Flexible Solid-state Supercapacitor Device Research Articles

Flower-like FeCoNi ternary composite formed by interweaving nano needles for positive electrode material of supercapacitor

Ternary layered double hydroxide (LDH) are potential electrode material choices for supercapacitors (SCs) due to their various oxidation states and high theoretical specific capacitance. In this paper, FeCoNi-LDH composite with cross-braided flowers of nanoneedles has been prepared by a single-step hydrothermal method. By highlighting the structural and morphological advantages, the obtained ternary LDH shows lower resistivity in comparison with the binary LDH. As electrode material, the ternary LDH exhibits excellent electrochemical properties, such as superb specific capacitance of 2163.3 F·g−1 at 0.5 A·g−1 and good cycle retention rate of 93.8% after 5000 cycles at 20 A·g−1. Meanwhile, the assembled asymmetric flexible solid-state supercapacitor device can provide 44.8 Wh·kg−1 energy density at 807.5 W·kg−1. Moreover, two devices in series can also light up miniature light bulbs of different hues and maintain them for a long period when they are connected in series.

Vanadium telluride nanoparticles on MWCNTs prepared by successive ionic layer adsorption and reaction for solid-state supercapacitor

Anchoring of vanadium telluride (VxTey) nanoparticles onto the exterior layer of multi-walled carbon nanotubes (MWCNTs) has been successfully employed at room temperature (300 K) as first report by using successive ionic layer adsorption and reaction (SILAR) to yield VxTey/MWCNTs surface architecture. Mutualistic contribution from ion insertion/extraction introduced non-stoichiometric vanadium telluride with electric double-layer involved MWCNTs have been unified to enrich excellent electrochemical performance. Three-electrode system configured VxTey/MWCNTs electrode yields 16-fold enhancement in specific capacitance compared to the bare MWCNTs electrode. Achieved performance forced us to construct flexible solid-state supercapacitor device (FSS-SC). Symmetric electrode embedded with PVA-LiClO4 gel mediator harvests remarkable 2 V voltage window to gain 34.5 Wh/kg energy density and 0.7 kW/kg power density. Cycling over 10000 replications confirms the pronounced (82.5 %) stability of designed device and growing LED enables practical evidence; demonstrating its capacity as efficient energy storage device. Correlated density functional theory (DFT) has been manifested to confirm synergistic interactions between the VxTey and MWCNTs, and a corresponding enhancement in the electron density at the Fermi level of VxTey/MWCNTs describes the insight origin for enhanced supercapacitance.

Design and synthesis of novel electroactive 2,2′:5′,2″-terthiophene monomers including oxyethylene chains for solid-state flexible energy storage applications

Here, we present the synthesis of novel poly(2,2′:5′,2″-terthiophene) derivatives containing oxyethylene pendant groups for the fabrication of high performance flexible redox-active electrode materials. The poly(3′,4′-bis(2-methoxyethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN1), poly(3′,4′-bis(2-(2-methoxyethoxy)ethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN2) and poly(3′,4′-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN3) have been electrochemically polymerized on flexible stainless steel substrates without any binder and directly employed as redox-active materials. The effect of pendant group chain length on morphological characteristics of conducting polymer films have been systematically evaluated and correlated to the charge storage properties of redox-active electrode materials. Capacitive performance tests reveal that PSEDEN1, PSEDEN2 and PSEDEN3 could reach up to specific capacitances of 135 F g−1, 212.8 F g−1 and 403.3 F g−1, respectively, at constant current density of 2.5 mA cm−2 in the potential range of 0.4–1.8 V with good rate capability performances. In addition, symmetrical flexible solid-state supercapacitor devices based on polymer gel electrolyte have also been assembled using PSEDEN1, PSEDEN2 and PSEDEN3 coated flexible stainless steel substrates and tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy techniques in detail. Fabricated devices (Cell 1, Cell 2 and Cell 3) have delivered maximum specific capacitances of Cspec= 29.3 F g−1, 92.1 F g−1 and 162.4 F g−1, energy densities of SE= 6.35 W h kg−1, 22.9 W h kg−1 and 41.1 W h kg−1 and power densities of SP= 929 W kg−1, 937.7 W kg−1 and 986.4 W kg−1 at a current density of 2.5 mA cm−2 in two-electrode cell configuration. Furthermore, flexible supercapacitor devices have achieved high cycle life performances with good capacitance retention values of 80.2%, 84.7% and 91.4% over 10 000 consecutive galvanic charge/discharge cycles at 2.5 mA cm−2 constant current density from 0.4 to 1.8 V. Similarly, excellent mechanical stabilities have also been observed with 3.4%, 4.66% and 1.97% capacitance losses under various bending conditions from 0° to 170° for all flexible supercapacitor devices. These results confirm that PSEDEN1, PSEDEN2 and PSEDEN3 redox-active materials with gratifying capacitive performances and excellent flexibilities have a great potential for utilization in innovative flexible or wearable energy storage solutions.Keywords

