[PDF] Charge Storage And Aging Phenomena In Electrochemical Double Layer Capacitors eBook

Author : Patrick Ruch
Publisher : Cuvillier Verlag
Page : 424 pages
File Size : 28,42 MB
Release : 2009-11-12
Category : Science
ISBN : 3736931395

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The storage of electrical charge in electrochemical double layer capacitors (EDLCs) is ideal for short-term energy storage in stationary and mobile or portable applications in which intermittent power demands and reliability are of prime importance. A significant limitation of the currently employed EDLC technology is the low energy density, whereby a promising approach towards increasing the energy content of present EDLC systems is a widening of the operational voltage window. However, a significant reduction of the device lifetime is observed under elevated voltage conditions. In the present work, the contribution of interfacial charge transfer towards charge storage in and aging of EDLCs based on non-aqueous electrolyte solutions at elevated voltages is considered. The possible charge transfer mechanisms are thus conveniently classified as ionic or electronic. Through an improved understanding of these processes, possible routes for optimizing charge storage and avoiding aging at elevated voltages may be developed. A coconut shell derived activated carbon was selected as electrode material in non-aqueous solutions of 1 M Et4NBF4 in acetonitrile (AN) and in propylene carbonate (PC). Through an electrochemical characterization of these systems via cyclic voltammetry, the potential regions of essentially ideal polarizability could be identified and separated from the regions in which irreversible charge transfer took place. The region of ideal polarizability was characterized by in situ Raman spectroscopy, electrical resistance measurements and electrochemical dilatometry. The results are discussed in the context of those obtained on single-walled carbon nanotubes (SWCNTs) in order to establish a comparison with a high surface area electrode material of well-defined geometric and electronic structure. Fundamental differences in the reversible doping behavior of the two materials were observed, indicating that a conceptual representation of the carbonaceous framework of the activated carbon must take into account the presence of significant disorder and deviations from the idealized assembly of graphene fragments. Differences in the capacitive charging behavior could be attributed to the different electronic density of states of the materials, thus highlighting the importance of the electronic structure of carbonaceous electrodes for the storage of charge in EDLCs. In order to investigate the possibility of ionic charge transfer in EDLC systems, the contribution of ion insertion processes to the charge storage and electrode degradation of both graphitic and activated carbon electrodes was studied using in situ electrochemical dilatometry, X-ray diffraction and small-angle X-ray scattering. It was found that the insertion of ions into graphite proceeds via well-defined intercalation sites, with the electrochemical intercalation of BF4– leading to staging and solvent cointercalation for both AN- and PC-based electrolytes. Further, the crystallinity of the graphitic electrodes was found to degrade markedly in the direction perpendicular to the graphene sheets, which could largely be attributed to the electrochemical decomposition of intercalated electrolyte species, i.e. a combination of ionic and electronic charge transfer. On the the other hand, ion insertion processes in activated carbon could be attributed to the accumulation of ions within the confined insertion sites offered by micropores during charging. The steric requirements of these ions result in a macroscopically observable, reversible electrode expansion. A comparison with the expansion of entangled SWCNT electrodes and an expanded graphite electrode proved that the occupation of insertion sites depends directly on the electrode potential and the accessibility of the insertion site. As a particular example of this behavior, it was shown that the interstitial porosity of SWCNT bundles can be made accessible by electrochemical polarization, leading to an intrinsic capacitance enhancement. As an important conclusion, the accessibility of such sites must be evaluated in situ in order to determine their possible contribution to charge storage within the stability limits of the electrolyte solution. Studies of the electronic charge transfer contribution towards the aging of EDLCs in the present work emphasized the possible formation of insoluble solid electrolyte degradation products. Systematic aging experiments using laboratory-scale test cells at elevated voltages enabled to distinguish between the loss of electrochemical performance and physicochemical modification of the activated carbon electrodes on the single electrode level. The rapid rate of aging at elevated voltages was found to depend notably on the solvent. In the AN-based electrolyte solution, the performance loss at a cell voltage of 3.5 V could be primarily attributed to the blockage of porosity at the positive electrode by the formation of solid degradation products within the porous structure of the activated carbon, most likely due to the oxidation of AN. This aging mechanism is promoted by the defluorination of the polymeric binder at the negative electrode, which results in unfavorable potential window shifts during aging. Preliminary studies regarding aging in the PC-based electrolyte indicated a different primary aging mechanism, likely due to reductive processes involving PC at the negative electrode. Notably, the detrimental effects of electrolyte degradation on the EDLC performance appeared to be significantly more pronounced than the contribution of ion insertion processes to aging. Finally, suggestions for future research are made in order to deepen and exploit the insights gained regarding the insertion of ions in carbonaceous electrodes as well as the aging of EDLCs at elevated voltages. Patrick Ruch was born in Atlanta, USA, in 1981 and studied Materials Science at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland, followed by a dissertation at the Paul Scherrer Institut in the field of electrochemical energy storage. His academic and scientific efforts have been rewarded with the Willi Studer Prize of the ETH Zurich (2005), the Empa Research Award (2005), the Alu-Award of the Swiss Aluminium Association (2006) and the Young Author Award of the Oronzio and Niccolò De Nora Foundation (2008). The research interests of Dr. Ruch include materials engineering, renewable energy as well as energy conversion and storage.

