High-energy Asymmetric Supercapacitors Research Articles

Room temperature and rapid synthesis of ZnMn2O4 nanostructured spinel using deep eutectic solvent for high energy asymmetric supercapacitors

Recently, binary metal oxides have drawn significant attention due to their interesting physico-chemical characteristics, makes them suitable for supercapacitor application. In the present work, high surface area spinel ZnMn2O4 is prepared using a reaction of deep eutectic solvent (DES) containing zinc chloride, choline chloride and glycerol with manganese precursor (KMnO4). The DES serves as both precursor and template for the growth of ZnMn2O4. Interestingly, the spinel structure of ZnMn2O4 is prepared within one-minute time at room temperature using DES route makes this process cost-effective. The reaction between DES and manganese precursors can be halted at any stage with the addition of water to the reaction mixture as it reduces existing bonding interaction between the reactants. With this advantage, we have varied reaction time between DES and KMnO4 and further studied the effect of reaction time on surface area and electrochemical properties of the obtained ZnMn2O4. The ZnMn2O4 sample, where DES and KMnO4 reacted for 10 min (ZnMnO-10) showed highest surface area of 118.5 m2/g with a pore volume of 0.19 cm3/g. Further, the ZnMnO-10 sample showed a good specific capacitance of 499.58 F/g at 0.1 A/g in a neutral electrolyte (1 M Na2SO4). The symmetric supercapacitor device fabricated using ZnMnO-10//ZnMnO-10 with energy and power density of 39.40 Wh/kg and 7.06 kW/kg, respectively. Further, the asymmetric supercapacitor device is also assembled using ZnMn2O4 and agro waste-derived carbon (HBC-800) showed an excellent Csp of 331.24 F/g at 0.2 A/g with energy density and power density of 74.50 Wh/kg and 5.4 kW/kg, respectively. The current work proposes the rapid and facile synthesis of spinel ZnMn2O4 utilizing green DES and the obtained ZnMn2O4 showed good specific capacitance and energy density for both symmetric and asymmetric supercapacitor devices.

Preparation of sustainable and binder-free electrode materials for high energy asymmetric supercapacitor applications: A cleaner alternative

Herein, we demonstrate a pioneering method for repurposing one of the most abundant and noxious weeds (Parthenium hysterophorus or PH) derived ultrahigh surface area carbon as capacitive electrode and design high performance asymmetric supercapacitor with leveraging ternary metal oxides (TMO) (Ni–Co–Mn–O or TMO-1 and Ni–Co–Zn–O or TMO-2) as binder-free pseudocapacitive positive electrodes to improve the performance and efficiency of supercapacitors. Furthermore, the ternary metal oxides (TMO-1 and TMO-2) were synthesized using a one-pot hydrothermal method, followed by annealing. In a three-electrode configuration, both TMO-1 and TMO-2 exhibited remarkable capacitances. At a current density of 0.5 A/g, a total stored charge of 557.23 C/g and 628.22 C/g was obtained for the TMO-1 and TMO-2, respectively. The asymmetric construction using PH-900-K as the negative electrode and TMO-1 or TMO-2 as the positive electrode demonstrated a maximum energy density of 49.29 Wh/kg for the TMO-1//PH-900-K configuration. While the TMO-2//PH-900-K configuration exhibited a maximum energy density of 70.86 Wh/kg.

Rapid synthesis and characterizations of defect-enhanced WO3-δ thin film electrode for effective energy storage application in asymmetric supercapacitor devices

