Chemical Thermal Runaway Modeling of Lithium‐Ion Batteries for Prediction of Heat and Gas Generation

Along with the increased usage of lithium-ion batteries and their development in energy densities, safety issues arise that have to be investigated. The most serious battery safety event is called thermal runaway. Herein, a chemical thermal runaway model with ten decomposition reactions is developed. It is coupled with thermal simulations in order to predict temperature curves as well as amount and composition of released gases during thermal runaway. Simulations are validated by thermal abuse experiments in an autoclave. Detailed temperature measurements and gas analysis are included. Simulations and experimental results prove to be in good agreement. The model is further applied to investigate thermal runaway behavior of cells with different energy densities

Energiespeicher für Energiewende und Elektromobilität.: Entwicklungen, Herausforderungen und systemische Analysen. Einführung in den Schwerpunkt

Die Energiewende bedingt eine Transformation des heutigen Energienetzes mit all seinen Elementen der Energieerzeugung, Energieübertragung, Energiespeicherung und nicht zuletzt des Energieverbrauchs. Vorteilhaft könnte sich dabei auswirken, dass in der Zukunft unsere Energienetze mit Mobilitätsnetzwerken stärker verschmelzen werden und damit Synergien genutzt werden können. In dieser Ausgabe wird hinterfragt, welchen Beitrag Energiespeicher bei diesem Transformationsprozess leisten können, aber auch, welche vielfältigen Herausforderungen und Probleme mit der Energiespeicherung auf der Forschungs-, Umsetzungs- und systemischen Bewertungsseite verbunden sind. Dabei spannt sich der Bogen von den Grundlagen und der Grundlagenentwicklung für Energiespeicher in Deutschland hin zu den vielfältigsten Einsatzmöglichkeiten.The energy transition means a transformation of today‘s energy grid with all its elements of energy production, energy transfer, energy storage and last but not least energy consumption. An advantage hereby could be that in the future our energy grids and mobility networks will increasingly merge allowing for synergies. The following thematic focus asks which contribution to these transformation processes energy storages can provide, but also what the various challenges and problems of energy storage are regarding research, implementation and systemic assessment. This ranges from basic research developments of energy storages in Germany to the diverse application possibilities

Investigation of the Influence of Silicon Oxide Content on Electrolyte Degradation, Gas Evolution, and Thickness Change in Silicon Oxide/Graphite Composite Anodes for Li-Ion Cells Using Operando Techniques

This research paper investigates the influence of varying silicon oxide (SiO_) content on the performance and aging of lithium-ion cells. In-depth investigations encompass charge and discharge curves, thickness changes, electrolyte degradation, gas evolution, and chemical analysis of cells with different silicon oxide proportions in the anode and their associated cathodes. The results show that a higher silicon oxide content in the anode increases the voltage hysteresis between charge and discharge. Moreover, the first-cycle efficiencies decrease with a higher silicon oxide content, attributed to irreversible Li_Si_ formation and the subsequent loss of active lithium from the cathode during formation. The anodes experience higher thickness changes with increased silicon oxide content, and peaks in differential voltage curves can be correlated with specific anode active materials and their thickness change. A gas analysis reveals conductive salt and electrolyte intermediates as well as silicon-containing gaseous fragments, indicating continuous electrolyte decomposition and silicon oxide aging, respectively. Additionally, a chemical analysis confirms increased silicon-derived products and electrolyte degradation on electrode surfaces. These findings underscore the importance of a holistic aging investigation and help understand the complex chemical changes in electrode materials for designing efficient and durable lithium-ion cells

Improvement of safe bromine electrolytes and their cell performance in H2_{2}/Br2_{2} flow batteries caused by tuning the bromine complexation equilibrium

Hydrogen bromine redox flow batteries utilize bromine electrolytes in their positive half cell, offering capacities larger than 100 Ah L$^{-1}$. Addition of quaternary ammonium compounds, so-called bromine complexing agents (BCA), may increase safety as they reduce the vapour pressure of bromine in the posolyte. However, they have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction of membrane conductivity and (b) they form a low conductive ionic liquid with polybromides, leading to high overvoltage if the formation happens at the electrode. In this work a solution to this problem is proposed by an excess addition of Br$_{2}$ to these electrolytes. The excess bromine leads to a permanent bromine fused salt phase in the tank. Bromine formed in the cell stays in the aqueous phase and bromine transfer between the two phases happens in the tank. Transfer of Br2 without the transfer of [BCA]$^{+}$ cations exists between the phases, while [C2Py]$^{+}$ cations remain in the fused salt and do not influence cell performance. For the first time a posolyte capacity of 179.6 Ah L$^{-1}$ based on 7.7 M hydrobromic acid with BCA is achieved compared to previous investigations with e.g. 53.9 Ah L$^{-1}$