Carbon-carbon dense network composite with hierarchical structure for additive-free and high volumetric performance supercapacitor

High density carbon composite (AC3/G) with hierarchical porous structure is prepared by packing biomass-based carbon (ACs) into graphene network (rGO), via microwave-assisted hydrothermal treatment followed by capillary evaporation-induced drying. Graphene oxide is reduced during the treating process and acts as frame network to embed the ACs. ACs are packed into the network with a density up to 1.23 g/cm3 for AC3/G. ACs can prevent the agglomeration of rGO, and channels formed between rGO sheets and ACs facilitate the hierarchical porous structure. When AC3/G is used as a binder and conductive additive-free electrode in the three-electrode system, a high volumetric capacitance of 775 F/cm3 at 0.5 A/g is achieved with excellent cycling stability of 97.05%. When assembled into a flexible solid-state supercapacitor device with lignin hydrogel electrolytes, the high-density electrode delivers high volumetric and gravimetric energy densities of 9.7 W h/L and 7.9 W h/kg, with volumetric capacitance of 326 F/cm3 at 0.5 A/g. Remarkably, the study paves a new idea for preparation of energy devices with high volumetric performance using biomass resources.

Porous MnO2–CNTs–Cellophane Nanocomposite for High-Voltage Flexible Supercapacitors

Flexible MnO2–CNTs–cellophane electrode was easily fabricated via addition of NaHCO3 in matrix of manganese dioxide-carbon nanotubes-cellophane composite followed by selective etching of NaHCO3 in acidic solution to produce a porous network structure as result of CO2 (g) bubbling. Under the optimized mass loading, the flexible-porous electrode presented favorite electrochemical capacitance behavior with the areal capacitance of 121 and 55.5 mF cm−2 at the current density of 0.6 mA cm−2 in 1.0 M H2SO4 and Na2SO4 electrolytes, respectively. A symmetric all-solid-state supercapacitor assembled with the flexible MnO2/CNTs/cellophane electrode showed a wide working voltage (2.0 V), a high areal capacitance of 82.5 mF cm−2 at a current density of 2.0 mA cm−2, favorite flexibility and good cycling stability (83% after 2000 cycles at a current density of 2.0 mA cm−2). Therefore, such a simple and scalable procedure to produce flexible supercapacitor device based MnO2–CNTs composite is offering for future flexible energy storage systems. Flexible solid-state supercapacitor device based on MnO2–CNTs–cellophane electrode.

Facile synthesis of freestanding cellulose/RGO/silver/Fe2O3 hybrid film for ultrahigh-areal-energy-density flexible solid-state supercapacitor

We report the design of a freestanding cellulose/RGO/silver/Fe2O3 hybrid film for direct use as electrodes for construction of high-performance flexible solid-state supercapacitor (FSS). It is well characterized and found to feature noticeable capacitive properties due to the unique structure, high conductivity and dual electroactive species (i.e., RGO and Fe2O3) for charge storage. As demonstrated in a three-electrode system, such film electrode achieves the maximum areal and volumetric capacitance of 2044 mF cm−2 and 75.7 F cm−3, respectively, with prominent rate performance and long-term cyclic durability. Later, a symmetric FSS device is constructed by employing this film as both anode and cathode electrodes. The as-assembled device offers the highest areal and volumetric capacitance of 1132 mF cm−2 and 18.2 F cm−3, respectively, displays inconspicuous performance degradation under different curved states, and possesses the largest areal energy density of 226.4 μWh cm−2, which is far better than that of many advanced symmetric and asymmetric flexible supercapacitors. The attractive capacitive behaviors and easy fabrication processes could render cellulose/RGO/silver/Fe2O3 hybrid film a promising material for the applications in next-generation flexible and wearable electronics in the future.

High-Energy Flexible Supercapacitor-Synergistic Effects of Polyhydroquinone and RuO2· xH2O with Microsized, Few-Layered, Self-Supportive Exfoliated-Graphite Sheets.

