Solid-state Supercapacitor Research Articles

Sodium polyacrylate hydrogel electrolyte: Flexible rechargeable supercapacitor using thermally reduced graphene oxide nanosheets

The alternative source of the gel polymer electrolyte (GPE) is introduced by developing the sodium polyacrylate (S-PANa) solid hydrogel electrolyte, which is the front runner in the recent flexible and wearable electronic devices due to their excellent mechanical property, high ionic conductivity, and electrochemical stability. In this work, we synthesized the S-PANa solid hydrogel electrolyte and utilized it for the flexible symmetric supercapacitor using thermally reduced graphene oxide nanosheets (TRGO) coated on carbon cloth as an electrode. The prepared S-PANa hydrogel is of a highly porous nature and has better surface roughness, as examined by the Field Emission Scanning Electron Microscopy (FE-SEM) and 3D nano profiler analysis. The electrochemical characterization of the assembled flexible solid-state hydrogel supercapacitor (FSHSC) reveals the electric double-layer capacitive behavior with an excellent device capacitance of 45.77 mF/cm2. The significant role of diffusion charge re-distribution, overcharging issues, ohmic drop, and leakage current of the FSHSC is studied, followed by self-discharge and leakage current analysis. Moreover, the FSHSC device delivers the maximum energy density of 5.15 μWh/cm2 with a remarkable retention capacitance of 99 % over 10,000 continuous cycles. Further, in practical utilization, the solar-charged FSHSC device can effectively power the electronic LED for a long duration and enhance its efficiency for the development of a sustainable backup power system. Overall, these experimental results demonstrated the significant use of the S-PANa hydrogel-based flexible device, which can be an alternative source in future energy storage systems instead of using gel electrolyte-based flexible devices.

Lignin-Based N-Carbon Dots Anchoring NiCo2S4/Graphene Hydrogel Exhibits Excellent Performance as Anodes for Hybrid Supercapacitor

A NiCo2S4/N-CDs/RGO ternary composite hydrogel was prepared via a one-step hydrothermal method, utilizing lignin-based nitrogen-doped carbon dots as a bridge connecting NiCo2S4 and graphene. The specific capacitance of NiCo2S4/N-CDs/RGO significantly outperforms that of the GH and NiCo2S4/RGO electrodes, achieving 1050 F g−1. The 3D mesh porous hydrogel structure mitigates NiCo2S4 nanoparticle aggregation, providing a larger specific surface area for enhanced charge storage. The abundant functional groups of N-CDs interact with Ni (II) and Co (III) cations, favoring NiCo2S4 particle synthesis. Additionally, an assembled solid-state asymmetric supercapacitor employing NiCo2S4/N-CDs/RGO as the positive electrode exhibited excellent energy density (68.4 Wh kg−1) and cycle stability (82% capacitance retention after 10,000 constant current charge–discharge cycles).

Acid-treated waste sisal fiber derived activated carbon as efficient electrode material for solid-state supercapacitor

Activated Carbon (AC), obtained from biomass is highly adaptable and valued for its versatile benefits including high surface area, conductivity, chemical inertness, etc. in various applications. It is also used as an electrode in supercapacitors for applications requiring a high-power supply. Sisal fiber, derived from the Agave sisalana plant, has several advantages, including its fibrous and porous framework, that make it suitable for conversion into activated carbon for energy storage applications in the context of sustainability and reduced environmental impact. In this study, we have prepared H2SO4 treated KOH activated carbon from residual Sisal fiber (SFH2AC) which is then utilized as an electrode material for supercapacitors. SFH2AC exhibits hierarchical and structure-based porosity with a large specific surface area (SA) of 1185 m2/g and shows the maximum specific capacitance (Cs) of 340 F/g @ 0.5 A/g in 6 M KOH electrolyte. In KOH electrolyte, strong cycling retention (during the length of 9000 GCD cycles) is attained as; 98 % up to the first 3000 cycles at 10 A/g, 93 % up to next 3000 cycles at 20 A/g, and 90 % up to the last 3000 cycles at 30 A/g. Furthermore, the SFH2AC//SFH2AC(Gel) device was built by using SFH2AC as electrodes with PVA/KOH gel as an electrolyte in order to assess the supercapacitor performance in real time. The device has a specific power density of 7500 W/kg and a maximum energy density of 12 W h/kg. The device reveals an exceptional 97 % cycling stability, maintaining up to 9000 repeated GCD cycles at an increased current density (CD) of 30 A/g.

