High-performance Solid-state Supercapacitors Research Articles

Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo2O4 In Situ Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors.

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g-1 (1503.3 C g-1) at 1 A g-1, a superior rate performance of 2335.2 F g-1 at 20 A g-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg-1 at a power density of 800 W kg-1, and the energy density at a peak power density of 20004 W kg-1 still remained at 48.9 Wh kg-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.

Engineered nano-architecture for enhanced energy storage capabilities of MoS2/CNT-heterostructures: A potential supercapacitor electrode

Hydrothermal synthesis was utilized to achieve the direct growth of molybdenum disulphide (MoS2) nanoflakes on carbon nanotubes (CNT). Through this method, MoS2/CNT heterostructures with engineered microstructure have been obtained by suitably optimizing the synthesis conditions. Raman, X-ray photoelectron spectroscopy, and electron microscopy have been utilized to characterize the heterostructure. The present study investigated the influence of varying amounts of CNT and MoS2 within the heterostructure on its electrochemical properties. The optimization of the heterostructure morphology has resulted in enhanced electrochemical performance, with a high specific capacitance of ∼436 F/g at 1 A/g, along with good rate capability. The charge storage mechanism was explained by using Dunn's power law. Further, the MoS2/CNT heterostructure was employed to fabricate a solid-state symmetric supercapacitor. The device exhibited a specific capacitance of ∼164 F/g at 1 A/g, along with good cyclic stability, retaining 96 % of its capacitance after 1000 cycles. Additionally, the device demonstrated high energy and power density values of ∼27 Wh/Kg and 603 W/Kg, respectively. The present study indicates that the MoS2/CNT heterostructure holds great promise as an electrode material for high-performance solid-state supercapacitor devices.

Unification of DAQ-rGO-PEDOT as binder-free ternary nanocomposite electrode for high performance solid-state symmetrical supercapacitor

A high energy density hybrid supercapacitor has been developed from highly π-conjugated 1,4-diaminioanthraquinone covalently bonded to reduced graphene oxide (DAQ:rGO). The drop casting of DAQ:rGO suspension onto nanostructured PEDOT matrixes has enhanced the microstructure/orderliness, higher homogeneity as confirmed by Raman, FE-SEM and HRTEM studies. The high gravimetric capacitance (622.4 F g−1 at 1 A g−1) emerges from extensively porous matrix of nanostructured PEDOT and low band gap of DAQ:rGO evident from a voltage window of -0.2 to 0.8 V facilitating the redox activity of DAQ. In addition, solid-state symmetric supercapacitor based on ternary electrode with free standing PVA-H2SO4 gel electrolyte possesses specific capacitance of 492.5 F g−1 at 1.5 A g−1 with exceptional energy density (68.39 W h kg−1) and excellent cyclic stability (retaining 100% capacitance after 10,000 cycles. The ability of the four devices to illuminate the LED for 120 s manifests utility of the nanocomposite for future microelectronics.

Synthesis and performance assessment of silica dispersed nano-composite polymer gel electrolyte for high-performance solid-state supercapacitors

Nano-composite polymer gel electrolyte (NCPGE) films are prepared by incorporating liquid electrolyte (EC-PC-TEABF4) into polyvinyldinefloroide co-hexafluoropropylene (PVDF-HFP) polymer with dispersed SiO2 nano-particles using solution cast technique. The NCPGE is optimized for the highest ionic conductivity by varying wt% of SiO2 nanoparticles in PGE [(1:4){PVDF-HFP + EC-PC-TEABF4}]. Highest conductivity of 8.2 × 10−3 Scm−1 is found for optimized composition [(1:4){PVDF-HFP + EC-PC-TEABF4} + SiO2 (15 wt%)] of NCPGE. Structural and morphological studies have been done using XRD, FTIR, and SEM. Frequency dependent dielectric behaviour is understood using dielectric constant and modulus analysis in a wide range of frequencies. The ionic transference number is 0.96 and an electrochemical potential window of ∼ 3.5 V has been obtained. Fabrication of electric double layer capacitor (EDLC) is done by sandwiching NCPGE between activated carbon (AC) electrodes. The electrochemical performance of fabricated supercapacitor is evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge techniques. Results show significant improvement in the quality of synthesized electrolyte.

Construction of high-performance solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/CuS positive electrode and Fe2O3@rGO negative electrode

The reasonable and logical construction of electrode materials along with greater electrochemical features and solid architectural design is an effective strategy for boosting the electrochemical performance of supercapacitors. In this paper, Ti3C2Tx MXene/CuS composites have been synthesized using an electrostatic attraction connection of negatively charged 2D few-layered Ti3C2Tx MXene sheets with positively charged CuS nanoparticles and are investigated as an asymmetric supercapacitor active material. The addition of MXene enhances the conductivity and specific surface area of the MXene/CuS electrode compared to their individual components. The as-prepared MXene/CuS electrode exhibits a high specific capacity (1541.6C g−1 (2569.3 F g−1)) at 1 A g−1 and an excellent cycle performance with 93.5 % capacity retention after 10,000 cycles. Furthermore, Fe2O3 nanoparticles/reduced graphene oxide (rGO) nanosheets (Fe2O3@rGO) composite electrode is also produced. The designed Fe2O3@rGO negative electrode with a wide operation voltage window of 1.1 V can deliver a capacity of 255.6C g−1 at 1 A g−1. Ultimately, the MXene/CuS//Fe2O3@rGO device displays energy density of 74.1 Wh kg−1 and power density of 849.8 W kg−1. In addition, the ASC shows excellent cycling stability of 91.3 % capacity retention after 10,000 cycles.

High-performance solid-state asymmetric Supercapacitor based on α-Fe2O3/r-GO/GCN composite electrode material for energy storage application

Herein, a 3D/2D/2D of α-Fe2O3/r-GO/GCN composites were synthesized by combined reflux condensation and sonochemical-assisted wet-impregnation techniques. The physicochemical properties of the prepared materials were inspected by various analytical techniques. Morphology analysis techniques of different electron microscopes were employed to confirm the rhombohedral (3D) and two-dimensional (2D) sheets' morphology. The electrochemical behaviour of the as-synthesised electrode materials was assessed for use in a redox electrolyte-based energy storage system. Electrochemical measurements in a 6M KOH solution revealed that the electrode exhibited good supercapacitive behaviour. The 3D/2D/2D -α-Fe2O3/r-GO/GCN composite had a higher capacitance rate of roughly 810 F g−1 than α-Fe2O3 nanoparticles at 1Ag−1. From cyclic stability, ternary composite has good cyclic retention (98.9%) after 10,000 cycles at 10 Ag−1. The surface characteristics of metal oxide nanostructures and the efficient conductive networks of r-GO and GCN sheets are primarily responsible for the ternary α-Fe2O3/r-GO/GCN composite's superior electrochemical performance. Asymmetric supercapacitor (ASC) devices were constructed using 3D/2D/2D anodic material and activated carbon as a cathode material with a power density of 929 Wkg−1, energy density of 40 WhKg−1, and 92 % of capacity retention.

Defective core–shell NiCo2S4/MnO2 nanocomposites for high performance solid-state hybrid supercapacitors

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo2S4/MnO2 core–shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO2 is well coated on the core-NiCo2S4. The hierarchical core–shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo2S4/MnO2 electrode of reduction for 60 min (NiCo2S4/MnO2-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo2S4/MnO2-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm−2 couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo2S4/MnO2-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg−1 at a power density of 384.21 W·kg−1 and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm−2 after 10,000 cycles. In general, the work demonstrates the significance of NiCo2S4/MnO2-60 as a highly redox active electrode material for future practical application in supercapacitors.

VARTM-assisted high-performance solid-state structural supercapacitor device based on the synergistic effect of Ni(OH)2-Co3S4 nanocomposite for widened potential window and charge storage mechanism

