7 research outputs found

    Printed Supercapacitors for Energy Storage and Functional Applications, Modeling, Analysis, and Integration

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    Supercapacitors (SCs), also known as ultracapacitors or electrochemical double-layer capacitors (EDLCs), have emerged as a remarkable class of energy storage devices that bridge the gap between conventional capacitors and batteries. These devices exhibit exceptional power density and long lifecycle, making them well-suited for a wide range of applications, from powering portable electronics to enabling rapid energy storage and release in various industrial systems. Unlike batteries, SCs store energy through the physical separation of charges at the electrode-electrolyte interface, leading to rapid charging and discharging capabilities. However, SCs are not without their challenges, notably leakage current and self-discharge, which can impact their long-term performance and practical utility. As the demand for energy-efficient and responsive power solutions intensifies, a thorough understanding of SCs’ behavior, coupled with accurate modeling techniques, becomes imperative. This thesis delves into this intricate realm, offering insights, models, and practical applications that collectively contribute to harnessing the potential of SCs across diverse domains. In the realm of energy storage and power management, this thesis presents a cohesive exploration of SCs’ behavior and its practical implications through a series of five interrelated research papers. Focusing on the context of charging and discharging within series-connected SC modules under varying load conditions, the research advances an innovative exponential model that elegantly captures complex behaviors with less than 4% simulation error over extended time frames (31 days). The initial study introduces an improved exponential equivalent circuit model (ECM) that elegantly characterizes the charging and discharging dynamics of series-connected SC modules. Leveraging a single-variable leakage resistance (VLR) approach, the model adeptly accounts for diverse self-discharge mechanisms. Unlike existing literature ECMs, this ECM’s simplicity and accuracy render it suitable for real-world applications in both short and long terms. The investigation extends to the modeling of multiple SC energy storage modules, providing insights into the behavior of SCs within varying configurations. Expanding into the domain of Internet of Things (IoT) applications, the research highlights the significance of energy storage devices for wireless sensor nodes. Acknowledging the limitations of traditional batteries, the study advocates for SCs as a viable solution. A refined exponential model is then proposed as a novel approach to predict the discharge behavior of disposable printed flexible SCs, ensuring concordance with experimental findings. This approach involves employing an innovative method to model the non-linearity of self-discharge in printed SCs, effectively capturing this phenomenon. This ECM’s adaptability and alignment with measured self-discharge results offer a promising avenue for optimal IoT device performance. Confronting the challenges of leakage current and self-discharge in SCs, the thesis presents a comprehensive framework. By proposing practical exponential ECMs, the study encapsulates nonlinear leakage and self-discharge phenomena. The empirical basis of these ECMs allows accurate prediction of discharge behaviors over extended periods, thereby holding potential for widespread practical application. A linear correlation was identified among the variables governing the exponential function of the equivalent parallel resistance (EPR) within the SC’s ECMs and the capacitance. The precision of the proposed ECMs was substantiated over an extended duration of 31 days, employing a diverse array of four distinct methodologies. The thesis also takes a statistical turn by conducting a meticulous analysis of experimental parameters across printed SCs. Employing established ECMs, the research unveils statistical distributions and correlations, empowering safer operation, and more informed decision-making. Monte Carlo simulation technique unveils the long-term performance of SCs, offering insights into consistency and aiding in risk assessment. The conducted statistical analysis has revealed a normal distribution pattern for all the parameters characterizing the printed SCs. Additionally, this thesis presents a methodology to ascertain the upper limit of potential standard deviation (std) in capacitance values across SCs within a module, aiming to ensure the seamless operation of the module without encountering malfunctions. Furthermore, an observed linear correlation has been established between the maximum potential std of capacitance values among SCs and the cumulative voltage stored within the module. Finally, the exploration expands to the activation of irreversible visual indicators (IVIs) through printed SCs, highlighting the potential of diverse monomer systems. The interplay of activation potential, coloration efficiency, and initial voltage underscores the feasibility of fully activating IVIs through series-connected SCs. In summary, this thesis intricately weaves together five research papers to construct a comprehensive narrative about the behavior, modeling, and application of SCs. From exponential models to statistical analyses and practical implementations, this work contributes to the broader understanding of SC dynamics and their potential within contemporary energy storage systems and IoT applications. The results-driven approach solidifies SCs' impact as a versatile energy storage device, emphasizing realworld performance, and evidence-based decisions

