Étude expérimentale du comportement au feu d’électrolytes de batteries Li-ion

Li-ion battery electrolytes composed of flammable organic carbonates and a lithium salt play an important role regarding electrochemical performances but also its chemical formulation contributes to battery behavior in case of failure. In order to better understand and formulate future electrolytes, integrating intrinsic safety aspect beyond performances, it is first necessary to understand the phenomena related to the electrolyte during a Li-ion battery failure. After assessing the fire behavior of individual organic carbonates solvents and their mixtures, the influence of the nature of the electrolyte salt on combustion phenomena and toxic gas release was studied in the framework of the DEGAS regional project. Fire tests were performed thanks to the Tewarson calorimeter on electrolytes containing a classical salt LiPF6 and on an electrolyte containing a salt under development, LiFSI. It was shown that the first stage of combustion is governed by the more volatile solvent (linear carbonate) and the influence of adding salt was observed in the second stage. The fire induced toxicity in well ventilated conditions is mainly governed by the nature of the salt, showing very limited concerns that emanate from the organic solvents.Parmi les systèmes de stockage électrochimiques existants, la technologie lithium-ion (Li-ion) s’impose comme l’une des principales solutions de stockage pour la décennie à venir en raison de sa densité d’énergie bien supérieure aux autres technologies de batteries rechargeables (Ni- Cd, Ni-MH, acide-plomb). La technologie Li-ion est en pleine croissance et couvre une large gamme de domaines d’applications, des équipements portables aux applications appelant plus de puissance ou d’énergie telles que l’électro-mobilité et les réseaux intelligents. Après avoir évalué le comportement au feu des solvants pris individuellement et en mélange, l’influence de la nature du sel de l’électrolyte sur les phénomènes de combustion et d’émission de gaz toxiques a été étudiée. Plusieurs formulations d’électrolytes contenant le sel classique LiPF6 et un électrolyte contenant un sel en développement, le LiFSI, ont été testés. Plusieurs formulations d’électrolytes contenant le sel classique LiPF6 et un électrolyte contenant un sel en développement, le LiFSI, ont été testés (Tableau 1). Ces études ont été réalisées dans le cadre du projet de recherche régional DEGAS

Vers une utilisation de liquides ioniques basés sur le cation pyrrolidinium pour sécuriser les batteries au lithium-ion ?

A comprehensive insight into the thermal hazard and combustion behaviour in fire conditions of a series of pyrrolidinium based ionic liquids (ILs) associated with a fluorine-containing anion targeted for energy storage applications is provided. The work has been carried out in collaboration with the German institute HUI. Results constitute a solid database for sustainable use of these alternative solvents to conventional organic carbonate to build up safer electrolytes for lithium and sodium batteries, integrating tradeoff between safety and functionality in terms of conductivity and viscosity of pyrrolidinium based ILs. Safety advantages are clearly rated with their bias according to changes in alkyl chain length, anion used and use or an ether function.Depuis 2010, l’Ineris consolide l’évaluation des profils de danger présenté par les liquides ioniques (LIs) [1 ; 2 ] dont l’utilisation est étudiée pour diverses applications, en particulier le stockage d’énergie [3]. Pour les batteries lithium et sodium-ion, un intérêt de plus en plus marqué pour les LIs de type pyrrolidinium [PYR1,y]+[anion fluoré] est confirmé par la littérature. Dans le cadre d’une recherche collaborative avec l’institut de recherche allemand Helmoltz-Institut Ulm (HIU), l’Ineris a mené une étude paramétrique sur une dizaine de liquides ioniques appartenant à cette sous-famille de LIs construite sur le cation pyrrolidinium. Les structures chimiques détaillées des liquides ioniques étudiés ainsi que les paramètres de l’étude sont illustrés à la Figure 1

Safety-focused analysis of solvents used in electrolytes for large scale lithium-ion batteries

