Modeling and Simulation the Thermal Runaway Behavior of Cylindrical Li-Ion Cells—Computing of Critical Parameter

The thermal behavior of Li-ion cells is an important safety issue and has to be known under varying thermal conditions. The main objectives of this work is to gain a better understanding of the temperature increase within the cell considering different heat sources under specified working conditions. With respect to the governing physical parameters, the major aim is to find out under which thermal conditions a so called Thermal Runaway occurs. Therefore, a mathematical electrochemical-thermal model based on the Newman model has been extended with a simple combustion model from reaction kinetics including various types of heat sources assumed to be based on an Arrhenius law. This model was realized in COMSOL Multiphysics modeling software. First simulations were performed for a cylindrical 1860 cell with a -cathode to calculate the temperature increase under two various simple electric load profiles and to compute critical system parameters. It has been found that the critical cell temperature [Math Processing Error] , above which a thermal runaway may occur is approximately [Math Processing Error] , which is near the starting temperature of the decomposition of the Solid-Electrolyte-Interface in the anode at [Math Processing Error] . Furthermore, it has been found that a thermal runaway can be described in three main stages

Progress in thermal management and safety of cells and packs by testing in battery calorimeters

With increasing energy density the safety and the thermal management of Li-ion batteries is becoming more and more important, because the thermal runaway can cause an ignition or even explosion of the battery with simultaneous release of toxic gases. In the last nine years we have established battery calorimetry as a powerful and versatile electrochemical-thermal characterization technique, which allows both advancements for the thermal management and the safety of batteries. With six adiabatic Accelerating Rate Calorimeters (ARC) of different sizes and two sensitive Tian-Calvet calorimeters, all of them combined with cyclers, the IAM-AWP now operates Europe’s largest battery calorimeter center, which enables the evaluation of thermodynamic, thermal and safety data on material, cell and pack level under quasiadiabatic and isoperibolic environments for both normal and abuse conditions (thermal, electrical, mechanical). It will be shown how sophisticated battery calorimetry allows finding new and quantitative correlations between different critical thermally and safety related parameters that will help to design safer systems. For an optimized design with regard to safety cells and packs have to be characterized not only for their temperature behavior but also for the heat dissipation and the pressure development in a quantitative manner. Calorimetry allows the collection of quantitative data required for optimum battery performance and safety. This information can then be used to define the requirements for cooling and thermal management and adapt them accordingly. The battery calorimeters can be used for studies on heat generation and dissipation of Li-ion cells and are coupled to a battery cycler in order to perform the measurements during charging and discharging of the cells under defined thermal conditions. Isoperibolic (constant temperature of the calori-meter) or quasiadiabatic (no heat exchange with the calorimeter) ambient conditions are adjusted by heaters and thermocouples that are located in lid, bottom and side walls of the calorimeter chamber, in which the cell is inserted. For improving the thermal management system, the measured temperature data are converted into generated and dissipated heat data [1] by determination of specific heat capacity and heat transfer coefficient using heat flux sensors. Concerning safety aspects it will be presented how battery calorimeters provide thermal stability data on materials level, e.g. of anodes, cathodes or electrolytes or there combinations and to perform safety tests on cell and pack level by applying thermal [2], mechanical or electrical [3] abuse conditions. The studies on materials level are especially important for Post-Li cells, which make use of more abundant materials, such as sodium or magnesium instead of Li, nickel and cobalt, because these data help to develop safe cells from the beginning all along the value chain. For the advanced Li-ion technology, a holistic safety assessment is in the focus, because the thermal runaway can have multiple interacting causes and effects. A test in the calorimeter is much more sensitive than a hotbox test and reveals the entire process of the thermal runaway with the different stages of exothermic reactions. Self-heating, thermal stability and thermal runaway are characterized and the critical parameters and their thresholds for safe cell operation are determined. As a result of the different tests quantitative and system relevant data for temperature, heat and pressure development of materials and cells are provided. In addition it will be explained how calorimeters allow studying the thermal runaway propagation in order to develop and qualify suitable countermeasures, such as heat protection barriers, which is currently becoming a very hot topic, because a global technical regulation (GTR) on electric vehicle safety is being developed, which includes thermal propagation. There is still the open question, which is the best initialization method to become a standard. We hope that the research in the Calorimeter Center will help to make progress in this field as well. References: [1] C. Ziebert et al., in: L.M. Rodriguez, N. Omar, eds., EMERGING NANOTECHNOLOGIES IN RECHARGABLE ENERGY STORAGE SYSTEMS, Elsevier Inc., ISBN 978032342977, 195-229. 2017. [2] B. Lei, W. Zhao, C. Ziebert, et al., Experimental analysis of thermal runaway in 18650 cylindrical cells using an accelerating rate calorimeter, Batteries 3 (2017) 14, doi:10.3390/batteries3020014.. [3] A. Hofmann, N. Uhlmann, C. Ziebert, O. Wiegand, A. Schmidt, Th. Hanemann, Preventing Li-ion cell explosion during thermal runaway with reduced pressure, Appl. Thermal Eng. 124 (2017) 539-544

Thermophysical Properties of Lithium Aluminum Germanium Phosphate with Different Compositions

