• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 31
  • 19
  • 12
  • 2
  • 2
  • Tagged with
  • 66
  • 46
  • 14
  • 14
  • 13
  • 13
  • 12
  • 11
  • 10
  • 10
  • 10
  • 10
  • 10
  • 8
  • 8
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Study of Electric and Dielectric Properties of Ionic Liquids / Study of Electric and Dielectric Properties of Ionic Liquids

Altšmíd, Jakub January 2019 (has links)
Dizertační práce je zaměřena na studium elektrických a dielektrických vlastností iontových kapalin. Iontové kapaliny mohou nacházet uplatnění v široké škále aplikací, především pak v elektrotechnice. Teoretická část se věnuje popisu základních vlastností iontových kapalin a možností jejich uplatnění v kondenzátorech a elektrochemických senzorech plynů. Experimentální část se věnuje použitým metodám charakterizace vlastností iontových kapalin, jsou zde popsány teoretické poznatky o dielektrické spektroskopii včetně metod stanovení fyzikálních vlastností a vyhodnocení experimentálních dat. Experimentální část je rozdělena na dvě základní části. První se věnuje studiu iontových kapalin pro použití jako elektrolytu v kondenzátorech, druhá část se věnuje studiu vlastností připravených experimentálních senzorů na NO2, zejména vlivem vlastností iontových kapalin na sledované parametry senzoru.
32

Synthesis of glass-ceramic Li2S-P2S5-based electrolyte for solid-state batteries / Syntes av glaskeramisk Li2S-P2S5 elektrolyt för fastfasbatterier

Sjörén, Leo January 2023 (has links)
In this project, solid sulphur based Li3PS4 electrolytes doped with Li4SiO4 were synthesised using two methods. In method A, a bought β-Li3PS4 electrolyte from Nei Corp was doped with 5 mole per cent Li4SiO4, resulting in a glass-ceramic electrolyte. In method B, the electrolyte was synthesised using 5Li4SiO4-95(75Li2S-25P2S5), resulting in a glassy material. In addition, a reference was synthesised using 75Li2S-25P2S5. Ball milling was the method of choice to dope the glass ceramic electrolyte and synthesise the glassy electrolyte. The dopant Li4SiO4 was synthesised using the chemicals SiO2 and Li2CO3. All samples were analysed using Raman, XPS, XRD, and EIS. In the end, it was found that doping the bought β-Li3PS4electrolyte with Li4SiO4 increased the ionic conductivity. While introducing Li4SiO4 to the glassy electrolyte lowered the ionic conductivity. The increase in ionic conductivity in the glass ceramic electrolyte was partly attributed to the increase in amorphous content, which happened when it was ball-milled and suppressed P-S-P bonds. The decrease in ionic conductivity that happened when doping the glassy material, is most likely caused by residual Li2S that seems unable to react due to the dopant.
33

Morphological and ageing studies of an electrolyte contaminated lithium-ion battery vent / Morfologiska studier och åldrandestudier av en elektrolytkontaminerad litiumjonbatteriventil

Govindarajan, Bharathan January 2022 (has links)
Undersökning av hur elektrolytkontamination på ventilen på prismatiska litiumjonbattericeller påverkar legeringsytan och påverkar batteriets säkerhet. Åldringsstudier utförs för att påskynda interaktionen av elektrolytförorenade batteriventiler vid önskade miljöförhållanden. Materialegenskaper hos elektrolyt och batteriventil studeras. Ytmorfologin och ventilens mekaniska prestanda analyseras. / Investigation of how electrolyte contamination on the vent of prismatic lithium-ion battery cells affects the alloy surface and impacts the safety of the battery. Ageing studies are carried-out to accelerate the interaction of electrolyte contaminated battery vent at desired environmental conditions. Material properties of electrolyte and battery vent are studied. The surface morphology and mechanical performance of the vent are analyzed.
34

A comparison between aqueous and organic electrolytes for lithium ion batteries / En jämförelse mellan vattenbaserade och organiska elektrolyter för litium-jonbatterier