To better rule out the complex fire risk related to large format lithium ion cells, a detail and new brand systematic evaluation, both at components and cell levels could be an invaluable milestone. Therefore, combustion analysis was conducted for major single organic solvents and their mixtures used in lithium ion battery technology, both in oxygen rich and lean environments using a Tewarson calorimeter. Well controlled test conditions have enabled the determination of key parameters governing the fire induced hazards such as flash point, ease of ignition , heat release rate, effective heat of combustion, specific mass loss rate, as well as the assessment of fire induced toxicity and criteria pollutants. An excellent convergence was obtained from the two calorimetry techniques, namely O2 consumption (OC), and Carbon Dioxide Generation (CDG) for the evaluation of the rates of heat release and effective heat of combustion in the experimental fires of all tested samples in our test conditions. Moreover, a rule of thumb for the screening of new solvents such as the Boie correlation and N-factor were introduced for predicting the heat of combustion and kinetics respectively prior to conducting any experimental work. Fire induced toxicity of single solvents and their mixtures were also briefly examined according to toxic gas measurements performed

Scenario-based prediction of Li-ion batteries fire-induced toxicity

International audienceThe development of high energy Li-ion batteries with improved durability and increased safety mostlyrelies on the use of newly developed electrolytes. A detailed appraisal of fire-induced thermal andchemical threats on LiPF6- and LiFSI-based electrolytes by means of the so-called “fire propagationapparatus” had highlighted that the salt anion was responsible for the emission of a non negligiblecontent of irritant gas as HF (PF6-) or HF and SO2 (FSI-). A more thorough comparative investigation of thetoxicity threat in the case of larger-size 0.4 kWh Li-ion modules was thus undertaken.A modeling approach that consists in extrapolating the experimental data obtained from 1.3AhLiFePO4/graphite pouch cells under fire conditions and in using the state-of-the-art fire safety internationalstandards for the evaluation of fire toxicity was applied under two different real-scale simulatingscenarios. The obtained results reveal that critical thresholds are highly dependent on the nature of thesalt, LiPF6 or LiFSI, and on the cells state of charge. Hence, this approach can help define appropriate firesafety engineering measures for a given technology (different chemistry) or application (fully chargedbackup batteries or batteries subjected to deep discharge)

Comprehensive investigation on the thermal stability, biodegradability and fire-induced hazards of pyrrolidinium-based ionic liquids

One of the viable option to meet the stringent safety requirements of large-format LIBs is to replace the existing highly flammable/combustible, state-of-the-art organic based, electrolytes with safer ones. In this regard, the use of room temperature ionic liquids, RTILs, as advanced electrolytes in electrochemical energy storage devices has been one of the most enticing and emerging option. Though some imidazolium and chiefly pyrrolidinium based ILs are hailed as safer electrolytes, overcoming the limitations imposed by the highly volatile/combustible carbonate based electrolytes, the full scale and precise appraisal of their global (thermal stability, biodegradability, fire-induced) safety levels under abuse conditions remain to be fully addressed. With the aim of providing the requested level of information on the safety aspects of ILs, we embarked on a detailed investigation of the short and long term thermal stability, combustion behavior and biodegradability tests of various pyrrolidinium-based ILs, synthesized in our laboratory. ILs enlisting the effect of alkyl chain length, [Pyr1A]+ (A=3-10), anion, Pyr14 (TFSI, FSI and BETI), cation, [Pyr14]+/ [Pyr12O1]+ [TFSI]andsalt addition (e.g. LiTFSI/Pyr14TFSI) were methodically investigated. Through the use of myriad of techniques, i.e. ramped/isothermal thermogravimetric analysis, oxygen bomb calorimetry and multi-purpose fire propagation apparatus (FPA, ISO12136), key parameters governing the thermal and fire induced hazards such as ease of ignition, heat release rate, effective heat of combustion and fire induced toxicity (CO, Soot, THCs, SO2, HF, NO, N2O, and HCN) were determined. A number of biodegradability tests including Modified Sturm, Manometric Respirometry, and Zahn-Wellens/EMPA were conducted. The thermal stability,combustion and biodegradability tests of pyrrolidinium - based ILs are specific to the nature of the anion, cation, alkyl chain length as well the addition of lithium salt. In general, our detailed study provides a new systematic approach towards understanding the thermal stability, biodegradability and fire-induced hazard evaluation of large families of pyrrolidinium based ILs as well as access to data needed for a performance based approach of the evaluation of their safety benefits

