Supercapacitors Ageing Research Articles

Thermal Analysis of a Fast Charger for Public Service Electric Vehicles Based on Supercapacitors

The aging of supercapacitors (SCs) depends on several factors, with temperature being one of the most important. When this is high, degradation of the electrolyte occurs. The impurities generated in its decomposition reduce the accessibility of the ions to the porous structure on the surface of the electrode, which reduces its capacity and increases its internal resistance. In some applications, such as electric vehicles whose storage system consists of SCs, fast chargers, which supply very high power, are used. This can lead to an increase in temperature and accelerated aging of the cells. Therefore, it is important to know how the temperature of the SCs evolves in these cases and what parameters it depends on, both electrical and thermal. In this contribution, mathematical formulae have been developed to determine the evolution of the temperature in time and its maximum value during the transient state. The formulae for obtaining the mean and maximum temperature, once the thermal steady state (TSS) has been reached, are also shown, considering that the charger cells are recharged from the grid at a constant current. Based on this formulation, the thermal analysis of a specific case is determined.

The Many Deaths of Supercapacitors: Degradation, Aging, and Performance Fading

AbstractHigh‐performance electrochemical applications have expedited the research in high‐power devices. As such, supercapacitors, including electrical double‐layer capacitors (EDLCs) and pseudocapacitors, have gained significant attention due to their high power density, long cycle life, and fast charging capabilities. Yet, no device lasts forever. It is essential to understand the mechanisms behind performance degradation and aging so that these bottlenecks can be addressed and tailored solutions can be developed. Herein, the factors contributing to the aging and degradation of supercapacitors, including electrode materials, electrolytes, and other aspects of the system, such as pore blocking, electrode compositions, functional groups, and corrosion of current collectors are examined. The monitoring and characterizing of the performance degradation of supercapacitors, including electrochemical methods, in situ, and ex situ techniques are explored. In addition, the degradation mechanisms of different types of electrolytes and electrode materials and the effects of aging from an industrial application standpoint are analyzed. Next, how electrode degradations and electrolyte decompositions can lead to failure, and pore blocking, electrode composition, and other factors that affect the device's lifespan are examined. Finally, the future directions and challenges for reducing supercapacitors' performance degradation, including developing new materials and methods for characterizing and monitoring the devices are summarized.