Highly conductive V4C3T x MXene-enhanced polyvinyl alcohol hydrogel electrolytes for flexible all-solid-state supercapacitors.

Hydrogel electrolytes are an integral part of flexible solid-state supercapacitors. To further improve the low ionic conductivity, large interfacial resistance and poor cycling stability for hydrogel electrolytes, the V4C3T x MXene-enhanced polyvinyl alcohol hydrogel electrolyte was fabricated to enhance its mechanical and electrochemical performance. The high-conductivity V4C3T x MXene (16,465.3Sm-1) bonding transport network was embedded into the PVA-H2SO4 hydrogel electrolyte (PVA- H2SO4-V4C3T x MXene). Results indicate that compared to the pure PVA-H2SO4 hydrogel electrolyte (105.3mScm-1, 48.4%@2,800 cycles), the optimal PVA-H2SO4-V4C3T x MXene hydrogel electrolyte demonstrates high ionic conductivity (133.3mScm-1) and commendable long-cycle stability for the flexible solid-state supercapacitors (99.4%@5,500 cycles), as well as favorable mechanical flexibility and self-healing capability. Besides, the electrode of the flexible solid-state supercapacitor with the optimal PVA-H2SO4-V4C3T x MXene hydrogel as the solid-state electrolyte has a capacitance of 370Fg-1 with almost no degradation in capacitance even under bending from 0° to 180°. The corresponding energy density for flexible device is 4.6Whkg-1, which is twice for that of PVA-H2SO4 hydrogel as the solid-state electrolyte.

A LiPF6 gel-polymer electrolyte for a solid-state supercapacitor with polyaniline/MnCo layered double hydroxide nanosheets as active electrode material

This paper introduces a novel solid-state electrolyte for supercapacitors (SCs), employing a LiPF6 gel polymer coupled with innovative electrodes composed of MnCo-layered double hydroxide (LDH) nanosheets. The newly synthesized LiPF6 gel polymer electrolyte exhibits superior ionic conductivity and mechanical flexibility, making it an ideal candidate for advanced energy storage devices that require bending and twisting capabilities. The thermal analyses and morphological characterizations were evaluated using DSC, XRD, FT-IR, BET, TEM and FE-SEM techniques. The MnCo-LDH nanosheets, synthesized via a facile co-precipitation method, served as the electrode material. It was expected that the collaborative interaction between the LiPF6 polymer matrix and the multifaceted nanoflower-shaped MnCo-LDH nanosheets could improve electron mobility and supply an increased surface area for redox processes. Electrochemical analyses, including cyclic voltammetry and galvanostatic charge-discharge tests, reveal a marked improvement in the specific capacitance, rate capability, and cyclic stability of the assembled SCs. This novel electrolyte-electrode configuration yielded a specific capacity of up to 198.66 F g−1 at 1.6 A g−1 and exhibited rate performance with retention of 89.15 % at an elevated current density of 10 A g−1 for 2-Hydroxyehtyl cellulose: LiPF6 gel polymer with molar ratio of 1: 2. Moreover, it demonstrates enduring cyclic stability with no capacity decay after 10,000 cycles. We delineated the pivotal role of Mn in facilitating electron transfer kinetics and moderating interactions with Co ions. The introduction of strain within the LDH structure promulgates a conducive environment for electrochemical reactions.

Surface-modified composites of metal–organic framework and wood-derived carbon for high-performance supercapacitors

