Scalable 2D Hierarchical Porous Carbon Nanosheets for Flexible Supercapacitors with Ultrahigh Energy Density

2D carbon nanomaterials such as graphene and its derivatives, have gained tremendous research interests in energy storage because of their high capacitance and chemical stability. However, scalable synthesis of ultrathin carbon nanosheets with well-defined pore architectures remains a great challenge. Herein, the first synthesis of 2D hierarchical porous carbon nanosheets (2D-HPCs) with rich nitrogen dopants is reported, which is prepared with high scalability through a rapid polymerization of a nitrogen-containing thermoset and a subsequent one-step pyrolysis and activation into 2D porous nanosheets. 2D-HPCs, which are typically 1.5 nm thick and 1-3 µm wide, show a high surface area (2406 m² g^-1 ) and with hierarchical micro-, meso-, and macropores. This 2D and hierarchical porous structure leads to robust flexibility and good energy-storage capability, being 139 Wh kg^-1 for a symmetric supercapacitor. Flexible supercapacitor devices fabricated by these 2D-HPCs also present an ultrahigh volumetric energy density of 8.4 mWh cm^-3 at a power density of 24.9 mW cm^-3 , which is retained at 80% even when the power density is increased by 20-fold. The devices show very high electrochemical life (96% retention after 10000 charge/discharge cycles) and excellent mechanical flexibility.

Scalable High-Performance Ultraminiature Graphene Micro-Supercapacitors by a Hybrid Technique Combining Direct Writing and Controllable Microdroplet Transfer

Miniaturization of energy storage devices can significantly decrease the overall size of electronic systems. However, this miniaturization is limited by the reduction of electrode dimensions and the reproducible transfer of small electrolyte drops. This paper reports first a simple scalable direct writing method for the production of ultraminiature microsupercapacitor (MSC) electrodes, based on femtosecond laser reduced graphene oxide (fsrGO) interlaced pads. These pads, separated by 2 μm spacing, are 100 μm long and 8 μm wide. A second stage involves the accurate transfer of an electrolyte microdroplet on top of each individual electrode, which can avoid any interference of the electrolyte with other electronic components. Abundant in-plane mesopores in fsrGO induced by a fs laser together with ultrashort interelectrode spacing enables MSCs to exhibit a high specific capacitance (6.3 mF cm^-2 and 105 F cm^-3) and ∼100% retention after 1000 cycles. An all graphene resistor-capacitor (RC) filter is also constructed by combining the MSC and a fsrGO resistor, which is confirmed to exhibit highly enhanced performance characteristics. This new hybrid technique combining fs laser direct writing and precise microdroplet transfer easily enables scalable production of ultraminiature MSCs, which is believed to be significant for practical application of micro-supercapacitor microelectronic systems.

NiO/NixCo3−xO4 porous ultrathin nanosheet/nanowire composite structures as high-performance supercapacitor electrodes

The demand for a new generation of high-safety, long-lifespan, and high-capacity power sources increases rapidly with the growth of energy consumption in the world. Here we report a facile method for preparing architecture materials made of NiO/Ni_xCo_3−xO₄ porous nanosheets coupled with NiO/Ni_xCo_3−xO₄ porous nanowires grown in situ on nickel foams using a hydrothermal method without any binder followed by a heat treatment process. The nanosheet-shaped NiO/Ni_xCo_3−xO₄ species in the nanosheet matrix function well as a scaffold and support for the dispersion of the Ni_xCo_3−xO₄ nanowires, resulting in a relatively loose and open structure within the electrode matrix. Among all composite electrodes prepared, the one annealed in air at 300 °C displays the best electrochemical behavior, achieving a specific capacitance of 270 mF cm⁻² at 5 mA cm⁻² while maintaining excellent stability (retaining ≈ 89% of the max capacitance after 20 000 cycles), demonstrating its potential for practical application in power storage devices.

