Explore the vast range of titles available.

Supercapacitors have gained e wide attention because of high power density, fast charging and discharging, as well as good cycle performance. Recently, expanded graphite (EG) has been widely investigated as an effective electrode material for supercapacitors owing to its excellent physical, chemical, electrical, and mechanical properties. Based on charge storage mechanism, supercapacitors have been divided into symmetric, asymmetric, and hybrid supercapacitors. Here, we review the study progress of EG-based materials to be electrode materials. Furthermore, we discuss the application prospects and challenges of EG-based materials in supercapacitors.

HighlightsBased on the drying-mediated self-assembly behavior of passivated graphene, a new kind of 2D micro-flake inks is developed to directly print high-resolution patterns with multiscale porous microstructure.The new ink allows to directly print complex 3D structures comprising multiple layers of heterogeneous materials.High-rate all-solid-state 3D micro-supercapacitors have been fully inkjet-printed with an areal capacitance surpassing 10 mF cm−2 at a high scan rate of 1 V s−1.Scalable fabrication of high-rate micro-supercapacitors (MSCs) is highly desired for on-chip integration of energy storage components. By virtue of the special self-assembly behavior of 2D materials during drying thin films of their liquid dispersion, a new inkjet printing technique of passivated graphene micro-flakes is developed to directly print MSCs with 3D networked porous microstructure. The presence of macroscale through-thickness pores provides fast ion transport pathways and improves the rate capability of the devices even with solid-state electrolytes. During multiple-pass printing, the porous microstructure effectively absorbs the successively printed inks, allowing full printing of 3D structured MSCs comprising multiple vertically stacked cycles of current collectors, electrodes, and sold-state electrolytes. The all-solid-state heterogeneous 3D MSCs exhibit excellent vertical scalability and high areal energy density and power density, evidently outperforming the MSCs fabricated through general printing techniques.

Design and fabrication of electrochemical energy storage systems with both high energy and power densities as well as long cycling life is of great importance. As one of these systems, Battery‐supercapacitor hybrid device (BSH) is typically constructed with a high‐capacity battery‐type electrode and a high‐rate capacitive electrode, which has attracted enormous attention due to its potential applications in future electric vehicles, smart electric grids, and even miniaturized electronic/optoelectronic devices, etc. With proper design, BSH will provide unique advantages such as high performance, cheapness, safety, and environmental friendliness. This review first addresses the fundamental scientific principle, structure, and possible classification of BSHs, and then reviews the recent advances on various existing and emerging BSHs such as Li‐/Na‐ion BSHs, acidic/alkaline BSHs, BSH with redox electrolytes, and BSH with pseudocapacitive electrode, with the focus on materials and electrochemical performances. Furthermore, recent progresses in BSH devices with specific functionalities of flexibility and transparency, etc. will be highlighted. Finally, the future developing trends and directions as well as the challenges will also be discussed; especially, two conceptual BSHs with aqueous high voltage window and integrated 3D electrode/electrolyte architecture will be proposed. The fundamental scientific principle, structure, and possible classification of battery‐supercapacitor hybrid devices (BSHs), outlining the recent advances on various existing and emerging BSHs, with the focus on materials and electrochemical performances, and finally providing the future developing trends and directions as well as the challenges are addressed in this review.

Metal oxide and metal dichalcogenide heterostructure composites are promising candidates for electrochemical use. In this study, a hybrid heterostructure composite electrode material was made using a straightforward hydrothermal process using transition metal oxide (NiO) and metal dichalcogenide (MoS2). The surface of the flower-like structured MoS2 was grown with granular structured NiO, and this heterostructure composite exhibited considerably improved specific capacitance when compared to the pure NiO and MoS2 materials. The pseudocapacitive performance was effectively supported by the heterostructure combination of transition metal oxide (TMOs) and metal dichalcogenide (MDC), which greatly improved ion transport within the material and storage. At a current density of 1 A/g, the prepared heterostructure composite electrode material exhibited a specific capacitance of 289 F/g, and, after 2000 cycles, the capacitance retained 101% of its initial value. The symmetric device was constructed and put through tests using LED light. This finding opens up a new avenue for the quickly increasing the field of heterostructure materials.

