Investigation of silicon containing anode material for high energy lithium-ion batteries

Für die Automobilindustrie ist speziell die volumetrische Energiedichte von Bedeutung, welche neben einer Optimierung des Zelldesigns insbesondere durch Implementierung neuer Aktivmaterialien für die positive Elektrode bzw. die negative Elektrode gesteigert werden kann. Mit einer verhältnismäßig niedrigen Lithiierungsspannung vs. Li/Li+ und einer gegenüber kommerziell eingesetztem Graphit (C, 372 mAh/g) um den Faktor 10 höheren spezifischen Kapazität, ist Silicium (Si) eine vielversprechende Alternative, um die Energiedichte von Lithium-Ionen-Batteriezellen deutlich zu steigern. Die Herausforderungen bei der Kommerzialisierung siliciumhaltiger Anoden mit Si-Gewichtsanteilen von über 5 wt% gehen auf die enorme Volumenänderung der Si-Partikel um 280 % während der Lithiierung und Delithiierung zurück. Trotz diverser Ansätze, ist über einen Zeitraum von über 20 Jahren kein nennenswerter Durchbruch erzielt worden. In dieser Arbeit wird ein Grundverständnis für die Abhängigkeit der Lithiierungskinetik und der Lebensdauer von den verschiedenen Materialcharakteristika, vom Si-Gehalt, dem Ausnutzungsgrad des Siliciums und der Flächenkapazität abgeleitet. Ausgehend von diesen Erkenntnissen werden neue Optimierungsansätze erschlossen und deren Effekte auf die Degradation der siliciumhaltigen Anoden untersucht. Es wird ein neuartiges Bindersystem vorgestellt, welches nicht nur die mechanischen Eigenschaften der Elektroden deutlich verbessert, sondern auch die Lebensdauer signifikant erhöht. Das innovative dreidimensionale Bindernetzwerk umschließt die Si-Partikel, reduziert die irreversible Verformung der Elektroden und beeinflusst damit die Performance siliciumhaltiger Anoden positiv. Des Weiteren werden verschiedene Methoden zur Modifikation der Grenzflächeneigenschaften und Generierung einer „artificial SEI“ (Solid Electrolyte Interphase) bewertet. Neben der Untersuchung von Kombinationen vielversprechender Additive wird ein Protokoll für eine vorgeschaltete Formierung entwickelt und Partikel sowie Elektroden mittels ALD-Verfahren beschichtet. Es kann gezeigt werden, dass die Präformierung nicht nur die irreversible Kapazität, sondern auch die Formierungszeit deutlich reduziert, während die ALD-Beschichtung über großes Potential zur Verbesserung der Lebensdauer und der Lithiierungskinetik verfügt und die elementare Wichtigkeit einer stabilen SEI für die andauernde Funktion der Zelle unterstreicht.For the automotive industry, volumetric energy density in particular is of paramount importance and can be raised by alteration of the cell design and implementation of new active materials into the positive and negative electrode. With a comparably low discharge potential vs. Li/Li+ and a 10-fold specific capacity compared to commercially used graphite (C, 372 mAh/g), silicon (Si) is an exceptionally promising candidate to increase the energy density of lithium-ion batteries. However, major challenges arise when it comes to the commercialization of anodes with Si-contents higher than 5 wt%, all connected to the huge volume expansion of the silicon particles (280 %) during lithiation and delithiation and its detrimental effects on the electrode framework. Despite of various approaches, that were pursued to address this issue, ranging from structural and compositional modification of the silicon material structure itself, to the optimization of the electrode fabrication and the electrolyte composition, a nameable breakthrough has not been achieved, so far. Within this thesis, a fundamental understanding of the relationship between lithiation kinetics and cycle life is linked to the different material characteristics, the silicon content and the areal electrode capacity. Based on these results, novel optimization approaches are derived and evaluated with regard to the degradation of Si-containing anodes. A new binder system, that greatly improves the mechanical properties of the electrodes and significantly prolongs cycle life, is identified. The innovative three-dimensional binder network enwraps the Si-particles, reduces the irreversible deformation of the electrode and thereby enhances the electrochemical performance of Si-anodes. Furthermore, different methods for interfacial modification and generation of an “artificial SEI” (solid electrolyte interphase) are evaluated. Besides testing of different combinations of promising additives, a preformation protocol is developed, and silicon-particles as well as electrodes are coated by atomic layer deposition (ALD). It is shown that the preformation does not only reduce the irreversible capacity loss, but also the formation time, while ALD-coating technology bears great potential to enhance cycle life and lithiation kinetics, underlining the elemental function of a stable SEI for improved battery performance

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente

Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

A search for the direct production of the supersymmetric partners ofτ-leptons (staus) in final stateswith two hadronically decayingτ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of139fb−1, recorded with the ATLAS detector at the LargeHadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected StandardModel background is observed. Limits are derived in scenarios of direct production of stau pairs with eachstau decaying into the stable lightest neutralino and oneτ-lepton in simplified models where the two staumass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidencelevel for a massless lightest neutralino

Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector

A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13  TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV

Combined measurement of differential and total cross sections in the H → γγ and the H → ZZ* → 4ℓ decay channels at s=13 TeV with the ATLAS detector

A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb−1 of 13 TeV proton–proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H→γγ and H→ZZ*(→4ℓ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0−5.9 +6.0 (stat.) −3.3 +4.0 (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions

Search for High-Mass Resonances Decaying to τν in pp Collisions at √s=13 TeV with the ATLAS Detector

A search for high-mass resonances decaying to τν using proton-proton collisions at √s=13 TeV produced by the Large Hadron Collider is presented. Only τ-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb−1. No statistically significant excess above the standard model expectation is observed; model-independent upper limits are set on the visible τν production cross section. Heavy W′ bosons with masses less than 3.7 TeV in the sequential standard model and masses less than 2.2–3.8 TeV depending on the coupling in the nonuniversal G(221) model are excluded at the 95% credibility level

Measurement of jet fragmentation in Pb+Pb and pp collisions at √s NN =5.02 TeV with the ATLAS detector

This paper presents a measurement of jet fragmentation functions in 0.49 nb −1 of Pb+Pb collisions and 25 pb −1 of pp collisions at √ sNN =5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultra-relativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmentation functions are measured for jets with transverse momentum between 126 GeV and 398 GeV and with an absolute value of jet rapidity less than 2.1. An enhancement of particles carrying a small fraction of the jet momentum is observed, which increases with centrality and with increasing jet transverse momentum. Yields of particles carrying a very large fraction of the jet momentum are also observed to be enhanced. Between these two enhancements of the fragmentation functions a suppression of particles carrying an intermediate fraction of the jet momentum is observed in Pb+Pb collisions. A small dependence of the modifications on jet rapidity is observed

Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in √s =13 TeV pp collisions with the ATLAS detector

A search for the bb ¯ decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channels and a photon-associated channel. Results are reported from the analysis of up to 30.6 fb −1 of pp data at s √ =13 TeV collected with the ATLAS detector at the LHC. The measured signal strength relative to the Standard Model prediction from the combined analysis is 2.5 +1.4 −1.3 for inclusive Higgs boson production and 3.0 +1.7 −1.6 for vector-boson fusion production only

Search for long-lived particles produced in pp collisions at √s=13 TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer

A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb−1 of proton-proton collision data at √s=13 TeV recorded in 2015–2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two-vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined