Thermal Runaway Risk Research Articles

A multi-factor evaluation method for the thermal runaway risk of lithium-ion batteries

To systematically and quantitatively establish a multi-factor evaluation method for the thermal runaway risk of lithium-ion batteries (LIBs), the fuzzy analytic hierarchy process was adopted in this paper. The own hazardous factor of battery, hazardous factor of vented gases, jet fire and high-temperature mixture (JFHM), ejected powder and their corresponding sub-factors were evaluated and analyzed. Combined with literature, the model of multi-factor evaluation method was established and the index system was determined. The pair-wise comparison matrixes for the thermal runaway risk were drawn, the triangular fuzzy method was used to calculate and the evaluation weight was obtained. The factors' ranges of the criteria risk grades were quantitatively determined. The risk of thermal runaway consequences under the selected abuse condition was analyzed with a case study. The result shows that the thermal runaway risk from LIBs under the selected abuse condition is level III: the LIB is more dangerous after thermal runaway. Meanwhile, in this method, the lower explosion limit of gas and the maximum height/ length of the JFHM are the two factors with the greatest weights. In the actual design and use process, people should pay attention to the protection of the runaway gas explosion and the harm of JFHM.

Evaluation method of lithium battery safety based on thermal runaway risk index

Evaluation method of lithium battery safety based on thermal runaway risk index

Thermal Hazard Analysis of Styrene Polymerization in Microreactor of Varying Diameter

Polymerization is a typical exothermic reaction in the fine chemical industry, which is easy to cause thermal runaway. In order to lower the thermal runaway risk of polymerization, a microreactor was adopted in this study to carry out styrene thermal polymerization. The hydrodynamic model and the fluid–solid coupling model of thermal polymerization of styrene were combined by using the computation fluid dynamics (CFD) method to build a three-dimensional steady-state model of the batch and the microreactor and compare. The results indicated that the maximum temperature of the polymerization in the microreactor was only 150.23 °C, while in the batch reactor, it was up to 371.1 °C. Therefore, the reaction temperature in the microreactor could be controlled more effectively compared with that in the batch reactor. During the reaction process, jacket cooling may fail, which would lead to an adiabatic situation. According to the divergence criterion (DIV), the thermal runaway of the polymerization occurred in microreactors with different tube diameters under an adiabatic situation. Further, the diameter of the microreactor had a considerable effect on the distribution of the inside temperature field under normal jacket cooling. The maximum temperature difference in the microreactor with a diameter of 6 mm was controlled at 25.33 °C. However, the effects of the inlet velocity (0.001, 0.0015, 0.002, 0.0025, 0.003 m/s), jacket temperature (150, 170, 180, 190, 200 °C) and residence time (400, 500, 600, 750 s) were relatively small. In addition, the jacket temperature had significant effects on viscosity, while other conditions had little effect. The DIV criterion indicated that the styrene thermal polymerization reactions could be safely performed in the microreactor when the jacket was cooled normally.

Investigation into maximum temperature of synthesis reaction for single kinetically controlled liquid–liquid semibatch reactions with arbitrary reaction order

Maximum temperature of synthesis reaction (MTSR) is an essential concept to assess the thermal runaway risk and design safe operating conditions for semibatch reactors (SBRs). According to the definition, the values of MTSR will change with the reaction temperature (T). So far, the behavior of MTSR for liquid–liquid semibatch reactions with arbitrary reaction order has not been thoroughly researched. In this work, it is theoretically and experimentally verified that MTSR versus T profiles are prone to present an ‘S’ shape for strongly exothermic kinetically controlled liquid–liquid reactions. That means that the dependence of MTSR on T is complex. A theoretical criterion to determine whether MTSR will increase with T increasing is developed in this work. This criterion states that if the criterion is negative, MTSR will increase as T increases. To validate this criterion, the nitration of 4-chloro benzotrifluorid by mixed acid was conducted. The theoretical criterion can contribute to design safe operating conditions for SBRs.

Experimental study on thermal runaway risk of 18650 lithium ion battery under side-heating condition

To simulate the heat transfer process between lithium-ion batteries (LIBs), an electric heater with the same size and shape as LIB in this work is used to trigger thermal runaway event. The effect of state of charge (SOC), the power of heater, the cell spacing on thermal behavior of LIB was investigated as well the amount of transferred heat between the heater and LIB was calculated. The results indicate that 50% SOC is an unstable state for LIB, that a stronger jet flame becomes more likely when the SOC of LIB is higher than 50%. Additionally, the increased spacing, lower heating power and SOC can contribute to mitigate the severity of thermal runaway behavior. Further, the dominant path of heat transfer between the heater and LIB will also vary with operating conditions. The heat conduction through air is the main heat transfer path in tests with lower heating power. However, heat radiation will replace heat conduction as the primary heat transfer mode when there is a large temperature difference between the heater and LIB in tests with higher heating power. Understanding the leading heat transfer path between LIBs can provide valuable guidelines for the safety design of lithium-ion battery modules.

