Supercapacitor Charging Research Articles

Memory and nonlinear transport effects in charging–discharging of a supercapacitor

We report on the results of analysis of the kinetics of charge–discharge current of Panasonic supercapacitors in a wide range of time from 10–1 to 104 s. The non-Debye behavior of relaxation observed earlier by us and other authors is confirmed experimentally, and the influence of the supercapacitor charging regime on this process for various previous histories (values of applied voltage, charging time, and load resistance) is analyzed. The results are compared with available experimental data for paper–oil and electrolytic capacitors and with the results of calculations in the linear response model. It is found that in contrast to conventional capacitors, the response of the supercapacitor under investigation to variations of the charging regime does not match the linear response model. The relation of this nonlinearity to processes in the double electric layer, the morphology of the porous electrode, and the effect of charge reversal in pores is considered.

ALD titanium nitride on vertically aligned carbon nanotube forests for electrochemical supercapacitors

Titanium nitride (TiN) coating on vertically aligned carbon nanotube (VACNT) forest electrodes by means of atomic layer deposition (ALD) to store charge in electrochemical supercapacitors has been demonstrated. Experimental results show that after 400 cycles of ALD process, a roughly 20nm-thick TiN layer is coated uniformly on individual CNTs in the forest electrodes. The electrochemical characterizations show 2000 times higher capacitance of the ALD TiN-CNT device as compared to that of a flat-shape TiN electrode. Furthermore, over 500% enhancement of electrochemical capacitance of the ALD TiN-CNT device (81mF/cm2) as compared to bare CNT forest electrodes (14mF/cm2) has been accomplished due to the increased oxygen vacancies on the TiN surfaces. As such, this work presents a new path to increase energy density of supercapacitors using TiN-based porous electrode materials.

Dumbbell-like ZnO nanoparticles-CeO2 nanorods composite by one-pot hydrothermal route and their electrochemical charge storage

Dumbbell-like ZnO nanoparticles-CeO2 nanorods (ZnONPs-CeO2NRs) composites with superior electrochemical performance were fabricated by one-pot hydrothermal process and characterized by X-ray diffraction, an energy dispersive spectrum, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and nitrogen adsorption–desorption isotherms. The ZnONPs-CeO2NRs nanostructure possessed larger Brunauer–Emmett–Teller (BET) surface, crystallinity, lower resistance. The specific capacitance of ZnONPs-CeO2NRs composite (162.08mFg−1) was higher than that of precursor CeO2NRs (151.43mFg−1) in galvanostatic charge/discharge, and the super-capacitor charge storage of ZnONPs-CeO2NRs (581.39Fg−1) was more 12 times than the precursor (46.63Fg−1). The improved electrochemical performances could be ascribed to the import of ZnONPs, which induced variations in the structure, conductivity and surface morphology.

Supercapacitor Electrodes Delivering High Energy and Power Densities

Considerable progress has been achieved in developing supercapacitor materials with desirable charge storage properties; however, uniting energy density (ES) and power density (PS) in a single device is an elusive issue. We have explored diverse range of materials and structures such as (i) activated carbon from bio-resources, (ii) ceramic electrochemical materials as nanoparticles, nanowires, and nanoribbons, and (iii) layered materials to overcome this issue. An ES of ∼52.6 Wh kg-1 @ PS of ∼15000W kg-1 is delivered using nanowire nanocomposites based device which appear to be the best ever achieved in supercapacitor charge storage mode employing aqueous alkaline electrolytes.

Inverse dynamic analysis type of MPPT control strategy in a thermoelectric-solar hybrid energy harvesting system

This study presents the development of a novel inverse dynamic analysis-maximum power point tracking (IDA-MPPT) scheme in a hybrid energy harvesting system between thermoelectric module (TEM) and solar array (SA). The proposed method initially changes the harvested voltage response from both sources to be the third-order exponential function. This input function selection is based on the capability of this function to stabilize the initial response system and maintain its final position despite a prolonged response time. The mV voltage value from TEM is easily boosted up to nearly 5 V using this method. With this hybridization, the total obtained voltage is doubled to become 9.7 V, which results in a total power of 0.722 W. Furthermore, the method also allows for a fast tracking system, which enables faster voltage boosting and supercapacitor charging. The supercapacitor only requires less than 5 min to complete charging and boost the voltage to almost 5 V. Thus, a satisfactory value is obtained as compared with that of the TEM system with a chosen MPPC board.