Supercapacitor State of Health Estimation for Vehicular Applications

The transportation electrification requires an energy storage system that can absorb and deliver high amounts of energy during short periods of time, such us acceleration and breaking phases. One of the solutions applied is the using of electrical double layer capacitors (ELDC) or supercapacitors, due to their higher power density. However, the performance and the safety of these components depend on their state of health (SoH). Therefore, the health monitoring of supercpacitor cells is necessary to assure their integration and their safety in vehicular application. The aging of supercapacitors is usually correlated with the decreasing of their capacitance end the increasing of their internal resistance. Thus, the monitoring of these two parameters is necessary for the diagnosis of the state of heath. The measuring of these two parameters cannot be performed directly during the working conditions of supercapacitors in electrical vehicles. Therefore, an online estimation approach of these parameters is needed to enable the diagnosis of supercapacitors.This paper proposes a model-based method for supercapacitors state of health estimation. The approach uses the high gain observer to estimate the parameters of the equivalent RC network. The high gain observer, is one of the observers used for the system identification, it has shown its accuracy and robustness for dealing with nonlinear systems. The equivalent RC network used for modeling the system, simulates the energy and the electrical behavior of supercapacitors, it also presents a best tradeoff between accuracy and complexity. This approach enables the estimation of supercapacitors capacitance and internal resistance from current and voltage measurements.In order to test the proposed method, an experimental test was realized to validate this method. During this test two supercapacitors cells were cycled, in a climate chamber at high temperature T=45°C, in order to accelerate their aging. After each number of cycles, the supercapacitors cells are discharged using WLTC current profile (World harmonized Light-duty vehicles Test Cycle) presented in figure 1. Then, the capacitance and the internal resistance were measured to calculate their state of health.The WLTC current profiles is a dynamic current profile composed of charge and discharge current which allow to test the performance and the diagnosis method in conditions close to real electrical vehicles conditions.Since the aging of supercpacitor is correlated with the evolution of their capacitance and their internal resistance, then the state of health of these components is defined based on these two parameters using these two equations: and are the resistance and the capacitance measured at the beginning of life, and and and are and the resistance the capacitance measured at the end of each state of health k.After each number of cycles, the parameters of the RC equivalent circuit model were estimated, using the high gain observer, from the voltage and current measured during WLTC current profile. In order to compare results, the Root mean square error (RMSE) is calculated between the measured and the estimated SoHr and SoHc.The results presented in figure 2 and figure 3 and table I, show that the high gain observer presents a good accuracy for the state of health estimation, with an RMSE less than 0.77% for the SoHc and less than 1.58% for SoHr estimation. These results, indicate to robustness and the accuracy of this approach to estimate the supercpacitor parameters from a dynamic current profile such as WLTC, which make the used approach a good candidate for on board diagnosis in vehicular applications. The future work of this study is to implement this algorithm in microprocessor in order to test its performance in a real time.References Chaoui, A. El Mejdoubi, A. Oukaour, and H. Gualous: "Online System Identification for Lifetime Diagnostic of Supercapacitors with Guaranteed Stability", IEEE Transactions on Control Systems Technology, Volume: 24, Issue: 6, pages 2094-2102, November 2016.Li and K. Wang, "The Literature Review on Control Methods of SOH and SOC for Supercapacitors," 2019 4th International Conference on Control, Robotics and Cybernetics (CRC), 2019, pp. 17-21, doi: 10.1109/CRC.2019.00013.Saha, P. Saha and M. Khanra, "Performance Comparison of Nonlinear State Estimators for State-of-Charge Estimation of Supercapacitor," 2021 IEEE Second International Conference on Control, Measurement and Instrumentation (CMI), 2021, pp. 105-109, doi: 10.1109/CMI50323.2021.9362850.El Mejdoubi, H. Chaoui, H. Gualous and J. Sabor, "Online Parameter Identification for Supercapacitor State-of-Health Diagnosis for Vehicular Applications," in IEEE Transactions on Power Electronics, vol. 32, no. 12, pp. 9355-9363, Dec. 2017, doi: 10.1109/TPEL.2017.2655578. Figure 1

Batteries and Supercapacitors Aging

Electrochemical energy storage is a key element of systems in a wide range of sectors, such as electro-mobility, portable devices, or renewable energy [...]

Consensus-Based Cell Balancing of Reconfigurable Supercapacitors

Reconfigurable circuits have emerged as a promising cell balancing solution in supercapacitor echelon applications. However, the classical decentralized control method of reconfigurable supercapacitors results in high-voltage profiles of cells, which degrades the lifetime of supercapacitors. In this article, we propose a consensus-based cell balancing approach for reconfigurable supercapacitors, where the cell voltages are synchronized and maintained as low as possible to alleviate the aging of supercapacitors. The switched systems theory and graph theory are utilized to characterize the cyber-physical model of reconfigurable supercapacitors. A consensus-based tracking control is designed to balance cell voltages. It is rigorously proved that the proposed cell balancing method can guarantee cell voltages converge to the reference voltage. A laboratory hardware testbed has been built to verify the effectiveness of the proposed method. Extensive experiment results show that the proposed method can prolong the lifetime of cells considerably when compared with existing methods. Some practical issues of the proposed method are also discussed.

Supercapacitor Prognosis for POWER Electronic Applications

The lifetime of an energy storage component is the time required to fail. The failure is defined as the lack of ability of a component to fulfill it's specified function. One of its characteristics will be out of the specification. For example the capacitance will be below its specified limit value, or the series resistance will be above its specified value, the component will be leaking, or will be opened. This paper is about supercapacitor aging and prognosis. At the first, supercapacitor aging according to the temperature and to the voltage is performed. Experimental tests are realized at constant temperature when the supercapacitors are polarized at the maximum voltage. To quantify the supercapacitor aging, the equivalent series resistance and the equivalent capacitance are measured. To lead to the determination of the supercapacitor lifetime, Arrhenius law, that describes the effect of temperature on the velocity of a chemical reaction, is considered. The second part of this paper presents prognosis model for supercapacitors considering the aging conditions. The proposed model uses the particle filter (PF) to predict the posterior values of the aging indicators, i.e., capacitance and resistance. In order to validate the proposed method, experiments have been carried out under different aging conditions. The PF prognosis results are compared to the experimental ones using the different aging conditions in order to validate the proposed model performance. Figure 1