Oxygen vacancy-doped WO3-δ thin film electrode with improved conductivity and high areal capacitance was synthesized via mild electrochemical oxygen de-intercalation of electrodeposited WO3 thin film. The X-ray diffraction (XRD) analysis revealed the presence of monoclinic phase W18O49 of the doped thin film electrode. Raman spectroscopy analysis confirmed the presence of lower valence W5+ in the WO3-δ film. Electrical characterizations of doped WO3-δ and undoped WO3 films show that the doped electrode exhibits far lower sheet resistance and resistivity than the undoped WO3 sample. Mott-Schottky analysis of the samples shows that the vacancy-doped WO3-x possesses a higher donor concentration than the stoichiometric WO3. Electrochemical characterizations by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD,) and electrochemical impedance spectroscopy (EIS) confirmed the superior pseudocapacitive charge storage metrics via its improved volumetric capacitance of 366.12 F·cm−3 (16.0 mF·cm−2) and reduced equivalent series as well as charge transfer resistance over WO3 thin film. This study demonstrated the synthesis of oxygen vacancy-doped WO3-δ thin film using a homemade two-electrode cell facility instead of the popular energy-consuming vacuum-assisted film deposition under controlled-atmosphere conditions. Besides, the vacancy-doped WO3-δ electrode shows a strong charge storage capability in the far negative operating potential range, indicating its suitability as an anode electrode for fabricating high-energy asymmetric supercapacitors.

Porous NiCo2O4 electrodes for high-energy asymmetric supercapacitor: effect of annealing

Porous NiCo2O4 electrodes for high-energy asymmetric supercapacitor: effect of annealing

Construction of Hierarchical NiCoP@NiFe‐LDH Nanoflakes Heterostructure for High Energy Asymmetric Supercapacitor

Construction of Hierarchical NiCoP@NiFe‐LDH Nanoflakes Heterostructure for High Energy Asymmetric Supercapacitor

A High-Energy Asymmetric Supercapacitor Based on Tomato-Leaf-Derived Hierarchical Porous Activated Carbon and Electrochemically Deposited Polyaniline Electrodes for Battery-Free Heart-Pulse-Rate Monitoring.

A simple and scalable method to fabricate a novel high-energy asymmetric supercapacitor using tomato-leaf-derived hierarchical porous activated carbon (TAC) and electrochemically deposited polyaniline (PANI) for a battery-free heart-pulse-rate monitor is reported. In this study, TAC is prepared by simple pyrolysis, exhibiting nanosheet-type morphology and a high specific surface area of ≈1440 m2 g-1 , and PANI is electrochemically deposited onto carbon cloth. The TAC- and PANI- based asymmetric supercapacitor demonstrates an electrochemical performance superior to that of symmetric supercapacitors, delivering a high specific capacitance of 248 mF cm-2 at a current density of 1.0mA cm-2 . The developed asymmetric supercapacitor shows a high energy density of 270 µWh cm-2 at a power density of 1400 µW cm-2 , as well as an excellent cyclic stability of ≈95% capacitance retention after 10000 charging-discharging cycles while maintaining ≈98% Coulombic efficiency. Impressively, the series-connected asymmetric supercapacitors can operate a battery-free heart-pulse-rate monitor extremely efficiently upon solar-panel charging under regular laboratory illumination.

3D Ti3C2TX@PANI-reduced graphene oxide hydrogel and defective reduced graphene oxide hydrogel as anode and cathode for high-energy asymmetric supercapacitor

The rational constructions of asymmetric supercapacitors (ASCs) by extending the operating potential window has been verified as an effective tactic to break through the energy density of the device. In this work, Ti3C2TX @polyaniline (PANI) heterostructure is successfully synthesized by uniformly depositing PANI nanorods onto the surface of Ti3C2TX nanosheets through polymer polymerization, then via a low-temperature hydrothermal graphene oxide (GO)-gelation process, Ti3C2TX @PANI is assembled into a three-dimensional (3D) porous hydrogel. The resultant Ti3C2TX @PANI-reduced graphene oxide (RGO) hydrogel exhibits a high specific capacitance of 617.84 F g−1 at 0.5 A g−1. Separately, a defective reduced graphene oxide (DRGO) hydrogel is prepared by a cost-effective cobalt-catalyzed gasification procedure, which shows a higher specific capacitance (237.62 F g−1 at 0.5 A g−1) than that of untreated RGO hydrogel (158 F g−1). Finally, Ti3C2TX @PANI-RGO and DRGO are used as anode and cathode to construct the Ti3C2TX @PANI-RGO//DRGO ASC device, which features a stable operating voltage (−1.6 to 0.2 V), an ultra-high energy density (269.18 Wh kg−1 at 527.72 W kg−1 and 77.90 Wh kg−1 at 12,409.04 W kg−1), and durable cycling property (retaining 92.52% capacitance after 10,000 cycles at 10 A g−1). This research emphasizes the extraordinary superiority of Ti3C2TX-based structures for the construction of high-energy ASCs.

