Planar Supercapacitors Research Articles

Highly conductive templated-graphene fabrics for lightweight, flexible and foldable supercapacitors

The templated-rGO fabric, featuring high conductivity (<1.0 Ω □−1) and low density (160 mg cm−2), is prepared by a simple dip-coating technique with sequentially coating nickel via polymer-assisted metal deposition (PAMD) and reduced-graphene oxide (rGO) on textile fabric templates at very mild conditions and is used in the fabrication of energy storage devices. As a proof of concept, both the layered and planar supercapacitors (SCs) are successfully fabricated using the rGO fabrics as templates, and both exhibit excellent electrochemical performance, ultrahigh stability with 2000 charge–discharge cycles and mechanical flexibility at bending (r = 3 mm) and even folding states. It is found that the material of textile fabric used has a profound effect on the electrochemical property of SCs. The comparison result reveals that loose natural cotton fabrics are more suitable than tight man-made nylon fabrics for preparing high-performance SCs. In addition, such supercapacitor can be sewed into commercial textiles and powers a LED light, indicating promising applications in wearable electronics.

Bioinspired fractal electrodes for solar energy storages

Solar energy storage is an emerging technology which can promote the solar energy as the primary source of electricity. Recent development of laser scribed graphene electrodes exhibiting a high electrical conductivity have enabled a green technology platform for supercapacitor-based energy storage, resulting in cost-effective, environment-friendly features, and consequent readiness for on-chip integration. Due to the limitation of the ion-accessible active porous surface area, the energy densities of these supercapacitors are restricted below ~3 × 10−3 Whcm−3. In this paper, we demonstrate a new design of biomimetic laser scribed graphene electrodes for solar energy storage, which embraces the structure of Fern leaves characterized by the geometric family of space filling curves of fractals. This new conceptual design removes the limit of the conventional planar supercapacitors by significantly increasing the ratio of active surface area to volume of the new electrodes and reducing the electrolyte ionic path. The attained energy density is thus significantly increased to ~10−1 Whcm−3- more than 30 times higher than that achievable by the planar electrodes with ~95% coulombic efficiency of the solar energy storage. The energy storages with these novel electrodes open the prospects of efficient self-powered and solar-powered wearable, flexible and portable applications.

A Planar Graphene‐Based Film Supercapacitor Formed by Liquid–Air Interfacial Assembly

A liquid–air interfacial assembly is used to produce a flexible substrate‐supported graphene film, which does not need the tedious substrate‐transfer procedure that is generally required for many other film‐making methods. The graphene film is used as the active working electrode in its planar configuration and an acidic polymer gel is used as the electrolyte, which leads to a flexible planar graphene film supercapacitor with a large areal specific capacitance of 773 µF cm−2 and superior retention performance. In order to demonstrate the versatile application of interfacial assembly in obtaining graphene‐based hybrid film electrodes, graphene–manganese oxide and graphene–polyaniline hybrid films are assembled and used to construct planar film supercapacitors with areal specific capacitance of 963 and 2561 µF cm−2, respectively. Compared with the graphene film supercapacitor, the graphene–manganese oxide film supercapacitor, with neutral gel electrolyte, shows no apparent increase of specific capacitance, which is probably due to the larger electrolyte ions and hence the slower ion diffusion rate. Overall, the interfacial assembly is a universal technique for the fabrication of flexible, planar graphene‐based film supercapacitors, and this report demonstrates that such supercapacitors are promising as an advanced power system in wearable electronics.

Arbitrary-Shaped Graphene-Based Planar Sandwich Supercapacitors on One Substrate with Enhanced Flexibility and Integration.

The emerging smart power source-unitized electronics represent an utmost innovative paradigm requiring dramatic alteration from materials to device assembly and integration. However, traditional power sources with huge bottlenecks on the design and performance cannot keep pace with the revolutionized progress of shape-confirmable integrated circuits. Here, we demonstrate a versatile printable technology to fabricate arbitrary-shaped, printable graphene-based planar sandwich supercapacitors based on the layer-structured film of electrochemically exfoliated graphene as two electrodes and nanosized graphene oxide (lateral size of 100 nm) as a separator on one substrate. These monolithic planar supercapacitors not only possess arbitrary shapes, e.g., rectangle, hollow-square, "A" letter, "1" and "2" numbers, circle, and junction-wire shape, but also exhibit outstanding performance (∼280 F cm-3), excellent flexibility (no capacitance degradation under different bending states), and applicable scalability, which are far beyond those achieved by conventional technologies. More notably, such planar supercapacitors with superior integration can be readily interconnected in parallel and series, without use of metal interconnects and contacts, to modulate the output current and voltage of modular power sources for designable integrated circuits in various shapes and sizes.