Study on effects of applied current and voltage on the ageing of supercapacitors

To investigate the degradation mechanism of supercapacitors from world-famous commercial manufacture Nesscap at different failure-mode, post-mortem pore structure and chemical ageing analyses were applied for the positive and negative electrodes components, followed by the ageing behavior characterization during galvanostatic charge/discharge (GCD) cycling at room temperature for 60,000 cycles. From the test results, it can be observed that the supercapacitors were damaged to some extent at higher currents (>4 A), while the devices were destroyed at excess voltage (>3.2 V). The main reason in chemical composition for the difference was that a large amount of binder disappeared from the aged electrodes at higher voltage and there was a passivation film formed on the surface of the collector, while slight variation existed in the electrode materials of the aged supercapacitors at higher current. The components deterioration further damaged the unity of the electrodes and caused the increase of the resistance and the decrease of the capacity.

Supercapacitor Aging and Diagnosis

The lifetime of an energy storage component is the time required to fail. The failure is defined as the lack of ability of a component to fulfill it's specified function. One of its characteristics will be out of the specification. For example the capacitance will be below its specified limit value, or the series resistance will be above its specified value, the component will be leaking, or will be opened. This paper is about supercapacitor aging and diagnosis. At the first, supercapacitor aging according to the temperature and to the voltage is presented. Experimental tests are realized at constant temperature when the supercapacitors are polarized at the maximum voltage. To quantify the supercapacitor aging, the equivalent series resistance and the equivalent capacitance are measured. To lead to the determination of the supercapacitor lifetime, Arrhenius law, that describes the effect of temperature on the velocity of a chemical reaction, is considered. The second part of this paper presents an online diagnosis method for supercapacitors’ aging problem. The proposed strategy capitalizes on the capabilities of the sliding mode for the design of a sliding mode observer. Therefore, online parameters’ estimation is achieved, which yields State-of-Health (SoH) prediction. Unlike other methods such as electrochemical impedance spectroscopy, where estimation is performed offline and requires interruption of the system’s operation, this paper presents an online diagnosis method. Moreover, only voltage and current measurements are required. The effectiveness of the proposed online observer is shown through a set of experiments. Results highlight its good performance in parameters estimation with robustness to current’s nonlinearities.

Impact of Voltage Resets on Supercapacitors Aging

Compared to Li-ion batteries, supercapacitors (SCs) boast longer lifespan, higher power density, and wider operational temperature range. Nevertheless, SCs are expensive (almost 40 times more expensive per watthour than Li-ion batteries). SCs aging is critical. Two types of aging tests are usually performed. Floating aging tests apply constant constraints (voltage and temperature), and cycling aging tests apply multiple charges and discharges. We focus our study on floating aging [corresponding for instance to parking mode for electrical vehicles (95% of the time) or uninterruptible power supplies (UPSs) when they are not solicited (quite all the time)]. All results in the literature conclude that voltage level is an acceleration factor for SC aging. According to the literature, it would be interesting to totally discharge the SCs when they are not in active use (i.e., when the UPSs or vehicles are turned off ) to improve their lifespan. Contrary to the literature forecasts (i.e., lower voltage increases lifespan of SC), the results obtained in this paper by alternating voltage resets (0 V, 60 °C) and floating aging (2.8 V, 60 °C) show that discharging even very few times the SCs shortens their lifespan drastically. Physical interpretations are presented to explain aging increase with voltage resets.