Controllable synthesis of vanadium-doped nickel-chalcogenide/graphene cathodes and MnV2O6·2H2O/graphene anode for high-energy asymmetric supercapacitors

Exploring novel electrode materials with rational morphology and structure is crucial for the fabrication of high-performance supercapacitors. In this work, novel vanadium-doped nickel-chalcogenide/reduced graphene oxide cathodes (NiV-S/rGO and NiV-Se/rGO) and MnV2O6·2H2O/rGO anode are controllably prepared through a facile solvothermal method. Benefiting from the two-dimensional structure and desirable surface electronic environment, the graphene-supported NiV-X/rGO (X = S and Se) cathodes exhibit outstanding capacitive performance (1734.2 and 1577.2C·g−1 at 2 A·g−1), remarkable cycling stability and exceptional rate performance. Meanwhile, with the encapsulation of graphene protect layers, the MnV2O6·2H2O/rGO anode also shows a significantly enhanced specific capacity and superb cycling stability (95.8 % retention after 10,000 cycles). When assembled into asymmetric supercapacitors, the NiV-S/rGO//MnV2O6·2H2O/rGO and NiV-Se/rGO//MnV2O6·2H2O/rGO devices not only exhibit ultra-high energy densities (82.4 and 60.0 Wh·kg−1 at a power density of 800.0 W·kg−1), but also display superior cycling stabilities (91.5 % and 93.7 % retention after 10,000 cycles). These excellent properties demonstrate their potential application prospect in supercapacitor with high energy densities.

High-Energy Asymmetric Supercapacitor Based on the Nickel Cobalt Oxide (NiCo2O4) Nanostructure Material and Activated Carbon Derived from Cocoa Pods

Nickel cobalt oxide (NiCo2O4) nanoagglomerates were effectively synthesized through a simplistic low-temperature co-precipitation technique. The obtained material was further calcined to enhance its morphological properties and reduce the size of its individual particle of agglomerates. The as-synthesized NiCo2O4 agglomerates were characterized through the employment of various techniques, which include scanning/transmission electron microscopies (SEM/TEM), X-ray diffraction, Raman spectroscopy and X-ray fluorescence spectroscopy (XRF), and thermogravimetric analysis (TGA). Electrochemical performances of the as-synthesized electrode materials evaluated in a three-electrode configuration could deliver an optimized specific capacity of 95.6 mA h g–1 at a 0.5 A g–1 specific current. A fabricated hybrid asymmetric supercapacitor (SC) composed of NiCo2O4 and the activated carbon obtained from cocoa pods (Cocoa AC-700) as the positive and negative electrodes (NiCo2O4//AC cocoa-700), respectively, delivered a specific capacity of around 168.7 mA h g–1 at 0.5 A g–1 and a corresponding specific energy and power of 47.7 W h kg–1 and 430.0 W kg–1, respectively. The SC exhibited a substantial cycling stability, resulting in a Coulombic efficiency of 97.2% with a related capacity retention of 96.6% recorded after a cycling test of over 11,000 cycles at 5 A g–1.