The renewable nature, high carbon content, and unique hierarchical structure of wood-derived carbon make it an optimal self-supporting electrode for energy storage. However, the limitations in specific surface area and electrical conductivity defects pose challenges to achieving satisfactory charge storage in wood-derived carbon electrodes. Therefore, exploring diverse and effective surface strategies is crucial for enhancing the electrochemical energy storage performance. Herein, a decoration technique for enhancing aesthetic appeal involves applying a metal–organic framework (Ni/Co-MOF) containing nickel and cobalt onto the inner walls of wood tracheids. The sequential modification steps include carbonization, oxidation activation, and acid-etching. The Ni/NiO/CoO-CW-4 electrode, made by acid-etching carbonized wood (CW) doped with nickel, nickel oxide, and cobalt oxide for 4 h, has excellent surface area and pore size distribution, high graphitization degree, and exceptional conductivity. Furthermore, surface modification optimizes the surface chemistry and phase composition, resulting in a 0.8 mm thick Ni/NiO/CoO-CW-4 electrode with an exceptionally high areal capacitance of 16.76 F cm−2 at 5 mA cm−2. Meanwhile, the fabricated solid-state supercapacitor achieves an impressive energy density of 0.67 mWh cm−2 (8.38 mWh cm−3) at 2.5 mW cm−2 (31.25 mW cm−3), surpassing representative modified wood-based carbon electrodes by approximately 2–7 times. Additionally, the supercapacitor demonstrates exceptional stability, maintaining 96.21 % of capacitance even over 10,000 cycles. The parameters presented here demonstrate a significant improvement compared to those typically observed in most modified wood-derived carbon-based supercapacitors, effectively addressing common issues of low energy density and suboptimal cycling performance with wood carbon composites.

Pre-treated biomass waste melon peels for high energy density semi solid-state supercapacitors

Semi-solid-state supercapacitors employing highly porous activated carbon (AC) electrodes are promising, cost-effective, and environmentally friendly energy storage devices with exceptional power performance. In this work, for the first time in literature, we report a comparative study on different pre-treatments made on melon waste starting precursor to produce hierarchical large surface area porous AC. Also, for the first time in our knowledge, a gel polymer electrolyte (GPE) consisting in lithium trifluoromethanesulfonate in ethylmethylimidazolium trifluoromethanesulfonate, with a high ionic conductivity (∼3.3 × 10−3 S cm−1) and a working voltage window of ∼3.9 V vs Ag/Ag+, was used. The supercapacitors were electrochemically characterized with electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge tests. The working voltage window of the device was optimized in the range of 0–2.3V. Hydrothermally pre-treated AC-based supercapacitor is characterized by the best performance in terms of capacitance (∼161–170 F g−1), specific energy (29–31.34 Wh kg−1), and power density (839–860 W kg−1) at 1 A g−1. Supercapacitors based on ACs pre-treated via hydrothermal and ethanol soaking outperform devices based on simple chemically/physically ACs in rate performance, while hydrothermally pre-treated AC demonstrates superior stability over 8000 cycles, exhibits initial 15 % capacitance fading and coulombic efficiency close to 99–100 %.

PVA-based Hydrogel Materials for Underwater Energy Storage and Underwater Sensing.

As human exploration of marine continues to expand, the demand for underwater devices is also increasing. The unique properties of hydrogel materials make them well-suited for underwater applications. We propose a multi-functional polyvinyl alcohol (PVA) - NaCl @ Polyaniline (PANI) (PNP) hydrogel, which is characterized by easy fabrication, integrated structure, and flexibility, and can be directly applied in the fields of underwater energy storage and underwater sensing. Solid-state supercapacitors fabricated by the PNP hydrogel, due to integrated and all-solid-state design, can be charged and discharged underwater without encapsulation. What's more, the PNP supercapacitor can maintain a capacitance retention rate of over 90% after 5,000 cycles in simulated seawater, eliminating concerns about the hydrogel's dehydration when used underwater. The PNP hydrogel with an integrated three-layer structure can also be applied to the capacitive pressure sensors, which can also be directly used in underwater environments without the need for encapsulation, significantly reducing the structural complexity and preparation steps of the device. Finally, we demonstrate a "supercapacitor module"with a voltage window greater than 1.6 V created by directly connecting multiple PNP supercapacitors in series, as well as an underwater intelligent glove, providing new solutions for underwater energy storage and underwater wearable sensing applications.

Stable Efficient Solid-State Supercapacitors and Dye-Sensitized Solar Cells Using Ionic Liquid-Doped Solid Biopolymer Electrolyte.