Cycle behaviour of hydrogen bromine redox flow battery cells with bromine complexing agents

Bromine complexing agents (BCA) are used to improve the safety of aqueous bromine electrolytes versus bromine outgassing in bromine electrolytes. In this work, cycling performance of hydrogen-bromine redox flow battery cells with 1-ethylpyridin-1-ium bromide ([C2Py]Br) as BCA in a bromine electrolyte with a theoretical capacity of 179.6 A h L$^{-1}$ is investigated for the first time. The BCA leads to increased ohmic overvoltages. One cause of the ohmic drop can be attributed to [C2Py]$^{+}$ cation interaction with the perfluorosulfonic acid (PFSA) membrane, which results in a drop of its conductivity. The BCA also interacts with bromine in the cell, by forming a non-aqueous fused salt second phase which exhibits a ten times lower conductivity compared to the aqueous electrolyte. A steep rise in cell voltage at the beginning of the charge curve followed by a regeneration of the cell voltage is attributed to this effect. Electrolyte crossover leads to an accumulation of [C2Py]$^{+}$ in the electrolyte solution and intensifies both adverse processes. Under this condition only 30% of the theoretical electrolyte capacity of 179.6 A h L$^{-1}$ is available under long term cycle conditions. However, electrolyte capacity is high enough to compete with other flow battery technologies

Cycle behaviour of hydrogen bromine redox flow battery cells with bromine complexing agents

Bromine complexing agents (BCA) are used to improve the safety of aqueous bromine electrolytes versus bromine outgassing in bromine electrolytes. In this work, cycling performance of hydrogen-bromine redox flow battery cells with 1-ethylpyridin-1-ium bromide ([C2Py]Br) as BCA in a bromine electrolyte with a theoretical capacity of 179.6 A h L$^{-1}$ is investigated for the first time. The BCA leads to increased ohmic overvoltages. One cause of the ohmic drop can be attributed to [C2Py]$^{+}$ cation interaction with the perfluorosulfonic acid (PFSA) membrane, which results in a drop of its conductivity. The BCA also interacts with bromine in the cell, by forming a non-aqueous fused salt second phase which exhibits a ten times lower conductivity compared to the aqueous electrolyte. A steep rise in cell voltage at the beginning of the charge curve followed by a regeneration of the cell voltage is attributed to this effect. Electrolyte crossover leads to an accumulation of [C2Py]$^{+}$ in the electrolyte solution and intensifies both adverse processes. Under this condition only 30% of the theoretical electrolyte capacity of 179.6 A h L$^{-1}$ is available under long term cycle conditions. However, electrolyte capacity is high enough to compete with other flow battery technologies

Classification of Heat Evolution Terms in Li-Ion Batteries Regarding the OCV Hysteresis in a Li- and Mn-Rich NCM Cathode Material in Comparison to NCA

We investigate the heat release of Li- and Mn-rich NCM (LMR-NCM) and NCA half-cells during cycling at different C-rates and quantify the individual contributions to the overall heat flow using a combination of isothermal micro-calorimetry and electrochemical methods. The paper focuses in particular on the open-circuit voltage (OCV) hysteresis of the LMR-NCM material, which results in a significant reduction in energy round-trip efficiency (≈90% for LMR-NCM/Li cells vs ≈99% for NCA/Li cells at C/10) and therefore in an additional source of heat that has to be considered for the thermal management of the cell. The total heat release of the LMR-NCM/Li cells is found to be nine times higher than that of the corresponding NCA/Li cells (at C/10). In the case of the LMR-NCM cathode, the heat due to OCV hysteresis is responsible for up to 55% of the total energy loss. Using the applied approach, the OCV hysteresis heat is separated into its share during charge and discharge and is furthermore presented as a function of SOC. Additional sources of heat, such as reversible entropic heat, parasitic effects, and measurement limitations, are discussed in terms of their contribution to the overall energy balance of the two cell chemistries

Systematic study of quaternary ammonium cations for bromine sequestering application in high energy density electrolytes for hydrogen bromine redox flow batteries