Facile fabrication of all-solid-state flexible interdigitated MnO2 supercapacitor via in-situ catalytic solution route

Abstract With the rapid development of wearable and portable electronics, the demand for all-solid-state flexible energy storage devices with high performance, long-term cycling stability and bending stability has been aroused. Physical and chemical method for preparing thin-film materials has enabled planar flexible supercapacitors (SCs) to be fabricated for a variety of applications. In this work, we report on the facile fabrication of an all-solid-state flexible interdigitated supercapacitor with a convenient and efficient two-step method. 3-D nanostructured α-MnO 2 has been prepared on the surface of interdigitated Pt metal pattern on polyethylene terephthalate (PET) substrate as high-performance electrode material via in-situ catalytic solution route without any assistance of template or surfactant. The SCs are fabricated with PVA/H 3 PO 4 as solid-state electrolyte, which exhibited good electrochemical performance with areal capacitance as much as 20 mF cm −2 at a scan rate of 10 mV s −1 , relatively high energy density (3.6 × 10 −7 Wh cm −2 –1.9 × 10 −6 Wh cm −2 ) and power density (9 × 10 −5 W cm −2 –1.6 × 10 −4 W cm −2 ), and excellent long-term cycling stability with capacitance retention of 82.2% (10,000 times charge and discharge), and bending stability with capacitance retention of 89.6%.

2-Dimensional Supercapacitor Wires to Overcome Intrinsic Low Energy Density

Although a large number of reports on 2D flexible and stretchable energy storage devices have emerged within the past decade, 1D structure systems such as wires for higher flexibility, bio-compatibility and wearability have been desired for broader application of electronics. As a result of these requirements, wire-shaped devices among the cutting edge technologies in energy storage field are taking center stage for application to postmodern electronics and various fields such as fashion and culture. In view of mechanics, plane structures in 2D essentially have a unidirectional folding characteristics. On the other hand, wires with 1D structure have an omnidirectional serpentine structure in the other axes. In contrast to 2D planar formats, it is much easier for wire types to be integrated into more sophisticated structures such as woven textiles that can be used in our daily life. Although wire systems have a large structural potential, some fundamental obstacles hinder the use of wire-type energy storage. Electrochemical performances of wires are still underneath those of 2D plane cells. Many researchers have made efforts to overcome these barriers of wire-type energy storage devices. Most of them suggests ways to shape electrodes into cylindrical wires and a choice of material to maximize the performance as high as possible. In this study, however, we did not stick to using superb materials or constructing a cylinder, but theoretically analysed the origin of undefeatable charge-storage property of 2D plane over 1D wire. Based on this analysis we verified that a difference between wire-type and conventional planar supercapacitors induced the fundamental limits of wire-type supercapacitors. This limit is termed “energy lag effect.” With these derived information, we have first proposed the simultaneous incorporation of favorable electrochemical performance of 2D system and high flexibility of 1D system into solely one device. To exclude the identified limits, we designed a supercapacitor thread in unique structure that completely differs from conventional wire-type energy storage systems. The supercapacitor thread was designed as a dual plane-helix structure and proved not to show energy lag effects, experimentally or analytically.

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

Highly Flexible and Planar Supercapacitors Using Graphite Flakes/Polypyrrole in Polymer Lapping Film.

Flexible supercapacitor electrodes have been fabricated by simple fabrication technique using graphite nanoflakes on polymer lapping films as flexible substrate. An additional thin layer of conducting polymer polypyrrole over the electrode improved the surface conductivity and exhibited excellent electrochemical performances. Such capacitor films showed better energy density and power density with a maximum capacitance value of 37 mF cm(-2) in a half cell configuration using 1 M H2SO4 electrolyte, 23 mF cm(-2) in full cell, and 6 mF cm(-2) as planar cell configuration using poly(vinyl alcohol) (PVA)/phosphoric acid (H3PO4) solid state electrolyte. Moreover, the graphite nanoflakes/polypyrrole over polymer lapping film demonstrated good flexibility and cyclic stability.

