Asymmetric Micro-supercapacitors Research Articles

One-step electrodeposited MnxCo1−x(OH)2 nanosheet arrays as cathode for asymmetric on-chip micro-supercapacitors

Constructing on-chip microsupercapacitors (MSCs) with an asymmetric structure is the predominant choice for applications in miniaturized electronic devices. However, the complex fabrication methods of electrodes and the assembling process of devices restrict the development of on-chip MSCs. Herein, a planar asymmetric MSC with MnxCo1−x(OH)2 nanosheet arrays as the cathode and Fe3O4 nanoparticles as the anode is fabricated via a facile one-step electrodeposition method combined with microfabrication technology. The planar asymmetric MSC exhibits a wider operation voltage window (up to 1.65 V), a higher capacitance (32 mC cm−2), and a higher energy density (7.78 μW h cm−2) than those of previously reported MSCs with an alkaline aqueous electrolyte. This work demonstrates a model of the excellent combination of material synthesis and device fabrication towards large-scale manufacture of on-chip microdevices.

Polymer-MXene composite films formed by MXene-facilitated electrochemical polymerization for flexible solid-state microsupercapacitors

Materials with tailored properties are crucial for high performance electronics applications. Hybrid materials composed of inorganic and organic components can possess unique merits for broad application by synergy between the advantages the respective material type offers. Here we demonstrate a novel electrochemical polymerization (EP) enabled by a 2D transition metal carbide MXene for obtaining conjugated polymer-MXene composite films deposited on conducting substrates without using traditional electrolytes, indispensable compounds for commonly electrochemical polymerization. The universality of the process provides a novel approach for EP allowing fast facile process for obtaining different new polymer/MXene composites with controlled thickness and micro-pattern. Furthermore, high performance microsupercapacitors and asymmetric microsupercapacitors are realized based on the excellent composites benefiting from higher areal capacitance, better rate capabilities and lower contact resistance than conventional electropolymerized polymers. The AMSCs exhibit a maximum areal capacitance of 69.5 mF cm−2, an ultrahigh volumetric energy density (250.1 mWh cm−3) at 1.6 V, and excellent cycling stability up to 10000 cycles. The excellent electrochemical properties of the composite polymerized with MXene suggest a great potential of the method for various energy storage applications.

High-performance asymmetric micro-supercapacitors based on electrodeposited MnO2 and N-doped graphene

In-plane asymmetric micro-supercapacitors using nitrogen-doped graphene (NG) film as negative electrode and MnO2 nanostructures as positive electrode are fabricated onto a plastic substrate coated with Ni/Cu film. A laser-scribing machine is employed to make interdigital finger electrodes in the plastic substrate coated with NG film via a slurry coating process. MnO2 nanosheets are electrochemically deposited onto pre-coated NG film. In LiCl-based gelled electrolyte, the NG//MnO2 cell exhibits excellent electrochemical performance and a broad voltage window up to 1.8 V. The maximum specific capacitance of a single cell is measured to be 13 mF cm−2. In addition, several cells in series can be easily fabricated by combining the laser-scribing technique and the electrodeposition of MnO2 electrodes. As a proof of concept, four cells in a compact configuration and with high voltage output up to 7.2 V are demonstrated.

High-performance, flexible, solid-state micro-supercapacitors based on printed asymmetric interdigital electrodes and bio-hydrogel for on-chip electronics

Rapid development of miniature, portable and highly integrated electronics increases the demand for micro-sized power sources and on-chip energy storage units; micro-supercapacitors with in-plane electrode finger arrays are developed for this purpose. This study fabricates flexible, solid-state, interdigital micro-supercapacitors with MoO3-x nanorods as cathode fingers and glucose-derived activated carbon nanospheres as anode fingers via a facile and economic screen-printing technique. A highly concentrated sodium alginate bio-hydrogel is used as the non-toxic and biocompatible electrolyte, which provides wider electrochemical stability window (∼2.8 V) than that of conventional aqueous electrolytes (1.23 V). The fabricated asymmetric micro-supercapacitors present outstanding electrochemical performances, for example, high areal capacitance of 47.20 mF cm−2, superior energy density of 21.20 μWh cm−2 (47.11 mWh cm−3) at a power density of 0.18 mW cm−2 (0.40 W cm−3), and excellent capacitance retention of 95% after 10,000 cycles. The device also exhibits good mechanical stability and can be integrated into any printed circuits, demonstrating its potential application for highly customized power systems in the Internet of Things and wearable/implantable on-chip electronics with high safety requirement.

