Onset Shift of Li Plating on Si/Graphite Anodes with Increasing Si Content

Mixing graphite with Si particles in anodes of Li-ion batteries provides increased specific energy. In addition, higher Si contents lead to thinner anode coatings at constant areal capacity. In the present study, we systematically investigated the influence of the Si content on the susceptibility of Li plating on Si/graphite anodes. Si/graphite anodes with Si contents from 0 to 20.8 wt% combined with NMC622 cathodes were manufactured on pilot-scale. After initial characterization in coin half cells and by SEM, pouch full cells with fixed N/P ratios were built. Rate capability at different temperatures, and Post-Mortem analysis were carried out. Results from voltage relaxation, Li stripping, SEM measurements, glow discharge optical emission spectroscopy (GD-OES) depth profiling, and optical microscopy were validated against each other. A decreasing susceptibility to Li plating with increasing Si content in the anodes could be clearly observed. A critical C-rate was defined, at which Li plating was detected for the first time. It was also found that at 0 °C the critical C-rate increases with increasing Si contents. At 23 °C the SOC at which Li dendrites were first observed on the anode also increased with higher Si content

Reformation als Kommunikationsprozess

Beim Hussitismus bzw. Utraquismus in Böhmen und der reformatorische Bewegung ab 1517 in Sachsen handelt es sich um zwei unterschiedliche Reformationen, jedoch mit einer Fülle von sachlichen und personalen Verbindungslinien. Diese rücken im vorliegenden Band erstmalig in einen gemeinsamen Fokus.»Wir sind alle Hussiten«, bekannte Martin Luther 1520 nach der Lektüre von Schriften des tschechischen Reformators Jan Hus, der gut einhundert Jahre zuvor als Ketzer verbrannt worden war. Die beiden Reformatoren verbinden, ebenso wie die von ihnen ausgehenden Erweckungs- und Erneuerungsbewegungen, viele Ähnlichkeiten, Übereinstimmungen und parallele Entwicklungsverläufe. Dennoch werden sie meist getrennt betrachtet. Der Sammelband analysiert Aspekte der Reformation in Böhmen und Sachsen und rückt so die beiden religiösen Brennpunkte in einen gemeinsamen Fokus. Methodisch wählen die Beiträgerinnen und Beiträger dabei einen kommunikationsgeschichtlichen Zugang

Simulation of Li Plating in Si/Graphite Composite Electrodes

It is a common perception that the demand for high-performance batteries is constantly increasing. While the primary characteristics depend on the application, decisive criteria are energy density, safety, cost, and sustainability of the batteries. Here, Li-ion batteries play a key role especially for electric vehicles and portable electronics. How-ever, additional improvements are needed, for example, to achieve the fast charging criteria given by the automotive industry. The performance characteristics of the batteries such as high energy or power density can be tuned by the electrode microstructure, composition, or choice of materials. One such promising material for the negative electrode is Silicon: Si exhibits a high theoretical capacity and is very abundant. On the other hand, Si shows a large volume expansion and low Li mobility. Thus, to take advantage of the high theoretical capacity and to limit the deformation during cycling, Si is mixed with Graphite to produce more practical Si/Graphite composite electrodes. In order to increase the cycle life of Si containing electrodes, it is critical to trace the degradation processes responsible for their performance loss. One major aging mechanism causing fast degradation and fundamental safety risks is Li plating. This deposition of a metallic lithium phase on the surface of Si/Graphite anodes is barely studied in the literature yet crucial to improve the performance and safety of state-of-the-art Li-ion batteries. In our contribution we present simulation results of Si/Graphite composite electrodes including mod-els for Li plating on Graphite and Si particles in 3D microstructure-resolved simulations. While focus-sing on the differing lithiation behaviours of Graphite and Si, the findings are validated with experimental results from our project partners. More specifically, we compare our simulations to multiple complemen-tary techniques such as neutron depth profiling (NDP), post-mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling, and X-ray diffraction analysis (XRD). Under examination are commercial and self-manufactured full and half cells containing varying amounts of Si or SiC blend. Furthermore, we developed a homogenized p2D model of composite electrodes which also includes the volume changes during lithiation and delithiation of representative Si particles and the effect on transport processes. The studies serve as a starting point to understand Li plating in Si containing electrodes and, eventually, the design of better Si/Graphite composite electrodes

Charge Relaxation within Silicon/Graphite Anodes – A Multi-Method Study

As silicon/graphite (SiG) composites are more commonly used as the anode active material in commercial Li-ion batteries, investigation of the (de-)lithiation behavior of the blended anodes becomes increasingly important. In this study, the charge redistribution between graphite and silicon was investigated in graphite-NMC 622 and SiG (23 wt.-% Si) – NMC 622 bilayer pouch cells using in situ and operando X-ray diffraction (XRD). In addition to XRD, ex situ and in situ optical microscopy (IOM), as well as microstructural resolved simulations using digital twins of the cells, were used. Different SOC values (0%, 25%, 50%, 75%, and 100%) and two different C-rates (0.1C and 0.5C) were compared in cells during operation and in the relaxed state. Insights into the relaxation process at 75% SOC were gained by tracking of the charge redistribution in IOM cells. Ex situ optical microscopy measurements reinforced the findings of the IOM measurements. Both XRD and optical microscopy showed the disappearance of charge in the graphite component of the SiG anode during the relaxation period (≥24h) at SOC ≤75%, indicating a redistribution of Li from graphite into Si in the anode. The simulations allowed tracking of the concentration of Li in both active material components, verifying the observations on the charge relaxation processes observed in the XRD and microscopy experiments. The gained insights can support a better understanding of aging of blended SiG anodes during operation

