A comprehensive analysis of the degradation mechanisms on the surface of commercial LiNi0.5Co0.2Mn0.3O2 electrodes is presented. Irregularly distributed particle cracking and the formation of a ...cathode electrolyte interphase on the surface of the active material were identified to be the main degradation mechanisms. The particle cracking originates from inhomogeneity of the composite electrode, leading to deviations in the local current density and the state of charge which results in overcharge conditions for particular LiNi0.5Co0.2Mn0.3O2 particles. Therein, the highly delithiated structure suffers from anisotropic stress due to repulsive interactions between adjacent layers and the formation of new phases which eventually cause particle cracking. The structural changes were confirmed by the presence of a spinel phase on the surface of the cracked particles. Furthermore, the migration of transition metal ions in the highly delithiated structure can facilitate their dissolution into the electrolyte. The investigation of the re-deposited transition metals reveals a predominant dissolution of manganese from the overcharged particles. In addition, electrochemical cycling of the LiNi0.5Co0.2Mn0.3O2 electrodes in laboratory cells show an increasing severity of the particle cracking at higher C-rates which can influence the thermal stability of the active material. Moreover, an increased electrolyte decomposition was observed for higher cut-off potentials.
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•Degradation effects on commercial NCM-523 electrodes from 18650-type LIBs.•Particle cracking accompanied with phase changes and transition metal dissolution.•High current densities lead to severe particle cracking on the electrode surface.•High cut-off potentials lead to higher capacities but also enhanced degradation.•High current densities lead to a reduced thermal stability of NCM-523 electrodes.
Established safety of lithium ion batteries is key for the vast diversity of applications. The influence of aging on the thermal stability of individual cell components and complete cells is of ...particular interest. Commercial 18650-type lithium ion batteries based on LiNi0.5Co0.2Mn0.3O2/C are investigated after cycling at different temperatures. The variations in the electrochemical performance are mainly attributed to aging effects on the anode side considering the formation of an effective solid-electrolyte interphase (SEI) during cycling at 45 °C and a thick decomposition layer on the anode surface at 20 °C. The thermal stability of the anodes is investigated including the analysis of the evolving gases which confirmed the severe degradation of the electrolyte and active material during cycling at 20 °C. In addition, the presence of metallic lithium deposits could strongly affect the thermal stability. Thermal safety tests using quasi-adiabatic conditions show variations in the cells response to elevated temperatures according to the state-of-charge, i.e. a reduced reactivity in the discharged state. Furthermore, it is revealed that the onset of exothermic reactions correlates with the thermal stability of the SEI, while the thermal runaway is mainly attributed to the decomposition of the cathode and the subsequent reactions with the electrolyte.
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•Comprehensive study on the thermal stability of commercial 18650-type LIBs.•Strong influence of cycling temperature on the thermal stability of the SEI.•Onset temperatures for exothermic reactions correlate with SOC for fresh LIBs.•Metallic lithium deposits on the anode reduce safety properties of the cell.•Thermally stable SEI impedes de-intercalation of lithium ions.
This Letter reports on the measurement of the energy loss and the projectile charge states of argon ions at an energy of 4 MeV/u penetrating a fully ionized carbon plasma. The plasma of n(e)≈10(20) ...cm(-3) and T(e)≈180 eV is created by two laser beams at λ(Las)=532 nm incident from opposite sides on a thin carbon foil. The resulting plasma is spatially homogenous and allows us to record precise experimental data. The data show an increase of a factor of 2 in the stopping power which is in very good agreement with a specifically developed Monte Carlo code, that allows the calculation of the heavy ion beam's charge state distribution and its energy loss in the plasma.
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► Hard X-ray grating interferometry shows promising results in phase and scattering imaging. ► Two-dimensional structures help improve image quality and provide directional ...scattering. ► We present a fabrication process for μm sized high aspect ratio two-dimensional diffraction gratings.
Hard X-ray grating interferometry has shown promising results in phase and scattering imaging, as well as in metrology applications. Recently, the technique has been extended to two dimensions, recording the full phase gradient vector and a directional scattering signal. Here, we present a process for fabricating the key optical elements required for this technique: phase and absorption gratings with periods of few micrometers and high aspect ratios, with a particular focus on two-dimensional grating structures. The fabrication process is based on deep reactive ion etching in silicon and electroplating of gold.
Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) has been used to investigate numerically crystal dynamics in an existing pilot-scale batch crystallizer. The CFD-DEM ...combination provides a detailed description of crystal dynamics considering a four-way coupling. In a previous analysis, CFD had been coupled with a discrete phase model (DPM) using a simple one-way coupling. The corresponding predictions are then compared with those obtained through four-way coupling considering KH2PO4 crystals in water. From the CFD-DEM simulation, it is possible to investigate quantitatively the driving force controlling crystal growth and the interaction of crystals with reactor walls, baffles, and impellers. This delivers essential data for process improvement. Different seeding procedures were also compared. The seed crystals have been injected either within the complete liquid volume or, as in the experiments, through a funnel. By varying the most important crystallization process parameters, we found optimal conditions for a liquid phase volume in the crystallizer of 24 L, for injection through a funnel above the baffle, and for an initial seed crystal size of 0.5 mm.
