105 research outputs found
A Comparative Study of the Mott-Schottky Behavior of Oxide Films on Stainless Steels in Ionic Liquids and in Aqueous Solutions
No full textThe semiconducting properties of passive films formed on AISI304 steel, thermally at 400°C or anodically in a borate buffer solution, were comparatively studied by capacitance measurements and the usual Mott-Shottky (MS) approach in an aqueous borate buffer solution of pH 9.2 and in BMMITFSI, a room temperature ionic liquid. This ionic liquid was used due to its wide electrochemical window of circa 4.3 V, enabling the verification of the accuracy of the MS approach. Two regions corresponding to p and n-type semiconduction were observed in both electrolytes, but calculated dopant concentrations were not always equal. In the ionic liquid a second deeper donor level was always present, which must be further investigated. ©The Electrochemical Society.No Full Tex
Participatory identification of indicators for assessing options for climate compatible development of smallholder farmers in the Central Rift Valley of Ethiopia.
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Performance, Modeling, and Characteristics of LFP pack for HEV using FUDS (depleting) in Hot and Arid Conditions
No full textabstract: There was a growing trend in the automotive market on the adoption of Hybrid Electric Vehicles (HEVs) for consumers to purchase. This was partially due to external pressures such as the effects of global warming, cost of petroleum, governmental regulations, and popularity of the vehicle type. HEV technology relied on a variety of factors which included the powertrain (PT) of the system, external driving conditions, and the type of driving pattern being driven. The core foundation for HEVs depended heavily on the battery pack and chemistry being adopted for the vehicle performance and operations. This paper focused on the effects of hot and arid temperatures on the performance of LiFePO4 (LFP) battery packs and presented a possible modeling method for overall performance.
Lithium-ion battery (LIB) packs were subjected to room and high temperature settings while being cycled under a current profile created from a drive cycle. The Federal Urban Driving Schedule (FUDS) was selected and modified to simulate normal city driving situation using an electric only drive mode. Capacity and impedance fade of the LIB packs were monitored over the lifetime of the pack to determine the overall performance through the variables of energy and power fade. Regression analysis was done on the energy and power fade of the LIB pack to determine the duration life of LIB packs for HEV applications. This was done by comparing energy and power fade with the average lifetime mileage of a vehicle.
The collected capacity and impedance data was used to create an electrical equivalent model (EEM). The model was produced through the process of a modified Randles circuit and the creation of the inverse constant phase element (ICPE). Results indicated the model had a potential for high fidelity as long as a sufficient amount of data was gathered. X-ray powder diffraction (XRD) and a scanning electron microscope (SEM) was performed on a fresh and cycled LFP battery. SEM results suggested a dramatic growth on LFP crystals with a reduction in carbon coating after cycling. XRD effects showed a slight uniformed strain and decrease in size of LFP olivine crystals after cycling.Dissertation/ThesisMasters Thesis Engineering 201
Convergence of Newton’s Method for Steady-State Load Flow Problems in Multi-Carrier Energy Systems
No full textCoupling single-carrier networks into multi-carrier energy systems (MESs) has recently become more important. Various formulations of the single-carrier load flow problem (LFP) are used. Moreover, different coupling models lead to different integrated systems of equations for the LFP of MESs. Both could affect the convergence of the Newton-Raphson method (NR) used to solve the nonlinear system of equations. This paper considers the steady-state LFP for example MESs of varying size, with various coupling models and topologies, and various formulations in the single-carrier parts. Based on numerical experiments, this paper compares the convergence behavior of NR for the various single- and multi-carrier systems. For these examples, NR of the steady-state LFP of the MESs is independent of the size of the network and of the coupling, and NR requires at most as many iterations as the slowest single-carrier network.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Numerical Analysi
Climate impact evaluation of LFP (lithium iron phosphate) cathode material through the creation of a dynamic model