As synthetic and nonbiodegradable compounds are becoming a great challenge for the environment, developing polymer electrolytes using naturally occurring biodegradable polymers has drawn considerable research interest to replace traditional aqueous electrolytes and synthetic polymer-based polymer electrolytes. This study shows the development of a highly conducting ionic liquid (1-hexyl-3-methylimidazolium iodide)-doped corn starch-based polymer electrolyte. A simple solution cast method is used to prepare biopolymer-based polymer electrolytes and characterized using different electrical, structural, and photoelectrochemical studies. Prepared polymer electrolytes are optimized based on ionic conductivity, which shows an ionic conductivity as high as 1.90 × 10-3 S/cm. Fourier transform infrared spectroscopy (FTIR) confirms the complexation and composite nature, while X-ray diffraction (XRD) and polarized optical microscopy (POM) affirm the reduction of crystallinity in biopolymer electrolytes after doping with ionic liquid (IL). Thermal and photoelectrochemical studies further affirm that synthesized material is well stable above 200 °C and shows a wide electrochemical window of 3.91 V. The ionic transference number measurement (t ion) confirms the predominance of ionic charge carriers in the present system. An electric double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC) were fabricated by using the highest conducting corn starch polymer electrolyte. The fabricated EDLC and DSSC delivered an average specific capacitance of 130 F/g and an efficiency of 1.73% in one sun condition, respectively.

Facile combustion synthesis of Granular-like La1-xSrxMnO3 Perovskites as electrode material for supercapacitor application

This study focuses on synthesizing a series of perovskite-type La1-xSrxMnO3 materials using a solution combustion method to investigate the impact of varying concentrations of La and Sr. The samples were prepared with different La and Sr concentrations (La1-xSrxMnO3, X = 0, 0.2, 0.4, 0.6, and 0.8) and labeled as LSMO-2 (La0.8Sr0.2MnO3), LSMO-3 (La0.6Sr0.4MnO3), LSMO-4 (La0.4Sr0.6MnO3), LSMO-5 (La0.2Sr0.8MnO3. The structural, morphological, and compositional characteristics of the synthesized electrodes were thoroughly analyzed. X-ray diffraction (XRD) confirmed the formation of a rhombohedral structure with an R-3c space group, while Fourier-transform infrared spectroscopy (FT-IR) verified the presence of all functional groups in the samples. Field emission scanning electron microscopy (FE-SEM) revealed a cluster of nanopowder morphology, and compositional analysis further validated the formation of the prepared samples. The electrodes were then screen-printed onto Ni-foam and evaluated for their electrochemical performance. Notably, the La1-xSrxMnO3 electrode demonstrated a high specific capacitance of 1271.5 F/g at a current density of 10 mA/cm2 and maintained 83.45 % cyclic stability after 10,000 cycles. Moreover, the power law was employed to investigate the charge storage mechanism of the LMSO-4 electrode. To assess the practical application potential of the La1-xSrxMnO3 electrode, a solid-state supercapacitor device was fabricated, and its performance was investigated. The device achieved a maximum specific capacitance of 206 F/g at 5 mA, with an energy density of 16 Wh/kg and a power density of 2400 W/kg, retaining 94 % of its performance after 5000 cycles. Overall, La1-xSrxMnO3 electrodes show great promise as materials for supercapacitor applications due to their impressive electrochemical properties.

Soy protein isolate–based gel polymer electrolyte for flexible solid-state supercapacitor

At present, the polymer matrices of most polymer electrolytes are derived from petroleum-based synthetic polymers. Herein, sustainable and renewable soy protein isolate (SPI) was grafted with methacrylic acid (MAA) and then cross-linked by ring-opening reaction with polyethylene glycol diglycidyl ether as cross-linking agent to obtain a biomass-based polymer electrolyte. Results show that when the added amount of MAA is twice the quality of SPI, gel polymer electrolyte displays the best comprehensive properties and presents the highest ionic conductivity of 5.24 × 10−3 S/cm. The flexible supercapacitor was fabricated by using SPI-based gel polymer electrolyte with activated carbon electrodes, which exhibited excellent specific capacitance (128.63 F/g) and energy density (9.52 Wh/kg) at 0.5 A/g with a decent capacitance retention of 93% after 5000 charge–discharge cycles. It can be ascribed that grafting modification of SPI improves the interface performance of electrode–polymer electrolyte. Furthermore, potassium iodide is introduced to form a redox polymer electrolyte to achieve a high-energy-density supercapacitor, which provides outstanding energy density of 24.40 Wh/kg at 1.0 A/g. This work demonstrates that sustainable and renewable biomass can be converted into matrix of polymer electrolyte for high performance supercapacitor based on aqueous polymer electrolyte.