NMR Study of Ion Dynamics and Charge Storage in Ionic Liquid Supercapacitors.

Ionic liquids are emerging as promising new electrolytes for supercapacitors. While their higher operating voltages allow the storage of more energy than organic electrolytes, they cannot currently compete in terms of power performance. More fundamental studies of the mechanism and dynamics of charge storage are required to facilitate the development and application of these materials. Here we demonstrate the application of nuclear magnetic resonance spectroscopy to study the structure and dynamics of ionic liquids confined in porous carbon electrodes. The measurements reveal that ionic liquids spontaneously wet the carbon micropores in the absence of any applied potential and that on application of a potential supercapacitor charging takes place by adsorption of counterions and desorption of co-ions from the pores. We find that adsorption and desorption of anions surprisingly plays a more dominant role than that of the cations. Having elucidated the charging mechanism, we go on to study the factors that affect the rate of ionic diffusion in the carbon micropores in an effort to understand supercapacitor charging dynamics. We show that the line shape of the resonance arising from adsorbed ions is a sensitive probe of their effective diffusion rate, which is found to depend on the ionic liquid studied, as well as the presence of any solvent additives. Taken as whole, our NMR measurements allow us to rationalize the power performances of different electrolytes in supercapacitors.

Study on a Planar Interdigitated MEMS Supercapacitor Using Modeling and Simulation Method

In this paper, a modeling and simulation method for planar interdigitated ruthenium oxide MEMS supercapacitor was proposed based on the electrochemical reaction mechanism of supercapacitor. The study simulated the planar interdigitated ruthenium oxide MEMS super capacitor using Comsol software. The highly accurate charge and discharge curves of the super capacitor, electric potential distribution graph and the concentration distribution graph were got through simulation. The effects of two structure-parameters were discussed in the research.

High performance solid state flexible supercapacitor based on molybdenum sulfide hierarchical nanospheres

Molybdenum sulfide (MoS2) hierarchical nanospheres are synthesized using a hydrothermal method and characterized by X-ray powder diffraction, Brunauer–Emmett–Teller, scanning electron microscopy and transmission electron microscopy. The prepared MoS2 is used to fabricate solid state flexible supercapacitors which show excellent electrochemical performance such as high capacitance 368 F g−1 at a scan rate of 5 mV s−1 and high power density of 128 W kg−1 at energy density of 5.42 Wh kg−1. The fabricated supercapacitor presents good characteristics such as lightweight, low cast, portability, high flexibility, and long term cycling stability by retaining 96.5% after 5000 cycles at constant discharge current of 0.8 mA. Electrochemical impedance spectroscopy (EIS) results reveal low resistance and suggest that MoS2 nanospheres would be a promising candidate for supercapacitors. Three charged supercapacitors connected in series can light 8 red color commercial light emitting diodes (LEDs) for 2 min, demonstrating its capability as a good storage device.