Nickel molybdate nanorods supported on three-dimensional, porous nickel film coated on copper wire as an advanced binder-free electrode for flexible wire-type asymmetric micro-supercapacitors with enhanced electrochemical performances

Wire-shaped micro-supercapacitors attracted extensive attentions in next-generation portable and wearable electronics, due to advantages of miniature size, lightweight and flexibility. Herein, NiMoO4 nanorods supported on Ni film coated Cu wire are successfully fabricated thorough direct deposition of Ni film onto Cu wire as the conductive substrate, followed by growth of the NiMoO4 nanorods on Ni film coated Cu wire substrate by means a hydrothermal annealing process. The prepared 3D, porous electrode demonstrates extremely high areal specific capacitance of 12.03F cm−2 at the current density of 4 mA cm−2 and retained capacitance of 8.23 F cm−2 at a much higher current density of 80 mAcm−2. The electrode, also, shows an excellent cycling stability with capacitance retention of 99.3% after 3000 cycles. The superior electrochemical performance can be attributed to the high area surface, low contact resistance between NiMoO4 nanorods and Cu wire current collector and presence of a 3D and porous structure provides many electroactive sites and sufficient open space for easy diffusion of the electrolyte ions during redox reactions. Benefiting from their structural features, a fiber shaped asymmetric micro-supercapacitor based on NiMoO4/Ni film/Cu wire as the positive electrode and carbon fiber coated with reduced graphene oxide as the negative electrode is assembled. The fabricated fiber device presents a wide potential window between 0 and 1.7 V and exhibits high specific capacitance of 0.504F cm−2 (38.8F cm−3) at a current density of 4.8 mA cm−2 with a high energy density of 202 µWh cm−2 (15.6 mWh cm−3) at a power density of 4050 µW cm−2 (313 mWh cm−3). The energy density retains 124 µWh cm−2 (9.54 mWh cm−3) when the power density is increased to 13530 µW cm−2 (1040.73 mWh cm−3). In addition, the asymmetric device exhibits an outstanding cycling stability (98.5% capacitance retention after 1000 consecutive cycles) and good mechanical stability. Therefore, this work suggested the promising potential of NiMoO4 nanorods supported on Ni film coated Cu wire as an advanced electrode material for construction of flexible and portable next-generation energy storage micro-devices with superior electrochemical performances.

Nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films for in-plane asymmetric micro-supercapacitors with ultrahigh energy density

In-plane asymmetric micro-supercapacitors with ultrahigh energy density are rationally constructed using nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films.

Shape-tailorable high-energy asymmetric micro-supercapacitors based on plasma reduced and nitrogen-doped graphene oxide and MoO2 nanoparticles

High-energy asymmetric micro-supercapacitors have been fabricated with diversified planar geometries.

2D mesoporous MnO2 nanosheets for high-energy asymmetric micro-supercapacitors in water-in-salt gel electrolyte