The NASICON system LAGP (Li$_{1+x}$Al$_{x}$Ge$_{2-x}$ (PO$_{4}$)$_{3}$ was studied, which is a candidate material for solid state electrolytes. LAGP substrates with different compositions (x = 0.3–0.7) were prepared using a melt quenching route with subsequent heat treatment. In order to develop a better understanding of the relationships between the structure and the ionic as well as the thermal conductivity, respectively, the samples were characterized by X-ray diffraction. The ionic conductivity was measured using impedance spectroscopy while the thermal diffusivity and the specific heat were determined by Laser Flash technique and differential scanning calorimetry, respectively. Additionally, thermal analysis was performed in order to evaluate the thermal stability a higher temperatures and, also to identify the optimum temperature range of the thermal post-processing. The measured values of the ionic conductivities were in the range of 10$^{-4}$Ω$^{-1}$·cm$^{-1}$ to 10$^{-3}$ Ω$^{-1}$·cm$^{-1}$ at room temperature, but exhibited an increasing behavior as a function of temperature reaching a level of the order 10$^{-2}$ Ω$^{-1}$· cm$^{-1}$ above 200 °C. The thermal conductivity varies only slowly as a function of temperature but its level depends on the composition. The apparent specific heat depends also on the composition and exhibits enthalpy changes due to phase transitions at higher temperatures for LAGP samples with x > 0.5. The compositional dependencies of the ionic and thermal transport properties are not simply correlated. However, the compound with the highest Li-doping level shows the highest ionic conductivity but the lowest thermal conductivity, while the lowest doping level is associated with highest thermal conductivity but the lowest ionic conductivity

Comprehensive Electrochemical, Calorimetric Heat Generation and Safety Analysis of Na0.53_{0.53}MnO2_{2} Cathode Material in Coin Cells

The sodium ion cells were assembled by using Na$_{0.5}$3MnO$_{2}$ as cathode material, pure sodium metal as anode in case of half coin cells and coconut shell-derived hard carbon in case of full coin cells. Cyclic voltammetry, galvanostatic charge-discharge, and self-discharge analysis were conducted. A good rate capability, capacity retention, coulombic efficiency (99.5%), reproducibility and reversible Na-ion intercalation revealed a satisfactory performance of this cathode material. The safety related parameters including the heat generation during charging-discharging and thermal abuse tests have been executed by the means of sophisticated calorimetry instruments. It was observed that during the charging process less heat was generated than during discharging process. The exothermic reactions during thermal runaway were identified by using an accelerating rate calorimeter and pressure measurements during this thermal abuse test were performed as well. The thermal runaway of full coin cells occurred beyond 190 °C with a temperature rate (dT/dt) of 2.5 °C min$^{−1}$. Such detailed analysis of heat generation and thermal abuse helps finding new and quantitative correlations between different critical thermal and safety related issues in future post Li batteries that are a prerequisite for the design of safer batteries, the safe upscaling and for the adaptation of the thermal management system

Thermophysical Characterization of a Layered P2 Type Structure Na₀.₅₃MnO₂Cathode Material for Sodium Ion Batteries

Over the last decade, the demand for safer batteries with excellent performance and lowercosts has been intensively increasing. The abundantly available precursors and environmentalfriendliness are generating more and more interest in sodium ion batteries (SIBs), especially becauseof the lower material costs compared to Li-ion batteries. Therefore, significant efforts are beingdedicated to investigating new cathode materials for SIBs. Since the thermal characterization ofcathode materials is one of the key factors for designing safe batteries, the thermophysical propertiesof a commercial layered P2 type structure Na0.53MnO2cathode material in powder form weremeasured in the temperature range between−20 and 1200◦C by differential scanning calorimetry(DSC), laser flash analysis (LFA), and thermogravimetry (TG). The thermogravimetry (TG) wascombined with mass spectrometry (MS) to study the thermal decomposition of the cathode materialwith respect to the evolved gas analysis (EGA) and was performed from room temperature up to1200◦C. The specific heat (Cp) and the thermal diffusivity (α) were measured up to 400◦C becausebeyond this temperature, the cathode material starts to decompose. The thermal conductivity (λ)as a function of temperature was calculated from the thermal diffusivity, the specific heat capacity,and the density. Such thermophysical data are highly relevant and important for thermal simulationstudies, thermal management, and the mitigation of thermal runaway

Safer Sodium Battery: Thermal and electrochemical studies of Na-ion based cells

In the recent decade, the community emphasizes the crucial need for the improvement of battery safety and safety remains a critical barrier for this technology. Despite safer battery materials, battery thermal management could be a key to safer post Lithium technology. In that respect, sodium ion based batteries were studied using different electrolyte routes. Thermo-physical and electrochemical analyses depicted the performance of the battery material and the coin cell characteristics. The safety related parameters including the heat generation during charging-discharging and thermal abuse test have been executed by the means of sophisticated calorimetry instruments. Quantitative measurement of the thermal data was performed, and out-gasing during thermal decomposition of the electrolytes has been analysed in order to design a safer battery. This work helps finding new and quantitative correlations between different critical thermal and safety related issues in future post Li batteries. The determined thermal data, gas compositions and safety parameters on coin cell level are needed for the design of a safer battery, the safe upscaling and for the adaptation of the thermal management system

Safer Sodium Battery: Thermal and electrochemical studies of Na-ion based batteries

In the recent decade, the community emphasizes the crucial need for the improvement of battery safety and safety remains a critical barrier for this technology. Despite safer battery materials, battery thermal management could be a key to safer post Lithium technology. In that respect, sodium ion based batteries were studied using different electrolyte routes. Thermo-physical and electrochemical analyses depicted the performance of the battery material and the coin cell characteristics. The safety related parameters including the heat generation during charging-discharging and thermal abuse test have been executed by the means of sophisticated calorimetry instruments. Quantitative measurement of the thermal data was performed, and out-gasing during thermal decomposition of the electrolytes has been analysed in order to design a safer battery. This work helps finding new and quantitative correlations between different critical thermal and safety related issues in future post Li batteries. The determined thermal data, gas compositions and safety parameters on coin cell level are needed for the design of a safer battery, the safe upscaling and for the adaptation of the thermal management system