Evaluation de l'efficacité de prélèvement d'un précipitateur électrostatique

National audienceEasy-to-use particle sampling techniques leading to easy-to-analyze samples is a growing need for nanosafety. Electrostatic precipitation [Dickens 1999] commercialized by TSI (Nanometer Aerosol Sampler model 3089) could be an answer. However, more information is needed on the performance of this instruments. On the one hand, real time sampling efficiency of the NAS regarding voltage has been studied. On the other hand, the sampling efficiency for 80 nm polystyrene particles has been considered through both real time CPC measurements and TEM analysis: these methods lead to very different results, respectively 62-70% and < 0,1 %. These results are discussed regarding literatureConnaître la composition des particules constitue un enjeu grandissant dans le domaine des particules ultrafines. Il est essentiel de disposer de techniques de prélèvement simples, pouvant permettre une analyse différée, tout particulièrement par microscopie électronique. A ce titre, le prélèvement par précipitateur électrostatique semble être une technique prometteuse. La société TSI commercialise depuis quelques années un échantillonneur de ce type, le modèle 3089 NAS (Nanometer Aerosol Sampler). Le travail présenté ici a pour objectif d'étudier l'efficacité de prélèvement de cet appareil, dans le cas d'une mise en oeuvre en aval d'un analyseur de mobilité électrique. Pour ce faire, un aérosol monodispersé a été produit par atomisation et extraction par analyse de mobilité. L'efficacité de prélèvement a été considérée pour différents modes de fonctionnement. Il ressort de cette étude que si une efficacité notable de dépôt est relevée à l'échelle du NAS, ce dépôt ne se ferait que de manière minoritaire sur la grille de prélèvement. Ces résultats sont discutés au regard de références bibliographique

Study of the Role of LiNi1/3Mn1/3Co1/3O2/Graphite Li-Ion Pouch Cells Confinement, Electrolyte Composition and Separator Coating on Thermal Runaway and Off-Gas Toxicity

A reliable heating device coupled with a FTIR gas analyzer has been tailored with the aim of evaluating the role of state-of-the-art lithium-ion battery components and environmental conditions on thermal and toxic hazards. Here, we demonstrate its effectiveness in accurately assessing the role of fully charged 0.6 Ah pouch cells confinement, electrolyte composition and separator coating on heat release and toxic gas generation-related risks. The fire safety international standards developed by the ISO TC92 SC3 subcommittee were used to determine the asphyxiant and irritant gases toxicity. Cells tighting confinement proves to be a very efficient way to diminish and delay (from 180 to 245 degrees C) the thermal runaway phenomenon occurrence and relating toxic gas release. Vinylene carbonate as electrolyte additive is able to shift (+20 degrees C) the onset temperature, while substitution of 1/3 M LiPF6 by LiFSI does not modify the thermal behavior, nor the toxic risks. The coating of a tri-layer separator influences the irritant gas toxicity related risk, by decreasing fluorinated components release. This study highlights that some improvements regarding LIB safety can be achieved through appropriate component selection and cells integration design at a module/pack level

Safety Evaluation of a Sodium-Ion Cell: Assessment of Vent Gas Emissions under Thermal Runaway

International audienceNa-ion batteries are presented as a complementary technology to Li-ion batteries, that comply with the performance requirements of various applications without being submitted to the critical raw material dependencies pertaining to Li-ion batteries. Several major industrial actors are now committed to produce these batteries, advocating among others the safety gain of such technology. Available data on their behavior under thermal runaway are nonetheless very limited. This experimental work brings new elements of vent gas characteristics of Na-ion (Na3V2(PO4)2F3, NVPF) cells when thermally abused. A detailed gas analysis was performed in order to determine both composition of the gas mixture and related emitted volume. In our test configuration, no flames were observed, and the fumes were mainly composed of electrolyte compounds (organic carbonates). A simple comparison with Li-ion technology showed similarities with LiFePO4 (LFP) chemistries in terms of the nature and quantity of emitted gas

New insight on the risk profile pertaining to lithium-ion batteries under thermal runaway as affected by system modularity and subsequent oxidation regime

International audienceIt is now well established that lithium-ion battery technology is a key electrical energy storage device in the fight against the global warming, helping us to make transportation more sustainable and securing intermittent renewable energy sources. The requirement to keep the thermal runaway (TR) hazard under control is among remaining issues for continuous and sustainable use of lithium-ion batteries. This experimental work brings a new insight on the issue, by performing and analyzing of a series of NMC pouch cell internal short circuit tests reflecting progressively the overall level of integration of such cells when modularly assembled in sub-systems to constitute the full pack. While replicating always the same TR triggering procedure in these experiments, our heat, gas and particle emission analyses reveal that the consequences in terms of chemical (e.g. toxic and corrosive) and thermal threats arising from a default cell running into thermal runaway may greatly vary according of the level of integration mocked up during the abuse test. This work also shows that thermochemical reactions/combustion regimes and their transitions following TR (towards possible flaming combustion or simply ending-up by hot gas degassing) are among key determinants of the whole risk pattern

Facile reduction of pseudo-carbonates : promoting solid electrolyte interphases with dicyanoketene alkylene acetals in lithium-ion batteries

In recent years, greener transportation has become of major interest to limit air pollution and global warming. For this purpose, Li-ion batteries (LIBs) are considered as the most promising power source for electric vehicles (EV) and hybrid electric vehicles (HEV) due to their high energy density. The use of high-energy multi-cell battery packs imposes ever more stringent requirements on LIBs in term of safety and long-term cyclability. The formation of an effective SEI passivation layer at the negative electrode / electrolyte interface was found to be of paramount importance in order to enable LIB long-life cycling and controlling the threshold for thermal runaway. This is why SEI-forming additives have been used in the electrolyte to reinforce these protective properties, with the most common additives being vinylene carbonate (VC) (1), fluoroethylene carbonate (FEC) (2), and vinyl ethylene carbonate (VEC) (3). To our knowledge, the modification of EC and PC on the carbonyl group, rather than on the alkylene bridge as for VC, VEC, or FEC, has not previously been attempted.(4,5) It is known that the =C(CN)2 group is an “oxygen equivalent” being even slightly more electronegative than O itself and extending considerably the conjugation. Hence, we hypothesized that modified EC or PC, with C=C(CN)2 replacing the carbonyl groups, could lead to a more facile reduction at higher potentials and a stable SEI. The dicyanoketene propylene (and ethylene) acetal, DCKPA (DCKEA), have both been synthesized according to a simple procedure.(6) The reduction process has been investigated for DCKPA by means of GC/MS and IR analysis and the efficiency as a SEI-reinforcing additive demonstrated by the analysis of the soluble products using liquid GC/MS. The cycling tests using a pouch cell configuration at both 20 and 45°C were realized with only 0.5 wt.% of additive in the electrolyte and resulted in higher capacity retention. Moreover, a post-mortem analysis by DSC revealed an improvement in term of safety due to an improved lithiated graphite/electrolyte interface