Quintans De Souza, Gabriel January 2021 (has links)
Många batteriers användningsområden kräver att batterierna har hög upp- och urladdningshastighet samt låg kostnad. För dessa användningsområden är vattenbaserade laddningsbara batterier (ARB) ett möjligt alternativ i och med att de är svårantändliga, har god jonledningsförmåga, lägre inre resistans, billigare elektrolytlösning och tillverkning och har potentiellt högre upp- och urladdningshastigheter.  Genom att utgå från en cell med LiMn2O4 och V2O5 som katod respektive anod, utvecklades en cell med en spänning på 1 V och prestanda för 2 mol/L LiTSFI i organisk respektive vattenlöslig lösning jämfördes i ett SEI-fritt system. Prestandan kvantifierades med avseende på urladdningskapaciteten vid olika urladdningshastigheter samt fördelningen av de interna överpotentialerna. Vid C/4 behöll den organiska elektrolyten 88,3% av den initiala kapaciteten efter 10 cykler medan den vattenlösliga behöll 98,8%. En gräns på 20 °C påvisades för den organiska elektrolyten och vid försök att gå över denna hastighet svällde pouch cellen upp. Den vattenlösliga elektrolyten, å andra sidan, bevarade 37 mAh/g vid 50 °C.  Skillnaden i potentialfördelning i de två systemen analyserades även genom att använda tunnare elektroder. Den organiska elektrolyten visade då en förbättring av prestandan vid höga hastigheter, med en urladdningskapacitet på 8,8 mAh/g vid 50 °C, jämfört med 30 mAh/g för den vattenlösliga elektrolyten. IR-fallet var 7 gånger högre för den organiska elektrolyten. Eventuell skillnad i laddningsöverföring och por-resistans kunde inte analyseras då flera processer ägde rum på samma gång i systemen, vilket gav ett impedansspektrum med en komplex associerad ekvivalent krets. / For several battery applications, high dis-/charge rate and low cost are imperatives. It is for these applications that aqueous rechargeable batteries (ARB) rise as potential candidates given the non-flammability, potentially higher ionic conductivity and dis-/charge rates, lower internal resistances and lower price of the electrolyte solvents and manufacture. By benchmarking a cell with LiMn2O4 and V2O5 as cathode and anode, respectively, a cell with an operating voltage window of 1 V was developed and the performance of 2 mol/L LiTFSI in organic and aqueous solvent compared in a SEI-free system. This performance was quantified in terms of discharge capacity at different rates of discharge and the distribution of internal overpotentials. At C/4, the organic electrolyte held 88.3% of the initial capacity after 10 cycles while the aqueous, 98.8%. A limit of 20 °C for the organic electrolyte was seen, and at the attempt of cycling above this rate, swelling of the pouch cell took place. The aqueous electrolyte, on the other hand, conserved 37 mAh/g at 50 °C. The difference of overpotentials distribution in both systems was also assessed by employing thinner electrodes. The organic electrolyte showed then an improvement on high-rate performance, reaching 50 °C, but with a discharge capacity of 8.8 mAh/g, against 30 mAh/g for the aqueous electrolyte. The IR-drop was 7 times higher for the organic electrolyte. The differentiation between charge-transfer and pore resistance, however, was not possible, because of the presence of several processes taking place at similar time-scales in both systems, yielding an impedance spectra with a complex associated equivalent circuit.
35

Mesoporöse Kohlenstoffmaterialien und Nanokomposite für die Anwendung in Superkondensatoren

