Design Of Supercapacitors Research Articles

Mesoporous structure favorable for high voltage and high energy supercapacitor based on green tea waste-derived activated carbon

Designing high voltage, high energy, and activated carbon-based supercapacitors has been a long-time wish for meeting various electronic module requirements. This paper focuses on the approach of synthesizing the hierarchical porous activated carbon with dominant mesopores using eco-friendly green tea waste. The desirable ample pore space achieved by changing the weight ratio of KOH activating agent renders more ionic accessibility and space charge distribution. This feature leads to the achievement of 4 V double layer supercapacitor with a remarkable specific energy of 142 Wh kg−1 and specific power of 3192 W kg−1, respectively using an acetonitrile organic electrolyte. The fabricated cell also exhibits a superior 104% capacitance retention after 25 000 charge-discharge cycles at the working potential of ≥3 V. Besides, the hierarchical porous activated carbon soaked in an aqueous KOH electrolyte shows a high specific capacitance of 397 F g−1 at 5 mA cm−2, high rate capability of 100 mA cm−2, and excellent cycle life of 116% capacitance retention after 50 000 cycles tested at 200 mA cm−2. The larger Debye length of the diffuse ion layer permitted by the mesopores is proposed to explain the higher voltage window as against low voltage of micropore dominated commercial activated carbon. The present research may pave the way toward the design of high-energy supercapacitors through recycling tea waste.

Design and fabrication of high performance supercapacitor with cellulosic paper electrode and plant-derived redox active molecules

As a promising substrate, cellulose fibers were widely investigated in supercapacitors for their low cost and sustainability. However, the low performance created great barrier for the future applications of the cellulosic paper-based supercapacitors. The performance of paper-based supercapaciors may be improved by the addition of redox active molecule. As a plant derived redox active molecule, Alizarin red S was used to improve the performance of PEDOT paper-based electrode via a simple post-treatment process. By combination of the treated paper electrode and the redox electrolyte, a symmetric paper-based supercapacitor with a superior performance of 2191.3 m F/cm2 (at 5 mA/cm2) and 4.87 mW h/cm3 (at power density of 36 mW/cm3) were fabricated. The charge and mass transfer mechanisms of paper electrode were detailed discussed. The simple and efficient strategy developed in this work opens up new doors for the development of other cellulose related high performance energy storage devices.

Laminate composite-based highly durable and flexible supercapacitors for wearable energy storage

Flexible supercapacitors are promising power sources for next-generation flexible electronics because they are safe, mechanically stable and durable compared with current batteries. However, flexible supercapacitor devices reported so far have not demonstrated adequate mechanical properties to withstand critical deformations for real-world applications. Here we present our design and construction of flexible supercapacitors using laminate composites to achieve exceptional mechanical properties, including foldability, twistability, and machine washability. The electrode layer is made of a polymer electrolyte/carbon electrode (matrix/filler) composite, with mechanical and electrochemical performance optimized simultaneously in its making. Calculations and experimental results show that proper volume ratio of the electrolyte matrix and fiber-based electrode fillers leads to desired flexibility, strength, as well as high areal capacitance. The prototypes show adjustable areal capacitances of over 40 mF/cm2 with comparable thickness and flexibility to wearable fabrics. The electrochemical performance has remained unchanged after repeated folding and twisting tests. Moreover, a prototype device sewed onto a wearable fabric show non-detectable mechanical damage or capacitance degradation after machine washing.

Two-Dimensional Transition Metal Oxide and Hydroxide-Based Hierarchical Architectures for Advanced Supercapacitor Materials.

The supercapacitor has been widely seen as one of the most promising emerging energy storage devices, by which electricity is converted from chemical energy and stored. Two-dimensional (2D) metal oxides/hydroxides (TMOs/TMHs) are revolutionizing the design of high-performance supercapacitors because of their high theoretical specific capacitance, abundance of electrochemically active sites, and feasibility for assembly in hierarchical structures by integrating with graphitic carbon, conductive polymers, and so on. The hierarchical structures achieved can not only overcome the limitations of using a single material but also bring new breakthroughs in performance. In this article, the research progress on 2D TMOs/TMHs and their use in hierarchical structures as supercapacitor materials are reviewed, including the evolution of supercapacitor materials, the configurations of hierarchical structures, the electrical properties regulated, and the existence of advantages and drawbacks. Finally, a perspective covering directions and challenges related to the development of supercapacitor materials is provided.