Herein, we synthesized Ni(OH)2-Co3S4 nanocomposite through facile hydrothermal synthesis, where Ni(OH)2 NPs interact synergistically with Co3S4 layers. Remarkably, the interaction of Co3S4 NPs influenced the Ni-O bond interface, and synergistic impact stimulated the development of defects and ultimately improved the characteristics of the Ni(OH)2-Co3S4 NCs. The results indicate that at a current density of 2 A/g, the specific capacitance of Ni(OH)2-Co3S4 nanocomposites using a three-electrode system was twice that of Co3S4 nanoparticles and three times that of Ni(OH)2 nanoparticles, measuring 1187.05 F/g, 573.33 F/g, and 435.20 F/g, respectively. Similarly, Ni(OH)2-Co3S4 NCs electrodes retained the capacitance over 10,000 cycles with 92% stability. Further practical applicability was demonstrated by growing NCs on woven carbon fiber, and the structured supercapacitor device was fabricated using the VARTM technique, yielding a specific capacitance of 0.92 F/cm2 at 0.20 A/cm2. This device exhibited a maximum energy density of 74.30 Wh/kg at a power density of 500 W/kg and maintained excellent cycle stability for up to 100,000 cycles, retaining 48% of its initial capacitance. These outcomes emphasize the significance of interfacial nanoengineering and give essential information for building energy storage devices for the future.

Nitrogen and oxygen codoped porous carbon based on a synthetic polymer for high-performance solid-state supercapacitors

Most commercial supercapacitors are fabricated using porous carbon; however, their energy densities are relatively low. To further improve the energy storage performance of supercapacitors assembled using carbon materials, a novel synthetic polymer-derived carbon (SPMA-BQ-x-T) material was prepared by a facile and low-cost strategy. The SPMA-BQ-x-T materials exhibit coexistent structure of micropores and mesopores, homogeneous N, O codoping, and connected spherical morphology. In addition, although SPMA-BQ-x-T materials have low N-doping content (<2 %), they show large specific surface area of approximately 2000 m2 g−1, which maybe partly attribute to the abundance CN single bonds existed in the precursor of SPMA-BQ. They are further used as the electrode materials in supercapacitors. The electrodes (SPMA-BQ-5-800) prepared under the optimal conditions show a high specific capacitance of 414.6 F g−1 at 0.5 A g−1 in a three-electrode system and 254 F g−1 at 0.5 A g−1 in solid-state supercapacitors (SSCs). The SSCs also display high energy density, long-term cycling stability, and good rate capability, suggesting their application potential in energy storage fields. This work achieves good electrochemical effect without pursuing high N-doping content by using a facile and low-cost preparation strategy, which has certain significance for the trade-off of specific surface area and N-doping content.

High-performance solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/VS2 cathode and Fe3O4@rGO hydrogel anode

Herein, we report the synthesis of MXene/VS2 composites for asymmetric supercapacitors using a hydrothermal method. Impressively, the resulting MXene/VS2 electrode shows an outstanding specific capacity of 895.7 C g−1 (1791.4 F g−1) at 1 A g−1, rate capability (587.5 C g−1 (1175.0 F g−1) at 20 A g−1), and cycle performance (90.6% capacity retention after 10,000 cycles), owing to its specific microstructures with connected nanosheets and enhanced electrochemical conductivity arising from the synergistic effect of VS2 and conductive MXene. To achieve higher energy density in the solid-state asymmetric supercapacitor (ASC) device, Fe3O4 nanoparticles uniformly dispersed and encapsulated into the rGO sheets (Fe3O4@rGO) as a negative electrode is also designed. The obtained MXene/VS2 was used as a cathode and Fe3O4@rGO acted as a anode. Further, an assembled MXene/VS2//Fe3O4@rGO ASC device delivered an impressive specific capacitance of 365.4 C g−1 (228.4 F g−1) at 1 A g−1, in addition, the device yielded the specific energy of up to 73.9 Wh kg−1 at the corresponding specific power of 728.2 W kg−1 with superior cycling performance (90.7% capacity retention after 10,000 cycles at 8 A g−1), demonstrating its high potential for applications in high-porformance energy storage devices.

Direct growth of hierarchically SnS2 layered nanostructure on nickel foam for high-performance solid-state supercapacitors

SnS2 is a promising candidate for an electrode material in lithium-ion batteries and photocatalysts due to its high accessible surface area and significant interlayer nanostructure. Here, we have synthesized hierarchically SnS2 layered nanostructure developed on nickel foam through a facile one-step template-free solvothermal process. FESEM images show the two-dimensional (2D) layer structure of SnS2 arranged in a flower petallike configuration. Further, the electrochemical properties of hierarchically SnS2 were investigated in 1 M KOH electrolyte for supercapacitor (SC) implementation. Synthesized SnS2 electrode material shows excellent specific capacitance of 604F g−1 at 1 mVs−1 and better cyclic stability of 86.2 % over 3000 cycles because the unique layered nanostructure increases the active sites and ion/electron transfer at the electrolyte/electrode interface. The hierarchically structured SnS2 electrode and its potential practical applications were tested by fabricating an SSC device to effectively light a commercial light-emitting diode (LED). This research shows that layered 3D SnS2 electrodes are a promising technology for sustainable energy storage applications. The above results indicated that hierarchically SnS2 with a 2D layered structure has a huge capability as an electrode material for high-performance SC applications and a promising potential for future energy storage devices.