Wood based biochar supported MnO2 nanorods for high energy asymmetric supercapacitor applications

Eco-friendly Acacia leucophloea wood sawdust based Biochar (BC) is used as a substrate material to support nanorod-like MnO2 through an easy-to-operate in-situ redox reaction between the biochar and KMnO4. The physical and chemical properties of the prepared materials are characterized by using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) with EDAX, X-ray Photoelectron Spectroscopy (XPS), BET surface area with BJH pore size distribution and bio-logic electrochemical analyzer. The XRD result reveals the bare manganese oxide has tetragonal phase group with the space group of I4/m. FESEM image of BC and BC@MnO2 materials exhibits highly porous nature and bundle of nanorod like morphologies respectively. The XPS result reveals the chemical bonding and oxidation state of BC@MnO2 nanocomposite material. The N2 adsorption and desorption result reveals that the prepared materials BC, MnO2 and BC@MnO2 exhibit high surface area of 550, 152.3 and 613.8 m2 /g respectively. Electrochemical properties are characterized by three and two electrode set-up. The BC@MnO2 composite electrode exhibits high specific capacitance of 512 Fg−1 at 0.5 Ag−1 and cyclic stability of 93% after 10,000 cycles. The assembled ASC cell BC@MnO2//AC delivers high specific capacitance of 209 Fg−1 at 0.5Ag−1and cyclic stability of 97.1% after 10,000 cycles. Further, ASC cell exhibits huge energy density of 74.3 Whkg−1 and power density of 1996.4 Wkg−1 at 0.5 Ag−1.

Binder-free polyaniline sheathed crumpled cobalt diselenide nanoparticles as an advanced electrode for high specific energy asymmetric supercapacitor

Herein, we report for the first time a novel and binder-free polyaniline sheathed 3D crumpled CoSe2 nanoparticles on Ni foam (PANI/CoSe2/NF) electrode was developed by a simple co-electrodeposition method for supercapacitor application. The as-electrodeposited 3D CoSe2 with PANI sheets on Ni foam morphology was confirmed through in-depth material characterizations. The PANI/CoSe2/NF as supercapacitor electrode delivered a superior specific capacitance of 1980 F g−1 or 3825 F g−1 (with the integral area) and a specific capacity of 792 C g−1 at 2 A g−1 in a three-electrode cell configuration. The assembled PANI/CoSe2/NF//sulfonated activated carbon from oak nutshell (AC) hybrid supercapacitor cell delivered excellent specific energy of 118 Wh kg−1 and good cyclic stability by retaining 82% of initial capacitance after 10,000 charge-discharge cycles. The high electrochemical performance of the electrode is due to the synergistic effect between PANI and CoSe2 nanostructures, high electrical conductivity, and hydrophilic functional groups of PANI contributing to the low internal resistance and effective diffusion of ions. These results demonstrate that the PANI/CoSe2/NF, with its unique 3D morphology, has great potential in energy applications.

Phosphine-Based Porous Organic Polymer/rGO Composite Anode and α-MnO2 Nanowire Cathode Cooperatively Enabling High-Voltage Aqueous Asymmetric Supercapacitors

Aqueous supercapacitors often yield a restricted cell voltage, resulting in a low specific energy, due to unwanted water electrolysis and a narrow electrode potential range. Herein, a novel hierarchical nanostructured phosphine based porous organic polymer (PP)/reduced graphene oxide (rGO) aerogel composite anode is fabricated. Benefitting from the excellent electrical conductivity and ultra-thin protection layer of rGO aerogel, PP/rGO could extend the potential window to -1.0-0 V, exhibiting significantly enhanced specific capacitance (380.2 F/g@2 A/g) and good rate capability (165.0 F/g@4 A/g). To complement the wide potential window, α-MnO2 nanowire is employed as cathode due to its large and stable potential window (0 to 0.8 V). Remarkably, a 2 V aqueous PP/rGO//α-MnO2 asymmetric supercapacitor (ASC) is successfully fabricated, exhibiting a high specific energy of 39 Wh/kg with extraordinary cycling stability and rate capability (96% retention after 10000 cycles), outperforming most of the previously reported rGO based ASCs. Furthermore, a coin-type PP/rGO//α-MnO2 ASC device is further fabricated that can illuminate a red LED for 3 mins, demonstrating its great potential for practical application. The knowledge gained in this study using in situ formed hetero-nanostructure to expand the voltage window will open up new possibilities for electrode design targeting a widen potential window and high energy ASCs.