Effect of PANI and PPy on Electrochemical Performance of rGO/ZnMn2O4 Aerogels as Electrodes for Supercapacitors

Conductive polymers, such as polyaniline (PANI) and polypyrrole (PPy), are widely used in the design of supercapacitors because of their high pseudo-capacitive performance as well as facile synthesis and low cost. In this study, hybrid aerogels based on reduced graphene oxide and ZnMn2O4 were modified by PANI and PPy. The 3D structure of the hybrid aerogels was obtained by using a one-step hydrothermal co-assembly method. Then, aniline and pyrrole were polymerized on and within the structure of the hybrid aerogel through in situ polymerization. The electrochemical properties of the hybrid aerogels were studied via cyclic voltammetry and galvanostatic charge–discharge testing to identify the effects of conductive polymers on the electrochemical properties of materials. It has been established that PANI and PPy facilitate an increase of the specific capacitance of rGO/ZnMn2O4 aerogels up to 297.8 F/g and 108.24 F/g at 0.2 A/g scan rate, respectively.

Two-step synthesis of millimeter-scale flexible tubular supercapacitors

Flexible supercapacitors have been demonstrated to be ideal energy storage devices owing to their lightweight and flexible nature and their high power density. However, conventional film-shaped devices struggle to meet the requirements of application in complicated situations, including medical instruments and wearable electronics. Here we report a hollow-structured flexible tubular supercapacitor prepared from a scalable method with the same diameter as electric wires. This new supercapacitor design allows for a large specific capacitance of 102 F g−1 at a current density of 1 A g−1 with excellent air-working stability over 10,000 cycles. It also shows a high energy density of 14.2 Wh kg−1 with good rate capability even at a current density of 10 A g−1, which is superior to commercial devices (3–10 Wh kg−1). Moreover, the device delivers a stable energy storage capacity when encountering different flexible conditions, such as elongated, tangled and bent states, showing wide potentials in flexible and even wearable applications. Especially, it retains stable specific capacitance even after 500 bending cycles with a bending angle of 180°. The two-step fabrication method of these flexible tubular supercapacitors may allow for possible mass production, as they could be easily integrated with other functional components, and used in realistic scenarios that conventional film devices struggle to realize.

Interface engineering boosts electrochemical performance by fabricating CeO2@CoP Schottky conjunction for hybrid supercapacitors

A novel strategy of boosting electrochemical performance of hybrid supercapacitor cathode based on interface engineering by fabrication of Schottky-type conjunction is proposed. The electrode is composed of binder free 3D CoP nanoflowers decorated by CeO2 nanoparticles, which was directly grown on nickel foam, forming a conjunction interface. Compared to CoP, the CeO2@CoP electrode exhibits remarkable enhanced electrochemical performance. The significantly boosted performance can be attributed to the CeO2@CoP interface, which promotes electrons migration from CoP to CeO2 and eventually forms positive holes on CoP. These positive holes can easily capture more OH−, creating more active sites for redox process. Furthermore, a hybrid supercapacitor full cell composed of CeO2@CoP and activated carbon was assembled, which exhibits outstanding energy storage performance with a specific capacity of 486.5 mC cm−2 at 1 mA cm−2 and outstanding cycle stability of 89% after 5000 cycles. The energy density is 55.4 Wh kg−1 at a power density of 955.9 W kg−1. This work not only demonstrates that CeO2 is an attractive additive for supercapacitor electrodes, but also provides an experimental/theoretical understanding of the enhanced electrochemical performance by electrons migration process on CeO2@CoP interfaces, which is important for the design of supercapacitors.

The accurate control of the La2O3 hierarchical structure of the flower-like microspheres accompanied with vertical-standing nanopetals and the electrowetting responses with low voltage actuation

A simple hydrothermal method is successfully used to prepare the La2O3 film, and the accurate control of its surface structure is realized through the hydrothermal temperature and time from the sparsely dispersed compact microspheres to closely packed microsphere film, then from the hierarchical structure of the sparsely dispersed compact and flower-like microspheres accompanied with the discrete vertical-standing nanopetals to the hierarchical structure constituted by the closely packed compact microspheres and dense vertical-standing nanopetals. The XRD analysis shows the prepared film is mainly made of hexagonal La2O3 accompanied with some impurities of La(OH)2NO3, La(OH)3 and La2TiO5. Valuably, the prepared La2O3 film has high capacitance which can be modulated by surface structure, and achieves the maximum when the surface structure is hierarchical structure constituted by the closely packed compact microspheres and vertical-standing nanopetals. Eventually, the high capacitance leads to the electrowetting-on-dielectric (EWOD) responses with low voltage actuation below 8 V and wide contact angle modulation range of about 131°. The works are very beneficial to the design and preparation of supercapacitor and EWOD devices with high performance.

