Solid-state Supercapacitor Device Research Articles

The fabrication of bowl-shaped polypyrrole/graphene nanostructural electrodes and its application in all-solid-state supercapacitor devices

Conductive polymers (CPs) have potential for commercial energy storage applications because of their high electrochemical activity and low cost. However, one of the obstacles in developing CPs based supercapacitors is to overcome the capacitance degradation during the charge-discharge process, along with the poor rate performance. In this work, a unique bowl-shaped graphene/polypyrrole (PPy) nanostructure is uniformly grown on a graphite substrate by two facile electrochemical steps. The graphene is uniformly coated by PPy layers, while the thickness of the PPy layer depends on deposition time. The unique structural design for the PPy layer exhibits a significant influence on its electrochemical properties, and competitive performance is achieved by the GP-1200 based supercapacitor devices. It exhibits a maximum energy density of 5.18 mWh·cm−3 and a maximum power density of 250.5 mW cm−3, which are both comparable to values obtained from other solid-state supercapacitor devices.

Self-assembled nis-sns heterostructure via facile successive adsorption and reaction method for high-performance solid-state asymmetric supercapacitors

Herein, a green, scalable and template-free deposition of self-assembled NiS-SnS (NTS) heterostructure is proposed by using SILAR (successive ionic layer adsorption and reaction method on a nickel foam substrate). In the assembled solid-state asymmetric supercapacitor devices, electrode materials of NTS hetero-structure exhibit remarkable high specific capacitance value of 1653 Fg−1 at a current density of 1 Ag−1, significant-high energy density of 83 Whkg−1 at a power density of 117 Wkg−1 with excellent rate capability and cyclic stability (98 % after 4000 cycles). Moreover, NTS heterostructures with high performance are highly efficient to lighten commercial light-emitting diode, substantiating that SILAR based formation of NTS hetero-structure is promising for the next generation superior supercapacitor devices.

Synthesis of Ce-V-Mo Oxide Nanocomposite for High Performance All Solid State Asymmetric Supercapacitors (ASSASs)

The depletion of non-renewable resources has prompted the continuous development of various energy storage systems to manage the world’s increasing demand for energy. Among the well-known energy storage systems, supercapacitors (SCs) exhibit superior performance because they can store more energy than conventional capacitors and have a higher power density than batteries. In this context, we have strategically synthesized ternary Ce-V-Mo oxide (CVMO) nanocomposite and directly utilized it in all solid state supercapacitor device. The phase purity, element composition and surface morphology were characterized by PXRD, EDS, FESEM, HRTEM and XPS measurements. The pseudocapacitive charge storage efficiency of CVMO was thoroughly studied by CV, GCD and EIS measurements. The CVMO offers a specific capacitance value of 5484 F g–1 at scan rate of 5 mV s–1 and 4330 F g–1 at a current density 4 Ag–1. The CVMO also retains ~87% of specific capacitance at a high current density of 20 A g–1. The EIS study shows low solution and charge transfer resistance of CVMO. An ASSAS device fabricated using N-rGO as the negative electrode material shows high rate capacitance, and superior energy density at elevated power density condition. The results presented here is significant in the context of developing high performance ASSASC devices for numerous technological viability.1-5

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.

Hierarchical WS2@NiCo2O4 Core-shell Heterostructure Arrays Supported on Carbon Cloth as High-Performance Electrodes for Symmetric Flexible Supercapacitors.

Nowadays, rationally preparing heterostructure materials can not only make up for the shortage of individual components, but also exert unexpected performance through synergistic interactions between the components. Herein, a core–shell of WS2@NiCo2O4 screw-like heterostructure arrays grown on carbon cloth (CC) was prepared by a two-step solvothermal method for supercapacitors. As a binder-free flexible electrode, a high areal capacitance of 2449.9 mF cm–2 can be achieved for WS2@NiCo2O4/CC at a current density of 1 mA cm–2. Benefiting from the core–shell of the WS2@NiCo2O4 heterostructure, the capacitive property of the flexible WS2@NiCo2O4/CC electrode is better than those of WS2/CC and NiCo2O4/CC electrodes. Based on WS2@NiCo2O4/CC electrodes, the assembled flexible solid-state symmetric supercapacitor (FSS) device shows a high energy density of ∼45.67 W h kg–1 at a power density of 992.83 W kg–1. Meantime, the WS2@NiCo2O4/CC-assembled FSS device also exhibits high cycling stability with an excellent capacity retention of ∼85.59% after 5000 cycles.