PRT 차량의 무선급전 시스템 설계 및 구현

최근 들어, 보다 효율적이고 경제성을 갖춘 전기자동차 기술이 등장함에 따라 철도의 전통적인 기술적 패러다임이 변화하고 있다. 오래전에 제안되었지만 이상적인 개념으로 평가받던 수요응답형 순환교통(PRT) 시스템의 경우에도 전기자동차 플랫폼의 활용을 통해서 실현 가능성을 높여가고 있다. 특히, 배터리에 의해 구동되는 차량의 경우 안정적이고 효율적인 운영의 측면에서 기술적인 어려움에 직면하고 있다. 그렇지만, 무선 급전에 의한 급속충전 기술과 고에너지 밀도의 슈퍼커패시터 적용은 이러한 기술적인 난제를 극복하고 도시 미관의 향상을 통해서 전기 에너지를 기반으로 한 신교통수단의 보급을 증대하는데 기여할 것으로 생각된다. 본 논문에서는 한국형 PRT 차량의 전력공급 시스템의 설계, 에너지 소모량 및 장치의 성능 해석과 하드웨어 제작 및 시험에 이르는 일련의 개발과정에 대해서 논한다. 그 결과, 테스트베드에서의 전력공급 모듈의 시험평가 결과가 요구하는 성능에 부합하는 것으로 확인되었다. Recently, the traditional paradigm in railroad technology is changing as more efficient and cost-effective electric vehicle (EV) technologies have emerged. The original concept of PRT (Personal Rapid Transit) proposed in the past has come to be regarded as unrealistic, but its feasibility is improving through the utilization of an EV platform. In particular, battery-powered vehicles pose difficult technical challenges in attempts to achieve reliable and efficient operation. However, based on the inductive power transfer (IPT) technology, the fast charging of supercapacitors with high energy density can contribute to overcoming this technical challenge and promote the transition to electric-powered ground transportation by improving the appearance of cities. This study discusses the development process of a power supply system for PRT, including concept design, numerical analysis, and device manufacturing, along with performance predictions and evaluations. In terms of results, the system was found to meet the performance requirements for power supply modules on a test-bed.

Low-order mathematical modelling of electric double layer supercapacitors using spectral methods

This work investigates two physics-based models that simulate the non-linear partial differential algebraic equations describing an electric double layer supercapacitor. In one model the linear dependence between electrolyte concentration and conductivity is accounted for, while in the other model it is not. A spectral element method is used to discretise the model equations and it is found that the error convergence rate with respect to the number of elements is faster compared to a finite difference method. The increased accuracy of the spectral element approach means that, for a similar level of solution accuracy, the model simulation computing time is approximately 50% of that of the finite difference method. This suggests that the spectral element model could be used for control and state estimation purposes. For a typical supercapacitor charging profile, the numerical solutions from both models closely match experimental voltage and current data. However, when the electrolyte is dilute or where there is a long charging time, a noticeable difference between the numerical solutions of the two models is observed. Electrical impedance spectroscopy simulations show that the capacitance of the two models rapidly decreases when the frequency of the perturbation current exceeds an upper threshold.

A load predictive energy management system for supercapacitor-battery hybrid energy storage system in solar application using the Support Vector Machine

This paper presents the use of a Support Vector Machine load predictive energy management system to control the energy flow between a solar energy source, a supercapacitor-battery hybrid energy storage combination and the load. The supercapacitor-battery hybrid energy storage system is deployed in a solar energy system to improve the reliability of delivered power. The combination of batteries and supercapacitors makes use of complementary characteristic that allow the overlapping of a battery’s high energy density with a supercapacitors’ high power density. This hybrid system produces a straightforward benefit over either individual system, by taking advantage of each characteristic. When the supercapacitor caters for the instantaneous peak power which prolongs the battery lifespan, it also minimizes the system cost and ensures a greener system by reducing the number of batteries. The resulting performance is highly dependent on the energy controls implemented in the system to exploit the strengths of the energy storage devices and minimize its weaknesses. It is crucial to use energy from the supercapacitor and therefore minimize jeopardizing the power system reliability especially when there is a sudden peak power demand. This study has been divided into two stages. The first stage is to obtain the optimum SVM load prediction model, and the second stage carries out the performance comparison of the proposed SVM-load predictive energy management system with conventional sequential programming control (if-else condition). An optimized load prediction classification model is investigated and implemented. This C-Support Vector Classification yields classification accuracy of 100% using 17 support vectors in 0.004866s of training time. The Polynomial kernel is the optimum kernel in our experiments where the C and g values are 2 and 0.25 respectively. However, for the load profile regression model which was implemented in the K-step ahead of load prediction, the radial basis function (RBF) kernel was chosen due to the highest squared correlation coefficient and the lowest mean squared error. Results obtained shows that the proposed SVM load predictive energy management system accurately identifies and predicts the load demand. This has been justified by the supercapacitor charging and leading the peak current demand by 200ms for different load profiles with different optimized regression models. This methodology optimizes the cost of the system by reducing the amount of power electronics within the hybrid energy storage system, and also prolongs the batteries’ lifespan as previously mentioned.