Ion conductivity through TEMPO-mediated oxidated and periodate oxidated cellulose membranes

Cellulose in different forms is increasingly used due to sustainability aspects. Even though cellulose itself is an isolating material, it might affect ion transport in electronic applications. This effect is important to understand for instance in the design of cellulose-based supercapacitors. To test the ion conductivity through membranes made from cellulose nanofibril (CNF) materials, different electrolytes chosen with respect to the Hofmeister series were studied. The CNF samples were oxidised to three different surface charge levels via 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), and a second batch was further cross-linked by periodate oxidation to increase wet strength and stability. The outcome showed that the CNF pre-treatment and choice of electrolyte are both crucial to the ion conductivity through the membranes. Significant specific ion effects were observed for the TEMPO-oxidised CNF. Periodate oxidated CNF showed low ion conductivity for all electrolytes tested due to an inhibited swelling caused by the crosslinking reaction.

Carbon dot-modified mesoporous carbon as a supercapacitor with enhanced light-assisted capacitance.

A light-charging energy storage device is a promising approach of utilizing solar energy, and the reasonable design of light-assisted supercapacitors with photosensitive materials is one of the efficient ways to realize solar energy conversion and storage. Here, the electrode material (OPC-CDs-700) prepared by combining procanthocyanins with carbon dots (CDs) can reach the specific capacitance of 312 F g-1 at 0.1 A g-1 under visible light, which is an increase of 54.4% compared with that of under dark conditions. Besides, this light-assisted supercapacitor exhibits excellent cyclic stability after 4000 cycles. A series of electrochemical measurements show that CDs could stabilize the charge under light illumination due to its photoactivity, thus increasing the accumulation and storage of charge on the surface of OPC-CDs-700. This study provides new prospects for the progress of photosensitive energy devices and application of solar energy.

Plane tree bark-derived mesopore-dominant hierarchical carbon for high-voltage supercapacitors

Wide potential range and high specific capacitance of electrode materials are critical to high performance supercapacitors. However, it remains challenging to simultaneously achieve both high capacitance and cell voltage, particularly in organic electrolytes. Herein, three dimensional (3D) mesopore-dominant hierarchical carbons are obtained by one-step pyrolysis-activation of seasonable biowaste, i.e., plane tree bark with nano-ZnO as a mild activator. The optimized biowaste-derived carbon shows an ultrahigh mesopore area and low oxygen content. With these merits, the carbon electrodes show both high capacitance and wide capacitive potential range in both aqueous and organic electrolyte. Particularly, a specific capacitance of 115.6F g−1 and a high cell voltage of 3 V are achieved with organic electrolyte. This study also reveals a mismatch between the specific capacitance and four commonly used specific surface area values. In a symmetrical supercapacitor with organic electrolyte, the positive electrode is the voltage-determining electrode. These findings may provide new perspectives on materials and device design of high-voltage supercapacitors.

Hierarchical architecture of polyaniline nanoneedle arrays on electrochemically exfoliated graphene for supercapacitors and sodium batteries cathode

This study reports an efficient and straightforward method to construct hierarchical architectures for electrochemical energy storage. The composites, which are based on needle-like polyaniline (PANI) and high quality electrochemical exfoliation graphene (EG), can be a potential candidate for sodium batteries cathode due to favorable structural and morphological properties. Kinetics analysis of cyclic voltammetry has evidenced the diffusion controlled and pseudocapacitive controlled contributions of charge storage in the EG-PANI composite cathode. For the first time, the full sodium cell based on the EG-PANI composite was constructed and the rate capacities reached up to 64 mA h g−1 at the current densities of 100 mA g−1. In addition, the readily available composites bearing high conductivity and high-quality contact interface also enable the design of efficient supercapacitor. Specifically, the specific capacitance of EG-PANI composites electrode is 736 F g−1 at 0.2 A g−1, and the specific capacitance can be achieved to 410 F g−1 under 10 A g−1 (high current density). The synergistic effect of EG and PANI provides a remarkable storage capacity. Our work has inspired the search for large scale and hierarchical architectures materials for electrochemical energy storage.