Two-dimensional (2D) mesoporous nanosheets as electrodes present a critical materials platform for dramatically boosting the performance of planar micro-supercapacitors (MSCs) due to their unique features of interconnected porous network, enriched nanopore arrays, and high specific surface area. However, efficient strategies for constructing such complicated mesoporous architectures are very limited. Here, we developed a supramolecular bottom-up self-assembly strategy for direct synthesis of ultrathin mesoporous manganese dioxide (m-MnO2) nanosheets for high-energy all-solid-state planar asymmetric MSCs (AMSCs). The m-MnO2 nanosheets exhibited ultrathin thickness of 10 nm, uniformly interconnected network of mesopores with size of 5–15 nm, high surface area of 128 m2 g−1, and remarkably enhanced capacitance of 243 F g−1 at 1 mV s−1 in comparison with non-mesoporous MnO2 nanosheets (123 F g−1). Further, all-solid-state AMSCs were assembled based on m-MnO2 nanosheets as positive electrode, porous VN nanosheets as negative electrode, and electrochemically exfoliated graphene as conductive agent and metal-free current collector in “water-in-salt” gel electrolyte. Importantly, our all-solid-state AMSCs operated stably at 2.0 V and offered impressive energy density of 21.6 mWh cm−3, outperforming most reported MnO2 based MSCs, and two times higher than lithium thin-film batteries (≤10 mWh cm−3). Also, they presented long-term cycling stability with 90% capacity retention after 5000 cycles, outstanding flexibility without observable capacitance decay under different bending angles, and facile serial and parallel interconnection for creating high-voltage and high-capacitance integrated bipolar cells. Therefore, our proposed strategy will open many opportunites for patterning novel 2D mesoporous metal oxide nanosheets for high-performance microscale electrochemical energy storage devices.

Flexible Asymmetric Microsupercapacitors from Freestanding Hollow Nickel Microfiber Electrodes

AbstractThe increasing demand for flexible and wearable microelectronics is a major driving force for the development of high‐performance small‐volume energy sources. Microsupercapacitors exhibit significant potential in energy storage as they provide high power and good cycle stability. Yet, most microsupercapacitors display low energy densities limiting their practical use in microelectronics. Here, synthesis of high surface area freestanding electrodes comprising hollow nickel microfibers is demonstrated. The microfiber nickel electrodes constitute a platform for flexible asymmetric microsupercapacitors exhibiting excellent mechanical resilience as well as high energy density (0.11 mWh cm−2) and power density (37.5 mW cm−2). The freestanding nature and extensive surface area of the electrodes contribute to pronounced areal and volumetric capacitance, energy storage values, and stability after numerous (hundreds) physical bending cycles. The simple preparation scheme and use of an inexpensive building block (e.g., nickel) underscore potential uses as light and flexible energy storage devices.

On-Chip Asymmetric Microsupercapacitors Combining Reduced Graphene Oxide and Manganese Oxide for High Energy-Power Tradeoff

Given the rapid miniaturization of technology, it is of interest to produce viable on-chip micro-electrochemical energy storage systems. In this study, interdigitated asymmetric microsupercapacitors were fabricated using photolithography, lift-off and electrodeposition methods. Manganese oxide (MnOx) and reduced graphene oxide (rGO) comprised the pseudocapacitive and the double layer component, respectively. Symmetric MnOx//MnOx, rGO//rGO as well as asymmetric rGO//MnOx microsupercapacitors with three different MnOx thicknesses were constructed and characterized in aqueous media. The asymmetric microsupercapacitor with the intermediate MnOx film thickness displayed the optimal energy-power trade-off superior to that of both the symmetric and well as the other asymmetric configurations. The optimal microsupercapacitor exhibited a high stack energy density of 1.02 mWh·cm−3 and a maximal power density of 3.44 W·cm−3. The high energy-power trade-off of the device is attributed to the synergistic effects of utilizing double layer and pseudocapacitive charge storage mechanisms along with in-plane interdigital microelectrode design within one optimized micro-device.

All-solid-state high-energy planar hybrid micro-supercapacitors based on 2D VN nanosheets and Co(OH)2 nanoflowers

Planar micro-supercapacitors are recognized as one of the most competitive on-chip power sources for integrated electronics. However, most reported symmetric micro-supercapacitors suffer from low energy density. Herein, we demonstrate the facile mask-assisted fabrication of new-type all-solid-state planar hybrid micro-supercapacitors with high energy density, based on interdigital patterned films of porous vanadium nitride nanosheets as negative electrode and Co(OH)2 nanoflowers as positive electrode. The resultant planar hybrid micro-supercapacitors display high areal capacitance of 21 mF cm−2 and volumetric capacitance of 39.7 F cm−3 at 0.2 mA cm−2, and exhibit remarkable energy density of 12.4 mWh cm−3 and power density of 1750 mW cm−3, based on the whole device, outperforming most reported planar hybrid micro-supercapacitors and planar asymmetric micro-supercapacitors. Moreover, all-solid-state planar hybrid micro-supercapacitors show excellent cyclability with 84% capacitance retention after 10000 cycles, and exceptionally mechanical flexibility. Therefore, our proposed strategy for the simplified construction of planar hybrid micro-supercapacitors will offer numerous opportunities of utilizing graphene and other 2D nanosheets for high-energy microscale supercapacitors for electronics.