A study of supercapacitor charge redistribution for applications in environmentally powered wireless sensor nodes

As an important energy storage device for wireless sensor nodes with energy harvesting capabilities, the characteristics of supercapacitors need to be taken into account in developing power management solutions. While supercapacitor self-discharge is usually considered because it causes voltage decay and energy loss, supercapacitor charge redistribution has not been well examined although this process may result in a greater voltage change than self-discharge. This paper studies the supercapacitor voltage change during charge redistribution. The supercapacitor voltage may increase, decrease, or remain almost constant during charge redistribution depending on the initial state. Three approaches are employed to investigate the supercapacitor voltage change during charge redistribution: analytical estimations, numerical simulations, and experimental measurements. Both the supercapacitor voltage change after a charge process and that after a discharge process are examined. Various parameters of the charge or discharge process such as charge current and discharge time that affect the initial state of supercapacitor charge redistribution are swept. The results obtained using different approaches are consistent. These results can be utilized by wireless sensor network application designers to estimate the supercapacitor voltage change during charge redistribution.

Single-file charge storage in conducting nanopores.

Charging of a conducting tubular nanopore in a nanostructured electrode is treated using an exactly solvable 1D lattice model, including ion correlations screened by ion-image interactions. Analytical expressions are obtained for the accumulated charge and capacitance as a function of voltage. They show that the mechanism of charge storage, and the qualitative form of the capacitance-voltage curve, are sensitive to how favorable it is for ions to occupy the unpolarized pore, and the pore radius. Qualitative predictions of the theory are corroborated by Monte Carlo simulations. These results highlight the effect of ion affinity to unpolarized pores on the charge and energy storage in supercapacitors. Furthermore, they suggest that the question of the occupancy of unpolarized pores could be answered by measuring the capacitance-voltage dependence.

Based on the Hybrid Energy Storage System in the Application of Stable DC Bus Voltage

Due to the large number of distributed power supply random connected to power grid, it has severely influenced on power quality of the grid. In the storage battery directly on the basis of the DC bus, adopting the method of hybrid energy storage system makes a research on the output characteristics of photovoltaic array and the charging and discharging of battery and super capacitor. Research results show that the hybrid energy storage system can take advantage of the DC/DC converter to coordinate photovoltaic array, energy storage unit and the energy flows among load, also that the stability of DC bus voltage can be ensured by the system switch from the different work patterns.

Research of Super Capacitor Charging and Discharging System Based on DSP28335

The application of new energy resources such as wind power gets more and more attention, with the environmental problems and energy issues have become increasingly prominent. But the volatility and the characteristics of intermittent has greatly restricted the efficient utilization of the new energy. This paper designed a control circuit, the super capacitor as the energy storage device and the 28335 as the core. This circuit controls the charging and discharging of the super capacitor through the system sampling by 28335, so as to realize to the instantaneous compensation effect on the power fluctuation of the grid connected wind turbine, smooth wind farms output power and voltage. Apply this method by super-capacitor and TMS320F28335, we can provide a useful reference and efficient application of new energy.

