Planar Micro-supercapacitors Research Articles

Graphene-Based Integrated Planar On-Chip Micro-Supercapacitors with No Internal Connection

A new series configuration without internal connection was designed and planar on-chip micro-supercapacitors with series structure were fabricated by liquid-air interface self-assembly and photolithography. Compared with the series structures of internal metal connection and graphene connection, the planar on-chip micro-supercapacitors with no internal connection greatly reduced internal resistance and saved device volume. The planar on-chip micro-supercapacitors with no internal connection were provided with high output voltage of 2 V, time constant of 0.042 ms, stack capacitance of 27.30 F cm-3 and capacitance retention of 89% after 10000 cycles of charging and discharging at scan rate of 100 V s-1.

3D knitted energy storage textiles using MXene-coated yarns

Abstract Textile-based energy storage devices offer an exciting replacement for bulky and uncomfortable batteries in commercial smart garments. Fiber and yarn-based supercapacitors, currently dominating research in this field, have demonstrated excellent performance below ∼4 cm in length, but suffer at longer lengths due to increased resistance. Herein, a new architecture of wearable energy storage devices, 3D knitted supercapacitors, is designed and prototyped with the intention of exploiting the architecture of a knit textile to improve the performance of long yarn electrodes. While Computer-Aided Design (CAD) knitting is a ubiquitous technology for producing textiles, knitted energy storage devices have been largely unexplored due to the need for meters of highly conductive yarn electrodes that meet the strenuous strength and flexibility requirements for CAD knitting. MXenes, a family of solution processable and conductive two-dimensional (2D) materials, have been realized as inks, slurries, pastes, and now dyes for the development of on-paper, on-plastic, and on-textile microsupercapacitor electrodes. In this work, Ti3C2Tx MXene was adopted as an active material for coating meters of commercial natural and synthetic yarns, enabling the production of knitted planar microsupercapacitors. The impact on electrochemical performance of knit structure and geometry was systematically studied in an attempt to produce energy storing textiles with power and energy densities that can be used for practical applications. The resulting energy storing textiles demonstrate high capacitance, up to 707 mF cm−2 and 519 mF cm−2 at 2 mV s−1 in 1 M H3PO4 and PVA-H3PO4 gel electrolyte, respectively, and excellent cycling stability over 10,000 cycles. This work represents an important step towards the mass production of MXene-based conductive yarns and 3D knitted energy storage devices and demonstrates how knit structure plays a significant role on device performance.

Boosting the electrochemical performance and reliability of conducting polymer microelectrode via intermediate graphene for on-chip asymmetric micro-supercapacitor

High-performance anode is hurdle for on-chip planar microsupercapacitor (MSC). Polypyrrole (PPy) is a highly attractive pseudocapacitive material, but its low cycling stability, and low adhesion with current collector hinder its practicability. Herein we propose one-prong generic strategy to boost the cycling stability of PPy. For our strategy, the electrochemical deposition of multilayered reduced graphene oxide (rGO) on micropatterned Au is utilized, and the resultant rGO@Au pattern is then used for growing highly porous PPy nanostructures by facile electrochemical polymerization. The fabricated PPy anode on rGO@Au has quasi rectangular cyclic voltammetry curves up to -0.7 V and exceptional cycling stability, retaining 82% of capacitance after 10,000 charge/discharge cycles in 2 M KCl electrolyte. The outstanding reliability of PPy on rGO@Au is due to the flexibility of rGO, accommodating structural pulverization and providing a promising background for the nucleation of highly porous nanostructure. Further, an all-polymer based asymmetric aqueous MSC (AMSC) is constructed with PPy anode and PEDOT cathode, which exhibited excellent electrochemical performance compared with conventional symmetric MSCs based on conducting polymers. The constructed AMSC delivered a maximum areal capacitance of 15.9 mF cm −2 (99.3 F cm −3 ), high specific energy and power densities of 4.3 µWh cm −2 (27.03 mWh cm −3 ) and 0.36 W cm −2 (0.68 W cm −3 ) at 1.4 V, respectively. The enhanced electrochemical performances can be illustrated by nucleation mechanism, in which surface topology of rGO generates a promising background for nucleation and electrochemical growth of nanoporous pseudocapacitive conducting polymers with superior interfacial contact and improved surface area. PPy@rGO//PEDOT@rGO-AMSC delivered a maximum areal capacitance of 15.9 mF cm −2 (99.3 F cm −3 ), high specific energy and power densities of 4.3 µWh cm −2 (27.03 mWh cm −3 ) and 0.36 W cm −2 (0.68 W cm −3 ) at 1.4 V.