Solid-state symmetric supercapacitor based on Y doped Sr(OH)2 using SILAR method

Supercapacitor is one of the most promising and emerging type of energy storage devices having the merits of both conventional battery and traditional capacitor. In this regard, we have deposited Yttrium doped Strontium hydroxide thin films on stainless steel substrate with the help of a facile, cost-effective successive ionic layer adsorption and reaction technique at room temperature without using any binder. Doping of Yttrium into Strontium hydroxide enhances both electronic conductivity and electrochemical performance of the electrode for energy storage. Nanorods like structure with the tuberose morphology has been obtained with the help of field emission scanning electron microscopy. The cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements show the pseudocapacitive battery like response. Among all the synthesised materials, 1.0 at. % Yttrium doped Strontium hydroxide shows a high specific capacity of 705.3 C g−1 at 0.4 mA current rate and stability of ∼82% at 2.5 mA current rate. The prototype light-weight solid-state symmetric supercapacitor device of Yttrium doped Strontium hydroxide electrodes has been fabricated by sandwiching PVA-Na2SO4 gel. Thus, we observe that this device has potential applications for the next-generation cost effective energy storage system.

Facile synthesis of Mn-doped NiCo2O4nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo2O4) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo2O4 NPs show an excellent specific capacity of 417 C g-1 at a scan rate of 10 mV s-1 and 204.3 C g-1 at a current density of 1 A g-1 in a standard three-electrode configuration, ca. 152-466% higher than that of pristine NiCo2O4 or MnCo2O4. In addition, Mn-doped NiCo2O4 NPs showed an excellent capacitance retention of 99% after 1000 charge-discharge cycles at a current density of 2 A g-1. The symmetric solid-state supercapacitor device assembled using this material delivered an energy density of 0.87 μW h cm-2 at a power density of 25 μW h cm-2 and 0.39 μW h cm-2 at a high power density of 500 μW h cm-2. The cost-effective synthesis and high electrochemical performance suggest that Mn-doped NiCo2O4 is a promising material for supercapacitors.

Improving the rate capability of ultrathin NiCo-LDH nanoflakes and FeOOH nanosheets on surface electrochemically modified graphite fibers for flexible asymmetric supercapacitors

A fiber asymmetric supercapacitor system is designed with NiCo-LDH nanoflakes and FeOOH nanosheets anchored on electrochemically activated graphite fibers as positive electrode and negative electrode, respectively. Due to the formation of COMetal bonding, the oxygen-functionalized carbon on electrochemically activated graphite fibers can bind strongly with NiCo-LDH and FeOOH, which assists in establishing the fast electron transfer routes and fluent ion transport avenues. Both NiCo-LDH and FeOOH anchored on electrochemically activated graphite fibers display a high rate performance, 80% and 87.3% of the electric capacity can be reserved with the current density increasing from 2 to 20 A g−1 and 2 to 10 A g−1, respectively, while the NiCo-LDH and FeOOH deposited on untreated graphite fibers can only retain 45% and 40%. The fabricated novel solid-state fiber asymmetric supercapacitor device exhibits an expanded operation potential window of 1.8 V with a maximum energy density (130 W h kg−1) when the power density is 1.8 kW kg−1. Furthermore, a high energy density (81 W h kg−1) is still achieved at a superhigh power density (10.8 kW kg−1). Additionally, a good cycling stability of the solid-state fiber asymmetric supercapacitor can be obtained (90% capacity retention after 10,000 cycles).

Intercalation pseudocapacitance in chemically stable Au-α-Fe2O3-Mn3O4 composite nanorod: Towards highly efficient solid-state symmetric supercapacitor device