Porous ultrathin nanosheet/nanowire composite structures are prepared as high-performance supercapacitor electrodes which exhibit excellent stability.

One-step synthesis of 2D-layered carbon wrapped transition metal nitrides from transition metal carbides (MXenes) for supercapacitors with ultrahigh cycling stability

A novel one-step method to synthesize 2D carbon wrapped transition metal nitrides was proposed via using 2D metal carbides (MXenes) as precursors.

Micro-supercapacitors based on oriented coordination polymer thin films for AC line-filtering

Reported herein is a facile solution-processed substrate-independent approach for preparation of oriented coordination polymer (Co-BTA) thin-film electrodes for on-chip micro-supercapacitors (MSCs). The Co-BTA-MSCs exhibited excellent AC line-filtering performance with an extremely short resistance–capacitance constant, making it capable of replacing aluminum electrolytic capacitors for AC line-filtering applications.

Micro-supercapacitors exhibiting excellent AC line-filtering with oriented coordination polymer thin-film electrodes are fabricated based on a substrate-independent electrode fabrication strategy.

Two-dimensional materials for miniaturized energy storage devices: from individual devices to smart integrated systems

This review summarizes recent advances, key challenges and perspectives regarding two-dimensional materials for miniaturized energy storage devices.

Quasi 2D Mesoporous Carbon Microbelts Derived from Fullerene Crystals as an Electrode Material for Electrochemical Supercapacitors

Fullerene C₆₀ microbelts were fabricated using the liquid-liquid interfacial precipitation method and converted into quasi 2D mesoporous carbon microbelts by heat treatment at elevated temperatures of 900 and 2000 °C. The carbon microbelts obtained by heat treatment of fullerene C₆₀ microbelts at 900 °C showed excellent electrochemical supercapacitive performance, exhibiting high specific capacitances ca. 360 F g^-1 (at 5 mV s^-1) and 290 F g^-1 (at 1 A g^-1) because of the enhanced surface area and the robust mesoporous framework structure. Additionally, the heat-treated carbon microbelt showed good rate performance, retaining 49% of capacitance at a high scan rate of 10 A g^-1. The carbon belts exhibit super cyclic stability. Capacity loss was not observed even after 10 000 charge/discharge cycles. These results demonstrate that the quasi 2D mesoporous carbon microbelts derived from a π-electron-rich carbon source, fullerene C₆₀ crystals, could be used as a new candidate material for electrochemical supercapacitor applications.

Recent Progress in Micro-Supercapacitors with In-Plane Interdigital Electrode Architecture

Due to the boom of miniaturized electronic devices in the last decade, there are great demands for ultrathin and flexible on-chip rechargeable energy storage microdevices. Supercapacitor, as one of the most hopeful appearing energy storage devices, can provide a wonderful alternative to batteries or electrolytic capacitors, owing to its fast charge and discharge rates, high power density, and long cycling stability. Especially for the recently developed micro-supercapacitors, the unique in-plane interdigital electrode architecture can fully meet the integration requirements of rapidly developed miniaturized electronic devices, and improve the power density of the unit via shortening the ionic diffusion distance between the interdigital electrodes. This concept introduces the recent advances on the design, fabrication, and application of planar micro-supercapacitors for on-chip energy storage from an overall perspective. Moreover, challenges and future development trends are discussed.

The ideal porous structure of EDLC carbon electrodes with extremely high capacitance

We propose an ideal porous structure of carbon electrodes for electric double-layer capacitors (EDLCs). The porous carbon successfully improved the gravimetric capacitance above ∼200 F g^-1 even in an organic electrolyte by utilizing the carbon nanopore surface more effectively. High-resolution transmission electron microscopy images and X-ray diffraction patterns classified 15 different porous carbon electrodes into slit-shape and worm-like-shape, and the pore size distributions of the carbons were carefully determined applying the grand canonical Monte Carlo method to N₂ adsorption isotherms at 77 K. The ratio of pores where solvated ions and/or desolvated ions can penetrate also has a significant effect on the EDL capacitance as well as the pore shape. The detailed study on the effect of porous morphologies on the EDLC performance indicates that a hierarchical porous structure with a worm-like shaped surface and a pore size ranging from a solvated ion to a solvent molecule is an ideal electrode structure.