Magnetic nanoparticles of NiFe2O4 were successfully prepared by utilizing the sol–gel techniques. The prepared samples were investigated through various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), dielectric spectroscopy, DC magnetization and electrochemical measurements. XRD data analysed using Rietveld refinement procedure inferred that NiFe2O4 nanoparticles displayed a single-phase nature with face-centred cubic crystallinity with space group Fd-3m. Average crystallite size estimated using the XRD patterns was observed to be ~10 nm. The ring pattern observed in the selected area electron diffraction pattern (SAED) also confirmed the single-phase formation in NiFe2O4 nanoparticles. TEM micrographs confirmed the uniformly distributed nanoparticles with spherical shape and an average particle size of 9.7 nm. Raman spectroscopy showed characteristic bands corresponding to NiFe2O4 with a shift of the A1g mode, which may be due to possible development of oxygen vacancies. Dielectric constant, measured at different temperatures, increased with temperature and decreased with increase in frequency at all temperatures. The Havrilliak–Negami model used to study the dielectric spectroscopy indicated that a NiFe2O4 nanoparticles display non-Debye type relaxation. Jonscher’s power law was utilized for the calculation of the exponent and DC conductivity. The exponent values clearly demonstrated the non-ohmic behaviour of NiFe2O4 nanoparticles. The dielectric constant of the nanoparticles was found to be >300, showing a normal dispersive behaviour. AC conductivity showed an increase with the rise in temperature with the highest value of 3.4 × 10−9 S/cm at 323 K. The M-H curves revealed the ferromagnetic behaviour of a NiFe2O4 nanoparticle. The ZFC and FC studies suggested a blocking temperature of ~64 K. The saturation of magnetization determined using the law of approach to saturation was ~61.4 emu/g at 10 K, corresponding to the magnetic anisotropy ~2.9 × 104 erg/cm3. Electrochemical studies showed that a specific capacitance of ~600 F g−1 was observed from the cyclic voltammetry and galvanostatic charge–discharge, which suggested its utilization as a potential electrode for supercapacitor applications.

Stretchable micropower sources with high energy density and stability under repeated tensile deformation are key components of flexible/wearable microelectronics. Herein, through the combination of strain engineering and modulation of the interlayer spacing, freestanding and lightweight MXene/bacterial cellulose (BC) composite papers with excellent mechanical stability and a high electrochemical performance are first designed and prepared via a facile all‐solution‐based paper‐making process. Following a simple laser‐cutting kirigami patterning process, bendable, twistable, and stretchable all‐solid‐state micro‐supercapacitor arrays (MSCAs) are further fabricated. As expected, benefiting from the high‐performance MXene/BC composite electrodes and rational sectional structural design, the resulting kirigami MSCAs exhibit a high areal capacitance of 111.5 mF cm−2, and are stable upon stretching of up to 100% elongation, and in bent or twisted states. The demonstrated combination of an all‐solution‐based MXene/BC composite paper‐making method and an easily manipulated laser‐cutting kirigami patterning technique enables the fabrication of MXene‐based deformable all‐solid‐state planar MSCAs in a simple and efficient manner while achieving excellent areal performance metrics and high stretchability, making them promising micropower sources that are compatible with flexible/wearable microelectronics. The demonstrated combination of an all‐solution‐based MXene/bacterial cellulose composite paper‐making method and easily manipulated laser‐cutting kirigami patterning technique enables the fabrication of MXene‐based all‐solid‐state stretchable micro‐supercapacitor arrays in a simple and efficient manner while achieving both a high areal capacitance of 111.5 mF cm−2 and a high elongation of 100%, making them promising compatible micropower sources for flexible/wearable microelectronics.