ZIF-67 derived NiCoP nanosheets on carbon cloth as a flexible cathode for high-performance solid-state asymmetric supercapacitors

Herein, unique bimetallic phosphide of NiCoP with nanosheet structure coated on carbon cloth (NiCoP@CC) was synthesized. Three-dimensional cobalt-based ZIF-67 (Co-ZIF-67) with dodecahedron morphology was first grown on carbon cloth, and then the NiCoP nanosheets were formed through a synthesis procedure involving Ni2+-induced template scarification of the Co-ZIF-67 and the phosphorization calcination. Impressively, the resulting NiCoP@CC electrode shows a remarkable specific capacity of 1149.2 C g−1 (6.09 C cm−2) at 1 A g−1 and superior cycle performance (the capacity retains 99.7 % after cycled for 10,000 cycles at 6 A g−1), owing to the optimized ZIF-67-template modification, unique morphology, good electronic conductivity, superiority of the bimetallic phosphides, and the battery type feature. Further, a solid-state asymmetric supercapacitor (ASC) was fabricated by using the obtained NiCoP@CC as the cathode and using active carbon (AC) as the anode. The assembled ASC device delivers a high specific energy of 78.5 Wh kg−1 at the specific power of 799.5 W kg−1, and remains 90.3 % capacity retention over 10,000 cycles at 8 A g−1, demonstrating its high potential for applications in the field of high-capacity supercapacitors. These results illustrate the promise of NiCoP@CC as a promising cathode material in supercapacitor.

In-situ construction of carbon cloth-supported amorphous/crystalline hybrid NiCo-sulfide with permeable concrete-like morphology for high-performance solid-state hybrid supercapacitors

Constructing the amorphous/crystalline hybrid materials has been proved to be an effective strategy to boost the specific capacity, rate capability, and cycle durability of supercapacitors. Presently, the amorphous/crystalline hybrid materials are generally constructed by simply overlaying one amorphous material on or under another crystalline material. In this work, we successfully constructed carbon cloth-supported amorphous/crystalline hybrid NiCo-sulfide with a permeable concrete-like morphology (NiCo-sulfide@CCH) by in-suit partially converting the crystalline NiCo-sulfide into the amorphous phase in a specially-made quartz reactor. The obtained NiCo-sulfide@CCH material exhibits a high specific capacity of 250.16 mAh/g (1801.13F g−1 or 900.6C g−1) at 1 A/g, outstanding cycle stability, and good rate capability. The solid-state hybrid supercapacitor (SSHSC) device based on the prepared NiCo-sulfide@CCH material delivers high specific energy of 57.71 Wh kg−1 at a specific power of 1.56 kW kg−1 with remarkable specific energy retention of 97.9 % after 5000 cycles. The developed scheme is expected to promote the application of the amorphous/crystalline hybrid materials in high-performance supercapacitors.

(Ni,Co)Se2 nanoparticles on vertical graphene nanosheets@carbon microtubes for high-performance solid-state asymmetric supercapacitors