An effective and straightforward route for tailoring the self-supporting, exfoliated flexible graphite substrate (E-FGS) using electrochemical anodization is proposed. E-FGS has essential features of highly exfoliated, few-layered, two-dimensional graphite sheets with the size of several tens of micrometers, interconnected along the axis of the substrate surface. The novel hierarchical porous structural morphology of E-FGS enables large active sites for efficient electrolyte ion and charge transport when used as electrode material for a supercapacitor. In order to effectively utilize this promising E-FGS electrode for energy storage purpose, a ternary composite is further synthesized with pseudocapacitive polyhydroquinone (PHQ) and hydrous RuO2 (hRO). hRO is synthesized via a sol-gel route, while electropolymerization is utilized for the electrodeposition of PHQ over E-FGS. Ultimately, the fabricated self-supporting E-FGS-based flexible supercapacitor is capable of delivering areal specific capacitance values as high as 378 mF cm-2 at a current density of 1 mA cm-2. Addition of the pseudocapacitive component to the E-FGS texture leads to ∼10 times increase of the electrochemical charge storage capability. The imposition of mechanical forces to this flexible supercapacitor device results in trivial changes in electrochemical properties and is still capable of retaining 91% of the initial specific capacitance after 10 000 cycles. Alongside, the fabricated symmetrical solid-state flexible device exhibited a high energy density of 8.4 μWh cm-2. The excellent performance along with the ease of synthesis and fabrication process of the flexible solid-state supercapacitor device using PHQ/hRO/E-FGS holds promise for large-scale production.

Boosting the capacitive storage performance of MOF-derived carbon frameworks via structural modulation for supercapacitors

Reasonable options about carbon-based electrode materials and electrolyte play crucial roles in the pursuant path of high-performance supercapacitors. Herein, the synthesis of hierarchical porous honeycomb-like carbon frameworks (HHCF) is reported, which was prepared through pyrolysis of metal-organic framework composite and subsequent activation process. HHCF with a high surface area and hierarchical meso-/micropores, can provide more adsorption sites and facilitate the fast ion transport. The HHCF electrode delivers a high specific capacitance of 361 F g−1 at a current density of 1 A g−1 in aqueous electrolyte and retains 182 F g−1 at 100 A g−1. Furthermore, the symmetric supercapacitors fabricated in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte exhibits great specific capacitance of 174 F g−1 at 1 A g−1 and delivers excellent energy density of 74 Wh kg−1 at a power density of 872 W kg−1. More importantly, the flexible solid-state supercapacitor device assembled by HHCF electrodes and EMIMBF4/PVDF-HEP polymer gel electrolyte also presents soaring energy density and excellent flexibility performance. Our work may provide new insight in the design of MOF-derived carbon-based supercapacitor with high energy/power density.

Chemically crosslinked liquid crystalline poly(ionic liquid)s/halloysite nanotubes nanocomposite ionogels with superior ionic conductivity, high anisotropic conductivity and a high modulus.

A novel type of chemically crosslinked liquid crystalline nanocomposite ionogel electrolyte based on poly(ionic liquid) (PIL) with superior ionic conductivity and high anisotropic conductivity was designed and synthesized using the in situ photopolymerization of sheared soft ionogels containing charged halloysite nanotubes (HNTs) and ionic liquid monomers. The oriented structure was investigated using scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS). The chemically crosslinked backbone of the PIL and the addition of HNTs endowed the flexible ionogels with a combined very high modulus (up to 26.7 MPa) and mechanical strength (up to 4.4 MPa). Crucially, the obtained ionogels exhibited high mechanical stability even at temperatures up to 200 °C. Remarkably, in terms of the conductivities, the resulting pre-sheared ionogels displayed superior room temperature ionic conductivity (up to 6 mS cm-1) and a very high conductivity anisotropy ratio (up to 1600), owing to the alignment of the HNTs with oppositely charged surfaces and the high ionic conductivity of the polyelectrolyte PILs. Furthermore, flexible solid-state supercapacitor devices based on the high ion-conductive nanocomposite ionogels were fabricated, which demonstrated high and temperature-dependent specific capacitance, and remarkable cycling stability and flexible performance.

Redox additive enhanced capacitance: Multi-walled carbon nanotubes/polyaniline nanocomposite based symmetric supercapacitors for rapid charge storage