On-chip interdigitated supercapacitor based on nano-porous gold/manganese oxide nanowires hybrid electrode

The rapid development of micro-sized electronics has aroused demand for on-chip energy storage devices of high reliability, stability and performance. Micro fabrication technology has now enabled planar supercapacitors (SCs), based on various electrode materials, to be prepared onto a chip for a variety of applications. Nano-porous metal/manganese oxide hybrid electrode with enhanced conductivity and capacitive performance has been proven to be a promising candidate for SCs but has not yet been utilized for interdigitated on-chip energy storage. Herein, we demonstrate a scalable preparation of nano-porous gold/manganese oxide nanowires thin film electrode material, which can be further fabricated to on-chip interdigitated all-solid-state supercapacitors on silicon wafers so that they can be integrated with MEMS or CMOS. Also the nucleation and growth mechanism of manganese oxide nanowires on nano-porous gold has been investigated. Remarkably, the miniaturized SCs based on the nano-porous gold/manganese oxide nanowires hybrid material exhibits excellent cycle stability and superior frequency response (4ms) and demonstrates energy density of 55μWhcm−3 and power density of 3.4Wcm−3, which is relatively high compared with other manganese oxide based supercapacitors.

Multilayer graphene synthesized using magnetron sputtering for planar supercapacitor application

This study reports the direct preparation of graphene-based films using magnetron sputtering of graphite target. The nanomaterial was deposited at a low temperature of 620 °C on silicon wafers and on metallic foils including aluminum. The films were used in fabrication of supercapacitors with a planar geometry. Electrochemical characterizations demonstrated that the films produced showed nearly ideal electrical capacitive behavior. The maximum capacitance obtained from cyclic voltammetry analysis was 325 F/g for a scan rate of 1 mV/s. The device is capable of delivering an energy density of 13.9 Wh/kg at a very high power density of 50 000 W/kg for ultrafast scan rate of 1000 mV/s. The graphene nanomaterial electrode retains the electrochemical stability over a large number of charge-discharge cycles.

Chemically Integrated Hybrid 2-D Materials for Flexible Energy Storage Devices

Two-dimensional (2-D) materials have been a promising material platform for making powerful energy devices including highly flexible energy storage devices. Owing to their advantageous features of flexibility, large surface area and open ion transport pathway within 2D layers, highly electroactive 2-D transition-metal oxide and phosphate nanosheets materials show promise in flexible supercapacitors with high power and energy densities. Here I will present our recent progress on chemically integrated hybrid 2-D materials to build ultraflexible, high-performance energy storage devices. One example is the building of integrated hybrid vanadyl phosphate VOPO4/graphene ultrathin-film solid-state pseudocapacitors (1). The other is the development of MnO2/graphene hybrid nanostructures based flexible planar supercapacitors (2).Rational material and structural design demonstrated in these studies show hybrid structures not only take advantage of excellent electronic conductivity of graphene nanosheets but also introduce more electrochemically active surfaces for absorption/desorption of electrolyte ions, which can greatly facilitate charge transport during electrochemical processes.References(1) Wu, C.; Lu, X.; Peng, L.; Xu, K.; Peng, X.; Huang, J.; Yu, G.; Xie, Y. Nature Communications 2013, 4, 2431.(2) Peng, L.; Peng, X.; Liu, B.; Wu, C.; Xie, Y.; Yu, G. Nano Letters 2013, 13, 2151.

Flexible symmetrical planar supercapacitors based on multi-layered MnO2/Ni/graphite/paper electrodes with high-efficient electrochemical energy storage

We develop a cheap and simple drawing-electrodeposition method to fabricate highly flexible MnO2/Ni/graphite/paper electrodes and assemble a paper-based energy storage device with high specific capacitance and excellent cycle stability.

Two-dimensional graphene/quasi-two-dimensional graphene analogues for flexible supercapacitor in all-solid-state

Two-dimensional (2D) graphene/quasi-two-dimensional inorganic materials have been widely explored for construction of energy- related applications. Catering for rapid development of portable electronic devices, energy storage devices with ultra-thin and high flexibility are urgently needed. Very recently, planar supercapacitor with novel configurations has been rapidly developed as important energy storage devices. In this regard, the assembled thin film of 2D graphene and quasi-2D graphene analogues acted as the vital role for the planar configurations as well as the enhanced performances in the construction of planar energy storage device. This review summarized the construction concept of flexible supercapacitors in all-solid-state based on 2D graphene and quasi-2D graphene analogues. We also surveyed how to select quasi-2D graphene analogues with high electrochemical properties, and even how to use the synergic advantages of hybrid structure for further performance enhancement of planar supercapacitors. Recent progresses and possible future applications on planar supercapacitors were also reviewed and outlooked.

