2 flakes with the aid of cetyltrimethylammonium bromide (CTAB). The intercalation of V2O5 particles in the interlayer of Ti3C2 establishes a hierarchical structure and facilitates the electrolyte penetration. As a result, the prepared CT-Ti3C2@V2O5 composite electrode achieves a high areal capacitance of 2065 mF cm−2 at 3 mA cm−2 and superior active mass loading (15 mg cm−2). Meanwhile, over 93% capacitance is maintained after 6000 cycles at 18 mA cm−2. The ASSS based on CT-Ti3C2@V2O5 delivers a high areal capacitance of 477 mF cm−2 at 1 mV s−1 and exhibits stable performance at different bending states, which reaches to the advanced level for the ASSSs based on MXenes.

Two-dimensional layered materials InSe nanoflakes/carbon nanotubes composite for flexible all-solid-state supercapacitors

With the rapid development of wearable electronic and smart electronic devices, the flexible supercapacitors have attracted special attention in energy storage and conversion. Indium selenide (InSe) as a novel two-dimensional layered material has been widely investigated in photodetector, solar cell, and so on due to high electron mobility, anomalous optical response and tuning the bandgap. InSe nanoflakes are obtained from bulk layered InSe materials via a liquid-exfoliation technique and used as electrodes materials of supercapacitors. Flexible all-solid-state supercapacitors (ASSPs) with sandwich structure using InSe nanoflakes have a volumetric capacitance of 3.48 F cm−3 at a scan rate of 0.005 V s−1. For improving the performance of ASSPs based on InSe, highly conductive carbon nanotubes (CNTs) are added into InSe nanoflakes to enhance the conductivity of InSe/CNTs composites used as electrodes of ASSPs. InSe/CNTs (mass ratio 6:1) ASSPs deliver high volumetric capacitance of 25.1 F cm−3 at a scan rate of 0.005 V s−1, good mechanical properties (93.2% capacitance at 180° bending) and long cycle stability (88.3% capacitance after 10000 cycles). In addition, ASSPs based on InSe/CNTs composites exhibit a high power density of 410.15 W cm−3 and a superior energy density of 3.48 mWh cm−3. The InSe/CNTs composite is expected to have a potential candidate in high-performance electrochemical energy storage devices.

Multifunctional microporous activated carbon nanotubes anchored on graphite fibers for high-strength and high-rate flexible all-solid-state supercapacitors

Flexible all-solid-state supercapacitors (ASSSCs) based on stable gel electrolyte have attracted enormous attention due to their potential application for wearable and portable electronic devices, but usually suffer from lack of structural stability for integrated devices during the bending and folding process, mainly due to the weak interfacial interaction force between electrode materials and gel electrolyte. We report a novel high-strength ASSSC based on activated multiwalled carbon nanotubes anchored on graphite fibers (GF@aMWNTs) by electrostatic assembly and electrophoretic deposition (EPD). With high areal density of aMWNTs, the GF@aMWNTs fabricated by EPD technique exhibit the maximum tensile strength of 47.9 ± 2.0 MPa for the sandwich-type GF@aMWNT/PVA/GF@aMWNT films, mainly attributed to the microporous aMWNTs as an important “bridging” role in the combination of GF electrodes and PVA electrolyte. The assembled symmetric ASSSC based on the GF@aMWNT electrodes, can provide an outstanding specific capacitance of 177 F g−1 at 1 A g−1, a maximum power density of 25 kW kg−1 (13.1 Wh kg−1) as well as excellent capacitance stability in cycling test and bending state. This high-rate ASSSC is anticipated to open up an exciting route to enhance the structural strength of integrated devices for high-efficient energy storage.