Scalable Fabrication and Integration of Graphene Microsupercapacitors through Full Inkjet Printing

A simple full-inkjet-printing technique is developed for the scalable fabrication of graphene-based microsupercapacitors (MSCs) on various substrates. High-performance graphene inks are formulated by integrating the electrochemically exfoliated graphene with a solvent exchange technique to reliably print graphene interdigitated electrodes with tunable geometry and thickness. Along with the printed polyelectrolyte, poly(4-styrenesulfonic acid), the fully printed graphene-based MSCs attain the highest areal capacitance of ∼0.7 mF/cm², substantially advancing the state-of-art of all-solid-state MSCs with printed graphene electrodes. The full printing solution enables scalable fabrication of MSCs and effective connection of them in parallel and/or in series at various scales. Remarkably, more than 100 devices have been connected to form large-scale MSC arrays as power banks on both silicon wafers and Kapton. Without any extra protection or encapsulation, the MSC arrays can be reliably charged up to 12 V and retain the performance even 8 months after fabrication.

Rapid, all dry microfabrication of three-dimensional Co3O4/Pt nanonetworks for high-performance microsupercapacitors

On-chip electrochemical energy storage devices have attracted growing attention due to the decreasing size of electronic devices. Various approaches have been applied for constructing the microsupercapacitors. However, the microfabrication of high-performance microsupercapacitors by conventional and fully compatible semiconductor microfabrication technologies is still a critical challenge. Herein, unique three-dimensional (3D) Co₃O₄ nanonetwork microelectrodes formed by the interconnection of Co₃O₄ nanosheets are constructed by controllable physical vapor deposition combined with rapid thermal annealing. This construction process is an all dry and rapid (≤5 minutes) procedure. Afterward, by sputtering highly electrically conductive Pt nanoparticles on the microelectrodes, the 3D Co₃O₄/Pt nanonetworks based microsupercapacitor is fabricated, showing a high volume capacitance (35.7 F cm^-3) at a scan rate of 20 mV s^-1 due to the unique interconnected structures, high electrical conductivity and high surface area of the microelectrodes. This microfabrication process is also used to construct high-performance flexible microsupercapacitors, and it can be applied in the construction of wearable devices. The proposed strategy is completely compatible with the current semiconductor microfabrication and shows great potential in the applications of the large-scale integration of micro/nano and wearable devices.

Anchoring Ultrafine ZnFe2O4/C Nanoparticles on 3D ZnFe2O4 Nanoflakes for Boosting Cycle Stability and Energy Density of Flexible Asymmetric Supercapacitor

Heterostructure-based metal oxide thin films are recognized as the leading material for new generation, high-performance, stable, and flexible supercapacitors. However, morphologies, like nanoflakes, nanotubes, nanorods, and so forth, have been found to suffer from issues related to poor cycle stability and energy density. Thus, to circumvent these problems, herein, we have developed a low-cost, high surface area, and environmentally benign self-assembled ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructure electrode via anchoring ZnFe₂O₄ and carbon nanoparticles using an in situ biomediated green rotational chemical bath deposition approach for the first time. The synthesized ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructure thin films demonstrate an excellent specific capacitance of 1884 F g^-1 at a current density of 5 mA cm^-2. Additionally, all solid-state flexible asymmetric supercapacitor devices were designed on the basis of ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructures as the negative electrode and reduced graphene oxide and energy density of 81 Wh kg^-1 at a power density of 3.9 kW kg^-1. Similarly, the asymmetric device exhibits ultralong cycle stability of 35 000 cycles by losing only 2% capacitance. The excellent performance of the device is attributed to the self-assembled organization of the heterostructures. Moreover, the in situ biomediated green strategy is also applicable for the synthesis of other metal oxide and carbon-based heterostructure electrodes.