    A Modified Exponential Equivalent Parallel Resistance (EPR) Model for Predicting Self-Discharge Behavior of Printed Flexible Supercapacitors

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    Typically, batteries are used to power interconnected Internet of Things (IoT) devices. Intermittent manual replacement of batteries or recharging them after complete depletion is one of their major disadvantages, which increases the cost of maintaining and restricts the large-scale use of devices. Considering the longevity of devices and battery limitations, and in order to achieve the integrated and efficient operation of IoT devices, the development of alternative power sources and power management strategies is inevitable. The supercapacitor is a suitable energy storage option for energy-harvesting powered autonomous wireless sensor nodes in IoT applications. The leakage current value provided for the supercapacitors by the manufacturers is tested after the supercapacitor has been floated at a constant voltage for a long time. This raises concerns about the uncertainty of dynamic leakage current behavior during repeated charging and discharging of the supercapacitor in IoT applications. At present, there is no effective method to estimate and predict leakage current and the discharging behavior of supercapacitors in IoT applications with the aim of achieving optimal performance. In this work, an improved simplified exponential model is presented in order to simulate the non-linear discharge behavior of our fabricated printed flexible supercapacitors in long-term (31 days). The printed supercapacitors are disposable and have been fabricated using low-cost and non-toxic processes and materials. The model proposed in this work is very well adapted to the experimentally measured self-discharge results of the supercapacitors. In addition, according to the experimental and data fitting results of 10 fabricated supercapacitors, all the parameters defined in this model show good statistical values and have a Gaussian (normal) distribution.acceptedVersionPeer reviewe

    Simplified exponential equivalent circuit models for prediction of printed supercapacitor's discharge behavior - Simulations and experiments

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    Although supercapacitors (SCs) are promising devices for energy storage systems due to their high-power density and long lifecycle, they suffer from high leakage current and self-discharge. In this work, a simple and practical exponential equivalent circuit model (ECM) and three sub-ECMs based on electrical parameters and self-discharge profile of 12 printed flexible SCs are proposed to account for non-linear leakage and self-discharge phenomena in SCs. The capacitance and equivalent series resistance (ESR) of SCs are determined from the experiments. Besides, rather than modelling different self-discharge mechanisms within a SC cell, an exponential current/voltage function is employed for each SC in this study as a variable leakage resistance (VLR). The proposed ECMs are based on empirical parameters, without considering the physical mechanisms. Using the ECMs and only knowing two to four parameters for each SC cell, the discharge behaviors of SCs, electrochemical double-layer capacitors (EDLCs) type may be predicted with a high degree of accuracy over the long term (maximum simulation error in 31 days: less than 4%). Accordingly, the proposed ECMs, in contrast to those published in the literature, have the potential to be used in practical applications in the long-term as a result of their simplicity and high accuracy.publishedVersionPeer reviewe

    Statistical analysis and Monte-Carlo simulation of printed supercapacitors for energy storage systems

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    This study presents a comprehensive statistical analysis of experimental parameters for 12 printed supercapacitors (SCs) using previously proposed equivalent circuit models (ECMs). Statistical distributions and descriptive statistics, including mean, P-value, and standard deviation (std), are reported indicating a normal distribution for various SC parameters. A statistical method is introduced to determine the maximum potential std in capacitance of multiple SCs within an energy storage module, ensuring voltage limits are not exceeded. A linear relationship is discovered between the applied voltage on the module comprising three SCs in series and the maximum potential std of capacitance, ensuring safe operation. Additionally, a statistical method predicts the energy window range of the SC module after operating an IC chip, enabling better decision-making and system management. Monte-Carlo (MC) simulations predict the long-term charge and discharge performance of individual SCs and the series-connected modules. Results indicate that as long as the parameters’ std remains below a defined threshold, charging behavior remains consistent. The MC simulations provide insight into voltage window ranges after 31 days of self-discharge, aiding in performance prediction and risk assessment. The statistical study approach empowers researchers in the field of printed SC energy storage, supporting performance evaluation, design validation, and evidence-based decision-making.publishedVersionPeer reviewe