Commercial-Level Energy Storage via Free-Standing Stacking Electrodes

Summary Pseudocapacitors with a fast faradic redox reaction during the electrochemical charge/discharge process hold great promise for delivering high power and high energy. Here, we used emerging oxygenated carbon nitride (OCN) as a model for nitrogen- and oxygen-enriched carbons and found an anion-selective charging behavior in aqueous electrolytes. The N- and O-mediated hydroxyl anion-selective charging originates from inbuilt surface-positive electrostatic potential localized at heptazine and quaternary N atom structural units. The carbon atoms in heptazine adjacent to pyridinic N act as the electron transfer active sites for faradic pseudocapacitance. The OCN free-standing films (FSFs) were developed as current collector-free electrodes, and stacking OCN FSFs can confer a cell with loading weight over a commercial level. For demonstration, a symmetrical cell with 17.7 mg cm−2 delivers an energy of 140.9 mW h at a high power of 2,499.9 mW, and almost 100% capacitance retention after 20,000 charge/discharge cycles at 50 mA.

Design of Machine-Washable and Wearable Supercapacitors Using Composite Laminates

Flexible and wearable supercapacitors, as a rechargeable energy storage device, are promising power sources for next-generation wearable electronics and electronic textiles in many consumer, medical, and military applications, as they offer safety, mechanical flexibility, stability, and durability that are lacking in current batteries. However, flexible supercapacitor prototypes reported so far have not demonstrated sufficient mechanical properties that could withstand critical situations, such as folding, twisting, and machine washing, which are commonly happening for real-world applications. Here we present the design of flexible supercapacitors that are foldable, twistable, and machine-washable due to exceptional mechanical properties of the materials. The devices are constructed using thin composite laminates as electrodes and ion-conducting separators. Each layer of the laminates is composed of randomly distributed activated carbon fibers or glass fibers in polymer electrolyte matrix. Calculations and simulations show that such laminates with proper fiber length and volume fraction of fibers can provide both high strength and high flexibility that enable them to survive critical mechanical deformations, while traditional particle-based electrodes cannot. The electrochemical and mechanical tests demonstrate that the activation of the carbon fiber surface does not affect much of the mechanical properties of the laminates, but greatly improves the surface area of electrodes, which leads to two orders increase in their electrical double-layer capacitance. The prototypes made of electrode/separator/electrode laminates show adjustable areal capacitances of over 10 mF/cm2. The electrochemical performance has remained unchanged after repeated folding and twisting tests. Moreover, we sewed the devices onto fabrics and washed them together with daily garments in a washing machine, after which we observed no mechanical damage or capacitance degradation. In conclusion, we believe that the excellent electrochemical performance, flexibility and mechanical durability make the composite laminates-based flexible supercapacitors promising to be integrated with daily garments to power various wearable electronics. The design rules and results are also applicable to developing other flexible functional devices that require extraordinary mechanical properties without sacrificing another function.

Quantum capacitance of transition metal and nitrogen co-doped graphenes as supercapacitors electrodes: A DFT study

Quantum capacitance is one of the key parameters determining the energy density of graphene-based supercapacitors. The present article explored the effects of the co-doping of transition metal (Mn, Fe, Co, Ni) and N atoms (TMNx, x = 1–4) on the structural stability, quantum capacitance and surface storage charge of graphene using density functional theory calculations. We find that the formation energies and magnetic moments can be regulated by changing the type of dopant transition metal and the number of dopants N atoms. The quantum capacitance and surface storage charge of graphene are enhanced significantly with the co-doping of transition metal and N atoms. By checking the density of states, it can be found that the quantum capacitance is directly related to the density of state around the Fermi level. The enhancement of quantum capacitance is caused by the introduced localized states around the Fermi level contributed mainly from transition metal. In addition, the quantum capacitance and surface storage charge are found to increase monotonically with the increase of co-doping concentrations of transition metal and N atoms. The results can provide an effective and simple new idea for the design of graphene-based supercapacitors with high energy density.

The production of a low cost printing device for energy storage systems and the application for supercapacitors

• Development of 3D printing device for miniature supercapacitor fabrication. • Cheap fabrication technique for miniature printer. • Printed supercapacitor design. The miniature printing device was produced by using 3- axis stage and the stage was controlled by microprocessor. The ink section was fixed at the top of the stage and the substrate was mobile in the system. The ink was produced by using graphene as an electrode material and it was printed on a non-conductive substrate. It was used a 1 M KOH for an electrolyte material and electrochemical performance of the device were investigated. It was obtained that the first cycle specific capacity of the device is 102 F/g and it was decreased to 88 F/g for 1000 cycle. So it may say that the device is very useful for energy storage device and it is cheaper than that of the commercial systems.