Simulation of Li Plating in Si/Graphite Composite Electrodes

Li-ion batteries play a key role especially for electric vehicles and portable electronics. However, additional improvements are needed, for example, to achieve the fast charging criteria given by the automotive industry. The performance characteristics of the batteries such as high energy or power density can be tuned by the electrode microstructure, composition, or choice of materials. One such promising material for the negative electrode is Silicon: Si exhibits a high theoretical capacity and is very abundant. On the other hand, Si shows a large volume expansion and low Li mobility. Thus, to take advantage of the high theoretical capacity and to limit the deformation during cycling, Si is mixed with Graphite to produce more practical Si/Graphite composite electrodes. In order to increase the cycle life of Si containing electrodes, it is critical to trace the degradation processes responsible for their performance loss. One major aging mechanism causing fast degradation and fundamental safety risks is Li plating. This deposition of a metallic Li phase on the surface of Si/Graphite anodes is barely studied in the literature yet crucial to improve the performance and safety of state-of-the-art Li-ion batteries. In our contribution we present simulation results of Si/Graphite composite electrodes including models for Li plating on Graphite and Si particles in 3D microstructure-resolved simulations. While focusing on the differing lithiation behaviors of Graphite and Si, the findings are validated with experimental results from our project partners. More specifically, we compare our simulations to multiple complementary techniques such as neutron depth profiling (NDP), post-mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling, and X-ray diffraction analysis (XRD). We examine commercial and self-manufactured full- and half-cells containing varying amounts of Si or SiC blend. Since inhomogeneities in the amount of Li plating were observed, studies on simplified half-cells are conducted to clarify the impact of relevant material parameters. Furthermore, we developed a homogenized p2D model of composite electrodes which also includes the volume changes during lithiation and delithiation of representative Si particles and the effect on transport processes. Not only provides the complementarity of sophisticated experimental and simulative studies a better understanding of how Li plating takes place in Si containing electrodes, but also enables an improved possibility to optimize the design of Si/Graphite composite electrodes

Reformation als Kommunikationsprozess

Beim Hussitismus bzw. Utraquismus in Böhmen und der reformatorische Bewegung ab 1517 in Sachsen handelt es sich um zwei unterschiedliche Reformationen, jedoch mit einer Fülle von sachlichen und personalen Verbindungslinien. Diese rücken im vorliegenden Band erstmalig in einen gemeinsamen Fokus.»Wir sind alle Hussiten«, bekannte Martin Luther 1520 nach der Lektüre von Schriften des tschechischen Reformators Jan Hus, der gut einhundert Jahre zuvor als Ketzer verbrannt worden war. Die beiden Reformatoren verbinden, ebenso wie die von ihnen ausgehenden Erweckungs- und Erneuerungsbewegungen, viele Ähnlichkeiten, Übereinstimmungen und parallele Entwicklungsverläufe. Dennoch werden sie meist getrennt betrachtet. Der Sammelband analysiert Aspekte der Reformation in Böhmen und Sachsen und rückt so die beiden religiösen Brennpunkte in einen gemeinsamen Fokus. Methodisch wählen die Beiträgerinnen und Beiträger dabei einen kommunikationsgeschichtlichen Zugang

Oxygen targets and 6-month outcome after out of hospital cardiac arrest: a pre-planned sub-analysis of the targeted hypothermia versus targeted normothermia after Out-of-Hospital Cardiac Arrest (TTM2) trial

International audienceAbstract Background Optimal oxygen targets in patients resuscitated after cardiac arrest are uncertain. The primary aim of this study was to describe the values of partial pressure of oxygen values (PaO 2 ) and the episodes of hypoxemia and hyperoxemia occurring within the first 72 h of mechanical ventilation in out of hospital cardiac arrest (OHCA) patients. The secondary aim was to evaluate the association of PaO 2 with patients’ outcome. Methods Preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after OHCA (TTM2) trial. Arterial blood gases values were collected from randomization every 4 h for the first 32 h, and then, every 8 h until day 3. Hypoxemia was defined as PaO 2  300 mmHg. Mortality and poor neurological outcome (defined according to modified Rankin scale) were collected at 6 months. Results 1418 patients were included in the analysis. The mean age was 64 ± 14 years, and 292 patients (20.6%) were female. 24.9% of patients had at least one episode of hypoxemia, and 7.6% of patients had at least one episode of severe hyperoxemia. Both hypoxemia and hyperoxemia were independently associated with 6-month mortality, but not with poor neurological outcome. The best cutoff point associated with 6-month mortality for hypoxemia was 69 mmHg (Risk Ratio, RR = 1.009, 95% CI 0.93–1.09), and for hyperoxemia was 195 mmHg (RR = 1.006, 95% CI 0.95–1.06). The time exposure, i.e., the area under the curve (PaO 2 -AUC), for hyperoxemia was significantly associated with mortality ( p = 0.003). Conclusions In OHCA patients, both hypoxemia and hyperoxemia are associated with 6-months mortality, with an effect mediated by the timing exposure to high values of oxygen. Precise titration of oxygen levels should be considered in this group of patients. Trial registration : clinicaltrials.gov NCT02908308 , Registered September 20, 2016

Ventilatory settings in the initial 72 h and their association with outcome in out-of-hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out-of-hospital cardiac arrest (TTM2) trial

International audienc