    Integration of printed supercapacitor modules and irreversible electrochromic displays

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    It is widely acknowledged that supercapacitors are outstanding energy storage devices with remarkable electrochemical properties, including rapid charge/discharge rates, high specific power density, large specific capacitances, and a long-life expectancy. Supercapacitor applications have been developed by incorporating smart features such as electrochromism. In recent years, electrochromic devices have become widely utilized in energy-saving applications due to the coloration of electrodes. Within the project CHARISMA, a smart temperature tracker label is being developed, which includes an irreversible electrochromic indicator powered by a printed supercapacitor module. In this study, printed supercapacitors are used to activate electrochromic displays fabricated using four different monomers (EDOT, Bi-EDOT, Bi-Thiophene, Ter-Thiophene) of varying concentrations. In order to activate electrochromic displays, supercapacitor energy modules with two or three supercapacitors connected in series are used. A variety of optical characteristics such as absorbency, transmittance, charge and optical density, coloration efficiency etc. and electrical characteristics are measured during the activation, as well as the response of the different materials to two- and three-cell supercapacitor modules. Other power sources, such as batteries and potentiostat, are also used to carry out the measurements in order to compare the results and evaluate the performance of the printed supercapacitors. The results of these investigations suggest that printed supercapacitors can provide comparable and even better activation results for electrochromic displays than other sources, and that they may be a viable alternative to other energy sources in this application.othe

    Integration of Supercapacitors to Trigger In-Situ Electropolymerization for Irreversible Visual Indicators

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    Printed supercapacitors (SCs) are demonstrated to activate 1 x 1 cm2 Irreversible Visual Indicators (IVIs) based on four different monomer systems: 3,4-Ethylenedioxythiophene (EDOT), bis-3,4-Ethylenedioxythiophene (BiEDOT), 2,2’- Bithiophene (Bithiophene), and 2,2‘:5’,2”-Terthiophene (Terthiophene). The key parameters which determine whether the IVIs can be fully activated (A Optical Density > 0.9) are the activation potential, the coloration efficiency (CE) of the lVI's, and the initial voltage and charge density of the SCs. All four monomer systems can be fully activated by three of the printed SCs connected in series (3.55 V), but only BiEDOT and TerThiophene can be fully activated by two series connected printed SCs (2.35 V).Peer reviewe

    An improved exponential model for charge and discharge behavior of printed supercapacitor modules under varying load conditions

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    We report an improved and simple exponential model for the charging and discharging behavior of series- connected modules of supercapacitors under varying load conditions and over extended periods of time. In this work, only a single variable leakage resistance (VLR) with exponential current/voltage profile is used to model the effects of different self-discharge mechanisms of a supercapacitor. Due to the simplicity and accuracy of the simulations, the proposed model can be implemented in practical applications, both short-term and long- term, unlike the two-, three-branch, and exponential models with voltage/time profile reported in the literature. We have modeled four different energy modules using the electrical parameters of 12 printed supercapacitors in order to study and compare the series connected supercapacitors’ behavior in each energy module. The key parameters such as capacitance and equivalent series resistance (ESR) of supercapacitors were based on experimental results. The numerical exponential method reported here enables modelling of the nonlinear behavior of self-discharge and leakage current over a wide range of load conditions and time periods. Furthermore, we have modified the linear model reported in the literature for leakage and self-discharge and compared the results with our nonlinear model.publishedVersionPeer reviewe
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