Much attention has been draw to transitional metal selenides (TMSe) for energy storage, especially the high-performance supercapacitor devices, so it is research hotspots to construct free-standing electrode with TMSe loading. In this work, 3D carbon microtubes (CMTs) wrapped by vertical graphene nanosheets (VGNs), were fabricated by plasma-enhanced chemical vapor deposition (PECVD) method using SiO2 nanowires as templates, which were served as free-standing, conductive and flexible substrates for supporting (Ni,Co)Se2 nanoparticles. Benefiting from the structural merits, such as the interwoven CMTs network, high conductive VGNs substrate, and the synergistical effect of nanostructured (Ni,Co)Se2, the fabricated CMTs@VGNs@(Ni,Co)Se2 membrane electrode exhibits excellent electrochemical performance in terms of high specific capacitance (1740 F g−1 at 1 A g−1), good rate capability (71.8 % capacitance retention at 20 A g−1), and superior cycling stability (89.6 % capacitance retention after 10,000 cycles). Notably, the solid-state asymmetric supercapacitor (ASC) assembled with CMTs@VGNs@(Ni,Co)Se2 membrane and activated carbon (AC), not only delivers a high energy density of 41.6 Wh kg−1 at a power density of 0.75 kW kg−1, but also shows long cycle life with excellent performance stability. More impressively, our work provides a new idea for structural construction of 3D carbon-based nano-substrates and self-supporting electrodes for supercapacitors.

Self-supported and hierarchically porous activated carbon nanotube/carbonized wood electrodes for high-performance solid-state supercapacitors

Though the low tortuosity and the vertically aligned porous channels of wood-derived carbon can facilitate the electrolyte permeation and charge transport, pristine wood-derived carbon electrodes usually deliver poor electrochemical performances. Herein, high-performance solid-state supercapacitors with high areal capacitance and excellent cycling stability are fabricated with self-supported fir wood-derived carbon electrodes with low tortuosity and hierarchically porous structure. Carbon nanotubes are introduced to provide large specific surface area, continues electron transport, and excellent chemical stability. Importantly, the hierarchically porous channels with low tortuosity and high porosity are constructed by incorporating the vertically aligned macro-channels from fir wood-derived carbon and the massive meso- and micro-channels created by KOH activation, which are beneficial for diffusion of ions. The hydrophilic and conductive activated carbon nanotube/wood carbon electrode exhibits an ultrahigh specific surface area of 1646.6 m2 g−1, a superior capacitance of 24.0 F cm−2 (493.7 F g−1) at 1 mA cm−2, and an excellent cycling stability with a capacitance retention of 98% after 10,000 cycles at 100 mA cm−2. Furthermore, the assembled solid-state symmetric supercapacitor possesses a highest power density of 15.7 mW cm−2 and a maximum energy density of 1.1 mWh cm−2.

High-performance solid-state supercapacitors integrated with thermal management systems based on phase change materials: All in one

Electrochemical energy storage (EES) devices such as batteries and supercapacitors (SCs) have been widely used in electric vehicles and portable electronics. However, safety issues and performance degradation of these devices, particularly when working at elevated temperatures, limit their further applications. Here, we propose a new all-in-one design of high-performance solid-state SCs integrated with thermal management systems by developing a multifunctional solid-state polymer electrolyte (SPE) with encapsulated phase change materials (PCMs). The PCM-containing SPEs exhibited a homogenously dispersed core–shell-like structure. The paraffin wax (PW) core ─ a typical organic PCM ─ could store a large amount of thermal energy upon phase transitions. The shell, polyvinyl alcohol (PVA)/H2SO4 frameworks, could provide interconnected ion-conducting pathways, keep the encapsulated PW in the form of micro-sized particles and prevent it from leaking during the melting, and serve as separators. Consequently, the temperature rise of the all-in-one, solid-state SCs integrated with PCMs can be effectively suppressed under thermal abuse conditions. Moreover, the all-in-one devices can retain high capacitance, outstanding rate capability, and excellent stability upon charge/discharge and heating/cooling cycles. Therefore, the rationally designed multifunctional SPEs may open a new pathway to design novel high-performance and safe all-in-one devices with integrated EES and thermal management systems.

High-performance solid-state asymmetric supercapacitor based on Co3V2O8/carbon nanotube nanocomposite and gel polymer electrolyte