Pinkert, Katja 28 October 2014 (has links) (PDF)
Die effiziente Speicherung von elektrischer Energie im elektrochemischen System des Superkondensators wird realisiert durch die Ausrichtung von Elektrolytionen im elektrischen Feld polarisierter, poröser Kohlenstoffelektroden. Der Energieinhalt und die Leistungscharakteristika der elektrostatischen Zwischenspeicherung von Energie bei Lade- und Entladezeiten von wenigen Sekunden bis zu einigen Minuten wird entscheidend durch die Eigenschaften der zur Ladungsspeicherung genutzten Grenzfläche zwischen dem Elektrodenmaterial und dem Elektrolyten bestimmt. Für die Optimierung des Energieinhaltes und der Leistungscharakteristika von Superkondensatoren durch die rationale Modifizierung dieser Grenzfläche konnten entscheidende Trends herausgearbeitet werden. Durch Einbindung eines pseudokapazitiven Eisenoxids in die spezifische Oberfläche des mesoporösen CMK-3 im Redoxverfahren ist die Darstellung einer neuartigen Nanokompositstruktur möglich. Diese weißt eine dreifach höhere spezifische Kapazität im Vergleich zur nicht-modifizierten Kohlenstoffoberfläche unter Beibehaltung der Strombelastbarkeit der Kohlenstoffmatrix auf. Entscheidend für die Weiterentwicklung von Synthesestrategien und die anwendungsorientierte Optimierung für Nanokompositstrukturen ist deren ausführliche Charakterisierung mittels angepasster Verfahren. Die in dieser Arbeit erstmals zur Analyse von porösen CMK-3 basierten Nanokompositstrukturen verwendeten Methoden der Aufnahme eines Tiefenprofils mittels Auger Elektronen Spektroskopie (DP-AES) und der energiegefilterten Transmissionselektronenmikroskopie (EF-TEM) lieferten die Grundlage zur Weiterentwicklung der rationalen, nanoskaligen Grenzflächenfunktionalisierung. In einem weiteren, stark vereinfachten und effektiveren Verfahren der Schmelzimprägnierung der porösen Matrix mit Nitrathydraten, sowie deren anschließendes Kalzinieren zum Übergangsmetall, respektive pseudokapazitiven Übergangsmetalloxid, konnte eine nochmals optimierte Nanokompositstruktur dargestellt werden. Das entwickelte Verfahren wurde für die Einbettung von Nickel/Nickeloxid und Eisen/Eisenoxid in die Oberfläche des mesoporösen CMK-3 eingesetzt. Ein gesteigerter Energieinhalt, wie auch eine deutlich gesteigerte Stabilität der Kapazität bei hohen Strombelastungen für die resultierenden Elektrodenmaterialien konnte eindeutig nachgewiesen werden. Die signifikante Erhöhung der Leistungscharakteristika ist dabei auf die optimale Kontaktierung des Übergangsmetalloxids durch das Übergangsmetall als Leitfähigkeitsadditiv im Sinne einer Kern-Schale Struktur realisiert. Der für das Nanokomposit C-FeO10 berechnete Kapazitätsverlust von < 11 % bei Erhöhung der spezifischen Stromstärke von 1 A/g auf 10 A/g verdeutlicht die beeindruckende Strombelastbarkeit des Materials. In einem weiteren in dieser Arbeit diskutierten Ansatz zur Steigerung des Energieinhaltes eines Superkondensators wurde auf die Verwendung von Ionischen Flüssigkeiten (IL) als Elektrolyt eingegangen. Die gezielte Darstellung eines oberflächenmodifizierten aus Cabiden gewonnen Kohlenstoffmaterials (CDC) unter Beibehaltung der Textur des porösen Systems ermöglichte die Untersuchung des Einflusses der Oberflächencharakteristika des Elektrodenmaterials auf die Strombelastbarkeit des Energiespeichers. Es konnte klar herausgestellt werden, dass für den vielversprechenden IL-Elektrolyten EMIBF4 eine verminderte Polarität, sowie die Abwesenheit azider Protonen an der Oberfläche des Kohlenstoffs deutlich zur Steigerung der Strombelastbarkeit des Speichers beiträgt. Realisiert wurde die Modifizierung der Oberfläche durch deren Chlorierung. Die Einordnung der vielversprechenden Kombinationen aus maßgeschneiderten Elektrodenmaterialien und Elektrolytsystemen wurde anhand der Kenngrößen im Ragone-Diagramm vorgenommen. Die Ergebnisse der Arbeit reihen sich in die derzeit schnell voranschreitende Technologieentwicklung bei Superkondensatoren ein.
36

Inkjet deposition of electrolyte : Towards Fully Printed Light-emitting Electrochemical Cells