Synergistic engineering of fluorine doping and oxygen vacancies towards high-energy and long-lifespan flexible solid-state asymmetric supercapacitor

The low electron conductivity and scarce electrochemically active sites impede the practical application of bimetal oxides for supercapacitors. Herein, fluorine-doped and oxygen vacancy–enrich NiMoO4 (F-NiMoO4-x) nanosheet arrays are constructed via facile hydrothermal and wet chemical reduction processes on carbon cloth fibers (CFC). The structural and electronic properties in F-NiMoO4-x can be modulated by the synergistic effect of dopant F and O vacancies to boost the electrical conductivity and enhance Faradaic redox sites. The obtained flexible F-NiMoO4-x@CFC as a self-supporting electrode can provide superior areal capacitance of 2.45 F cm−2 at 1 mA cm−2, 6-fold higher than that of pristine NiMoO4@CFC electrode. Moreover, the assembled flexible solid-state asymmetric supercapacitor (ASC) delivers an impressive energy density of 336.5 μWh cm−2 at a power density of 1790 μW cm−2 with a wide voltage window of 1.8 V. Moreover, the ASC can work at different bending angels with an ultralong and stable lifespan.

Marigold flower like structured Cu2NiSnS4 electrode for high energy asymmetric solid state supercapacitors

The growth in energy devices and the role of supercapacitors are increasingly important in today’s world. Designing an electrode material for supercapacitors using metals that have high performance, superior structure, are eco-friendly, inexpensive and highly abundant is essentially required for commercialization. In this point of view, quaternary chalcogenide Cu2NiSnS4 with fascinating marigold flower like microstructured electrodes are synthesized using different concentrations of citric acid (0, 0.05 M, 0.1 M and 0.2 M) by employing solvothermal method. The electrode materials physicochemical characteristics are deliberated in detail using the basic characterization techniques. The electrochemical studies revealed better electrochemical performances, in particular, Cu2NiSnS4@0.1 M-CA electrode revealed high 1029 F/g specific capacitance at 0.5 A/g current density. Further, it retained 78.65% capacity over 5000 cycles. To prove the practical applicability, a full-cell asymmetric solid-state device is fabricated, and it delivered 41.25 Wh/Kg and 750 Wh/Kg energy and power density at 0.5 A/g. The optimum citric acid added Cu2NiSnS4 electrode is shown to be a promising candidate for supercapacitor applications.

MoO2 coated few layers of MoS2 and FeS2 nanoflower decorated S-doped graphene interoverlapped network for high-energy asymmetric supercapacitor

Herein, the ultra-thin layer MoS2 coverd MoO2 nanocrystal arraying on sulfur-doped graphene framework (MoS2-MoO2/3DSG) is obtained via a simple hydrothermal procedure accompanied with high temperature annealing. Sodium thiosulfate and ethanethiol are used as sulfur sources to form three-dimensional sulfur doped graphene (3DSG) in the hydrothermal process. Importantly, MoO2 nano-particles are uniformly loaded on MoS2 nanosheets and 3DSG via in-situ collaborative technology. As a result, the stable conductive network take full use of the characteristics of high specific capacitance of MoO2 nanoparticles, convenient ion transport channel of two-dimensional MoS2 nanoflakes and efficient charge transfer and cross-linked 3DSG to improve the electrochemical activity and enhance the dynamics of electrons / ions, which is up to 1150.37 F g−1 specific capacitance and maintains 94.6% of the original capacitance after 10,000 cycles. Also, FeS2 nanoflowers in situ loading on 3DSG (FeS2/3DSG) with enhanced the overall performance of the device are fabricated. The asymmetric supercapacitor with the positive electrode of MoS2-MoO2/3DSG and the negative electrode of FeS2/3DSG can work efficiently and stably under the voltage of 1.7 V, and provide energy density of 87.38 Wh kg−1 at the power density of 683.94 Wkg−1, displaying an outstanding application prospect for energy storage.