Pseudocapacitance generally appears due to the surface or near-surface reversible Faradaic reactions. In this regard, 2D layered materials have gained substantial attention as a potential source for driving a myriad of energy storage applications owing to their unique surface-structure relationship. Here, we have demonstrated that a pseudocapacitive mechanism becomes increasingly operative when H+ ions are intercalated easily into the enhanced van der Waals gap of layered material α-Fe2O3 in Au-α-Fe2O3-Mn3O4 nanocomposite. Theoretical studies have shown an enhancement of van der Waals gap which is attributed to the intercalation of Au into the layers of α-Fe2O3. Structural and compositional characterizations have been carried out in detailed by different physical methods and are supported by theoretical studies. Electrochemical measurements show excellent specific capacitance of 580 F g−1 at 1 A g−1 along with improved capacity retention compared to the mother component α-Fe2O3 (205 F g−1 at 1 A g−1) in 0.5 M H2SO4 electrolyte in a potential window of 1.2 V. Further, electrokinetic measurements revealed that total charge stored in the nanocomposite is based on a dominant capacitive mechanism (70% of the total capacitance) along with diffusive mechanism (30% of the total capacitance) at scan rate 5 mV s−1 whereas, α-Fe2O3 exhibits 34% capacitive and 66% diffusive at same scan rate. The synthesized composite nanorod as an efficient electrode material in a solid-state symmetric supercapacitor device exhibits excellent energy density of 36.12 Wh kg−1 and power density of 1994 W kg−1 at 1 A g−1 and 10 A g−1, respectively with outstanding stability (89%) up to 2000 successive charge-discharge cycles at 10 A g−1. This work may offer a new scope for further development of intercalation pseudocapacitive nanomaterials towards achieving high energy storage supercapacitors.

Fabrication of ZIF-67 Derived Co3S4-WS2 Heterostructures for All-Solid-State Symmetrical Supercapacitors

Development and modification of the existing material for renewable energy area is gaining its significance however a long way to get commercialization. Transition metal dichalcogenides (TMDs) are gaining interest rapidly in the field of supercapacitors due to their 2D layered morphology, however loses interest for long cyclic stability. Herein we employed hollow Co3S4 microspheres using nitrogen rich ZIF-67 as a precursor. Furthermore, these hollow Co3S4 microspheres are insitu modified by covering with WS2 nanostructures to enhance its energy density. The obtained Co3S4/WS2 composite when employed as an electrode, delivers the specific capacitance of 412.7 F/g at the current density of 1 A/g. Furthermore, the Co3S4/WS2 composite electrodes are used to fabricate an all solid-state symmetrical supercapacitor device, exhibiting a wide potential window of 2 V. The assembled device delivers a very high energy density of 70.7 Wh/kg along with a high-power density of 10.2 kW/kg. The excellent electrochemical performance with 92 % capacity retention proves its potential toward the practical application. The high value of specific capacitance and splendid cycle stability is attributed to the synergy of high surface area ZIF-67 derived Co3S4 microsphere with 2D networked WS2 material.

Hierarchical NiMn-layered double hydroxides@CuO core-shell heterostructure in-situ generated on Cu(OH)2 nanorod arrays for high performance supercapacitors

Supercapacitors are attracting tremendous research interest because they are expected to achieve battery-level energy density while having long calendar life and short charging time. Ultrathin layered double hydroxide nanosheets (LDHs) are promising candidates as electrode materials for energy storage. Herein, we have successfully designed and synthesized a hierarchical NiMn-LDH@CuO/CF core-shell heterostructure which comprises a vertical and intercrossing ultrathin NiMn-LDHs nanosheets shell and a slightly curly and tops tangled CuO nanowires core. The synthesized NiMn-LDH@CuO/CF electrode exhibits a high areal capacitance of 6077 mF cm−2 (2430.8 F g−1) at a current density of 2 mA cm−2 (0.8 A g−1), which is significant higher than those of CF, Cu(OH)2/CF, CuO/CF, NiMn-LDH/CF and NiMn-LDH electrodes. Moreover, a superior cycling stability of 89.22% retention after 8000 cycles at a high current density of 50 mA cm−2 is observed and a low internal resistance Rs (0.584 Ω) can be achieved. Furthermore, an all solid-state asymmetric supercapacitor (ASC) device based on the as-synthesized hierarchical NiMn-LDH@CuO/CF core-shell heterostructure hybrid material as positive electrode and activated carbon as negative electrode is successfully fabricated and exhibits an energy density of 10.8 W h kg−1 at a power density of 100 W kg−1. Additionally, a LED indicator can be lit up for eight minutes when three ASCs are connected in series. The excellent electrochemical performances can be credited to the significant enhancement of the specific surface area, charge transport and mechanical stability resulted from the ultrathin LDH shell, the highly conductive CuO nanowires core-shell nanostructure. This strategy for the fabrication of hierarchical core-shell heterostructure could have enormous potential for applications in high performance energy storage devices.

Self-Standing Metallic Mesh with MnO2 Multiscale Microstructures for High-Capacity Flexible Transparent Energy Storage.