One-Step Device Fabrication of Phosphorene and Graphene Interdigital Micro-Supercapacitors with High Energy Density

Rational engineering and simplified fabrication of high-energy micro-supercapacitors (MSCs) using graphene and other 2D nanosheets are of great value for flexible and integrated electronics. Here we develop one-step mask-assisted simplified fabrication of high-energy MSCs (PG-MSCs) based on the interdigital hybrid electrode (PG) patterns of stacking high-quality phosphorene nanosheets and electrochemically exfoliated graphene in ionic liquid electrolyte. The hybrid PG films with interdigital patterns were directly manufactured by layer-by-layer deposition of phosphorene and graphene nanosheets with the assistance of a customized interdigital mask, and directly transferred onto a flexible substrate. The resultant patterned PG films present outstanding uniformity, flexibility, conductivity (319 S cm^-1), and structural integration, which can directly serve as binder- and additive-free flexible electrodes for MSCs. Remarkably, PG-MSCs deliver remarkable energy density of 11.6 mWh cm^-3, outperforming most nanocarbon-based MSCs. Moreover, our PG-MSCs show outstanding flexibility and stable performance with slight capacitance fluctuation even under highly folded states. In addition, our simplified mask-assisted strategy for PG-MSCs is highly flexible for simplified production of parallelly and serially interconnected modular power sources, without need of conventional metal-based interconnects and contacts, for designable integrated circuits with high output current and voltage.

Paper-Based Electrodes for Flexible Energy Storage Devices

Paper-based materials are emerging as a new category of advanced electrodes for flexible energy storage devices, including supercapacitors, Li-ion batteries, Li-S batteries, Li-oxygen batteries. This review summarizes recent advances in the synthesis of paper-based electrodes, including paper-supported electrodes and paper-like electrodes. Their structural features, electrochemical performances and implementation as electrodes for flexible energy storage devices including supercapacitors and batteries are highlighted and compared. Finally, we also discuss the challenges and opportunity of paper-based electrodes and energy storage devices.

Vertically Aligned Niobium Nanowire Arrays for Fast-Charging Micro-Supercapacitors

Planar micro-supercapacitors are attractive for system on chip technologies and surface mount devices due to their large areal capacitance and energy/power density compared to the traditional oxide-based capacitors. In the present work, a novel material, niobium nanowires, in form of vertically aligned electrodes for application in high performance planar micro-supercapacitors is introduced. Specific capacitance of up to 1 kF m^-2 (100 mF cm^-2 ) with peak energy and power density of 2 kJ m^-2 (6.2 MJ m^-3 or 1.7 mWh cm^-3 ) and 150 kW m^-2 (480 MW m^-3 or 480 W cm^-3 ), respectively, is achieved. This remarkable power density, originating from the extremely low equivalent series resistance value of 0.27 Ω (2.49 µΩ m² or 24.9 mΩ cm² ) and large specific capacitance, is among the highest for planar micro-supercapacitors electrodes made of nanomaterials.

Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale

Fundamental understanding of structure-property relationships in hierarchically organized nanostructures is crucial for the development of new functionality, yet quantifying structure across multiple length scales is challenging. In this work, we used nondestructive X-ray scattering to quantitatively map the multiscale structure of hierarchically self-organized carbon nanotube (CNT) "forests" across 4 orders of magnitude in length scale, from 2.0 Å to 1.5 μm. Fully resolved structural features include the graphitic honeycomb lattice and interlayer walls (atomic), CNT diameter (nano), as well as the greater CNT ensemble (meso) and large corrugations (micro). Correlating orientational order across hierarchical levels revealed a cascading decrease as we probed finer structural feature sizes with enhanced sensitivity to small-scale disorder. Furthermore, we established qualitative relationships for single-, few-, and multiwall CNT forest characteristics, showing that multiscale orientational order is directly correlated with number density spanning 10⁹-10¹² cm^-2, yet order is inversely proportional to CNT diameter, number of walls, and atomic defects. Lastly, we captured and quantified ultralow-q meridional scattering features and built a phenomenological model of the large-scale CNT forest morphology, which predicted and confirmed that these features arise due to microscale corrugations along the vertical forest direction. Providing detailed structural information at multiple length scales is important for design and synthesis of CNT materials as well as other hierarchically organized nanostructures.