Modelling of current and temperature effects on supercapacitors ageing. Part II: State-of-Health assessment

This second part of the paper proposes a model for predicting the State-of-Health (SOH) of electrochemical double layers supercapacitors (SCs) during combined high-pulsed power cycling and high-temperature life endurance stresses. The evolutions of the SC capacitance, CSC, during these specific types of stresses have been discussed in part I and, based on the phenomenological observations we made, we here predict the CSC evolution by means of a dedicated model. The inputs of the proposed model are the SC delivered charge and the duration of the temperature stress above the rated one; the output is the CSC. The main virtue of the model is its capability to take into account the presence of the CSC recovering and accelerated ageing that cannot be represented by other models available in the literature. The validation of the proposed SC ageing model is carried out by means of experimental results, other than those used to infer the model, obtained on a 365F SC stressed by combined life-endurance and power-cycling stresses over a time window of 35 days.

Modelling of current and temperature effects on supercapacitors ageing. Part I: Review of driving phenomenology

The paper proposes a study of the phenomenology driving the ageing mechanisms of electrochemical double layer supercapacitors (SCs) during their most common operating conditions. In particular, the paper focuses on the so-called life endurance (LE) and power cycling (PC) stresses. The paper first provides a description of the variables governing the SC behaviour at the microscopic scale (i.e., porosity of the electrode surface, diffusion and conductivity of the electrolyte). Then, the paper discusses the link between these variables and the ones describing the SC behaviour at the macroscopic scale (i.e., temperature of the electrolyte and delivered current). This analysis is applied to both LE and PC stresses and as well as to their combination. The discussions make reference to experimental results obtained at the Author’s laboratory by means of a dedicated test bench.

Study on specific effects of high frequency ripple currents and temperature on supercapacitors ageing

Although supercapacitors can store less energy than batteries, they are particularly appealing for hybrid vehicle applications (for example, for braking energy recovery, or stop and start systems supply…). As power networks in hybrid vehicle experience high frequency ripple currents due to power electronics components such as static converters, experiments are done to study the impact of high frequency ripple currents on supercapacitor ageing. The results suggest that high frequency ripple currents do not create new ageing mechanisms. A complementary ageing test is also carried out to study the effect of temperature on supercapacitor ageing at very low voltage. It clearly shows that a significant part of increase in supercapacitor resistance is only linked to temperature, instead of the combined effect of temperature and voltage as assumed by literature for supercapacitor ageing. Whereas tests demonstrate that capacitance loss through time is linked (for the most part) to the combined effect of voltage and temperature. Hence, this paper shows that resistance increase is only partially linked to capacitance loss.

Impact of Supercapacitor Ageing Model on Optimal Sizing and Control of a HEV using Combinatorial Optimization

This paper presents an optimization problem for sizing and energy management of a hybrid electric vehicle including a fuel cell system and supercapacitors pack. From a predefined cycle and including ageing and thermal models of supercapacitors, the objective is to minimize the total cost of ownership of the hybrid power supply system. The ageing model is based on Eyring law and a thermal model of supercapacitor pack. This problem is solved using a Branch and Cut algorithm with an iterative strategy. Some results are presented and the impact of ageing model is discussed.

Study of Supercapacitor Aging and Lifetime Estimation According to Voltage, Temperature, and RMS Current

Due to its capacity to store or supply energy with high power, the supercapacitor is becoming an attractive component. Because of the electrostatic nature of energy storage, the endurance of this component toward repetitive charge and discharge cycles is relatively high. The goal of this paper is to demonstrate that cycling has an impact on the degradation of the supercapacitor and, as a result, on its lifetime. Based on accelerated cycling tests, some supercapacitors were studied using a dedicated test bench. Temperature, voltage, and current, which are the parameters that accelerate aging, are monitored. In fact, observations during the cycling tests show an important acceleration in the degradation compared with a similar static test having the same voltage and core temperature but without cycling. This paper proposes a method to quantify the acceleration of aging during a cycling phase.