We report a quasidifferential upper limit on the extremely-high-energy (EHE) neutrino flux above 5×106 GeV based on an analysis of nine years of IceCube data. The astrophysical neutrino flux ...measured by IceCube extends to PeV energies, and it is a background flux when searching for an independent signal flux at higher energies, such as the cosmogenic neutrino signal. We have developed a new method to place robust limits on the EHE neutrino flux in the presence of an astrophysical background, whose spectrum has yet to be understood with high precision at PeV energies. A distinct event with a deposited energy above 106 GeV was found in the new two-year sample, in addition to the one event previously found in the seven-year EHE neutrino search. These two events represent a neutrino flux that is incompatible with predictions for a cosmogenic neutrino flux and are considered to be an astrophysical background in the current study. The obtained limit is the most stringent to date in the energy range between 5×106 and 2×1010 GeV. This result constrains neutrino models predicting a three-flavor neutrino flux of Eν2ϕνe+νμ+ντ≃2×10−8 GeV/cm2 sec sr at 109 GeV. A significant part of the parameter space for EHE neutrino production scenarios assuming a proton-dominated composition of ultra-high-energy cosmic rays is disfavored independently of uncertain models of the extragalactic background light which previous IceCube constraints partially relied on.
Safety properties of lithium metal batteries (LMBs) are key for potential commercialization. The few studies reported focus predominantly on pristine materials or as-assembled cells disregarding ...potential safety risks induced by cyclic aging and the associated formation of high surface area lithium deposits. Herein, LMBs using organic carbonate-solvent electrolyte were investigated to decipher the influence of the lithium metal deposition behavior on the thermal stability. For this purpose, cells were cycled to different states of health, states of charge and at varied current densities during charging before analyzing the thermal stability on material and cell level via differential scanning calorimetry. In combination with cryogenic-focused ion beam-scanning electron microscopy it is possible to correlate the lithium metal deposition morphology with the thermal stability. Therein, accumulation of highly porous lithium metal deposits during cycling leads to a significant increase of released heat caused by highly exothermic reactions between deposited lithium and the electrolyte. Consequently, a denser deposition morphology shifts the onset for exothermic decomposition reactions to higher temperatures. Overall, this study introduces the combination of different analytical techniques to evaluate LMB safety properties and reveals the safety-relevant impact of cyclic aging on thermal stability.
Plant growth and developmental processes are mainly controlled by plant growth regulators in dependence on light quality and quantity. Rare information of the influence of light resources on ...grapevine somatic embryogenesis is available. LEDs have high advantages compared with conventional used light sources in in vitro culture like working with defined wavelengths and photon flux, excellent energy-efficiency and longer life. Thus this study was focused on the evaluation of effects of white (450, 545, 580 nm), blue (450 nm) or red (640 nm) light emitting diodes (LED) on the germination of somatic embryos of grapevine (Vitis vinifera) compared with commonly used fluorescent tubes in culture rooms. Somatic embryos in heart and early torpedo stages were cultured on different basal media, partly supplemented with combinations of PGR or charcoal. The cultures were illuminated with 34 µmol m-2 s-1 photosynthetic active radiation in different combinations of red-white and red-blue wavelengths. Best results of conversion into normal plantlets could be obtained on full strength Murashige and Skoog medium containing plant growth regulator (BAP 0.13 µM and NES 0.054 µM) without activated charcoal by cultivation under increased blue light ratio. The addition of PGR resulted mainly in an enhanced leaf area. A higher portion of blue light resulted in a significantly increased leaf area compared with higher red light portion. Greatest leaf area was found in presence of plant growth regulator without activated charcoal.
The existence of diffuse Galactic neutrino production is expected from cosmic-ray interactions with Galactic gas and radiation fields. Thus, neutrinos are a unique messenger offering the opportunity ...to test the products of Galactic cosmic-ray interactions up to energies of hundreds of TeV. Here we present a search for this production using ten years of Astronomy with a Neutrino Telescope and Abyss environmental RESearch (ANTARES) track and shower data, as well as seven years of IceCube track data. The data are combined into a joint likelihood test for neutrino emission according to the KRA model assuming a 5 PeV per nucleon Galactic cosmic-ray cutoff. No significant excess is found. As a consequence, the limits presented in this Letter start constraining the model parameter space for Galactic cosmic-ray production and transport.
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