No full textLAUREA MAGISTRALEQuesta tesi è stata sviluppata presso il dipartimento PEM (Production Engineering of E-Mobility Components) dell'Università RWTH di Aachen. Il lavoro si concentra sullo sviluppo di un modello che simula la catena produttiva del materiale catodico delle batterie LFP calcolandone le emissioni. Ciò deriva dal bisogno di avere uno strumento che permetta di valutare in modo affidabile e dinamico l’impatto ambientale delle catene produttive delle batterie a ioni di litio, soprattutto dando alle aziende manifatturiere la possibilità di conoscere in modo più preciso le loro emissioni di scope 3 (altre emissioni indirette lungo la catena del valore, fuori dal controllo diretto dell'organizzazione). Ad oggi, infatti, aziende e policymakers possono fare affidamento solo su valori "statici" ovvero relativi ad un caso specifico difficilmente decontestualizzabile o troppo generici per applicazioni in situazioni differenti. I dati sui quali si basa il funzionamento del modello derivano da un'attenta consultazione di paper scientifici unita ai calcoli effettuati dall'autore per stabilire i valori di alcuni parametri. I risultati ottenuti utilizzando il tool sviluppato sono soddisfacenti e da considerarsi discretamente allineati ai risultati dichiarati da altri studi inerenti alla tematica. Il modello è quindi efficacie nello stabilire i flussi di materiale, energetici e le emissioni dei materiali precursori ma presenta alcune debolezze in relazione ai parametri usati per i processi produttivi che aggregano tali precursori per produrre la pasta catodica. Ciò è dovuto alla segretezza di questi metodi considerati un asset strategico dalle aziende manifatturiere e alla rapida evoluzione dei suddetti metodi. Il modello è una versione iniziale di quello che potrebbe diventare uno strumento potente per aziende e policymakers qualora si creasse una collaborazione tra ricercatori e sviluppatori che elabori un programma
open-source più completo e con più funzioni.This thesis was developed at the PEM (Production Engineering of E-Mobility Components) institute of RWTH University in Aachen. The work focuses on the development of a model that simulates the production chains of the LFP (lithium iron phosphate) cathode material and calculates its manufacturing emissions. This stems from the need to have a tool to reliably and dynamically assess the environmental impact of lithium-ion battery production chains especially by giving manufacturing companies the opportunity to know more precisely their scope 3 emissions (other indirect emissions along the value chain, outside the direct control of the organization). To date, indeed, companies and policymakers can only rely on "static" values, i.e. those relating to a specific case that are difficult to decontextualise or too generic for applications in different situations. The data on which the operation of the model is based are derived from careful consultation of scientific papers combined with calculations made by the author to establish the values of the parameters. The results obtained using the developed tool are satisfactory and to be considered fairly aligned with the results stated by other studies pertaining to the subject. Thus, the model is effective in establishing material, energy and emission flows of precursor materials but has some weaknesses in relation to the parameters used for the final production processes that aggregate these precursors to produce the cathode paste. This is due to the secrecy of these methods, considered a strategic asset of manufacturing companies, as well as the rapid evolution of these methods. The model is an early version of what could become a powerful tool for companies and policymakers if a collaboration of researchers and developers is created to come up with a more comprehensive open-source program with more features
Nanomaterials for Thermally Safe Lithium-Ion Batteries
No full textabstract: The two central goals of this project were 1) to develop a testing method utilizing coatings on ultra-thin stainless steel to measure the thermal conductivity (k) of battery electrode materials and composites, and 2) to measure and compare the thermal conductivities of lithium iron phosphate (LiFePO4, "LFP") in industry-standard graphite/LFP mixtures as well as graphene/LFP mixtures and a synthesized graphene/LFP nanocomposite. Graphene synthesis was attempted before purchasing graphene materials, and further exploration of graphene synthesis is recommended due to limitations in purchased product quality. While it was determined after extensive experimentation that the graphene/LFP nanocomposite could not be successfully synthesized according to current literature information, a mixed composite of graphene/LFP was successfully tested and found to have k = 0.23 W/m*K. This result provides a starting point for further thermal testing method development and k optimization in Li-ion battery electrode nanocomposites
CO2-Footprint of a Novel Pumped Hydro Energy Storage System
No full textZur Einhaltung des Pariser Klimaabkommens hat die erneuerbare Energieerzeugung eine zentrale Bedeutung. Der dafür notwendigen Transformation des Energiesystems sind nachhaltige Energiespeicher von hoher Relevanz. Eine neuartige Energiespeicher-Technologie ist Stored Energy in the Sea (StEnSea), welche am Fraunhofer-Institut für Energiewirtschaft und Energiesystemtechnik (IEE) entwickelt wird. Bei StEnSea wird das gleiche Prinzip wie bei Pumpspeicherkraftwerken (PSW) angewendet, mit dem Unterschied, dass das untere Speicherbecken durch eine hohle Betonkugel realisiert wird, die auf dem Meeresboden installiert wird.