High specific energy asymmetric supercapacitor based on alpha-manganese dioxide/activated expanded graphite composite and activated carbon-polyvinyl alcohol

Abstract In this study, alpha-manganese dioxide/activated expanded graphite (α-MnO2/AEG) composite was successfully synthesized using simple hydrothermal method. Morphology, structure, elemental composition and specific surface area of the material were characterised by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) spectroscopy, Raman spectroscopy, infrared Fourier transform spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) method. Electrochemical evaluations were achieved using three- and two-electrode configurations in 1 M Na2SO4 electrolyte. The maximum specific capacitance of 185.5 F g−1 at 1 A g−1 was recorded for three-electrode measurements. The half-cell retained an efficiency of 99.7% over 2000 cycles at 5 A g−1. The fabricated device using α-MnO2/AEG composite and activated carbon-polyvinyl alcohol (AC-PVA) as positive and negative electrodes, respectively, showed a remarkable capacitive property with a specific energy of 33 Wh kg−1 and specific power of 999 W kg−1 at 1 A g−1 within 2.0 V cell potential. Great stability of 97.8% was observed at a specific current of 5 A g−1 for over 10, 000 cycles. Further stability of the device was confirmed by performing a voltage holding of up to 70 h and retained 70% of its initial capacitance at 5 A g−1.

Ultrathin porous Mn(PO3)2 nanosheets and MoO2 nanocrystal arrays on N, P-dual-doped graphene for high-energy asymmetric supercapacitors

Recently, heteroatom doped graphene based architectures exhibit promising prospects in the commercial application of supercapacitors because of their higher electrical conductivity and a wider potential window. Herein, we report on ultrathin porous nanosheets Mn(PO3)2 and MoO2 nanocrystal array on N, P dual-doped graphene (NPG) framework and study their supercapacitor properties. The irregularly overhead Mn(PO3)2 present a unique structure, which provide clear electron/ion transport channels to accelerate charge transfer together with the three-dimensional NPG structure. The obtained Mn(PO3)2/NPG hybrid electrode exhibit an extraordinary specific capacity (2073.4F g−1, 1 A g−1) and good rate performance (capacity retention rate of 77.8% from 1 A g−1 to 20 A g−1). In addition, the 3D NPG coated with MoO2 nanocrystal have also made a great progress in electrochemical performance of large capacitance and merely 5.54% fading capacitance after 10,000 cycles. Subsequently, the asymmetric supercapacitor (ASC) hybrid devices based on Mn(PO3)2/NPG as the positive electrode and MoO2/NPG as the negative electrode has a wide voltage range of 0 ~ 1.8 V, delivers an excellent CF value of 213.8F g−1 and keeps 91.5% initial capacitance retention after 10,000 cycles. Furthermore, the as-prepared ASC also obtains an outstanding energy density of 96.2 W h kg−1 at a power performance of 726.73 W kg−1, which demonstrate that the reasonable conductive network of Mn(PO3)2/NPG//MoO2/NPG devices can greatly increase the utilization of active substances, improve the performance in all aspects and open up new avenues of the future application and development of supercapacitors.

Incorporation of electroactive NiCo2S4 and Fe2O3 into graphene aerogel for high-energy asymmetric supercapacitor

Incorporation of electroactive Fe2O3 and NiCo2S4 (NCS) into graphene aeorgel (GA) is presented in this work. The efficient adsorption of precursor ions on the graphene oxides sheets and subsequent hydrothermal gelation yield the GA-Fe2O3 and GA-NCS composites that can be used as negative and positive electrode, respectively, for constructing a high-energy asymmetric supercapacitor (ASC). Influences of mass contents of Fe2O3 and NCS on capacitive performances of GA-Fe2O3 and GA-NCS electrodes are systematically investigated in KOH aqueous electrolyte. The uniform distribution of Fe2O3 on the graphene sheets (GS) and the NCS nanoparticles wrapped by GS provide sufficient electroactive sites for Faradaic redox reactions, while the GA interconnected with macropores offers favorable channels for electrolyte transport. Thereby, the specific capacitance of 200 F g−1 (178 C g−1) and 386 F g−1 (170 C g−1) are achieved for GA-Fe2O3 (20 wt% Fe2O3) and GA-NCS (77 wt% NCS), respectively. A coin-type capacitor built with GA-Fe2O3 as negative electrode and GA-NCS as positive electrode delivers a specific capacitance of 93 F g−1 (128 C g−1) at 0.1 A g−1, corresponding to a maximum energy density of 25 Wh kg−1 at a power density of 54 W kg−1. Meanwhile, the ASC also exhibits a good rate capability and a satisfying cycling stability with 72.3 % capacitance retention after cycling at 2 A g−1 for 5000 cycles. These results show great potentials of GA-Fe2O3 and GA-NCS electrodes in electrochemical energy storage.