Study on Performance Improvement of AC-DC Converter

Study on Performance Improvement of AC-DC Converter

Performance of printable supercapacitors in an RF energy harvesting circuit

We report the fabrication of a supercapacitor on a plastic substrate with mass-production-compatible methods and its characterisation using galvanostatic and voltammetric methods. The supercapacitor is prepared in ambient conditions using activated carbon and an aqueous, non-acidic electrolyte. The obtained capacitances are 0.45F and 0.21F for device sizes of 4cm2 and 2cm2, respectively. Additionally, we demonstrate the utilisation of the supercapacitor in an autonomous energy harvesting and storage system. The RF energy harvester comprises a printed loop antenna and a half-wave organic diode rectifier operating at 13.56MHz frequency. The harvested energy is stored in two supercapacitors connected in series to increase the maximum operating voltage. In order to power a device such as a sensor or a small indicator display, voltage regulation is needed. A voltage regulator, implemented as an application specific integrated circuit (ASIC), was designed for this purpose, and fabricated commercially. We demonstrate the ability of the harvester storage unit to power the regulator for hours with a constant regulator output voltage and power. The effect of supercapacitor charging time on the actual supercapacitor charging state is also discussed, as a slower charging rate is found to have a significant effect on the output of the supercapacitor.

The Hydrogen Bus as a Mathematical Model in Matlab© - Its Actual Operation

The paper first outlines control strategies for all three cooperating energy sources of TriHyBus and conditions for their cooperation. For optimization of routine operation of the bus a mathematical model in MATLAB© - Simulink© has been developed at Department of Power Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague. The solution of power flow consists of control strategies for fuel cell, charging of batteries and supercapacitor, and conditions for both limiting situations: lack and surplus of energy on the main bus.. In the second part of the paper the MATLAB© model is tested and verified by data obtained from the actual operation of the bus and the conclusions about differences between the model and the actual operation are made.

Influence of porosity on charging speed of polypyrrole

The rate of charging of supercapacitor and battery electrodes is often limited by the transport of ions through the active electrode material. One way to accelerate this transport is to increase the porosity of the electrode, at the cost of electrode capacity. This tradeoff is studied through the fabrication and characterization of porous carbon nanofibre/polypyrrole films used as storage electrodes. Electrospun poly (acrylonitrile-co-acrylamide) fibres were carbonized and then electrochemically coated with variable amounts of polypyrrole. The resulting hybrid materials were characterized using both conventional methods such as cyclic voltammetry, electron microscopy and conductivity, as well as ionic conductivity and pulsed-field-gradient nuclear magnetic resonance which directly probe ion transport. It is found that with modest porosity, these materials retain much of the capacitance (∼50%) of bulk polypyrrole with dramatically increased (∼300 times) charge and discharge rates, suggesting the potential of the approach for increasing the useful frequency range of polypyrrole-based supercapacitors, as well as other storage materials whose porosity can be varied. Simple transport models based on series or parallel arrangements of electrolyte and active electrode are developed to explain the results and identify the factors limiting charge/discharge rates.

In situ NMR spectroscopy of supercapacitors: insight into the charge storage mechanism.

Electrochemical capacitors, commonly known as supercapacitors, are important energy storage devices with high power capabilities and long cycle lives. Here we report the development and application of in situ nuclear magnetic resonance (NMR) methodologies to study changes at the electrode–electrolyte interface in working devices as they charge and discharge. For a supercapacitor comprising activated carbon electrodes and an organic electrolyte, NMR experiments carried out at different charge states allow quantification of the number of charge storing species and show that there are at least two distinct charge storage regimes. At cell voltages below 0.75 V, electrolyte anions are increasingly desorbed from the carbon micropores at the negative electrode, while at the positive electrode there is little change in the number of anions that are adsorbed as the voltage is increased. However, above a cell voltage of 0.75 V, dramatic increases in the amount of adsorbed anions in the positive electrode are observed while anions continue to be desorbed at the negative electrode. NMR experiments with simultaneous cyclic voltammetry show that supercapacitor charging causes marked changes to the local environments of charge storing species, with periodic changes of their chemical shift observed. NMR calculations on a model carbon fragment show that the addition and removal of electrons from a delocalized system should lead to considerable increases in the nucleus-independent chemical shift of nearby species, in agreement with our experimental observations.