Targeting adequate thermal stability and fire safety in selecting ionic liquid-based electrolytes for energy storage

CAPLUS AN 2014:16740(Journal; Online Computer File)International audienceThe energy storage market relating to lithium based systems regularly grows in size and expands in terms of a portfolio of energy and power demanding applications. Thus safety focused research must more than ever accompany related technological breakthroughs regarding performance of cells, resulting in intensive research on the chemistry and materials science to design more reliable batteries. Formulating electrolyte solutions with nonvolatile and hardly flammable ionic liquids instead of actual carbonate mixtures could be safer. However, few definitions of thermal stability of electrolytes based on ionic liquids have been reported in the case of abuse conditions (fire, shortcut, overcharge or overdischarge). This work investigates thermal stability up to combustion of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C1C4Im][NTf2]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([PYR14][NTf2]) ionic liquids, and their corresponding electrolytes containing lithium bis(trifluoromethanesulfonyl)imide LiNTf2. Their possible routes of degradation during thermal abuse testings were investigated by thermodynamic studies under several experimental conditions. Their behaviours under fire were also tested, including the analysis of emitted compounds

Les liquides ioniques, leur utilisation et leur role comme solvants de réaction catalytique

Ionic liquids, associations of organic cations and anions, are media organized over several nanometers and present a segregation in polar and nonpolar microdomains. As they are used as solvents for catalytic reactions, they can induce specific solvation phenomena. For instance, ion exchange reactions in some catalytic systems and some p-cation interactions with unsaturated hydrocarbons have been observed by NMR. The consequences of the specific solvation on hydrogenation reactions have been studied. It appears that the stronger the interactions between IL and reactants are, the slower the reactions are.The presence of nonpolar and polar microdomains leads to a preferential solvation of organometallic complexes in apolar pockets that enable the use of these media as supramolecular matrices and to control the crystal growth of metal nanoparticles generated in situ according to the alkyl chain length and the temperature.Les liquides ioniques, associations de cations organiques et d'anions, sont des milieux structurés sur plusieurs nanomètres et présentent une ségrégation en domaines polaires et apolaires. Utilisés comme solvants de réactions catalytiques, ils peuvent de ce fait engendrer des phénomènes de solvatation spécifique. Ainsi des réactions d'échange d'ions dans certains systèmes catalytiques et des interactions de type p-cation avec les hydrocarbures insaturés ont été mises en évidence par RMN. Les conséquences de ces solvatations spécifiques sur des réactions d'hydrogénation ont été étudiées. Il ressort que plus l'interaction entre les liquides ioniques et les réactifs est grande, plus les réactions sont lentes. Enfin la présence de microdomaines polaires et apolaires conduit à une solubilisation préférentielle des complexes organométalliques dans les poches apolaires ce qui permet d'utiliser ces milieux comme moules supramoléculaires et de contrôler la croissance cristalline des nanoparticules de ruthénium générées in situ en fonction de la longueur de la chaîne alkyl et de la température

Ionic liquids (use and specific task as solvent in catalytic reaction)

Les liquides ioniques, associations de cations organiques et d anions, sont des milieux structurés sur plusieurs nanomètres et présentent une ségrégation en domaines polaires et apolaires. Utilisés comme solvants de réactions catalytiques, ils peuvent de ce fait engendrer des phénomènes de solvatation spécifique. Ainsi des réactions d échange d ions dans certains systèmes catalytiques et des interactions de type p-cation avec les hydrocarbures insaturés ont été mises en évidence par RMN. Les conséquences de ces solvatations spécifiques sur des réactions d hydrogénation ont été étudiées. Il ressort que plus l interaction entre les liquides ioniques et les réactifs est grande, plus les réactions sont lentes. Enfin la présence de microdomaines polaires et apolaires conduit à une solubilisation préférentielle des complexes organométalliques dans les poches apolaires ce qui permet d utiliser ces milieux comme moules supramoléculaires et de contrôler la croissance cristalline des nanoparticules de ruthénium générées in situ en fonction de la longueur de la chaîne alkyl et de la températureIonic liquids, associations of organic cations and anions, are media organized over several nanometers and present a segregation in polar and nonpolar microdomains. As they are used as solvents for catalytic reactions, they can induce specific solvation phenomena. For instance, ion exchange reactions in some catalytic systems and some p-cation interactions with unsaturated hydrocarbons have been observed by NMR. The consequences of the specific solvation on hydrogenation reactions have been studied. It appears that the stronger the interactions between IL and reactants are, the slower the reactions are.The presence of nonpolar and polar microdomains leads to a preferential solvation of organometallic complexes in apolar pockets that enable the use of these media as supramolecular matrices and to control the crystal growth of metal nanoparticles generated in situ according to the alkyl chain length and the temperatureLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Revealing Electrochemically Induced Antisite Defects in LiCoPO₄: Evolution upon Cycling

This article aims to reveal the formation of antisite defects that are induced in LiCoPO₄ crystals upon electrochemical charge/discharge cycles. This is achieved using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy that allows their direct visualization. By comparison with simulated images, their evolution is discussed and their quantification performed. In a sample free of defects, a disordering caused by the exchange between lithium and cobalt atoms is progressively created. It is the first time that evidence of antisite defect creation in an olivine-type compound upon electrochemical cycling has been reported. Their formation is shown to occur during the charging process. While they are heterogeneously distributed after the first charge/discharge cycle because of their concentration, such exchange defects appear to be more homogeneously dispersed in the lattice when their amount is much larger after the 30th charge/discharge cycle. This article provides new insight into the behavior of this compound and contributes to an explanation for the reason why such a high-capacity fading is observed when this material is used in a battery

Organic electrode materials: an alternative for greener lithium battery

International audienc

Organic electrode materials: an alternative for greener lithium battery

International audienc

Thermal stability of imidazolium-based ionic liquids

This work highlights the factors tuning the thermal stability of imidazolium-based ionic liquids (IL) associated to bis(trifluoromethanesulfonyl)imide anion [NTf2]. The decomposition temperatures (Td) were evaluated by thermogravimetric analyses (TGA) with optimized parameters to obtain reproducible Td. The impact of the alkyl chain length and of the presence of functional groups and unsaturations on Td were evaluated. The thermal behaviour was governed by Van der Waals interactions between alkyl chains, and by inter and intra coulombic interactions such as hydrogen bonds

Study of transport mechanisms of lithium in hybrid electrolytes for solid-state batteries

International audienceThe next generation of lithium-ion batteries needs to have better electrochemical performances and to be intrinsically safer. The replacement of liquid electrolytes by solid-state electrolytes can lead to higher specific or volumetric energy density, and to obtain more thermally stable batteries. Hybrid solid-state electrolytes, i.e. a dispersion of ceramic particles in a polymer matrix, could be a solution. The goal is to combine advantages of different materials: the easy implementation from conducting polymer that also offer good interfaces with the electrodes and the high ionic conductivity of ceramics. This study aims at estimating lithium diffusion coefficients in these hybrid materials by providing information about lithium diffusion paths. It will lead to a better understanding of lithium transport phenomena in the bulk and at interfaces. Methodologies based on characterisations of lithium isotopes (7Li, 6Li) are developed. 6Li-rich materials are used to label the lithium ions of a specific material to be able to differentiate these lithium ions from others. Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and 6/7Li solid-state Nuclear Magnetic Resonance spectroscopy (ssNMR) can distinguish between isotopes. That is why they are used to track the diffusion of lithium ions. ToF-SIMS and ssNMR analyses are complementary. On one hand, ToF-SIMS is a surface analysis, which gives local micrometric information on the molecular fragments, and a ratio of the lithium isotopes can be calculated. On the other hand, ssNMR analyses provide global information on lithium ions environment and quantitative experiments can lead to calculate isotopes concentrations

Les liquides ioniques, des électrolytes innovants pour sécuriser les batteries lithium-ion

Lithium-ion batteries are dominating nomad devices market, thus their safety must more than ever be carefully studied. Accordingly, replacing actual electrolytes (flammable and volatile carbonate mixtures) by hardly flammable and nonvolatile ionic liquids (IL) could be safer. However, little examination of the stability of ionic liquids under abuse conditions (fire, shortcut, overcharge…) was reported. This work investigates thermal stability of electrolytes based on carbonates and two IL. These IL are stable up to 300°C and are weakly combustible. However combustion tests revealed the emission of toxic or flammable species, requiring specific attention depending on the application. Based on this work, these IL-based electrolytes can be considered safer than carbonates and contribute to safety improvement in batteries.Les batteries lithium-ion dominent le marché des appareils nomades, mais sont susceptibles de poser des problèmes de sécurité à cause de la présence de l’électrolyte, constitué de carbonates inflammables et volatils. Pour sécuriser ces batteries, des liquides ioniques (LI) sont étudiés comme électrolytes. Ce sont des sels présentant une grande stabilité thermique et réputés non inflammables. Mais peu de données sont disponibles sur leur comportement en situations abusives (surchauffe, feu, surcharge…). Cet article présente la comparaison des stabilités thermiques d’électrolytes à base de deux LI et de carbonates. Ces LI se révèlent stables jusqu’à 300 °C et très peu combustibles. Cependant, la formation de gaz toxiques ou inflammables lors de la combustion est à prendre en compte selon les applications visées. Ces premiers résultats permettent de soutenir que les liquides ioniques constituent une voie prometteuse pour améliorer la sécurité des batteries