Energy storage devices that efficiently use energy, in particular renewable energy, are being actively pursued. Aqueous redox supercapacitors, which operate in high ionic conductivity and environmentally friendly aqueous electrolytes, storing and releasing high amounts of charge with rapid response rate and long cycling life, are emerging as a solution for energy storage applications. At the core of these devices, electrode materials and their assembling into rational configurations are the main factors governing the charge storage properties of supercapacitors. Redox‐active metal compounds, particularly oxides and hydroxides that store charge via reversible valence change redox reactions with electrolyte ions, are prospective candidates to optimize the electrochemical performance of supercapacitors. To address this target, collaborative investigations, addressing different streams, from fundamental charge storage mechanisms and electrode materials engineering to need‐tailored device assemblies, are the key. Over the last few years, significant achievements in metal oxide and hydroxide–based aqueous supercapacitors have been reported. This work discusses the most recent achievements and trends in this field and brings into the spotlight the authors' viewpoints. Metal oxide and hydroxide aqueous supercapacitors are promising devices to provide high energy and power densities. To achieve high‐performance devices that can be used for different purposes, fundamental charge storage mechanisms, electrode materials engineering, and device assemblies are being studied. The most recent achievements in the field are reviewed.

Recently, considerable research efforts to achieve advanced design of promising electroactive materials as well as unique structures in supercapacitor electrodes have been explored for high-performance energy storage systems. We suggest the development of novel electroactive materials with an enlarged surface area for sandpaper materials. Based on the inherent micro-structured morphologies of the sandpaper substrate, nano-structured Fe-V electroactive material can be coated on it by facile electrochemical deposition technique. A hierarchically designed electroactive surface is covered with FeV-layered double hydroxide (LDH) nano-flakes on Ni-sputtered sandpaper as a unique structural and compositional material. The successful growth of FeV-LDH is clearly revealed by surface analysis techniques. Further, electrochemical studies of the suggested electrodes are carried out to optimize the Fe-V composition as well as the grit number of the sandpaper substrate. Herein, optimized Fe0.75V0.25 LDHs coated on #15000 grit Ni-sputtered sandpaper are developed as advanced battery-type electrodes. Finally, along with the negative electrode of activated carbon and the FeV-LDH electrode, it is utilized for hybrid supercapacitor (HSC) assembly. The fabricated flexible HSC device indicates high energy and power density by showing excellent rate capability. This study is a remarkable approach to improving the electrochemical performance of energy storage devices using facile synthesis.

The demand for microgrids and their applications in buildings, industries and for very specific applications is increasing over time. Most of these microgrids are dependent on renewable energy sources, which brings along problems of intermittent energy production. To maintain the balance of the grid, normally storage devices are used. Supercapacitors (SCs) are emerging as one of the potential solutions to solve the issue of intermittent energy production by renewable sources because of their high-power densities and rapid charge/discharge capability. In other terms, SCs can charge, and discharge rather quickly as compared to traditional lithium-batteries. This usage makes it interesting for optimizing decentralized energy generation-based PV systems operations. In this paper, the authors propose the supercapacitors fast ageing control in residential microgrid, including electric vehicle charging station based Photovoltaic-Fuel Cell system. Supercapacitors fast ageing control concept focuses on keeping the electrical parameters of the SCs around the optimal operation points by smoothing the power fluctuations in the system. The used SCs model is essentially based on the intermittent current waveforms along with variable temperature conditions. It enables us to describe the degradation of the supercapacitor’s parameters based on the effects of the temperature and the DC-current undulation. To maintain the electrical parameters of SCs around the optimal operation points, the authors propose a new control based on maintaining the SCs resistance at a minimal level and its capacitance at a maximal level by adjusting the SCs current control according to the optimal operating points tracking. The results validate the effectiveness of the approach, this is important because controlling the fast degradation of capacitance optimizes the lifetime of SCs system. Future research may explore scalability to large microgrids and integration with diverse renewable energy systems.

Perovskite materials have recently emerged as promising candidates for energy storage applications due to their unique physicochemical properties, such as mixed ionic and electronic conductivity, tunable composition, and structural flexibility. This review critically discusses recent developments in perovskite-based materials as electrodes for supercapacitors, highlighting structural modifications, composite strategies, and electrochemical performance metrics. Drawing from recent literature, we summarize key contributions, analyze trends, and identify research gaps for further innovation in this field.