High-Performance Microsupercapacitors Based on Bioinspired Graphene Microfibers.

The miniaturization of portable electronic devices has fueled the development of microsupercapacitors that hold great potential to complement or even replace microbatteries and electrolytic capacitors. In spite of recent developments taking advantage of printing and lithography, it remains a great challenge to attain a high energy density without sacrificing the power density. Herein, a new protocol mimicking the spider's spinning process is developed to create highly oriented microfibers from graphene-based composites via a purpose-designed microfluidic chip. The orientation provides the microfibers with an electrical conductivity of ∼3 × 104 S m-1, which leads to a high power density; the energy density is sustained by nanocarbons and high-purity metallic molybdenum disulfide. The microfibers are patterned in-plane to fabricate asymmetric microsupercapacitors for flexible and on-chip energy storage. The on-chip microsupercapacitor with a high pattern resolution of 100 μm delivers energy density up to the order of 10-2 W h cm-3 and retains an ultrahigh power density exceeding 100 W cm-3 in an aqueous electrolyte. This work provides new design of flexible and on-chip asymmetric microsupercapacitors based on microfibers. The unique biomimetic microfluidic fabrication of graphene microfibers for energy storage may also stimulate thinking of the bionic design in many other fields.

Paper-based all-solid-state flexible asymmetric micro-supercapacitors fabricated by a simple pencil drawing methodology

Flexible micro-scale energy storage devices as the key component to power the flexible miniaturized electronic devices are attracting extensive attention. In this study, interdigitated asymmetric all-solid-state flexible micro-supercapacitors (MSCs) were fabricated by a simple pencil drawing process followed by electrodepositing MnO2 on one of the as-drawn graphite electrode as anode and the other as cathode. The as-prepared electrodes showed high areal specific capacitance of 220μF/cm2 at 2.5μA/cm2. The energy density and the corresponding power density of the resultant asymmetrical flexible MSCs were up to 110μWh/cm2 and 1.2μW/cm2, respectively. Furthermore, excellent cycling performance (91% retention of capacity after 1000 cycles) was achieved. The resultant devices also exhibited good electrochemical stability under bending conditions, demonstrating superior flexibility. This study provides a simple yet efficient methodology for designing and fabricating flexible supercapacitors applicable for portable and wearable electronics.

Flexible quasi-solid-state 2.4 V aqueous asymmetric microsupercapacitors with ultrahigh energy density

A simple and cost-effective cut-and-transfer method is demonstrated to fabricate flexible 2.4 V asymmetric microsupercapacitors by adopting hierarchical Na-MnOx nanosheets on 3D nitrogen-doped carbon fibers as the cathode and VN nanosheet arrays as the anode.

A Patterned Graphene/ZnO UV Sensor Driven by Integrated Asymmetric Micro‐Supercapacitors on a Liquid Metal Patterned Foldable Paper

A foldable array of patterned graphene/ZnO nanoparticle UV sensor and asymmetric micro‐supercapacitors (AMSCs) integrated on a paper substrate with patterned liquid metal interconnections is reported. The resistor type UV sensor based on graphene/ZnO nanoparticles is patterned to be driven by the stored energy of the integrated AMSCs. The AMSC consists of MnO2 nanoball deposited multiwalled carbon nanotubes (MWNTs) and V2O5 wrapped MWNTs as positive and negative electrodes, respectively. As an electrolyte, propylene carbonate‐poly(methyl methacrylate)‐LiClO4, an organic solvent‐based gel, is used. The UV sensor and AMSCs can be easily integrated on a liquid metal, Galinstan, patterned, waterproof mineral paper and show a mechanically stable UV sensing, regardless of repetitive folding cycles. This work demonstrates a novel foldable nanomaterial based sensor system driven by integrated energy storage devices, applicable to future wearable and portable electronics.