2-Methylimidazole-Derived Ni-Co Layered Double Hydroxide Nanosheets as High Rate Capability and High Energy Density Storage Material in Hybrid Supercapacitors

A new method based on one-step solvothermal reaction is demonstrated to synthesize ultrathin Ni-Co layered double hydroxide (LDH) nanosheets, which grow directly on a flexible carbon fiber cloth (NiCo-LDH/CFC). Through using 2-methylimidazole as complex and methanol as solvent, the as-prepared NiCo-LDH/CFC shows a (003) facet preferential growth and an expanded interlayer spacing structure, resulting in a unique 3D porous nanostructure with a thickness of nanosheets of around 5-7 nm that shows high energy storage performance. By controlling the ratio of Ni/Co = 4:1 in the precursor solution, the electrode shows a specific capacitance of 2762.7 F g^-1 (1243.2 C g^-1) at a current density of 1 A g^-1. Nevertheless, the optimal composition is obtained with Ni/Co = 1:1, which produces a specific capacitance of 2242.9 F g^-1 (1009.3 C g^-1) at 1 A g^-1 and shows an excellent rate capability with 61% of the original capacitance being retained at a current density of 60 A g^-1. The hybrid supercapacitor (HSC) based on the NiCo-LDH/CFC exhibits a maximum energy density of 59.2 Wh kg^-1 and power densities of 34 kW kg^-1, respectively. Long-term stability test shows that 82% of the original capacitance of the HSC remains after 5000 cycles. Importantly, the electrochemical performance of the solid-state flexible supercapacitors based on the prepared NiCo-LDH/CFC electrode showed a negligible change when the device was bent up to 180°. The performance of synthesized NiCo-LDH/CFC indicates the great potential of the material for delivering both high energy density and high power density in energy storage devices.

Solid-state synthesis of ordered mesoporous carbon catalysts via a mechanochemical assembly through coordination cross-linking

Ordered mesoporous carbons (OMCs) have demonstrated great potential in catalysis, and as supercapacitors and adsorbents. Since the introduction of the organic–organic self-assembly approach in 2004/2005 until now, the direct synthesis of OMCs is still limited to the wet processing of phenol-formaldehyde polycondensation, which involves soluble toxic precursors, and acid or alkali catalysts, and requires multiple synthesis steps, thus restricting the widespread application of OMCs. Herein, we report a simple, general, scalable and sustainable solid-state synthesis of OMCs and nickel OMCs with uniform and tunable mesopores (∼4–10 nm), large pore volumes (up to 0.96 cm³ g⁻¹) and high-surface areas exceeding 1,000 m² g⁻¹, based on a mechanochemical assembly between polyphenol-metal complexes and triblock co-polymers. Nickel nanoparticles (∼5.40 nm) confined in the cylindrical nanochannels show great thermal stability at 600 °C. Moreover, the nickel OMCs offer exceptional activity in the hydrogenation of bulky molecules (∼2 nm).

Ordered mesoporous carbons have shown promise in a range of applications, but sustainable methods to achieve their large scale production are lacking. Here, Dai and coworkers produce OMCs via the mechanochemical assembly of non-toxic polyphenol-metal complexes and triblock copolymers, followed by pyrolysis.