Ultrathin Two-Dimensional MnO2/Graphene Hybrid Nanostructures for High-Performance, Flexible Planar Supercapacitors

Planar supercapacitors have recently attracted much attention owing to their unique and advantageous design for 2D nanomaterials based energy storage devices. However, improving the electrochemical performance of planar supercapacitors still remains a great challenge. Here we report for the first time a novel, high-performance in-plane supercapacitor based on hybrid nanostructures of quasi-2D ultrathin MnO2/graphene nanosheets. Specifically, the planar structures based on the δ-MnO2 nanosheets integrated on graphene sheets not only introduce more electrochemically active surfaces for absorption/desorption of electrolyte ions, but also bring additional interfaces at the hybridized interlayer areas to facilitate charge transport during charging/discharging processes. The unique structural design for planar supercapacitors enables great performance enhancements compared to graphene-only devices, exhibiting high specific capacitances of 267 F/g at current density of 0.2 A/g and 208 F/g at 10 A/g and excellent rate capability and cycling stability with capacitance retention of 92% after 7000 charge/discharge cycles. Moreover, the high planar malleability of planar supercapacitors makes possible superior flexibility and robust cyclability, yielding capacitance retention over 90% after 1000 times of folding/unfolding. Ultrathin 2D nanomaterials represent a promising material platform to realize highly flexible planar energy storage devices as the power back-ups for stretchable/flexible electronic devices.

Electrical characteristics of double stacked Ppy-PVA supercapacitor for powering biomedical MEMS devices

This paper discusses planar and double stacked supercapacitors with interwoven electrodes. Here, we study surface charge densities and capacitance performances of planar and sandwiched double stacked interdigital electrodes MEMS supercapacitors, and compare the improvement in electrical parameters between the two designs. The double stacked supercapacitor was constructed of polypyrrole (Ppy) coated nickel electrode as current collector and polyvinyl alcohol (PVA) as solid state electrolyte. Double stacked supercapacitor has the advantage of having increased charging capacity while maintaining equal layout area compared to the planar design. The extra charging capacity comes from the stacking of two mirrored planar supercapacitor via flip-chip processes. Another significant advantage of this technique is the completed supercapacitor cells are readily ‘flip chip’ packaged at wafer level, thus protecting the die from damage during back end processes. The planar and double stacked supercapacitor designs were simulated using Coventorware 2008 for capacitance performance analysis and COMSOL ver. 4.2 for electrical performance verification. It is observed that capacitance increases linearly with increasing number of cell, due to charge interactions among adjacent cells. In terms of electrical performance, maximum current response of 1.6 A/m was achieved. Double stacked supercapacitor has same layout, only slightly thicker compared to the planar structure due to double stacking, but with much superior charging capacity.

Planar thin film supercapacitor based on cluster-assembled nanostructured carbon and ionic liquid electrolyte

The fabrication of a planar supercapacitor based on cluster-assembled nanostructured carbon (ns-C) thin films deposited by supersonic cluster beam deposition and ionic liquid as electrolyte has been demonstrated. Cluster-assembled carbon has a density of about 0.5g/cm3 and a highly disordered structure with predominant sp2 hybridization, high surface roughness and granular nanoscale morphology. The electric double layer capacity of ns-C films (thickness variable in the range of 140–500nm) was investigated by electrochemical impedance spectroscopy and cyclic voltammetry employing four different hydrophobic room-temperature ionic liquids featuring the same anion and with different cations as electrolyte. Evidence of good impregnation of the ns-C nanoporous matrix by the different ionic liquids was found. The highest EDL capacity, 75F/g, was obtained by using [Bmim][NTf2], the ionic liquid with the shortest alkyl chain. Using [Bmim][NTf2] a supercapacitor with single electrode area of 0.2cm2 and specific capacity of ∼80μF/cm2 was obtained.

Stacked multilayers of alternating reduced graphene oxide and carbon nanotubes for planar supercapacitors

A simple layer-by-layer approach has been developed for constructing 2D planar supercapacitors of multi-stacked reduced graphene oxide and carbon nanotubes. This sandwiched 2D architecture enables the full utilization of the maximum active surface area of rGO nanosheets by using a CNT layer as a porous physical spacer to enhance the permeation of a gel electrolyte inside the structure and reduce the agglomeration of rGO nanosheets along the vertical direction. As a result, the stacked multilayers of rGO and CNTs are capable of offering higher output voltage and current production.