High-performance, flexible planar microsupercapacitors based on crosslinked polyaniline using laser printing lithography

With the latest trend of miniaturization of modern portable electronic devices, the development of small-sized, flexible power sources is in great demand. Herein, we report the fabrication of flexible and high-performance planar microsupercapacitors (MSCs) on a poly-ethylene terephthalate substrate as portable energy storage devices. We employed a facile laser printing technology and thermal crosslinking route to fabricate crosslinked polyaniline (PANI) based MSCs, taking advantage of the low processing cost and high cyclic stability. The flexible PANI MSCs after heat treatment in Argon atmosphere exhibited a remarkably high areal capacitance of 54 mF cm−2 at the current density of 0.3 mA cm−2, which is much higher than that of PANI MSCs reported so far elsewhere. 79.8% of the initial capacitance was retained after 1000 cycles, indicating the excellent cyclic stability of the devices. This innovative approach provides a new strategy for the facile fabrication of flexible and high-performance planar energy storage devices.

Self-assembly of graphene-based planar micro-supercapacitor with selective laser etching-induced superhydrophobic/superhydrophilic pattern

Facile production of graphene-based in-plane interdigital electrode is critical for microscale supercapacitors but remains a great challenge (time consuming, expensive equipment needed, etc). The preparation of fine interdigital electrode planar micro-supercapacitors (MSCs) by selective laser etching of ceramic substrate is proposed, which provides an alternative method for rapid fabrication of planar MSCs. The formation of self-assembled electrode of graphene ink via the laser etching-induced heterogeneous surface wettability was firstly investigated, and then an all-solid-state MSCs microdevice was obtained by adding a polyvinyl alcohol–sulfuric acid gel electrolyte to the interdigital electrode region. The results of cyclic voltammetry test showed that the micro-supercapacitor device could offer an area capacitance of 5.5 mF cm−2 at a potential scan rate of 5 mV s−1 and the capacitance retention of 88.5% after 4500 cycles.

Memory Effect and Fractional Differential Dynamics in Planar Microsupercapacitors Based on Multiwalled Carbon Nanotube Arrays

The development of portable electronic devices has greatly stimulated the need for miniaturized power sources. Planar supercapacitors are micro-scale electrochemical energy storage devices that can be integrated with other microelectronic devices on a chip. In this paper, we study the behavior of microsupercapacitors with in-plane interdigital electrodes of carbon nanotube array under sinusoidal excitation, step voltage input and sawlike voltage input. Considering the anomalous diffusion of ions in the array and interelectrode space, we propose a fractional-order equivalent circuit model that successfully describes the measured impedance spectra. We demonstrate that the response of the investigated micro-supercapacitors is linear and the system is time-invariant. The numerical inversion of the Laplace transforms for electric current response in an equivalent circuit with a given impedance leads to results consistent with potentiostatic measurements and cyclic voltammograms. The use of electrodes based on an ordered array of nanotubes reduces the role of nonlinear effects in the behavior of a supercapacitor. The effect of the disordering of nanotubes with increasing array height on supercapacitor impedance is considered in the framework of a distributed-order subdiffusion model.

Impact of electrode geometry and thickness on planar on-chip microsupercapacitors.

We report an assessment of the influence of both finger geometry and vertically-oriented carbon nanofiber lengths in planar micro-supercapacitors. Increasing the finger number leads to an up-scaling in areal power densities, which increases with scan rate. Growing the nanofibers longer, however, does not lead to a proportional growth in capacitance, proposedly related to limited ion penetration of the electrode.

Flexible planar micro-supercapacitors based on carbon nanotubes

The boom in ultra-thin electronic devices and the growing need for humanization greatly facilitated the development of wearable flexible micro-devices. But the technology to deposit electrode material on flexible substrate is still in its infancy. Herein, the flexible symmetric micro-supercapacitors made of carbon nanotubes (CNTs) on commercial printing paper as electrode materials were fabricated by combining tetrahedral preparator auxiliary coating method and laser-cutting interdigital configuration technique on a large scale. The electrochemical performance of the obtained micro-supercapacitors can be controlled and tuned by simple choosing different models of tetrahedral preparatory to obtain CNTs film of different thicknesses. As expected, the micro-supercapacitor based on CNTs film can deliver an areal capacitance up to 4.56 mF/cm2 at current of 0.02 mA. Even if, micro-supercapacitor undergoes continuous 10000 cycles, the performance of device can still remain nearly 100%. The as-demonstrated tetrahedral preparator auxiliary coating method and laser-cutting interdigital configuration technique provide new perspective for preparing microelectronics in an economical way. The paper electrode appended by CNTs achieves steerable areal capacitance, showing broad application prospect in fabricating asymmetric micro-supercapacitor with flexible planar configurations in the future.