High Packing Density Unidirectional Arrays of Vertically Aligned Graphene with Enhanced Areal Capacitance for High-Power Micro-Supercapacitors

Interfacial integration of a shape-engineered electrode with a strongly bonded current collector is the key for minimizing both ionic and electronic resistance and then developing high-power supercapacitors. Herein, we demonstrated the construction of high-power micro-supercapacitors (VG-MSCs) based on high-density unidirectional arrays of vertically aligned graphene (VG) nanosheets, derived from a thermally decomposed SiC substrate. The as-grown VG arrays showed a standing basal plane orientation grown on a (0001̅) SiC substrate, tailored thickness (3.5-28 μm), high-density structurally ordering alignment of graphene consisting of 1-5 layers, vertically oriented edges, open intersheet channels, high electrical conductivity (192 S cm^-1), and strong bonding of the VG edges to the SiC substrate. As a result, the demonstrated VG-MSCs displayed a high areal capacitance of ∼7.3 mF cm^-2 and a fast frequency response with a short time constant of 9 ms. Furthermore, VG-MSCs in both an aqueous polymer gel electrolyte and nonaqueous ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate operated well at high scan rates of up to 200 V s^-1. More importantly, VG-MSCs offered a high power density of ∼15 W cm^-3 in gel electrolyte and ∼61 W cm^-3 in ionic liquid. Therefore, this strategy of producing high-density unidirectional VG nanosheets directly bonded on a SiC current collector demonstrated the feasibility of manufacturing high-power compact supercapacitors.

High Power In-Plane Micro-Supercapacitors Based on Mesoporous Polyaniline Patterned Graphene

Micro-supercapacitors (MSCs) based on mesoporous polyaniline patterned graphene are demonstrated. The synergic effect from both electron-double-layer-capacitive graphene and pseudocapacitive mesoporous-polyaniline leads to outstanding MSC device performances, in regard to excellent volumetric capacitance and rate capabilities, which further result in a high power density of 600 W cm^-3 , suggesting opportunities for future portable and wearable power supplies in diverse applications.

Bottom-Up Fabrication of Sulfur-Doped Graphene Films Derived from Sulfur-Annulated Nanographene for Ultrahigh Volumetric Capacitance Micro-Supercapacitors

Heteroatom doping of nanocarbon films can efficiently boost the pseudocapacitance of micro-supercapacitors (MSCs); however, wafer-scale fabrication of sulfur-doped graphene films with a tailored thickness and homogeneous doping for MSCs remains a great challenge. Here we demonstrate the bottom-up fabrication of continuous, uniform, and ultrathin sulfur-doped graphene (SG) films, derived from the peripherical trisulfur-annulated hexa-peri-hexabenzocoronene (SHBC), for ultrahigh-rate MSCs (SG-MSCs) with landmark volumetric capacitance. The SG film was prepared by thermal annealing of the spray-coated SHBC-based film, with assistance of a thin Au protecting layer, at 800 °C for 30 min. SHBC with 12 phenylthio groups decorated at the periphery is critical as a precursor for the formation of the continuous and ultrathin SG film, with a uniform thickness of ∼10.0 nm. Notably, the as-produced all-solid-state planar SG-MSCs exhibited a highly stable pseudocapacitive behavior with a volumetric capacitance of ∼582 F cm^-3 at 10 mV s^-1, excellent rate capability with a remarkable capacitance of 8.1 F cm^-3 even at an ultrahigh rate of 2000 V s^-1, ultrafast frequency response with a short time constant of 0.26 ms, and ultrahigh power density of ∼1191 W cm^-3. It is noteworthy that these values obtained are among the best values for carbon-based MSCs reported to date.

Galvanic displacement assembly of ultrathin Co3O4 nanosheet arrays on nickel foam for a high-performance supercapacitor

High-performance supercapacitors are very desirable for many portable electronic devices, electric vehicles and high-power electronic devices. Herein, a facile and binder-free synthesis method, galvanic displacement of the precursor followed by heat treatment, is used to fabricate ultrathin Co₃O₄ nanosheet arrays on nickel foam substrate. When used as a supercapacitor electrode the prepared Co₃O₄ on nickel foam exhibits a maximum specific capacitance of 1095 F g^-1 at a current density of 1 A g^-1 and good cycling stability of 71% retention after 2000 cycling tests. This excellent electrochemical performance can be ascribed to the high specific surface area of each Co₃O₄ nanosheet that comprises numerous nanoparticles.