Hollow Prussian blue analogue–derived (CoFe)Se2 composites: Structural designing for preparing flexible, high-performance solid-state supercapacitors

Selenides show higher corrosion and oxidation resistance than conventional materials. Moreover, bimetallic selenide materials typically show higher electrical conductivity than monometallic materials, which accelerates their electron transfer kinetics during charge–discharge cycling. The combination of two different metals in bimetallic selenides improves the energy-storage capacity and provides a stable electrochemical environment resulting from their unique electronic structure and interaction with the electrolyte. Among various bimetallic selenides, cobalt–iron selenides are especially noted for their excellent electrocatalytic properties. In this study, we synthesised co-doped hollow Prussian blue (PB) analogue nanocubes with large sizes, high specific surface areas and many active sites. When employed as the positive electrode in a flexible solid-state supercapacitor, bimetallic (CoFe)Se2 nanocomposites obtained at 500°C in nitrogen showed high supercapacitor performance, with a capacitance of 1710 F g−1 at 1 A g−1; extended cycle life (maintaining 98.5 % of their initial capacitance after 3000 cycles at 5 A g−1) and near 100 % Coulombic efficiency. Further, a flexible asymmetric supercapacitor ((CoFe)Se2//activated carbon (AC)) was developed using AC and (CoFe)Se2 as the negative and positive electrodes, respectively. (CoFe)Se2//AC achieved a Coulombic efficiency of 90 % and outstanding cycling stability, maintaining 93.5 % of its original capacity after 10,000 cycles at 5 A g−1. The specific capacitance and energy density were 40 F g−1 at 1 A g−1 and 750 W kg−1 (10.41 W kg−1), respectively. This research paves the way for rational and environmentally friendly synthesis of bimetallic selenides with distinct sizes and topologies. By varying the metal dopant, our method can potentially produce bimetallic selenides for diverse applications.

Coaxial direct writing of ultra-strong supercapacitors with braided continuous carbon fiber based electrodes

Supercapacitors produced based on 3D printing technology greatly expand the range of materials and geometric complexity. However, the production of fiber-based supercapacitors typicallyrequires subsequent steps. For the first time, we report a coaxial direct writing technique that enables the one-step fabrication of braided flexible solid-state supercapacitors. Continuous carbon fiber is used as a flexible substrate. α-manganese dioxide nanowires and activated carbon are used as active materials. The entire electrode assembly is coated with solid-state electrolyte and then braided. Through coaxial direct writing technology, the braided electrodes and sealings can be extruded by a coaxial nozzle to continuously print free-form ultra-strong supercapacitors with a tensile strength of the braided electrodes up to 636 MPa. Electrochemical measurement results show that the printed capacitor exhibits an excellent specific capacitance, and it still maintains a capacitance retention of 90.1% after 1000 cycles. The supercapacitor exhibits nearly identical electrochemical capacitive characteristics at various bent angles. This work paves the way for integrating enhanced durability and adaptability into next-generation wearable and portable electronic systems.

Effect of processing parameters on the properties of carbon paper as a free-standing supercapacitor electrode

As newly emerging energy storage devices, supercapacitors are being investigated thoroughly by researchers. Free-standing electrode is one of the major research focuses in this area, which not only avoids the use of resistive binders but also simplifies device assembly. The study describes the synthesis and study of carbon fiber-based carbon carbon composite paper (heat treated to different temperatures) as a free-standing supercapacitor electrode. Due to the inert nature of carbon paper, it was activated to create defect sites and to increase the specific surface area. Electrochemical studies suggested that activated carbon paper heat treated to 750°C (ACP-750) exhibited the highest areal capacitance of 11.4 F/cm2 (422.2 F/g) at the current density 2.5 mA/cm2 (0.09 A/g), probably due to the generation of larger number of defect sites (as depicted by XRD and RAMAN studies). ACP-750 electrode was used to fabricate the solid-state symmetric supercapacitor device that exhibited an energy density 0.77 Wh/cm2 at a power density of 2.34 W/cm2. The electrode was allowed to age (ACPA-750), after which it exhibited enhanced specific capacitance of 16.8 F/cm2 (622.2 F/g) at a current density 2.5 mA/cm2. ACPA-750//ACPA-750 device delivered maximum energy density of 1.66Wh/cm2 at a power density of 3 W/cm2. The device exhibited a coulombic efficiency of 96.1% and capacitance retention of 89% after 10,000 cycles.