In-Depth Interfacial Chemistry and Reactivity Focused Investigation of Lithium–Imide- and Lithium–Imidazole-Based Electrolytes

International audienceA comparative and in-depth investigation on the reactivity of various Li-based electrolytes and of the solid electrolyte interface (SEI) formed at graphite electrode is carried out using X-ray photoelectron spectroscopy (XPS), chemical simulation test, and differential scanning calorimetry (DSC). The electrolytes investigated include LiX (X = PF6, TFSI, TDI, FSI, and FTFSI), dissolved in EC-DMC. The reactivity and SEI nature of electrolytes containing the relatively new imide (LiFSI and LiFTFSI) and imidazole (LiTDI) salts are evaluated and compared to those of well-researched LiPF6− and LiTFSI-based electrolytes. The thermal reactivity of LixC6 in the various electrolytes is found to be in the order of LiFSI > LiTDI > LiTFSI > LiFTFSI > LiPF6 and LiFSI > LiFTFSI > LiPF6 > LiTFSI > LiTDI in terms of onset exothermic temperature and total heat generated, respectively. Surface and depth-profiling XPS analysis of the SEI formed with the diverse electrolyte formulations provide insight into the differences and similarities (composition, thickness, and evolution, etc.) emanating from the structure of the various salt anions

Interfacing Si‐Based Electrodes: Impact of Liquid Electrolyte and Its Components

As the demand for mobile energy storage devices has steadily increased during the past decades due to the rising popularity of portable electronics as well as the continued implementation of electromobility, energy density has become a crucial metric in the development of modern batteries. It was realized early on that the successful utilization of silicon as negative electrode material in lithium-ion batteries would be a quantum leap in improving achievable energy densities due to the roughly ten-fold increase in specific capacity compared to the state-of-the-art graphite material. However, being an alloying type material rather than an intercalation/insertion type, silicon poses numerous obstacles that need to be overcome for its successful implementation as a negative electrode material with the most prominent one being its extreme volume changes on (de-)lithiation. While, as of today, a plethora of different types of Si-based electrodes have been reported, a universally common feature is the interface between Si-based electrode and electrolyte. This review focuses on the knowledge gained thus far on the impact of different liquid electrolyte components/formulations on the interfaces and interphases encountered at Si-based electrodes

Fire behavior of carbonates-based electrolytes used in Li-ion rechargeable batteries with a focus on the role of the LiPF6 and LiFSI salts

International audienceA detailed investigation of the combustion behavior of LiPF6 or LiFSI-based carbonate electrolytes was conducted with the objective of getting better knowledge of lithium-ion battery system fire induced thermal and chemical threats. The well-controlled experimental conditions provided by the Tewarson calorimeter have enabled the accurate evaluation of fire hazard rating parameters such as heat release rate and effective heat of combustion and the quantification of toxic effluents (HF, SO2, NOx...). Results have shown that all the electrolytes tested burn in phases depending on the flammability nature of their mixture constituents. The first stage of combustion is solely governed by the more volatile solvent (linear carbonate) and the influence of adding salt comes into effect predominantly in the second stage. It has been also shown that combustion enthalpy of electrolytes lies in the solvent mixture, irrespective of the salt added. The fire induced toxicity in well-ventilated conditions is found to be mainly dictated by the salt and its chemical structure, showing very limited concerns that emanate from the organic solvents