Bromine complexing agents (BCAs) are used to reduce the vapor pressure of bromine in the aqueous electrolytes of bromine flow batteries. BCAs bind hazardous, volatile bromine by forming a second, heavy liquid fused salt. The properties of BCAs in a strongly acidic bromine electrolyte are largely unexplored. A total of 38 different quaternary ammonium halides are investigated ex situ regarding their properties and applicability in bromine electrolytes as BCAs. The focus is on the development of safe and performant HBr/Br$_{2}$/H$_{2}$O electrolytes with a theoretical capacity of 180 Ah L$^{-1}$ for hydrogen bromine redox flow batteries (H$_{2}$/Br$_{2}$-RFB). Stable liquid fused salts, moderate bromine complexation, large conductivities and large redox potentials in the aqueous phase of the electrolytes are investigated in order to determine the most applicable BCA for this kind of electrolyte. A detailed study on the properties of BCA cations in these parameters is provided for the first time, as well as for electrolyte mixtures at different states of charge of the electrolyte. 1-ethylpyridin-1-ium bromide [C$_{2}$Py]Br is selected from 38 BCAs based on its properties as a BCA that should be focused on for application in electrolytes for H$_{2}$/Br$_{2}$-RFB in the future

Implications of the Heat Generation of LMR-NCM on the Thermal Behavior of Large-Format Lithium-Ion Batteries

Lithium- and manganese-rich NCM (LMR-NCM) cathode active materials exhibit a pronounced energy inefficiency during charge and discharge that results in a strong heat generation during operation. The implications of such a heat generation are investigated for large-format lithium-ion batteries. Small laboratory cells are generally considered isothermal, but for larger cell formats this heat cannot be neglected. Therefore, the heat generation of LMR-NCM/graphite coin cells and NCA/graphite coin cells as a reference is measured for varying charge/discharge rates in an isothermal heat flow calorimeter and scaled to larger standardized cell formats. With the aid of thermal 3D models, the temperature evolution within these cell formats under different charge/discharge operations and cooling conditions is analyzed. Without an additional heat sink and any active cooling of larger LMR-NCM/graphite cells, discharge C-rates lower than C/2 are advisable to keep the cell temperature below a critical threshold. If the loads are increased, the cooling strategy has to be adapted to the specific cell format, otherwise critical temperatures above 60 °C are easily reached. For the investigated convective surface cooling and base plate cooling scenarios, thick prismatic cell formats with LMR-NCM are generally unfavorable, as the large amount of heat cannot be adequately dissipated

Lithium recovery from geothermal brine – an investigation into the desorption of lithium ions using manganese oxide adsorbents

Spinel type lithium manganese oxides (LMOs) are promising adsorption materials for selective recovery of lithium from salty brines. In this work a lithium-ion sieve material, H$_{1.6}$Mn$_{1.6}$O$_{4}$, derived from Li$_{1.6}$Mn$_{1.6}$O$_{4}$4, a spinel type LMO, was successfully prepared via hydrothermal synthesis. This lithium-ion sieve, H$_{1.6}$Mn$_{1.6}$O$_{4}$, was then used in laboratory tests to adsorb Li+ from a generic LiCl solution and geothermal brine from Bruchsal geothermal power plant. Desorption experiments were performed with the following desorption solutions: ammonium peroxydisulfate ((NH$_{4}$)$_{2}$S$_{2}$O$_{8}$), sodium peroxydisulfate (Na$_{2}$S$_{2}$O$_{8}$), acetic acid (CH$_{3}$COOH), sulfuric acid (H$_{2}$SO$_{4}$), carbonic acid (H$_{2}$CO$_{3}$), ascorbic (C$_{6}$H$_{8}$O$_{6}$) and hydrochloric acid (HCl). The results showed that C$_{6}$H$_{8}$O$_{6}$ led to adsorbent destruction and only small amount of lithium was desorbed with H$_{2}$CO$_{3}$. CH$_{3}$COOH and (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$ showed the best desorption performance with high lithium recovery and low Mn dissolution. The kinetic experiments indicate that more than 90% of equilibrium was reached after 4 hours. A decline in the adsorption/desorption capacity was measured for all desorption agents after eight cycles in the long-term experiments. These long-term tests revealed that higher lithium recovery in desorption with HCl and CH$_{3}$COOH was achieved compared to (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$. On the other hand, the use of CH$_{3}$COOH and (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$ seems to be advantageous to HCl because of lower Mn dissolution. According to the XRD results, the spinel structure of the treated adsorbents was preserved, but a weakening of the peak intensity was observed. Analyzing the adsorbent composition after eight cycles, an accumulation of competing ions was observed. This was especially remarkable when acetic acid was used