In the present study, we report all-solid-state high energy density symmetric supercapacitors based on partially exfoliated multi-walled carbon nanotubes (Px-MWCNT)/Polyaniline (PANI) nanocomposites with redox-active polymer gel as an electrolyte/separator. Fabrication of mechanically stable polymer gel electrolyte with high ionic conductivity, excellent compatibility with the active material, and long cycle life is pivotal to obtain superior electrochemical performance for flexible solid-state supercapacitor devices. An organically reversible redox-active (hydroquinone-HQ) non-covalent approach adopted to achieve the significant enhancement in specific capacitance. The highest specific capacitance of 186.1, 809.6 and 644.4 F g−1 was achieved at 25 mV s−1 for Px-MWCNT, Px-MWCNT/PANI and PANI based symmetric supercapacitor cells, respectively. The enhancement in capacitance was found to be increased in the order of 82.5%, 129% and 34.3% for Px-MWCNT, Px-MWCNT/PANI, and PANI respectively when compared with devices lacking in redox-active HQ. Moreover, incorporation of redox-active HQ transforms the pseudocapacitance to battery-type behavior. The polymer grafted morphology of nanocomposite (Px-MWCNT/PANI) in 1:1 wt ratio as an electrode material with redox-active gel polymer electrolyte exhibits synergistic effect in specific capacitance enhancement with excellent charge-discharge rate capability and electrochemical stability (78% capacitive retention after 2000 cycles) than pure PANI (69.4% capacitive retention after 2000 cycles) based supercapacitor.

Facile and fast microwave-assisted fabrication of activated and porous carbon cloth composites with graphene and MnO2 for flexible asymmetric supercapacitors

Current collectors and substrate materials are of pivotal importance for the design and preparation of electrodes and energy storage devices, because their surface areas, morphologies, ionic and electronic conductivities, and mechanical properties substantially influence electrochemical performances. Although carbon cloths (CCs) are widely considered the most promising current collectors for flexible energy storage devices, the majority of carbon-based textiles have poor capacitances due to their low surface areas and porosities, which reduce device performances. Here, we report a rapid and straightforward method for preparing CC-based electrode materials for high performance supercapacitors using microwaves. Microwave irradiation efficiently activates the surface pores of carbon fibers, and increases specific capacitance markedly as compared with pristine CC. In addition, surfaces of microwave-treated CCs (m-CCs) are coated with reduced graphene oxide (RGO) or MnO2, and the resulting electrode materials exhibit excellent electrochemical performances, such as, high specific capacitances, high rate capabilities, and long-term cycling stabilities. Flexible solid-state supercapacitor devices are fabricated using a RGO/m-CC as a negative electrode and a MnO2/m-CC as a positive electrode. The produced asymmetric supercapacitors show an excellent resilience to harsh electrochemical and mechanical conditions, and high energy and power densities.

Fabrication of a Graphene-Based Paper-Like Electrode for Flexible Solid-State Supercapacitor Devices

The increasing demand for portable and wearable electronics requires high reliability of devices for continuous miniaturization, and provides challenges for the dimensionally-confined bottom-up assembly methods which typically begin with materials such as graphene oxide (GO). However, GO based devices suffer from complicated synthesis procedures and lower device performance due to the presence of oxygen functionalities on the electrode materials, as well as the need to ensure a good interface between the electrode material and the electrolyte used. Here, a facile, two-step, top-down strategy was used to fabricate thin, all-in-one (PVA/H3PO4)/graphene/graphite paper-like electrodes. The assembled flexible, all-solid-state micro-supercapacitor devices exhibit excellent performance compared to previously reported values, such as a high volumetric capacitance of ∼3.6 F·cm−3 even after 20000 cycles. Notably, the devices also showed excellent rate performance with extremely high specific capacitance retention of up to 94% as the current density increased from 0.5 to 5 A·cm−3, indicating promise for high power applications. The paper-like electrodes were tailored to less than 0.5 mm width for further miniaturization and suffered from minimal capacitance attenuation. The excellent mechanical flexibility, capacity, and reliability indicate their promising application in energy storage devices.

Novel Conducting Polymer Hydrogels for Electrochemical Energy Storage Devices

Conductive polymer hydrogels (CPHs) represent a unique class of polymeric materials with 3D hierarchical networks of crosslinked polymer chains, and can synergize the advantageous features of hydrogels with electrical and optical properties of ‘organic metals’. They provide an excellent interface between the electrode and the electrolyte in electrochemical devices, as well as between soft and hard materials, and have been explored for a range of important technological applications from biosensors and medical electrodes, to energy storage devices such as supercapacitors and lithium-ion batteries. This talk will discuss our recent progress on rational syntheses and device studies of nanostructured CPHs with tunable structures and electrochemical properties for high-performance energy storage devices. Given their 3D hierarchical architecture and multi-scale porosity, high electrical conductivity and redox activity, the CPHs can enable the design of high-performance electrochemical storage devices, offering high power and energy densities as well as excellent cyclability. Two examples will be presented: 1) CPHs function as active electrodes for making flexible solid-state supercapacitor devices; 2) CPHs serve as functional components to chemically integrate with silicon particles to make stable, high-energy-density battery anodes.