Flexible transparent electrochemical supercapacitors are critical components for the rapid development of fully flexible transparent electronics; however, typical flexible transparent supercapacitor electrodes store limited energy due to the requirements of transparency. Self-standing core-shell structure metal oxide mesh electrodes with metal oxide as active "shell" and metallic mesh as current collector "core" are efficient for simultaneously achieving high capacity, flexibility, and transparency. In this work, we perform a morphology-controlled electrodeposition of MnO2 on a self-standing flexible transparent metallic Ni mesh electrode to achieve a high-capacity flexible transparent supercapacitor electrode. Under optimized conditions, the MnO2 nanosheet-composed flowerlike multiscale microstructure was constructed. The open, loose, and porous MnO2 multiscale microstructure "shell" and high electrical conductivity of self-standing metallic mesh "core" synergistically enable efficient ionic and electronic transport and meanwhile retain high structural stability. The metal oxide mesh electrode yields an outstanding areal capacitance of 1.15 F/cm2 at an optical transmittance of 69.4% and excellent cycling stability. The symmetric solid-state supercapacitor device exhibits a high areal capacitance value (78.46 mF/cm2), superior cycling life, as well as high optical transmittance and mechanical flexibility, superior to the most reported flexible transparent supercapacitors. This work provides a comprehensive understanding on how to achieve high-capacity flexible transparent supercapacitor electrodes and solid-state devices.

Cobalt-nickel silicate hydroxide on amorphous carbon derived from bamboo leaves for hybrid supercapacitors

3D hierarchical cobalt-nickel silicate hydroxide/C (CoxNi3−xSi2O5(OH)4, denoted as CoNiSi) composites are derived from bamboo leaves and explored as electrode materials for supercapacitor. The CoNiSi architectures with hierarchical petal-like shapes are in-situ generated on 3D amorphous carbon derived from bamboo leaves using the biomass-inherent SiO2 species as the silicon source. The CoNiSi/C electrode shows a 3D hierarchical porous structure, high specific surface area and remarkable electrochemical performance with 226 F g−1 at 0.5 A g−1 in the voltage window of −0.8 ~ 0.6 V, which is superior to the specific capacitances of SiO2/C, CoSi/C, NiSi/C and even the reported values of silicates-based materials. It also achieves excellent cycling performance with 99% after 10,000 cycles. Moreover, a high-performance solid-state hybrid supercapacitor (HSC) device is fabricated by CoNiSi/C and Ni(OH)2. This HSC device achieves an outstanding electrochemical performance with the capacitance up to 254 mF cm−2 (64 F g−1) at 2 mA cm−2, and the energy density up to 0.793 Wh m−2 (20.0 Wh kg−1) at 3.75 W m−2 (94.5 W kg−1), which are higher than a majority of former SCs based on silicates. Besides, the HSC device shows good cycle stability with 82% after 10,000 cycles and can light the red LED lasting for more than 2 min. These features demonstrate that the 3D CoNiSi/C architectures can be considered as a promising and efficient material for SCs with high performance.

Self-supporting graphene aerogel electrode intensified by NiCo2S4 nanoparticles for asymmetric supercapacitor

Transition bimetallic nickel cobalt sulfide has attracted extensive attention as a novel electrode for supercapacitors. In this study, facial solvothermal method is applied to prepare NiCo2S4 nanoparticles and nanosheets immobilized on graphene aerogel (NiCo2S4/GA). The microstructure of NiCo2S4 is significantly affected by altering the pH of the solution. Typically, the uniformly dispersed NiCo2S4 nanoparticles with diameter 25.94 nm are successfully grown on GA when the solution pH is 8.2. The NiCo2S4/GA electrode delivers an improved specific capacitance of 704.34 F g−1 at 1 A g−1, and maintains a favorable rate capability of 60.1% at 10 A g−1. Moreover, 80.3% of the initial specific capacitance is maintained after 1500 cycles at 2 A g−1. The impressive electrochemical performance results from the NiCo2S4 with high capacitance and GA with three-dimensional porous nanostructure, which can not only reduce the contact resistance but also efficiently shorten the electron and ion transport path. Furthermore, the solid-state asymmetric supercapacitor device based on NiCo2S4/GA electrode can present energy density of 20.9 Wh kg−1 at a power density of 800.2 W kg−1 and desirable cycling stability, showing the great application potential in the field of energy storage devices.

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.