Author : Guoping Xiong
Publisher : Springer
Page : 154 pages
File Size : 22,51 MB
Release : 2015-06-17
Category : Technology & Engineering
ISBN : 3319202421

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This Brief reviews contemporary research conducted in university and industry laboratories on thermal management in electrochemical energy storage systems (capacitors and batteries) that have been widely used as power sources in many practical applications, such as automobiles, hybrid transport, renewable energy installations, power backup and electronic devices. Placing a particular emphasis on supercapacitors, the authors discuss how supercapacitors, or ultra capacitors, are complementing and replacing, batteries because of their faster power delivery, longer life cycle and higher coulombic efficiency, while providing higher energy density than conventional electrolytic capacitors. Recent advances in both macro- and micro capacitor technologies are covered. The work facilitates systematic understanding of thermal transport in such devices that can help develop better power management systems.

Author : Syam G. Krishnan
Publisher : Elsevier
Page : 435 pages
File Size : 43,16 MB
Release : 2024-03-20
Category : Technology & Engineering
ISBN : 0443154775

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Supercapacitors: Materials, Design, and Commercialization provides a comprehensive overview of the latest research trends and opportunities in supercapacitors, and particularly in terms of novel materials and electrolytes.The book will address the transformation in supercapacitive technology from double layer capacitance to battery-type capacitance, providing a clear understanding of the conceptual differences between various charge storage processes for supercapacitors, charge storage based on materials and electrolytes, and calculation for capacitance for these charge processes. Detailed chapters discuss recent developments in materials, such as carbons, chalcogenides, MXene and phosphorene, various polymer nanocomposites, and polyoxometalates for supercapacitors. This is followed by in-depth coverage of electrolytes, including the evolution of electrolytes from aqueous to water-in-salt electrolytes and their role in improving the energy density of supercapacitors. The final part of the book examines the role of artificial intelligence in the design of supercapacitors, and latest developments in translating novel supercapacitor technologies from laboratory-scale research to a commercialization.This is a valuable resource for advanced students, researchers, and scientists in the fields of energy storage, electrical engineering, materials science, and chemical engineering, as well as engineers and R&D personnel working with supercapacitors or energy storage in an industrial setting. Brings together the latest developments in supercapacitor materials and electrolytes Discusses cutting-edge charge storage concepts and methods for supercapacitors Addresses the role of machine learning and the scale-up from laboratory to commercialization

Author : Anna Leone D'Entremont
Publisher :
Page : 277 pages
File Size : 47,49 MB
Release : 2015
Category :
ISBN :

