Optimized Nail for Penetration Test on Lithium-Ion Cells and Its Utilization for the Validation of a Multilayer Electro-Thermal Model

Nail penetration is one of the most critical scenarios for a lithium-ion cell: it involves the superposition of electrical, thermal and mechanical abusive loads. When an electrically conductive nail is introduced into the active layers of a lithium-ion cell, an electric short circuit takes place between the conductive components (electrodes and current collectors). Hence, for this load case, electro-thermal modeling must be performed considering each and every layer of the cell in order to predict the electric quantities and the cell temperature (with numerical models). When standard conic nails are used, as is typical for this class of tests, the electrical contact between conductive components and the nail itself suffers of poor reproducibility mainly due to the separator that interposes between the electrically conductive components. This phenomenon makes it difficult to validate electro-thermal models, since the electrical contact between nail and lithium-ion cell parts cannot be safely determined. In this work, an alternative nail with an optimized ratio between the external surface and volume is presented to overcome this issue. To demonstrate the effectiveness of the designed nail, five tests (with the same conditions) were conducted on five commercial lithium-ion pouch cells, monitoring the tabs voltage and surface temperature. In all tests, thermal runaway was reached within 30 s and the tabs voltage showed comparable behavior, indicating that the short circuit values for all five repetitions were similar. The investigation included the implementation of a detailed layers model to demonstrate how the validation of such model would be possible with the novel data

Fuel Consumption improvement of a LCV diesel engine by conventional measures, targeting post Euro 6 emission compliance

Within the EU funded Horizon 2020 “dieper” project (Diesel engine efficiency improvement and Particulate number Reduction), the authors are working to develop a Light Commercial Vehicle (LCV) demonstrator to enable emissions of 50% of Euro 6 limits and a >80% reduction in particulate numbers including the 10-23nm range. A fuel economy improvement of >5% is also required. The “dieper” project is yet in an initial phase. The paper will outline aspects of a Euro 6b compliant vehicle in the near-future testing environment (RDE, WLTP) with post Euro 6 emissions limits (2020). The baseline vehicle was measured at project start (2017) and the improved vehicle will be measured again the end of the project (2019) by an independent institution (Virtuelles Fahrzeug in Graz, ViF). The paper describes the baseline situation and improvement steps to reach the targets. Hybridization and electrification are excluded from this project and could be added in a further step to meet expected 2025 CO2 regulations

PERTA – Passive safety in road equipment

Bei einem Anprall gegen ein ortsfestes Hindernis ist mit tiefen Intrusionen in den Fahrzeuginnenraum zu rechnen, die zu schwersten Verletzungen führen können. Untersuchungen haben gezeigt, dass Kollisionen mit künstlichen Hindernissen an der Fahrbahnseite, wie Gabelständer, Trimasten, zu 80 % frontal angeprallt werden. Ziel des Forschungsprojektes war die Bewertung der passiven Sicherheit von Gabelständern und Trimasten, um anhand der Ergebnisse Empfehlungen für die Notwendigkeit einer Absicherung durch Schutzeinrichtungen zu erarbeiten. Als Methode wurde ein Mix aus Realversuchen und Finiten Elemente Simulationen gewählt. Ausgangspunkt bildeten je zwei Validierungsversuche für den Gabelständer und Trimast. Aufbauend auf diesen Versuchen wurden Simulationsmodelle validiert. Die Simulationsmodelle wurden modifiziert und die Insassensicherheit nach Kriterien der EN 12767 bewertet. Wesentliche Kriterien waren der Index für die Schwere der Beschleunigung (ASI: Acceleration Severity Index) und die theoretische Anprallgeschwindigkeit des Kopfes (THIV: Theoretical Head Impact Velocity). Der wesentliche Faktor zum Erreichen einer passiven Sicherheit wurde im Abreißen der Gurtrohre beim Anprall festgestellt. Ein Abreißen der Gurtrohre führt zum Unterschreiten der Grenzwerte für den ASI und THIV gemäß EN 12767. Von Bedeutung sind in diesem Zusammenhang der Gurtrohrdurchmesser und die Ausführung der Fußplatten. Fixierte Fußplatten begünstigen ein Abreißen der Gurtrohre und ein Unterschreiten der Grenzwerte für den ASI und insbesondere für den THIV. Die Masthöhe, die Spreizung und das Schild selbst haben nur einen geringen Einfluss auf die beiden Kennwerte. Unterschiedliche Diagonalrohranordnungen, Schwächung der Gurtrohre oder Reduktion des Schweißnahtumfangs wirken sich positiv auf das Abreißen der Gurtrohre aus und führen zum Unterschreiten der Grenzwerte des ASI und THIVIn the event of a collision against a stationary obstacle, deep intrusions into the vehicle interior can be expected which lead to severe injuries. Investigations of the impact configurations have shown that frontal collisions with stationary obstacles on the side of the road, such as traffic signs, posts or lighting poles, account for approximately 80% of all possible impact configurations. The aim of the study was to examine the passive safety of traffic signs (“Gabelständer” and “Trimast”). Based on the results recommendations should be developed if these traffic signs need to be shielded by road restraint systems. As method a mix of real tests and finite element simulations was chosen. Two tests for each traffic sign served as a basis for the validation of the simulation models. Based on the validated simulation models, the traffic signs were modified and in the simulations the passenger safety was evaluated according to the criteria of EN 12767. Essential criteria were the index for the severity of acceleration (ASI: Acceleration Severity Index) and the theoretical impact velocity of the head (THIV: Theoretical Head Impact Velocity). The main factor in achieving passive safety of traffic signs was found to be the tearing off of the belt tubes at the impact. If the belt tubes tear off, the values for ASI and THIV are below the limits according to EN 12767. Main factors were identified as belt tube diameter and the design of the foot plates. Fixed footplates support the tearing off of the belt tubes and the values for the ASI and especially the THIV are below the limits. The belt tube height, the distance between the belt tubes and the shield itself only have a minor influence. Different diagonal tube layout, weakening of the belt tubes or reduction of the weld circumference positively influence ASI and THIV