Solid-state graphene-based supercapacitor with high-density energy storage using ionic liquid gel electrolyte: electrochemical properties and performance in storing solar electricity

The electrochemical properties and high-density energy storage performance of graphene nano-platelet-based solid-state electrical double-layer supercapacitor device are reported. The graphene device is fabricated with electrolyte comprising of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) room temperature ionic liquid and LiClO4 dopant entrapped within polymer matrix formulated as a gel. The mesoporous graphene electrode was formed via dispersion in amorphous polyvinylidene (PVdF2) host over flexible graphite sheets with minimal graphene layer (< 5-layer) stacking. Exploiting the abundance of charge ion species in the ionic liquid gel electrolyte and pervasive accesses to the graphene platelets via voids, high double-layer specific capacitance of 214 Fg−1 was realized based on cyclic voltammetry data. Impedance studies show a low (0.79 Ω cm2) charge transfer resistance and a short Warburg range indicating highly diffusive ionic transport capability in the ionic liquid gel electrolyte. The Bode analysis showed high figure of merit for pulse power with 1145 ms response time and high-density (27 kWkg−1) pulsed power capability of the graphene supercapacitor. The charge–discharge data show graphene supercapacitor by availing high (~ 2 V) stable potential window in ionic liquid electrolyte gel greatly boosted the energy density to 33.3 Whkg−1 at power density 3 kWkg−1 with minimal decrement to 24.7 Whkg−1 at high ~ 3 Ag−1 discharge current density. By integration with solar cells, direct storage of light-generated electricity and discharge behavior of ionic liquid electrolyte graphene supercapacitor is reported.

Novel chemical route for CeO2/MWCNTs composite towards highly bendable solid-state supercapacitor device

Electrode materials having high capacitance with outstanding stability are the critical issues for the development of flexible supercapacitors (SCs), which have recently received increasing attention. To meet these demands, coating of CeO2 nanoparticles have been performed onto MWCNTs by using facile chemical bath deposition (CBD) method. The formed CeO2/MWCNTs nanocomposite exhibits excellent electrochemical specific capacitance of 1215.7 F/g with 92.3% remarkable cyclic stability at 10000 cycles. Light-weight flexible symmetric solid-state supercapacitor (FSSC) device have been engineered by sandwiching PVA-LiClO4 gel between two CeO2/MWCNTs electrodes which exhibit an excellent supercapacitive performance owing to the integration of pseudocapacitive CeO2 nanoparticles onto electrochemical double layer capacitance (EDLC) behaved MWCNTs complex web-like structure. Remarkable specific capacitance of 486.5 F/g with much higher energy density of 85.7 Wh/kg shows the inherent potential of the fabricated device. Moreover, the low internal resistance adds exceptional stability along with unperturbed behavior even under high mechanical stress which can explore its applicability towards high-performance flexible supercapacitor for advanced portable electronic devices.

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo 2 O 4 electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo 2 O 4 /Ni@NF) shows the superior specific capacity of 1142 C g −1 at 1 A g −1 with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g −1 . These values are about 3.7 times higher than that of the electrode (NiCo 2 O 4 @NF) without a seed layer, which shows the specific capacity of 305 C g −1 @1 A g −1 with cycle stability of 84% even at a lower current density of 1 A g −1 . The enhanced performance of the NiCo 2 O 4 /Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo 2 O 4 /Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe 2 O 3 nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo 2 O 4 /Ni20@NF//rGO-Fe 2 O 3 @NF asymmetric solid state device delivers an areal capacitance of 446 mF cm −2 with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm −2 (at 3.58 kW cm −2 ) and power density of 14.88 kW cm −2 (at 31.41 Wh cm −2 ).

Flexible heat-treated PAN nanofiber/MoO2/MoS2 composites as high performance supercapacitor electrodes

We have synthesized heat-treated PAN/MoO2/MoS2 (PMOS) ternary structure nanofibers by facile solvothermal approach and in-situ conversion reaction. At discharge current density of 1 A/g, the synthesized hierarchical flexible fibers exhibit high specific capacitance of 439.8 F/g. A lightweight and small asymmetric supercapacitor device based on heat-treated PMOS nanofibers//active carbon (AC) delivers a ultrahigh energy density of 46 Wh/kg at power density of 2246.9 W/kg, and long-term capacity retention of about 98.9% after 2000 cycles. Remarkably, the solid-state asymmetric supercapacitor device could light up a LED belt, and no significant change in the brightness and duration when the device bends into a ring, indicating that the material has perfect flexibility and stability. These encouraging findings indicate that the heat-treated PMOS composite electrodes may have a promising potential application for advanced energy storage devices in modern electronic industries.