All Two-Dimensional Pseudocapacitive Sheet Materials for Flexible Asymmetric Solid-State Planar Microsupercapacitors with High Energy Density.

With the rapid development of portable devices and wireless protocols, miniaturized energy storage units have become an important prerequisite. Although in-plane microsupercapacitors are emerging as competitive candidate devices, their practical applications have been severely hindered by their low energy density. Here, employing pseudocapacitive active materials working in complementary voltage windows, namely, manganese oxide (MnO2) and titanium carbide (Ti3C2), both in the two-dimensional sheet morphology, a flexible asymmetric interdigitated solid-state microsupercapacitor was assembled. Profiting from the perfect voltage complementarity of the two types of sheets, the high exposure of electrochemically active sites and the maximized utilization of the sheets due to the planar ion transport, the designed device achieved excellent electrochemical performance even when using a gel electrolyte. In particular, the device obtained a high specific capacitance of 106 F g-1 (295 mF cm-2), a wide potential window (2 V), an ultrahigh rate performance (retaining 83% even with a 20-fold in current density to 20 A g-1), an excellent cycling stability (87% retention after 104 cycles at 10 A g-1), and a competitive energy density of 58 W h kg-1 (162 μW h cm-2) that are even comparable to those of some microbatteries, while maintaining a high power density of 985 W kg-1 (2.7 mW cm-2). Importantly, this outstanding electrochemical performance was also stably maintained under various bending conditions. These results indicate that two-dimensional pseudocapacitive sheet materials have a plethora of possibilities for constructing flexible and wearable devices.

Photolithographic fabrication of graphene-based all-solid-state planar on-chip microsupercapacitors with ultrahigh power characteristics

The fabrication of all-solid-state planar on-chip microsupercapacitors with ultrahigh power characteristics was demonstrated by reduced graphene oxide and photolithography technology. In this paper, an ultrathin reduced graphene oxide film with a thickness of 8 nm was prepared by a modified spin coating method that makes the microsupercapacitors have higher power characteristics which appear in high conductivity and fast charge and discharge rates. The electrodes, with a width of 150 μm, are narrower than existing electrodes in the field and fabricated by photolithography. In terms of performance, these microsupercapacitors have an extremely short time constant which is 0.03 ms, a high power density which is 17.94 W cm−3, and an excellent cycle stability with a capacitance retention of 94.6% after 10 000 cycles.

Enhanced Performance of an Electric Double Layer Microsupercapacitor Based on Novel Carbon-Encapsulated Cu Nanowire Network Structure As the Electrode.

In this work, the performance of a novel three-dimensional carbon-based planar microsupercapacitor (MSC) electrode structure is investigated. An in situ template-free fabrication of the Cu nanowire network structure acting as the current collector is first prepared through a chemical oxidation phase of sputtered Cu films, followed by a thermal reduction phase. Carbon is subsequently grown over the Cu nanostructure. In a two-electrode electrochemical test, the patterned interdigitated carbon/Cu nanowire network device exhibits an excellent maximum areal and volumetric capacitance of 1.45 and 7.43 mF cm-3, respectively, while retaining 94.2% of its capacitance after 10 000 charge-discharge cycles. This relatively simple foundry-compatible fabrication process provides an excellent method in which planar MSCs can be patterned and fabricated for energy storage solutions in microelectronics.