Assessment of the Effectiveness of Different Safety Measures at Tunnel Lay-Bys and Portals to Protect Occupants in Passenger Cars

Tunnel portals and tunnel lay-bys are hazardous spots for road users. Different infrastructure safety measures are in use, but the protection level is not known. In this study the following safety measures for reducing the injury risk are investigated: angular positioned 4 m and 8 m concrete barrier, crash cushion Alpina F1-50 and Alpina <prototype> crash cushion. A passenger car equipped with a data acquisition unit is accelerated to 100 km/h and impacts the safety measure. The assessment of the latter is based on the EN 1317 criteria, specifically the Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV). Further assessment criteria are related to intrusions into the passenger compartment and post-crash motion. The best result in terms of ASI and THIV was achieved by the 8 m (ASI: 1.6, THIV: 30 km/h) concrete barrier. The crash cushion Alpina <prototype> showed good results for the ASI (1.8) but the THIV (57 km/h) was less satisfactory, while the angular positioned 4 m concrete barrier (ASI: 2.9, THIV: 53 km/h) and the crash cushion Alpina F1-50 (ASI: 3.3, THIV: 74 km/h) performed worst. Even though some of the measures showed good results, no protection measure tested currently complies with all the assessment criteria used

Analysis and Investigation of Thermal Runaway Propagation for a Mechanically Constrained Lithium-Ion Pouch Cell Module

In this paper, tests and analysis of thermal runaway propagation for commercial modules consisting of four 41 Ah Li-ion pouch cells are presented. Module samples were tested at 100% state-of-charge and mechanically constrained between two steel plates to provide thermal and mechanical contact between the parts. Voltage and temperature of each cell were monitored during the whole experiment. The triggering of the exothermal reactions was obtained by overheating one cell of the stack with a flat steel heater. In preliminary studies, the melting temperature of the separator was measured (from an extracted sample) with differential scanning calorimetry and thermogravimetric analysis techniques, revealing a tri-layers separator with two melting points (≈135 °C and ≈170 °C). The tests on module level revealed 8 distinct phases observed and analyzed in the respective temperature ranges, including smoking, venting, sparkling, and massive, short circuit condition. The triggering temperature of the cells resulted to be close to the melting temperature of the separator obtained in preliminary tests, confirming that the violent exothermal reactions of thermal runaway are caused by the internal separator failure. Postmortem inspections of the modules revealed the internal electrical failure path in one cell and the propagation of the internal short circuit in its active material volume, suggesting that the expansion of the electrolyte plays a role in the short circuit propagation at the single cell level. The complete thermal runaway propagation process was repeated on 5 modules and ended on average 60 s after the first thermal runaway triggered cell reached a top temperature of 1100 °C

Thermal Conductivity in Aged Li-Ion Cells under Various Compression Conditions and State-of-Charge

Thermal conductivity (TC) is a parameter, which significantly influences the spatial temperature gradients of lithium ion batteries in operative or abuse conditions. It affects the dissipation of the generated heat by the cell during normal operation or during thermal runaway propagation from one cell to the next after an external short circuit. Hence, the thermal conductivity is a parameter of great importance, which concurs to assess the safety of a Li-ion battery. In this work, an already validated, non-destructive measurement procedure was adopted for the determination of the evolution of the through-plane thermal conductivity of 41 Ah commercially available Li-ion pouch cells (LiNiMnCoO2-LiMn2O4/Graphite) as function of battery lifetime and state of charge (SOC). Results show a negative parabolic behaviour of the thermal conductivity over the battery SOC-range. In addition, an average decrease of TC in thickness direction of around 4% and 23% was measured for cells cycled at 60 °C with and without compression, respectively. It was shown that pretension force during cycling reduces battery degradation and thus minimises the effect of ageing on the thermal parameter deterioration. Nevertheless, this study highlights the need of adjustment of the battery pack cooling system due to the deterioration of thermal conductivity after certain battery lifetime with the aim of reducing the risk of battery overheating after certain product life

In Situ Measurement of Orthotropic Thermal Conductivity on Commercial Pouch Lithium-Ion Batteries with Thermoelectric Device

In this paper, the direct measurement of the orthotropic thermal conductivity on a commercial Li-ion pouch battery is presented. The samples under analysis are state-of-the art batteries obtained from a fully electric vehicle commercialized in 2016. The proposed methodology does not require a laboratory equipped to manage hazardous chemical substances as the battery does not need to be disassembled. The principle of the measurement methodology consists of forcing a thermal gradient on the battery along the desired direction and measuring the heat flux and temperature after the steady state condition has been reached. A thermoelectric device has been built in order to force the thermal gradient and keep it stable over a long period of time in order to be able to observe the temperatures in steady state condition. Aligned with other measurement methodologies, the results revealed that the thermal conductivity in the thickness direction (0.77 Wm−1K−1) is lower with respect to the other two directions (25.55 Wm−1K−1 and 25.74 Wm−1K−1) to about a factor ×35

Evaluation of the Austrian National Reform Programme: An update with a special focus on employment, liberal professions and international competition - Final Report ; Study on behalf of the Austrian Federal Ministry of Economics and Labour (BMWA)

from the Table of Contents: Executive Summary; Update of the 2006 NRP evaluation; International Competitiveness; Liberal Professions ("freie Berufe"); Active Labour Market Policies: Net Effects and Macro-economic outcome; Bibliography