Supercapacitors aging diagnosis using least square algorithm

Supercapacitor aging is mainly related to thermal and voltage constraints. This aging causes degradation in the supercapacitor performances which can lead to the failure of this component. To avoid this failure, it is necessary to determine the supercapacitor state of health. The aim of this study is the supercapacitor diagnosis. In this paper, aging tests of supercapacitor subjected to calendar aging constraints are presented. The supercapacitor is aged at constant temperature and constant bias voltage. During the aging process, the variations of the supercapacitor equivalent series resistance (ESR) and equivalent capacitance (C) are measured and analyzed. For diagnosis, a least square algorithm is used. This algorithm is used for ESR and C identification during the supercapacitor operation. For vehicle applications, the supercapacitor is considered as aged when the capacitance loss is in order of 20% of its initial value, or if the value of the equivalent series resistance increases by a factor of 2.

Impact of high frequency current ripple on supercapacitors ageing through floating ageing tests

Supercapacitors (SC) are energy storage systems (ESS) which are appreciated in hybrid vehicle. Hybrid vehicles electrical network is based on DC–DC converter which imply HF current ripple. This article proposes through ageing tests exploitation to study the influence of hybrid car HF current ripple on SC ageing (with current ripple of the same order of magnitude and frequency than for hybrid onboard network). Impedance parameter evolution is used to monitor SC state of health. Obtained results show that current ripple has significant effects on SC ageing kinetic and reliability (packaging failures). The packaging failures are linked to overpressure induced by HF current ripple. Finally a new model for SC ageing under current ripple is proposed thanks to electrolyte degradation by an electrical resonance process.

Calendar and cycling ageing of activated carbon supercapacitor for automotive application

This paper presents supercapacitor ageing as a function of voltage, temperature and charge/discharge cycling solicitations. To investigate their effects, a test bench of accelerated supercapacitor calendar and cycling ageing was carried out. Experimental tests are performed at constant temperature when the supercapacitors are polarized at the maximum voltage in the case of calendar ageing. In the case of cycling test, supercapacitors are charged and discharged at constant current. It can be noted that when the supercapacitors are charged and discharged at constant current the temperature of the supercapacitor increases and that the average voltage is not zero. To quantify the supercapacitor ageing, the equivalent series resistance (ESR) and the equivalent capacitance (C) are measured.

Investigations on the Aging Effect of Supercapacitors

ABSTRACTIn this paper, the degradation processes of commercial supercapacitors aged at 2.7 V and 65 °C for 2000 h were studied. The crystallinity, thermal stability, and specific surface areas of the carbon electrodes of the supercapacitors were measured. Significant changes and degradations in the carbon electrodes were observed for the aged supercapacitors. New functional groups were also found on the surface of the electrodes. The degradation of the lattice structures and the reduction in the specific surface area were as well observed for the aged supercapacitors. It was suggested that the aging of supercapacitors significantly changed the electrode surface which affects considerably electrical properties and functionality of supercapacitors. We have also performed experiments which suggest that the aging effect on the electrode is not uniformly distributed through its length.

Study of Accelerated Aging of Supercapacitors for Transport Applications

One important part of the electrical transportation systems is the energy-storage system. This can be based, for example, on supercapacitors. In this paper, we propose to study its behavior under constraints similar to their uses in power and railway-traction systems. We define an adequate measurement protocol for accelerated aging which is applied to supercapacitors according to two accelerated factors: effective current and temperature. We model the supercapacitors for different states of health. The modeling gives a good estimation of the variation of electrical parameters of the supercapacitor at different states. We reveal general indicators of the supercapacitor's aging, and we discuss about its life cycle.

Supercapacitor ageing at constant temperature and constant voltage and thermal shock

This paper presents supercapacitor ageing according to the voltage, the temperature and thermal shock tests. To investigate this effect, a test bench of accelerated supercapacitor calendar ageing was carried out. Experimental tests are realized at constant temperature when the supercapacitors are polarized at the maximum voltage. To quantify the supercapacitor ageing, the equivalent series resistance (ESR) and the equivalent capacitance (C) are measured using the DC and AC characterization. To lead to the determination of the supercapacitor lifetime, Arrhenius law, that describes the effect of temperature on the velocity of a chemical reaction, is considered. Finally, experimental results of supercapacitor thermal shock are presented.