Excellent oxidation resistive MXene aqueous ink for micro-supercapacitor application

Uniform and stable interdigitated electrodes are essential for planar micro-supercapacitor applications. Two-dimensional (2D) materials, such as transition-metal MXenes have become attractive nanomaterials for micro-supercapacitor applications due to their layered structure and high electrical conductivity. However, the low stability of MXenes in aqueous media limits their long-term storage and application. Here, we demonstrate in-situ synthesis and capping of Ti3C2Tx MXenes with sodium ascorbate (SA) to obtain SA-MXene dispersion with high resistance against oxidation even after 80 days of storage at ambient temperature and exposed to air. The in-situ synthesis process increases the interlayer spacing of SA-MXene sheets, and increases their energy storage efficiency, without compromising their electrical conductivity. A printable SA-MXene ink was prepared with Triton X-100 and propylene glycol as modifiers to print interdigitated micro-supercapacitor electrodes with an inkjet printer. Our solid-state micro-supercapacitor made without current collector exhibits areal and volumetric capacitance of 108.1 mF cm−2 and 720.7 F cm−3, respectively. This work highlights the potential application of ligand-capped stable MXenes as a water-based ink in printing devices for the fabrication of micro-electronics and supercapacitors.

Boosting capacitive charge storage of 3D-printed micro-pseudocapacitors via rational holey graphene engineering

Micro-pseudocapacitors (MPCs) are prospective power source candidates with compatible sizes as well as superior power densities for miniaturized electronic devices; however, their limited capacitive charge storage characteristics are still hindering their further development. Herein, an optimized 3D printing technique is employed to build remarkable reduced holey graphene oxide (rHGO) supported MPC microelectrodes. In such microelectrodes, the presence of macroscale pores introduced through freeze drying is beneficial to the accessibility to electrolyte ions. Moreover, with two additional pore modals including the microscale pores from pseudocapacitive nanoparticles stacking and nanoscale in-plane holes formed by rational HGO engineering, the MPC microelectrodes offer an enhancement in both electrical and ionic transports. The resultant 3D-printed planar MPCs exhibit a remarkable device specific charge storage capacity of 241.3 mC cm−2, which is approximately 1.7-fold that of a non-optimized one and much higher than most reported planar micro-supercapacitors. Superior rate capability and high capacity retention (91% capacity retention after 11000 charge and discharge cycles) are also achieved. Our porosity engineering strategy combined with 3D printing is expected to serve as a facile and general design in the roadmap for next-generation state-of-the-art customized electrochemical energy storage devices.

A perspective on two-dimensional materials for planar micro-supercapacitors

The increasing demand for portable, wearable, and miniaturized electronics has substantially promoted the immense development of planar microsupercapacitors (MSCs) built on a single substrate. Atomically thin two-dimensional (2D) nanosheets, by virtue of their intrinsically unique structure and fascinating electrochemical properties, provide a new material platform for the creation of high performance planar MSCs in which the electrolyte ions can completely utilize flat architecture and ultrathin thickness of 2D nanosheets, parallel to the direction of ionic diffusion along the plane of 2D nanosheets. Herein, we present an overview and perspective on diverse 2D materials for planar MSCs. First, an introduction is presented to highlight the advances of MSCs, the uniqueness of 2D materials in the assembly of planar MSCs with three different configurations, i.e., stacked, interdigital, and 3D planar geometries, and the progress of microfabrication techniques for microelectrodes of MSCs. Second, the state-of-the-art 2D materials to manufacture planar MSCs, including graphene, transition metal oxides/hydroxides, transition metal dichalcogenides, metal carbides, metal nitrides, phosphorene, boron nitride, metal-organic frameworks, and covalent-organic frameworks, are systemically discussed in detail. Special emphasis is given to the multiple roles of 2D materials for functional components as active materials, current collectors, additives/binders, and separators for planar MSCs. Finally, the existing challenges and prospective solutions of 2D materials for planar MSCs with high performance and various innovative form factors are proposed.

Influence of electrode width on performance of planar on-chip micro-supercapacitors based on self-assembled graphene at liquid-air interface

Planar on-chip micro-supercapacitors (POMSs) with interdigital configuration were produced by photolithography and self-assembly of liquid-air interface. It is notable that the electrochemical performance of the POMS was significantly enhanced by reducing the electrode width from 300 μm to 180 μm, which highlight the importance of adjusting the width of electrode when creating high-performance POMS. It produced an area capacitance of 0.26 μF cm−2. In addition, POMS provide a power density of 0.825W cm−3, much higher than the power density of the electrolytic capacitor, and capacitor retention rate after 2000 cycles stabilized at 82.5%.