Binary metal oxides have promise in several fields due to their tunable structure properties and high stabilities. Moreover, gel polymer electrolytes allow the fabrication of solid-state supercapacitors. In this work, to get higher specific capacitances in solid-state supercapacitors, Co3V2O8/carbon nanotube (Co3V2O8/CNT) nanocomposite with porous structure is proposed as the positive electrode material with appropriate morphological feature. The improved charge transfer rate at the electrode surface and quick ion diffusion due to the interconnected mesoporous channels of Co3V2O8/CNT nanocomposite result in extraordinary specific capacitance of 1959.92 F g−1 at the current density of 1 A g−1. The performance of the proposed electrode is investigated in various electrolytes including aqueous, organic, and gel polymer electrolytes. Finally, a hybrid asymmetric solid-state device is constructed with Co3V2O8/CNT as positive electrode, activated carbon (AC) as negative electrode, and polyvinyl alcohol/H2SO4 (PVA/H2SO4) as gel polymer electrolyte. The specific capacitance for the device is 120.17 F g−1 at a current density of 1 A g−1 and the energy density of 37.55 Wh kg−1, which is higher than the capacitance for the KOH and organic electrolyte-based devices. The solid-state device with gel polymer maintains excellent cycling stability with retention of 95.26% after 3000 cycles.

High performance solid-state supercapacitors based on highly conductive organogel electrolyte at low temperature

Solid-state supercapacitors have advantages of leakage free and flexibility but usually have low energy density at low temperature. This is largely due to the significantly declined ionic conductivity as well as the relatively low voltage window of the gel electrolytes. Here we designed a low temperature tolerant organogel electrolyte by systematically tuning the solvents’ ionic conductivity, melting point and electrochemical stability via acetonitrile (AN), methyl formate (MF), and propylene carbonate (PC), respectively. The tuned gel electrolyte of polymer metrix of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) with salt of ionic electrolyte 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) exhibited ionic conductivity of 2.95 mS cm−1, mechanical strain rate of 350% and voltage window of 0–4 V at low temperature of −60 °C. The stack cell of solid-state supercapacitor using activated carbon as electrode films exhibited capacitance retention of 98.5% at −60 °C compared with that under room temperature, a 3.9% capacitance attenuation after 10,000 charge/discharge cycles, and exceptional stack energy density of 30.8 Wh kg−1, at least three times higher than the state-of-the-art solid-state supercapacitors.

High-performance solid-state supercapacitor based on Ni-Co layered double hydroxide@Co3O4 nanocubes and spongy graphene electrodes

Increasing energy density and cycle stability pose the biggest challenges for developing efficient and affordable energy storage devices. Supercapacitor electrode materials with synergistic 3D architectural frameworks are designed to address the most crucial issues. Herein, 3D hierarchical Ni-Co layered double hydroxides (LDH) wrapped around porous Co3O4 nanocube (Nc) derived from ZIF-67 as a template are successfully synthesized. The Ni-Co LDH@Co3O4 Nc electrode has the highest specific capacitance (1866 F g−1) at 2 A g−1 with outstanding rate capability compared to all formulation material-based positive electrodes. Moreover, the asymmetric solid-state supercapacitor device (ASC) has been successfully synthesized and constructed based on a full cell with 3D Ni-Co LDH@Co3O4 Nc and three-dimensional spongy graphene (3DSGr). The ASC delivers the highest energy density of 66.7 Wh kg−1 with a power density of 800 W kg−1 and superior recyclability over 10,500 cycles with a holding capacitance retention ratio of 90.5% and 99.8% of Coulombic efficiency. The construction design of highly electrochemically active materials with an outstanding asymmetric configuration of the Ni-Co LDH@Co3O4 Nc//3DSGr provides an efficient, tunable, and affordable asymmetric supercapacitor device.

High performance flexible carbon cloth-based solid-state supercapacitors with redox-mediated gel electrolytes

The electrochemical performance of supercapacitors is mainly determined by both the electrodes and electrolytes. By integration of the flexible electrodes with redox-mediated gel electrolytes, high performance solid state supercapacitors were designed in the present work. The flexible carbon cloth (CC)-based electrodes were prepared by covalent immobilization of tetraaniline (TA) onto the oxidized carbon cloth (OCC). Hydroquinone (HQ) and p-phenylenediamine (PPD) were used as redox additive respectively to enhance the electrochemical property of the PVA-H2SO4 gel electrolyte. After optimization, high performance flexible solid-state symmetric supercapacitors (SSSCs) were obtained with specific capacitance of 834.0 mF/cm2, retention of 93.69% after 10,000 CV cycles and 108.5% after 500 cycles of 180°-bending, and energy density of 74.2 mWh/cm2 at power density of 405.3 mW/cm2. Such outstanding comprehensive performance makes them promising potential for practical application.