Enhancing the electrochemical performance of a nickel molybdenum nitride for an energy storage device using cobalt nitride and phosphorus doping

Compared to traditional energy storage devices, hybrid solid-state supercapacitors have gained a lot of attention because of their exceptional power, energy density and outstanding cyclic stability. Transition metal nitrides are eminent candidates with high-performance electrochemical properties for energy storage devices. In this work, a high-performance CoN/NiMoN interface with P-doping was prepared by a simple feasible strategy for the positive electrode of a supercapacitor. The electrochemical performance in a 2 M KOH electrolyte revealed a specific capacity of 2070C·g−1 at a 5 A·g−1, which is exceptional compared to recently reported literature. Encapsulating NiMoN with CoN and its P-doping, resulting in a three-dimensional structure with desirable textural properties and easy permeation of electrolyte, enhances the electrochemical performances prepared electrode. Further, a hybrid solid-state supercapacitor was prepared with P-CoN/NiMoN (positive) and activated carbon (negative) as a electrodes. The prepared P-CoN/NiMoN//activated carbon supercapacitor showed an operating potential window of 1.7 V with an admirable specific capacity of 573.99C·g−1, for 135.5 Wh·kg−1 energy and 850 W·kg−1 power density at a 1 A·g−1. The results provide a feasible strategy to prepare and modify the electrochemical properties of NiMoN by CoN encapsulation and P-doping. The method gives insights for the preparation of other transition metal nitrides for high-density energy storage without much change in the power density.

Hydrogen bond crosslinking hydrogel for high-performance ultra-low temperature MXene-based solid state supercapacitors

The electrochemical performance of aqueous electrolytes at low temperatures is frequently suboptimal due to their low freezing point (0 °C). In this study, we constructed MXene-based ultra-low temperature polyvinyl alcohol/nanocellulose-H2SO4 (PVA/CNF-H2SO4) hydrogel electrolytes utilising hydrogen bonding between water molecules and nanocellulose. The process results in a reduction in the amount of free water present in the hydrogel electrolyte, lowering its freezing point to -77.35 °C. PVA/CNF-H2SO4-based solid-state supercapacitors (C7-SSC) demonstrate a capacitance of up to 813 mF cm-2 at -50 °C, exhibiting high-rate performance at low temperatures. The capacitance remains at 45 F g-¹ at a current density of 20 A g-¹. The maximum areal energy and power densities of our C7-SSC achieve 113 μWh cm-² and 0.4 μW cm-² at -50 °C, respectively, surpassing the majority of state-of-the-art devices. This work provides new insights into MXene-based hydrogel manufacturing and expands the range of potential applications for such materials.

Hierarchical 2D/1D MOFs/electrospun ZIF-67 modified carbon nanofibers heterostructure electrode for high-performance asymmetric supercapacitor

In this paper, a 2 dimensional (2D) metal–organic frameworks (MOFs) nanosheets grown on 1D ZIF-67 modified carbon nanofibers (CNFs) was designed and fabricated with a hierarchical heterostructure. The hierarchical 2D/1D MOFs/CCNF offers rich electrochemical active sites and favorable ion/electron diffusion pathways. The synergistic effect of Co, CNFs and MOFs from heterostructures contributes to superb electrochemical activities. Benefiting from the hierarchical heterostructures optimized by the mass ratio of ZIF-67/PAN and CCNF/NiMOF as well as the type of substrates, CCNF-20@MOF showed a specific capacity of 361.50 C g−1 at 0.5 A g−1, whose charge storage mechanism is dominated by diffusion control. Meanwhile, a bamboo-derived carbon material (BBC) was designed in the solid-state asymmetric supercapacitor (CCNF-20@MOF//BBC). The device exhibited an energy density of 38.89 Wh kg−1 at the power density of 800.02 W kg−1 and excellent cycling stability, that exceed many MOFs based devices. Moreover, it could be successfully used for LED light-emitting, demonstrating a good application prospect. This work provides a feasible strategy for the improved performance of MOFs and CNFs based materials in the field of energy storage.

A Self-Healing and Sweat-Chargeable Hydrogel Electrolyte for All-in-One Flexible Supercapacitors.