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The present study rigorously develops continuum thermal models of electrochemical capacitors (ECs) accounting for the dominant interfacial and transport phenomena. It also aims to identify design rules and modeling tools to define safe modes of operation and to develop appropriate thermal management strategies. ECs are promising electrical energy storage devices, particularly for providing high power or long cycle life. They can be divided into two categories, namely electric double layer capacitors (EDLCs) storing charge electrostatically in the electric double layer (EDL) at the electrode/electrolyte interface and pseudocapacitors using both EDL and chemical charge storage. Unfortunately, ECs generate heat during operation due to a variety of interfacial and transport phenomena. Consequently, they may experience substantial changes in temperature, leading to problems such as accelerated aging and increased self-discharge rates. EC charge storage mechanisms involve complex multiphysics and multiscale transport phenomena and this complexity has impeded the physical understanding of EC heating. This study derives rigorous, physics-based continuum models for both EDLCs and pseudocapacitors from first principles. Then, detailed numerical simulations were performed to investigate characteristic thermal behavior, to physically interpret experimental measurements from the literature, and to develop design rules. First, thermal models were developed for EDLCs. The heat diffusion equation and associated heat generation rates were derived from first principles and coupled with the transient electrodiffusion of ions in binary and symmetric electrolyte. Irreversible Joule heating and reversible heat generation rates due to ion diffusion, steric effects, and changes in entropy of mixing in the electrolyte were formulated. The predicted temperature rise for planar EDLCs qualitatively reproduced experimental data from the literature under various charging/discharging conditions. Scaling analysis simplified this model from twelve independent design parameters to seven dimensionless similarity parameters. Scaling laws were developed for the heat generated during a charging step and for the maximum temperature oscillations under galvanostatic cycling. In addition, a first-order thermal analysis for EDLCs was developed based on the lumped-capacitance approximation and accounting for both irreversible and reversible heating. A simple analytical expression for the overall temperature rise during galvanostatic cycling was derived and scaled. This simple thermal model enables rapid estimation of temperature evolution in EDLCs without computationally intensive numerical simulations and was quantitatively validated with experimental measurements from commercial EDLC devices. Moreover, the first-principles thermal model was generalized to account for multiple ion species and/or asymmetric electrolytes. Simulations with binary and asymmetric electrolytes indicated that the irreversible Joule heating decreased with increasing valency and/or diffusion coefficient of either ion while the local reversible heating near a given electrode increased with increasing counterion valency and/or decreasing counterion diameter. Finally, the first-principles model was extended to hybrid pseudocapacitors by accounting for redox reactions and Li+ intercalation and by rigorously deriving the associated irreversible and reversible heat generation rates. The model accounted simultaneously for charge storage by EDL formation and by faradaic reactions. Simulations were performed for a planar hybrid pseudocapacitor to investigate the electrochemical interfacial and transport phenomena as well as the thermal behavior under galvanostatic cycling. Two asymptotic regimes were identified corresponding to (i) dominant faradaic charge storage at low current and low frequency or (ii) dominant EDL charge storage at high current and high frequency. Predicted cell potential, heat generation rates, and temperature showed good qualitative agreement with experimental measurements and can be used to physically interpret experimental observations.

Author : Mahmood Aliofkhazraei
Publisher : CRC Press
Page : 587 pages
File Size : 21,78 MB
Release : 2016-04-27
Category : Science
ISBN : 1466591285

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Explores Chemical-Based, Non-Chemical Based, and Advanced Fabrication MethodsThe Graphene Science Handbook is a six-volume set that describes graphene's special structural, electrical, and chemical properties. The book considers how these properties can be used in different applications (including the development of batteries, fuel cells, photovolt

Author : Jürgen Garche
Publisher : Newnes
Page : 4532 pages
File Size : 31,51 MB
Release : 2013-05-20
Category : Science
ISBN : 0444527451

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The Encyclopedia of Electrochemical Power Sources is a truly interdisciplinary reference for those working with batteries, fuel cells, electrolyzers, supercapacitors, and photo-electrochemical cells. With a focus on the environmental and economic impact of electrochemical power sources, this five-volume work consolidates coverage of the field and serves as an entry point to the literature for professionals and students alike. Covers the main types of power sources, including their operating principles, systems, materials, and applications Serves as a primary source of information for electrochemists, materials scientists, energy technologists, and engineers Incorporates nearly 350 articles, with timely coverage of such topics as environmental and sustainability considerations

Author : Pei Kang Shen
Publisher : CRC Press
Page : 1051 pages
File Size : 25,19 MB
Release : 2018-10-08
Category : Science
ISBN : 1351231200

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Electrochemical Energy: Advanced Materials and Technologies covers the development of advanced materials and technologies for electrochemical energy conversion and storage. The book was created by participants of the International Conference on Electrochemical Materials and Technologies for Clean Sustainable Energy (ICES-2013) held in Guangzhou, China, and incorporates select papers presented at the conference. More than 300 attendees from across the globe participated in ICES-2013 and gave presentations in six major themes: Fuel cells and hydrogen energy Lithium batteries and advanced secondary batteries Green energy for a clean environment Photo-Electrocatalysis Supercapacitors Electrochemical clean energy applications and markets Comprised of eight sections, this book includes 25 chapters featuring highlights from the conference and covering every facet of synthesis, characterization, and performance evaluation of the advanced materials for electrochemical energy. It thoroughly describes electrochemical energy conversion and storage technologies such as batteries, fuel cells, supercapacitors, hydrogen generation, and their associated materials. The book contains a number of topics that include electrochemical processes, materials, components, assembly and manufacturing, and degradation mechanisms. It also addresses challenges related to cost and performance, provides varying perspectives, and emphasizes existing and emerging solutions. The result of a conference encouraging enhanced research collaboration among members of the electrochemical energy community, Electrochemical Energy: Advanced Materials and Technologies is dedicated to the development of advanced materials and technologies for electrochemical energy conversion and storage and details the technologies, current achievements, and future directions in the field.