Construction of FeNiP@CoNi-layered double hydroxide hybrid nanosheets on carbon cloth for high energy asymmetric supercapacitors

The rational design and fabrication of flexible pseudocapacitive materials with high energy density and superior cycling stability is desirable to high-performance supercapacitors. A hybrid FeNiP@CoNi-LDH assembled from FeNiP nanosheets and CoNi-LDH nanosheets have been vertically grown on carbon cloth via a sequential hydrothermal reaction, phosphorization treatment and electrodeposition strategy. The as-prepared FeNiP@CoNi-LDH possesses a large surface area, 3D interconnected nanosheet arrays architecture, hierarchical pore structure, and abundant active sites with multiple valances, which provides rapid electron and mass transfer channels within its conducive network. Impressively, as a binder-free electrode for supercapacitors, the FeNiP@CoNi-LDH electrode exhibits a high specific capacitance of 2280.6 F g−1 at a current density of 1 A g−1, outstanding rate capability (1222.2 F g−1 at 20 A g−1), and significantly improved cyclic stability (70.4% capacitance retention after 5000 cycles) compared to pure FeNiP and CoNi-LDH nanosheets, owing to its well-designed nanostructure and synergetic effect between two well-matched pseudocapacitive materials. Besides, an aqueous asymmetric supercapacitor device based on FeNiP@CoNi-LDH and porous carbon delivers a maximum energy density of 87.3 Wh kg−1 at a power density of 408.8 W kg−1, and an excellent cycling stability with a capacitance retention of 73.9% after 20,000 cycles.

Hierarchically structured spherical nickel cobalt layered double hydroxides particles grown on biomass porous carbon as an advanced electrode for high specific energy asymmetric supercapacitor

Abstract Nickel cobalt layered double hydroxides (NiCo-LDHs) as electroactive material of supercapacitor have attracted a lot of attention during the recent years because of their high theoretical specific capacitance (3000 F g−1), environmental friendliness, and low cost. However, the low electrical conductivity of the NiCo-LDHs and thus leading to low rate capability and poor cycling stability limit their commercial application in practical supercapacitor. Herein, biomass porous carbon (BPC) with a high specific surface area is used as a conductive carbon layer, and the NiCo-LDHs/BPC composite, in which nickel-cobalt layered double hydroxides (NiCo-LDHs) with hierarchically structured spherical morphology which is consisted of self-assembled homogeneous nanosheets, are anchored on the surface of BPC by a facile solvothermal method. At the same time, the effects of nickel-cobalt molar ratio (R) on the electrochemical properties of the NiCo-LDHs/BPC composite are detailedly studied. It has been found that the NiCo-LDHs-1/BPC electrode (R = 1:0.5) possesses a high specific capacitance of 2047 F g−1 at 1 A g−1 due to synergistic effect between LDHs and BPC. And even at a high current density of 20 A g−1, NiCo-LDHs/BPC electrode still has a high specific capacitance of 1539 F g−1. Besides, the asymmetric supercapacitor based on the NiCo-LDHs-1/BPC cathode and the BPC/PPy anode delivers a high specific capacitance of 139 F g−1 at 1 A g−1, a high specific energy of 49 W h kg−1 at 1 A g−1, and good cycling performance (∼75.8% retention after 6000 cycles).