Graphene-based planar on-chip micro-supercapacitors with winding interdigitated microelectrodes

Planar on-chip micro-supercapacitors with winding interdigitated microelectrodes were fabricated by liquid-air interfacial assembly and lithography. The micro-supercapacitors with the microelectrodes (finger width of 210 μm and gap of 70 μm) can quickly complete charging and discharging in a very short time (84 ms), owing to the shortening of the ion path. They deliver an area capacitance of 90.39 μF cm−2 and a stack capacitance of 29.16 F cm−3. In addition, the energy density and the power density at 1 V s−1 are 4.05 mWh cm−3 and 145.79 mW cm−3, respectively. The micro-devices have excellent cycling stability with 98.5% capacitance retention after 2000 cyclic voltammetry cycles and can operate well at an ultrahigh scan rate of 5000 V s−1.

Inkjet-Printed High-Performance Flexible Micro-Supercapacitors with Porous Nanofiber-Like Electrode Structures.

Flexible planar micro-supercapacitors (MSCs) with unique loose and porous nanofiber-like electrode structures are fabricated by combining electrochemical deposition with inkjet printing. Benefiting from the resulting porous nanofiber-like structures, the areal capacitance of the inkjet-printed flexible planar MSCs is obviously enhanced to 46.6 mF cm-2 , which is among the highest values ever reported for MSCs. The complicated fabrication process is successfully averted as compared with previously reported best-performing planar MSCs. Besides excellent electrochemical performance, the resultant MSCs also show superior mechanical flexibility. The as-fabricated MSCs can be highly bent to 180° 1000 times with the capacitance retention still up to 86.8%. Intriguingly, because of the remarkable patterning capability of inkjet printing, various modular MSCs in serial and in parallel can be directly and facilely inkjet-printed without using external metal interconnects and tedious procedures. As a consequence, the electrochemical performance can be largely enhanced to better meet the demands of practical applications. Additionally, flexible serial MSCs with exquisite and aesthetic patterns are also inkjet-printed, showing great potential in fashionable wearable electronics. The results suggest a feasible strategy for the facile and cost-effective fabrication of high-performance flexible MSCs via inkjet printing.

Planar on-chip micro-supercapacitors based on graphene by chemical vapor deposition

Micro-supercapacitors (MSCs) are becoming one of the research frontiers in the field of chip storage devices. Here ultrahigh scanning rate, narrowing, planar interdigital graphene-based MSCs were fabricated by chemical vapor deposition (CVD) and photolithographic micro-fabrication. The energy density was up to 34.48 mWh cm−3 because of the interdigital architecture and monolayer graphene electrode. In addition, capacitance retention rates remained over 93.80% after 2500 charge/discharge cycles, which showed graphene-based MSCs good stability. More importantly, the MSCs can be operated well at an ultrahigh scan rate of up to 5000 V s−1. This paper provides an important reference for chip storage devices.

General Interfacial Self-Assembly Engineering for Patterning Two-Dimensional Polymers with Cylindrical Mesopores on Graphene.

Free-standing 2D porous nanomaterials have attracted considerable interest as ideal candidates of 2D film electrodes for planar energy storage devices. Nevertheless, the construction of well-defined mesopore arrays parallel to the lateral surface, which facilitate fast in-plane ionic diffusion, is a challenge. Now, a universal interface self-assembly strategy is used for patterning 2D porous polymers, for example, polypyrrole, polyaniline, and polydopamine, with cylindrical mesopores on graphene nanosheets. The resultant 2D sandwich-structured nanohybrids are employed as the interdigital microelectrodes for the assembly of planar micro-supercapacitors (MSCs), which deliver outstanding volumetric capacitance of 102 F cm-3 and energy density of 2.3 mWh cm-3 , outperforming most reported MSCs. The MSCs display remarkable flexibility and superior integration for boosting output voltage and capacitance.

Graphene-Based Planar On-Chip Micro-Supercapacitors with Whole Series/Parallel Configuration for Integration

The development of high-performance micro-supercapacitors is conducive to the growth of modern micro-electronic systems. However, it is still a great challenge to fabricate micro-supercapacitors with high output potential/current for integration. Here we demonstrate the whole fabrication of planar on-chip micro-supercapacitors (POMSs) based on reduced graphene oxide (RGO) films, produced by photolithography techniques, with whole series/parallel configuration. The RGO films have good surface morphologies, uniform thickness (6 ± 1.073 nm) and high conductivity (649.8 S cm−1) after hydroiodic acid treatment. Moreover, the operating potential of the RGO-POMS with whole series configuration has been obviously improved, which is two times that of a interdigital unit. The RGO-POMS with whole parallel configuration has larger current and better electrochemical performance than a single unit. Therefore, POMSs with whole series/parallel configuration have a good application foreground in the continuous development of integrated micro-devices.