Flexible solid-state supercapacitors (SCs) with hydrogel as an electrolyte and separator combine the advantages of wearability and energy storage and exhibit a broad application prospect in wearable energy textiles. However, irreversible electrolyte damage and unstable electrode-electrolyte interfaces during mechanical deformations remain bottlenecks in realizing truly wearable applications. Herein, poly(acrylic acid) (PAA)-Fe hydrogels were prepared through a simple thermal polymerization strategy. The dynamic reversible metal coordination bonds between Fe3+ and carboxylic acids confers the hydrogels with excellent self-healing properties. As expected, the prepared hydrogels exhibited superior mechanical strength (tensile stress of 45.80 kPa), ionic conductivity (0.076 S cm-1), and self-healing properties. Subsequently, the SCs were constructed using composite hydrogel electrodes (MnO2@CC embedded in the PAA-Fe hydrogels) as symmetrical electrodes (marked as MSCs). The reversible metal coordination bonds between composite hydrogel electrodes formed an ultrastable electrode/electrolyte interface in the all-in-one MSCs, thus revealing excellent mechanical durability. The all-in-one MSCs delivered a remarkable specific capacitance (30.98 F g-1 at 0.2 A g-1), excellent cyclic stability (87.24% after 5000 cycles), outstanding mechanical deformation stability, and impressive electrochemical output stability after self-healing (capacitance retention of 85.34% after five cycles of cutting/self-healing). It is noteworthy that the all-in-one MSCs employed NaCl as an electrolyte, which can be obtained from human sweat. As a proof of the self-charged concept, the all-in-one MSCs can be reused in sweat, whose capacitance was maintained at 90.05% of the initial state after three repetitions. This work is expected to shine light into the design of all-in-one and fabric-based SCs and the development of wearable energy textiles.

Theoretical and experimental studies on 2D β-NiS battery-type electrodes for high-performance supercapacitor

Recently, quirky features and eccentric structures of transition metal sulfides have grasped great attention to remove roadblocks and unwrap fresh avenues for electrodes in energy storage devices. Herein, we developed a 2D beta phase nickel sulfide nanosheets (2D β-NiS NSs) electrode with remarkable enhancement in charge storage properties. When served as active electrodes for electrochemical tests, 2D NiS NSs exhibited ultra-high capacitance of 2693 Fg−1 at 1 mVs−1 and specific capacity of 219 mAhg−1 at 1 Ag−1. The symmetric battery type solid-state supercapacitor device comprising 2D β-NiS NSs electrodes exhibits specific capacity of 83.43 mAhg−1at 2 Ag−1 over broad potential range of 0.7V with good cycling performance, and energy and power density of 28.9 Whkg−1 (@ 2 Ag−1) and 21 kWkg−1 (@ 6 Ag−1) respectively. Complementary first-principles density functional theory (DFT) calculations accomplished to explore the electrolyte ion interactions with nickel sulfide nanostructures defining 2D NiS NSs as a potential candidate for real-time applications.

Hydrothermally synthesized copper telluride nanoparticles: First approach to flexible solid-state symmetric supercapacitor

Supercapacitors, with their high-power density, rapid charge–discharge rates, and long cycle life, have emerged as promising energy storage devices for numerous applications. Among the various materials explored for supercapacitor electrodes, copper-based chalcogenides have gathered significant attention due to their intriguing electrochemical properties and simple synthesis routes. While there have been thorough investigations in other fields, only a limited number of studies have focused on the specific application of copper telluride nanoparticles as supercapacitors. In this study, we present a novel approach utilizing hydrothermally synthesized copper telluride (Cu2-xTe) nanoparticles as binder-free electrodes on flexible stainless steel (SS) substrates. The Cu2-xTe nanoparticles, with their small particle (38 nm) and highly crystalline structure, enhance charge storage and promotes a pseudocapacitive behavior, resulting in a high specific capacitance [381 F/g (163 mF/cm2) at 2 mV/s] in a 2 M KCl electrolyte solution. Moreover, we studied and explained the distinct contributions of surface-controlled and diffusion-limited processes to the overall charge storage capacity of the electrode. Our pioneering effort includes the fabrication and analysis of flexible, symmetric solid-state supercapacitor devices utilizing Cu2-xTe electrodes with PVA-LiClO4 gel electrolyte. These devices demonstrate an energy density of 11 Wh/kg, a power density of 800 W/kg, and an impressive 85 % retention of cyclic stability after 5000 cycles.