Coordination Polymer Framework Based On-Chip Micro-Supercapacitors with AC Line-Filtering Performance

On-chip micro-supercapacitors (MSCs) are important Si-compatible power-source backups for miniaturized electronics. Despite their tremendous advantages, current on-chip MSCs require harsh processing conditions and typically perform like resistors when filtering ripples from alternating current (AC). Herein, we demonstrated a facile layer-by-layer method towards on-chip MSCs based on an azulene-bridged coordination polymer framework (PiCBA). Owing to the good carrier mobility (5×10^-3  cm²  V^-1  s^-1 ) of PiCBA, the permanent dipole moment of azulene skeleton, and ultralow band gap of PiCBA, the fabricated MSCs delivered high specific capacitances of up to 34.1 F cm^-3 at 50 mV s^-1 and a high volumetric power density of 1323 W cm^-3 . Most importantly, such MCSs exhibited AC line-filtering performance (-73° at 120 Hz) with a short resistance-capacitance constant of circa 0.83 ms.

Design of Architectures and Materials in In-Plane Micro-supercapacitors: Current Status and Future Challenges

The rapid development of integrated electronics and the boom in miniaturized and portable devices have increased the demand for miniaturized and on-chip energy storage units. Currently thin-film batteries or microsized batteries are commercially available for miniaturized devices. However, they still suffer from several limitations, such as short lifetime, low power density, and complex architecture, which limit their integration. Supercapacitors can surmount all these limitations. Particularly for micro-supercapacitors with planar architectures, due to their unique design of the in-plane electrode finger arrays, they possess the merits of easy fabrication and integration into on-chip miniaturized electronics. Here, the focus is on the different strategies to design electrode finger arrays and the material engineering of in-plane micro-supercapacitors. It is expected that the advances in micro-supercapacitors with in-plane architectures will offer new opportunities for the miniaturization and integration of energy-storage units for portable devices and on-chip electronics.

Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible Electrochromic Window

Stimulus-responsive micro-supercapacitors (SR-MSCs) with ultrahigh volumetric energy density and reversible electrochromic effect are successfully fabricated by employing a vanadium pentoxide and electrochemical exfoliated graphene-based hybrid nanopaper and viologen as electrode and stimulus-responsive material, respectively. The fabricated high-performance SR-MSCs offer new opportunities for intuitively observing the working state of energy devices without the aid of extra equipment and techniques.

Flexible micro-supercapacitors prepared using direct-write nanofibers

A direct-write flexible micro-supercapacitor with high performance was demonstrated using a simple and versatile approach.

Microsupercapacitors as miniaturized energy-storage components for on-chip electronics

The push towards miniaturized electronics calls for the development of miniaturized energy-storage components that can enable sustained, autonomous operation of electronic devices for applications such as wearable gadgets and wireless sensor networks. Microsupercapacitors have been targeted as a viable route for this purpose, because, though storing less energy than microbatteries, they can be charged and discharged much more rapidly and have an almost unlimited lifetime. In this Review, we discuss the progress and the prospects of integrated miniaturized supercapacitors. In particular, we discuss their power performances and emphasize the need of a three-dimensional design to boost their energy-storage capacity. This is obtainable, for example, through self-supported nanostructured electrodes. We also critically evaluate the performance metrics currently used in the literature to characterize microsupercapacitors and offer general guidelines to benchmark performances towards prospective applications.

Charge storage mechanisms of electrospun Mn3O4 nanofibres for high-performance supercapacitors

Mixed oxidation states of manganese oxides are widely used as the electrodes in supercapacitors due to their high theoretical pseudocapacitances.