1,720,967 research outputs found
Comparison Between 18650 Lithium-ion Cells of Different Composition Subjected to Thermal Abuse
No full textLithium-ion Batteries (LIBs) are characterized by high energy and power density and long life and are currently used in many applications from portable devices to energy storage systems. These features increase safety concerns, especially when these devices are subject to thermal, mechanical, or electrical abuse. Abuse can lead to exothermic reactions of cell components and with each other, causing a rapid increase in temperature, called Thermal Runaway (TR), and pressure. The response to abuse depends on the physical-chemical characteristics of Li-ion cells, such as chemical composition and State of Charge (SOC). To study the effect of chemical composition, three different 18650 Li-ion cells were tested, i.e., Lithium Titanate Oxide (LTO), Lithium Iron Phosphate (LFP) and Lithium Nickel Cobalt Aluminium Oxide (NCA), at the same SOC (100 %). The cells were subjected to thermal abuse tests in a tubular reactor connected at the output to an online Fourier-transform infrared spectroscopy (FT-IR). All events, i.e., Current Interrupt Device (CID) activation, venting and TR, were recorded, and the gases emitted were traced back to the reactions that take place inside the cell. By comparing the response of the cells with different composition it was found that onset of TR occurs at lower temperature for NCA than the other cells (207 vs 233-234 °C), but the maximum temperature reached during TR by the NCA is higher (579 vs 310-338 °C). Regarding toxic emissions, for all three cells the values of hydrofluoric acid (HF) and carbon monoxide (CO) significantly exceed the Immediately Dangerous to Life or Health Limit (IDHL) defined by the National Institute for Occupational Safety and Health set at 30 ppm for HF and 1200 ppm for CO in 30 min, with maximum concentration of HF between 824 - 893 ppm and the maximum concentration of CO changing according to the chemistries: 231990 ppm for NCA, 140728 ppm for LTO and 97140 ppm for LFP
Investigation on temperatures and gases emitted during thermal abuse tests of commercial Li-ion 18650 cells
No full textIncreased use of lithium-ion batteries (LIBs) has shown the safety limits of these devices, especially when subjected to electrical, mechanical, or thermal abuse. Thermal abuse is caused by exposure of the cell to temperatures above or below the operating temperatures indicated by the safety window (i.e., specific temperature and voltage range). This abuse leads to the degradation of the internal components of the cell with consequent release of gases and vapors by venting, and the generation of heat which, when not exchanged efficiently, triggers thermal runaway (TR) with consequent fire or explosion. To characterize the different phases, in this work thermal abuse tests are conducted on Lithium Cobalt Oxide (NCR) 18650 cells. Abuse tests were performed in a stainless-steel tubular reactor, in inert gas (N2), heated up to 240°C at constant heating rate (2, 5 and 10°C/min). The analysis of gas emitted was conducted through a Fourier transform infrared spectroscope (FT-IR Spectrum 3, Perkin Elmer). The comparison between the results obtained at the three heating rates shown difference in terms of temperature and time for each event and the quantities of gases emitted. In a Li-ion cell heated by the slower heating rate the venting and the onset occurred a lower temperature (133.4 and 177.4°C) compared to the higher heating rate (197.1 and 221.9°C). The durations of catastrophic events are also not comparable, with longer durations for higher heating rate (such as TR of 125s vs 102s for 2°C/min). The intermediate test, 5°C/min, shows results closest to fast heating. The gases produced are similar in terms of composition, essentially composed by hydrofluoric acid (HF), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4) and the electrolytic solvents dimethyl carbonate (DMC), ethylene carbonate (EC) and diethyl carbonate (DEC), trend over time, greater release during venting and TR, and estimated concentration, HF maximum value above 400ppm while for the other gas percentages below 4%
Toxicity Assessment of Gas, Solid and Liquid Emissions from Li-Ion Cells of Different Chemistry Subjected to Thermal Abuse
No full textLithium-ion batteries (LIBs) are employed in a range of devices due to their high energy and power density. However, the increased power density of LIBs raises concerns regarding their safety when subjected to external abuse. The thermal behavior is influenced by a number of factors, i.e., the state of charge (SoC), the cell chemistry and the abuse conditions. In this study, three distinct cylindrical Li-ion cells, i.e., lithium nickel cobalt aluminum oxide (NCA), lithium titanate oxide (LTO), and lithium iron phosphate (LFP), were subjected to thermal abuse (heating rate of 5 °C/min) in an air flow reactor, with 100% SoC. Venting and thermal runaway (TR) were recorded in terms of temperature and pressure, while the emitted products (gas, solid, and liquid) were subjected to analysis by FT-IR and ICP-OES. The concentrations of the toxic gases (HF, CO) are significantly in
excess of the Immediate Danger to Life or Health Limit (IDLH). Furthermore, it is observed that the solid particles are the result of electrode degradation (metallic nature), whereas the liquid aerosol is derived from the electrolyte solvent. It is therefore evident that in the event of a LIB fire, in order to enhance the safety of the emergency responders, it is necessary to use appropriate personal protective equipment (PPE) in order to minimize exposure to toxic substances, i.e., particles and aerosol
Investigation of fires by unconventional IID (improvised incendiary device) and combustion residues on different materials by SPME-GC-MS
No full textIncendiary events are phenomena that have a different evolution depending on the place in which they occur, the type of fuel, combustive and ignition, the type of material involved and the time that elapses between ignition and extinction. In the past few months numerous riots or attacks in different part of the world were carried out by using petrol bombs or incendiary devices. To establish the dynamics of the incendiary event it is necessary to analyze the debris but to make the results reliable it is necessary that the sampling is carried out by expert personnel to ensure the chain of custody of the evidence collected. Once sampled, the samples must be properly stored and sent to the competent laboratory for subsequent analyzes, which must be conducted in line with the reference standards. For the analysis of volatile substances, headspace extraction (HS) with the microextraction in solid phase (SPME) is used with subsequent analysis in gas chromatography coupled to the mass spectrometer (GC-MS). Given the variability of the operating conditions, the materials involved and the ignition methods, it can be said that there are no identical incendiary events, so through the multivariate analysis of the data it is possible to highlight correlations and differences between the various events. The creation of a model that allows the classification of a sample since the comparison with the typical compounds of a primer allows to facilitate the analyzes and to have reliable results. In this way, by reconstructing the dynamics of the event, it is possible to verify any criminal liability related to the presence or absence of flammable liquids or solids extraneous to the scene. In order to make the scientific result easily accessible to non-experts, the verbal scale of the likelihood ratio (LR) was introduced by the ENFSI in 2010.