Lindh, Mattias January 2013 (has links)
Organic electronics is a hot and modern topic which holds great promise for present and future applications. One such application is the light-emitting electrochemical cell (LEC). It can be fully solution processed and driven at low voltage providing light emission from a large surface. Inkjet printers available today can print a variety of inks, both solutions and dispersions. The technique is scalable and a quick and easy way to accurately deposit small quantities of material in user definable patterns onto a substrate. This is desirable to make low cost and efficient optical devices like displays. In this thesis it has been shown that solid electrolytes, after being dissolved in a liquid solvent, can be inkjet printed into a set of well separated distinct drops with an average maximum thickness of 150 nm. The electrolytes are commonly used in LECs and comprised by poly(ethylene glycol) with molar masses ranging from 1 – 35 kg/mol, and potassium trifluoromethanesulfonate (KCF3 SO3 )—together dissolved incyclohexanone to form an ink. The smallest achieved edge to edge distance between the printed drops was 40 μm. Together with a drop diameter of 50 μm it yields a coverage of 24% at a resolution of 280 dpi. Profiles of dried deposited drops of electrolyte were examined with a profilometer, which showed adistinct coffee ring effect on each drop. In particular, the ridges of the coffee rings were broken into pillar like shapes, together forming a structure akin to a scandinavian ancient remnant called stone ship. Different drop diameters were measured in and between the indium tin oxide samples. The drops’ speeds and sizes atejection from the nozzles seemed unchanged, and wettability is most probably the physical phenomena tolook into in order to understand what generates the differences. Local changes in surface roughness and/or surface energy, possibly originating from the cleaning process of the samples, is most likely the cause. No indications towards large differences in surface tension between the printable inks were seen, however their viscoelastic properties were not measured. As part of the thesis work a LEC characterization set-up was built. It drives a LEC at constant currentand measures the driving voltage, -current, and luminance over time. The set-up is controlled by a Labview virtual instrument and the data exported to a text-file for later analysis. The precision of the luminance measurements is ±0.1 cd/m2 for readings &lt; 50 cd/m2 , but the accuracy is uncertain. The conclusion of this thesis is that it is indeed possible to print solid electrolytes dissolved in cyclo-hexanone with an inkjet printer. However, in order to fully understand the spreading and drying of thedrops, studies of the inks’ viscoelastic properties, together with surface roughness and -energy density ofthe substrates, are needed. The largest molar mass of nicely printable poly(ethylene glycol), at an ink concentration of 10 mg/ml, was 35 kg/mol. This is comparable to the molar mass of an active light-emittingmaterial, “SuperYellow”, often used in LECs. Even though their respective molecular structures are very different, this indicates that inkjet printing of complete LEC-inks, containing both the active material and solid electrolyte, is feasible. Most probably it would require substantial tuning of the printing parameters. This thesis provides further hope for future fully inkjet printed LECs.
37

Dlouhodobý vliv nízko-hořlavých elektrolytů na záporné elektrody / Long-term influence of low-flammable electrolytes on negative electrodes

Valoušek, Michal January 2020 (has links)
The thesis deals with the influence of low-flammable electrolytes on negative electrodes. The thesis describes materials used in lithium-ion batteries and functions of individual components. There is also a description of conductometry and electron microscopy, which is used in the practical part, ie during measurement. All findings are summarized at the end of the thesis.
38

Vliv příměsi kobaltu na parametry kladné elektrody Ni-Cd akumulátorů / The influence of cobalt additive on parameters of positive electrode for Ni-Cd accumulators

Svoboda, Michal January 2009 (has links)
The Master´s thesis deals with description of the influence of cobalt additive on positive electrode parameters for Ni-Cd accumulators. Trough the use of Electrochemical Quartz Crystal Microbalance are analysed the effects which decline effective life of positive electrode during accelerated cycling. Theoretical part describes important characteristics of Ni-Cd accumulators, the working principle and effects which are in progress on positive electrode during cycling. The next part deals with description of system EQCM and the pricnciples of doping active mass with cobalt additive. Practical part consists of EQCM system calibration and electrochemical measurements. The principal aim is detection of the influence of cobalt additve on active mass during cycling in different electrolytes. From the results of measurements is set the optimal amount of cobalt additive.
39

Gelové polymerní elektrolyty s vyšší požární bezpečností / Gel polymer electrolytes with high fire safety

Musil, Michal January 2010 (has links)
This work deals with preparation of PMMA based gel polymer electrolytes with high fire safety and high ionic conductivity. In the theoretical part of the work GPEs for Li – ion accumulators, fire safety tests, fire retardants are mentioned. Preparation of GPEs, electrical and other properties are described in the experimental part. Furthermore, new possible methods of gel preparation are discussed.
40

Vliv zinečnatanových iontů na kladnou hmotu Ni-Zn akumulátorů / The influence of zinc ion on possitive elektrode of Ni-Zn accumulators

Karásek, Stanislav January 2013 (has links)
This thesis deals with the establishment of zinc ions at the positive electrode of nickel-zinc batteries. The aim of the study was to measure the impedance characteristics of the positive electrode in various states of charge and observing the effect of ZnO on the changes of impedance spectra. The theoretical part is focused on nickel hydroxide as a construction material for positive electrode and its behavior during cycling in the electrolyte. The experimental part describes in detail the manufacture of the electrode system and the preparation of electrolytes with different degrees of saturation with zinc oxide. The cells were cycled and measured using impedance spectroscopy. The measured impedance curves were simulated with equivalent circuits for a better understanding of the ongoing processes.

Page generated in 0.0467 seconds