Capacitance and voltage matching between MnO2 nanoflake cathode and Fe2O3 nanoparticle anode for high-performance asymmetric micro-supercapacitors

Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices. Asymmetric structures have been widely investigated in micro-supercapacitors, and carbon-based materials are commonly applied in the electrodes. To integrate different metal oxides in both electrodes in micro-supercapacitors, the critical challenge is the pairing of different faradic metal oxides. Herein, we propose a strategy of matching the voltage and capacitance of two faradic materials that are fully integrated into one high-performance asymmetric micro-supercapacitor by a facile and controllable fabrication process. The fabricated micro-supercapacitors employ MnO2 as the positive active material and Fe2O3 as the negative active material, respectively. The planar asymmetric micro-supercapacitors possess a high capacitance of 60 F·cm–3, a high energy density of 12 mW·h·cm–3, and a broad operation voltage range up to 1.2 V.

Optimization of coplanar high rate supercapacitors

In this work, we describe two efficient methods to enhance the electrochemical performance of high-rate coplanar micro-supercapacitors (MSCs). Through introducing MnO2 nanosheets on vertical-aligned carbon nanotube (VACNT) array, the areal capacitance and volumetric energy density exhibit tremendous improvements which have been increased from 0.011 mF cm−2 to 0.017 mWh cm−3 to 0.479 mF cm−2 and 0.426 mWh cm−3 respectively at an ultrahigh scan rate of 50000 mV s−1. Subsequently, by fabricating an asymmetric MSC, the energy density could be increased to 0.167 mWh cm−3 as well. Moreover, as a result of applying MnO2/VACNT as the positive electrode and VACNT as the negative electrode, the cell operating voltage in aqueous electrolyte could be increased to as high as 2.0 V. Our advanced planar MSCs could operate well at different high scan rates and offer a promising integration potential with other in-plane devices on the same substrate.

All-solid state, flexible, high-energy integrated hybrid micro-supercapacitors based on 3D LSG/CoNi2S4 nanosheets.

3D LSG/CoNi2S4//LSG interdigitated microelectrodes have been firstly developed by a facile, scalable and low cost process for all-solid-state, flexible integrated asymmetric micro-supercapacitors. These devices can achieve energy densities of up to 49 W h l-1 which is comparable to those of lead acid batteries.

High-Performance Pseudocapacitive Microsupercapacitors from Laser-Induced Graphene.

All-solid-state, flexible, symmetric, and asymmetric microsupercapacitors are fabricated by a simple method in a scalable fashion from laser-induced graphene on commercial polyimide films, followed by electrodeposition of pseudocapacitive materials on the interdigitated in-plane architectures. These microsupercapacitors demonstrate comparable energy density to commercial lithium thin-film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility.

Engineering the Electrochemical Capacitive Properties of Microsupercapacitors Based on Graphene Quantum Dots/MnO2 Using Ionic Liquid Gel Electrolytes.

All-solid-state microsupercapacitors (MSCs) have been receiving intense interest due to their potential as micro/nanoscale energy storage devices, but their low energy density has limited practical applications. It has been reported that gel electrolytes based on ionic liquids (ionogels) with large potential windows can be used as solid electrolytes to enhance the energy density of MSCs, but a systematic study on how to select and evaluate such ionogels for MSCs is rare. In this study, we construct a series of all-solid-state asymmetric MSCs on the interdigital finger electrodes, using graphene quantum dots (GQDs) as the negative electrode, MnO2 nanosheets as the positive electrode, and different ionogels as the solid electrolytes. Among them, the MSC using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTF2]) with 4 wt % fumed SiO2 ionogel exhibited the best electrochemical performance, having excellent rate capability with the scan rate up to 2000 V s(-1), ultrafast frequency response (τ0 = 206.9 μs) and high energy density. The outstanding performance of this device mainly results from fast ion diffusion, high ion conductivity of the ionogel, and ionic liquid-matrix interactions. The results presented here provide guidance for picking out appropriate ionogels for use in high-performance all-solid-state MSCs to meet the growing requirement of micronanoscale energy storage devices. Additionally, the ultrafast frequency response of our MSCs suggests potential applications in ac line-filters.