A Review on Electrothermal Modeling of Supercapacitors for Energy Storage Applications

Supercapacitors (SCs) are drawing more and more attention in energy storage applications. This paper aims to discuss the state of the art of application-oriented electrothermal modeling methods for SCs and identify the limitations and future research opportunities. Electrothermal modeling is essential to model-based design, thermal management, and reliability analysis of SCs for energy storage applications. The review provides new perspectives with respect to the existing surveys, which focus mainly on materials, cell voltage balancing, electrical equivalent circuit models, and energy management systems. It covers the main aspects of electrothermal modeling of electric double-layer capacitors (EDLCs) and hybrid SCs, from heat generation mechanisms to different modeling and parameterization approaches. The outcome of the review is an archive of important research work in the topic area and an outlook on future efforts to be made.

Effective boron doping in three-dimensional nitrogen-containing carbon foam with mesoporous structure for enhanced all-solid-state supercapacitor performance

Herein, we prepare three-dimensional B-doped N-containing carbon foams with a mesoporous structure by annealing boric acid–impregnated commercial melamine foam and characterize the obtained samples by a range of instrumental techniques. The chemical composition, structure, and electrochemical performance of B-doped N-containing carbon foams are shown to be dependent on annealing temperature (500–900 °C), e.g., increasing the annealing temperature from 500 to 700 °C results in the formation of a mesoporous structure and promotes B doping, which increases the concentration of carriers, the rate of ion transport and electrical conductivity. However, a further increase of annealing temperature from 700 to 900 °C leads to the collapse of pore structure and the formation of insulating boron nitride, causing electrochemical performance deterioration. As a result, optimal performance is observed for samples annealed at 700 °C (capacity = 462 mF cm−2 at a current density of 0.2 mA cm−2). More importantly, the supercapacitor has an obvious improvement in the rate capability. The successful fabrication of B-doped N-containing carbon foams and in-depth study of the electrochemical performance highlights the importance of tuning the concentration of doped heteroatoms, pore structure, and electrical conductivity for the design of carbon-based supercapacitors.

High-Performance Flexible Supercapacitors Based on Hair Fiber-Shaped Electrode

In order to meet the new demand of wearable/stretchable electronic devices, supercapacitors, especially the fiber-shaped supercapacitors, have caused consideration attention. However, it is still a huge challenge to construct the fiber-shaped supercapacitors with outstanding performances at this stage. Meanwhile, the current performance of fiber-shaped supercapacitors is still not satisfactory such as low energy density, poor cycle stability, and poor cycle stability. To address these issues, we designed and constructed a flexible all-solid-state asymmetric supercapacitor with human hair/Ni/Graphene/MnO2 fiber as positive electrode and human hair/Ni/Graphene fiber as negative electrode. Excitingly, the resulting supercapacitors displayed large potential window up to 1.8 V, excellent rate capability, fast frequency response capability (With short relaxation time constant of 55 ms), high volumetric energy density, and long cycle stability (more than 90% retention after 10000 cycles). The method presented here not only provides a reference for the design of flexible supercapacitors, but also paves a new way for the preparation of other energy storage devices.

New design of all-solid state asymmetric flexible supercapacitor with high energy storage and long term cycling stability using m-CuO/FSS and h-CuS/FSS electrodes

Nanorods of copper oxide and nanoribbons of copper sulfide electrodes are synthesized by simple hydrothermal and successive ionic layer adsorption and reaction methods, respectively. The surface of electrode material is altered with reaction temperature and successive ionic layer adsorption and reaction cycles. The monoclinic copper oxide exhibits electrochemical features as, specific capacitance of 630 F g−1 at 5 mV s−1, energy density of 64.5 W h kg−1 and power density of 4.1 kW kg−1. Hexagonal copper sulfide shows specific capacitance of 924 F g-1, energy density of 67 W h kg−1 and power density of 3.3 kW kg−1. Furthermore, capacity retentions of m-CuO120/FSS and h-CuS100/FSS are 89.5 and 87.4% after 2000 charge-discharge cycles, respectively. Herein, for the first time, a new design of asymmetric supercapacitor by new combination of positive and negative electrodes using polyvinyl alcohol-potassium hydroxide gel electrolyte is reported. The maximum specific capacitance of 123 F g-1 is achieved at 5 mV s−1, with energy density of 22.8 W h kg−1, power density of 2.5 W kg−1 and the capacity retention of 96.3% after 5000 charge discharge cycles for asymmetric device. The actual demonstration of asymmetric m-CuO120/FSS//h-CuS100/FSS device realizes the charge storing capacity of device and future scope of device in portable electronics.