In dieser Arbeit wird der CO2-Äquivalent-Fußabdruck (CO2e) der StEnSea-Technologie berechnet und mit dem von Lithium-Ionen-Batterien (LIB) verglichen. Für die LIB werden insbesondere die beiden Zellchemien Nickel-Mangan-Cobalt (NMC) und Lithium-Eisenphosphat (LFP) analysiert, da diese die größten Marktanteile haben. Der Fußabdruck setzt sich aus zwei Komponenten zusammen, die einzeln für die Technologien berechnet werden, aber im Vergleich beide berücksichtigt werden müssen. Zum einen entstehen bei der Produktion, d.h. vor der Inbetriebnahme, Emissionen und zum anderen durch den Betrieb des Speichersystems. Für einen fairen Vergleich werden die Systeme mit der gleichen Spezifikation ausgelegt und die Analyse wird für den gleichen Anwendungsfall und Betrachtungszeitraum durchgeführt. Aus den Analysen geht hervor, dass StEnSea einen CO2e-Fußabdruck von 2.184 tCO2e pro Einheit in der Produktion hat, was einem spezifischen Fußabdruck von 98 kgCO2e/kWhinstalliert entspricht. Der größte Anteil der CO2e-Emissionen stammt mit 83% aus dem Herstellungsprozess der Betonkugel. Die restlichen 17% fallen auf das technische System. Im Bereich der Betonkugel können signifikante CO2e-Einsparungen durch den Einsatz von alternativen Materialien erzielt werden. Durch den Einsatz von Net-Zero Circulation Concrete (NZC) können bei der Produktion von der Betonkugel die Emissionen auf null gesenkt werden, was noch einige Jahre in der Entwicklung benötigt, damit die erforderten Mengen für StEnSea produziert werden können.
Im Vergleich zu den Batterien haben die StEnSea-Speicher eine deutlich höhere Lebensdauer und unterliegen keiner zyklischen Alterung. Um diese Aspekte zu berücksichtigen, wird ein Vergleich mit gleichen Anwendungsfällen durchgeführt und der Betrachtungszeitraum mit 50 Jahren auf die erwartete Lebensdauer von StEnSea-Kugeln festgelegt. Bereits bei Anwendungsfällen mit geringer Zyklenzahl liegen die spezifischen Emissionen auf dem gleichen Niveau. Für eine steigende Zyklenzahl sinken die spezifischen Emissionen von StEnSea unterhalb derer von NMC-Batterien. Im Vergleich zu LFP-Batterien, bei denen heute schon weniger Emissionen anfallen und die Zyklenfestigkeit höher ist, sind die spezifischen Emissionen in etwa doppelt so hoch. Hier würde der gleiche Effekt, den man für die NMC-Batterien beobachten kann, erst eintreten, wenn Anwendungen mit höherer Zyklenzahl berücksichtigt würden. Die aufgezeigten Unterschiede sind jedoch nicht so groß, dass eine Technologie deswegen aus zukünftigen Vergleichen ausgeschlossen werden sollte
Illuminating Router Vendor Diversity Within Providers and Along Network Paths
No full textThe Internet architecture has facilitated a multi-party, distributed, and heterogeneous physical infrastructure where routers from different vendors connect and inter-operate via IP. Such vendor heterogeneity can have important security and policy implications. For example, a security vulnerability may be specific to a particular vendor and implementation, and thus will have a disproportionate impact on particular networks and paths if exploited. From a policy perspective, governments are now explicitly banning particular vendors-or have threatened to do so.Despite these critical issues, the composition of router vendors across the Internet remains largely opaque. Remotely identifying router vendors is challenging due to their strict security posture, indistinguishability due to code sharing across vendors, and noise due to vendor mergers. We make progress in overcoming these challenges by developing LFP, a tool that improves the coverage, accuracy, and efficiency of router fingerprinting as compared to the current state-of-the-art. We leverage LFP to characterize the degree of router vendor homogeneity within networks and the regional distribution of vendors. We then take a path-centric view and apply LFP to better understand the potential for correlated failures and fate-sharing. Finally, we perform a case study on inter and intra-United States data paths to explore the feasibility to make vendor-based routing policy decisions, i.e., whether it is possible to avoid a particular vendor given the current infrastructure.Cyber Securit
Extracellular Potentials in the Hippocampus [electronic resource] : Sources and Biophysical Mechanisms /
No full textIn this thesis, the author investigates the biophysical basis of the local field potential (LFP) as a way of gaining a better understanding of its underlying physiological mechanisms. The results represent major advances in our understanding and interpretation of LFPs and brain oscillations. They highlight the importance of using suitable experimental and analytical methods to explore the activity of brain circuits and point to the LFP as a useful, but complex variable for this purpose.Introduction -- Methods -- Results -- Discussion -- Conclusions.In this thesis, the author investigates the biophysical basis of the local field potential (LFP) as a way of gaining a better understanding of its underlying physiological mechanisms. The results represent major advances in our understanding and interpretation of LFPs and brain oscillations. They highlight the importance of using suitable experimental and analytical methods to explore the activity of brain circuits and point to the LFP as a useful, but complex variable for this purpose
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