During the work a simulation was performed by using a Molotov device made with a diesel-sulfuric acidic mix (3:1). A cloth was used as a stopper separating a bag of paper containing potassium chlorate. When the bottle breaks, the mixture comes into contact with the salt giving the formation of a colorless flame that starts the reaction. We have planned experiments with 16 fireboxes, with negative controls for a total of 120 samples.
After the creation of the chemometric model on the basis of the simulation results, data relating to a real case of a malicious nature were used in the model to verify whether or not the considered flammable materials had been used. The insertion of the data in the classification model returned an ambiguity of the results, in fact 2 out of the 15 collected samples were incorrectly assigned to the kerosene class while the other 13 samples were assigned to the class of IED. In this case the uncertainty in the evaluation is not attributable to a defect in the model but rather to the liquid used to make the illicit act. From the investigations carried out by the competent authorities, the suspect used gasoil, an oil derivative such as kerosene but belonging to a different class and present in the ratio 3:1 with sulfuric acid of studied IED
Identification of Key Events and Emissions during Thermal Abuse Testing on NCA 18650 Cells
Full text linkThermal abuse of lithium-ion batteries (LIBs) leads to the emission of gases, solids, fires and/or explosions. Therefore, it is essential to define the temperatures at which key events occur (i.e., CID activation, venting, and thermal runaway (TR)) and to identify the related emissions for identifying the hazards to which people and especially rescue teams are exposed. For this purpose, thermal abuse tests were performed on commercial lithium nickel cobalt aluminum oxide (NCA) 18650 cells at 50% state of charge in a reactor connected to an FT-IR spectrometer by varying test conditions (feed gas of N2 or air; heating rates of 5 or 10 °C/min until 300 °C). In particular, the concentrations of the gases and the composition of the condensed-phase emissions were estimated. As regards gases, a high concentration (1695 ppmv) of hydrofluoric acid (HF) was measured, while the emissions of condensed matter consisted of organic compounds such as polyethylene oxide and paraffin oil, and inorganic compounds containing Li (0.173 mg/m3) and Al (0.344 mg/m3). The main safety concerns were caused by the temperatures (564 ± 85 °C) reached by the cell during TR, by the HF concentration which exceeded the toxicity limits of 30 ppm, the IDLH defined by the NIOSH, and the diameter of the particles (1.54 ± 0.69 µm) that rose the PM2.5 concentration. These results are also useful for identifying personal protection equipment for rescue teams
Fire Risk Evaluation of the Internal Components of the Li-ion Batteries
No full textThe advantages of Lithium-ion batteries (LIBs) are well known, anyway the LIBs are even considered hazardous products. In fact, outside the safety windows the Li-ion cells can undergo to an abuse that leads to the degradation of the internal components with the release of gases, vapour, and solid products. The reactivity of the LIBs and the relative products composition is strictly correlated to the chemical composition of the internal components. Because of a lack of regulation, safety data sheets (SDSs) of Li-ion cells are not mandatory but, generally they are available. However, there is a gap between the information reported in the SDS and the internal chemical composition, and usually the quantity of components is expressed as a range of weight percentages, and the chemical composition is not well specified. The most common lack of information concerns the electrolyte, which is usually defined as a mixture of organic carbonates without reporting the type of solvents (e.g., dimethyl carbonate, diethyl carbonate, and ethylene carbonate), the ratio between these components, and possible additives. The aim of this work was to characterize the internal components of various cylindrical 18650 cells available on the market, i.e., cell with Lithium Nickel Cobalt Aluminium Oxide (NCA) as cathode and graphite (C) or Lithium Titanate Oxide (LTO) as anode, and cells with Lithium Iron Phosphate (LFP) as cathode and C as anode. For this purpose, the cells were disassembled in a glovebox filled with argon (O2 and H2O ≤ 0.1 ppm) and then the different components were analysed by various techniques to define their chemical composition, i.e., metals of the electrodes by ICP-OES, the electrolyte by GC-FID and SPME-GC-MS, and the separator by ATR-FT-IR and DSC. The identification of those compounds is fundamental to understand the reactions occurring inside the cells and to evaluate the risks for human health and environment
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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