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Thermal Characterization of the Battery Electrolyte LiAsF6 – Safe Handling in the Glovebox

Introduction

Battery electrolytes play a crucial role in energy storage and are an essential component of modern battery technologies. These substances enable the flow of ions between the electrodes, which is essential for charging and discharging the battery. In recent years, research into battery electrolytes has made significant progress toward improving the efficiency, safety and lifespan of batteries. With the increasing importance of electric vehicles and renewable energy, understanding and advancing electrolytes is central to a sustainable energy future.

However, hazards such as overheating or Thermal runawayA thermal runaway is the situation where a chemical reactor is out of control with respect to temperature and/or pressure production caused by the chemical reaction itself. Simulation of a thermal runaway is usually carried out using a calorimeter device according to accelerated rate calorimetry (ARC).thermal runaway need to be considered and investigated. Thermal analysis provides insight into the thermal properties, such as Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transition or Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition, of these materials.

Representing the numerous battery electrolytes, the widely used lithium hexafluoroarsenate (LiAsF6) was examined for caloric effects and mass changes using simultaneous thermal analysis.

Measurement Conditions

Due to the hygroscopic properties of LiAsF6, the sample was prepared in the glovebox under argon to prevent the material from absorbing water. The STA measurement was also carried out in an argon-purged glovebox. Detailed measurement parameters can be found in table 1.

Table 1: Measurement parameter used for the invesitgation with the STA 449 Jupiter®

ParameterSample LiAsF6
Sample weight12.1 mg
CrucibleConcavus® Al, pierced lid
SensorTGA-DSC cp, type S
FurnaceSiC
Temperature programRT to 600°C
Heating rate10 K/min
Gas atmosphereArgon
Gas flow70 ml/min

Measurement Results

The TGA-DSC results are depicted in figure 1. The massloss curve shows two steps of 1.1% and 81.7%. The first mass-loss step can presumably be attributed to the release of moisture. The second mass-loss step is due to the Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition of the LiAsF6. Two EndothermicA sample transition or a reaction is endothermic if heat is needed for the conversion.endothermic effects with peak temperatures of 122.8°C and 497.7°C and enthalpies of 25.18 J/g and 337 J/g can be detected from the DSC curve; these correlate to the mass-loss steps. Besides that, at a temperature of 265°C, a reversible solid-solid Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transition of LiAsF6 changing from rhombohedral phase to cubic can be identified1.

1Gavrichev, K.S., Sharpataya, G.A., Gorbunov, V.E. et al. Thermodynamic Properties and Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. Decomposition of Lithium Hexafluoroarsenate, LiAsF6. Inorganic Materials 39, 175–182 (2003). https://doi.org/10.1023/A:1022102914631

1) Temperature-dependent mass-loss curve (TGA, green) and heat-flow curve (DSC, blue) of LiAsF6

Summary

The characterization of energetic effects and the Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition of the battery electrolyte LiAsF6 was successfully carried out using simultaneous thermal analysis. Thanks to the ability to carry out the sample preparation and STA measurement inside a glovebox, even materials that would otherwise react with the surrounding atmosphere – such as the LiAsF6 material investigated – can be successfully measured. Based on the data obtained, it can be seen that LiAsF6 remains stable until the solid-solid phase transformation at around 265°C. At temperatures above 300°C, the material decomposes under inert conditions. This information provides additional knowledge with regard to potential hazards such as overheating and Thermal runawayA thermal runaway is the situation where a chemical reactor is out of control with respect to temperature and/or pressure production caused by the chemical reaction itself. Simulation of a thermal runaway is usually carried out using a calorimeter device according to accelerated rate calorimetry (ARC).thermal runaway

All NETZSCH instruments can be operated in a glovebox, allowing the analysis of materials that are sensitive to environmental conditions or have toxic properties. By using a glovebox, such materials can be processed and analysed under controlled conditions, isolated from the surrounding environment. This allows experimental results to be obtained that would not be possible without these protective measures, as the material retains its properties while human safety is ensured.