Lithium metal batteries capable of stable operation at elevated temperature

Rechargeable lithium metal batteries have attracted wide attention due to high theoretical energy density. For practical applications, high-temperature performance of lithium batteries is essential due to complex application environments, in terms of safety and cycle life. However, it's difficult for normal operation of lithium metal batteries at high temperature above 55–60 °C using current lithium hexafluorophosphate (LiPF6) electrolyte systems. Herein, a kind of new electrolyte system is designed by adding two thermal-stable lithium salts together (i.e. lithium bis(trifluoromethanesulfonimide) (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB)) into carbonate solvents with high boiling/flashing point (i.e. ethylene carbonate (EC) and propylene carbonate(PC)). Small amount of LiPF6 is also added to prevent the corrosion of aluminum current collector. The results indicate that the new electrolyte possesses superior high-temperature performance, meanwhile, it effectively suppresses the formation of lithium dendrite by synergy effects of salts and solvents. Li/LiCoO2 cells with high LiCoO2 real capacity (2.4 mAh/cm2) using this kind of new electrolyte shows excellent cycling performance at elevated temperature up to 80 °C. Such performance is achieved for the first time for rechargeable Li metal battery using liquid organic electrolytes. It overcomes the operation temperature upper limit of traditional Li-ion batteries (i.e. 55–60 °C), which would effectively reduce thermal runaway risk and simplify the thermal management of Li metal batteries in reality.

Overcharge investigation of large format lithium-ion pouch cells with Li(Ni0.6Co0.2Mn0.2)O2 cathode for electric vehicles: Thermal runaway features and safety management method

In this paper, the overcharge-induced thermal runaway features of large format commercial lithium-ion batteries with Li(Ni0.6Co0.2Mn0.2)O2 (NCM622) cathode for electric vehicles under different current rates (C-rates) have been systematically studied at ambient temperature. The overcharge process is characterized as four stages. The temperature rise and the maximum temperature of the battery surface don't increase in proportion to the applied C-rates. However, with the increase of C-rates, the crest voltage of voltage curve rises linearly. When the voltage reaches approximately 5.1 V, a new voltage plateau appears in the cases below 2C. It is not sufficient that the temperature sensor is placed only near the terminal tab for most battery packs of EVs. In addition, the accumulated heat analysis demonstrates that side reactions dominate the temperature rise and contribute to most of the accumulated heat before thermal runaway. To mitigate the impact of overcharge and avoid the thermal runaway risk, a safety management method is proposed. Furthermore, the sharp drop in voltage before thermal runaway also provides a feasible approach to forewarn the users of the impending risk. These results are important for building safer batteries and providing information for the safety monitoring function of the battery management system (BMS).

New Thermal Runaway Risk Assessment Methods for Two Step Synthesis Reactions

In this study, in order to assess thermal runaway risk of two step synthesis reactions, two new risk assessment methods were proposed by combining the new assessment procedure with the risk matrix and the Stoessel criticality diagram. The thermal runaway risks of the tert-butyl peroxybenzoate (TBPB) synthesis process and the tert-butyl peracetate (TBPA) synthesis process, and the influence of the use of the pure target products on the assessment results were also studied by the new methods. The results showed that the new methods could obtain more accurate assessment results of two step synthesis reactions. Some measures should be taken to reduce the thermal runaway risks of the two synthesis processes. Furthermore, the use of the pure target products in the new methods would exaggerate the thermal runaway risks of the two step synthesis reactions.

Effect of inorganic salt and organic acid on the thermal runaway of hydrogen peroxide

Hydrogen peroxide with the presence of catalytic metal ions or incompatible organic matters has caused some fire and explosion accidents in recent years. This work further studied the effect of inorganic salt and organic acid on the thermal runaway behaviour of hydrogen peroxide via rapid screening device (RSD), accelerating rate calorimeter (ARC) and a batch reactor. Experimental results revealed that both the metal ions and their corresponding inorganic acid ions have significant influences on the thermal runaway of H2O2: the catalytic effect of metal ion followed Fe2+ > Fe3+ > Cu2+, and the synergistic effect of inorganic acid ion followed Cl− > SO42−. No explosion was detected under RSD and ARC test conditions. In addition, a one-step global reaction kinetic model characterized as adiabatic temperature increase and final exothermic temperature was briefly described to estimate the kinetic parameters of the mixture of H2O2 with/without organic acid. The analysis showed that the runaway reaction of H2O2 with formic acid or acetic acid is a first order reaction at a low temperature range (<100 °C) and the thermal runaway risk of H2O2/HCOOH > H2O2/CH3COOH, along with the decreasing apparent activation energy and pre-exponential factor.

Toward the Identification of Intensified Reaction Conditions Using Response Surface Methodology: A Case Study on 3-Methylpyridine N-Oxide Synthesis

Identification of inherently safer and intensified reaction conditions is a vital step for transformation of traditional batch/semibatch synthesis to continuous operation. Accelerating reactions is challenged by several safety and efficiency issues including thermal runaway risk, side reactions, final product degradation, and reactor overpressure. This work demonstrates the use of response surface methodology to identify inherently safer and more efficient intensified reaction conditions for 3-methylpyridine N-oxidation performed in a semibatch pressure-resistant isothermal calorimeter. The experimental conditions were selected to screen various operating-variable combinations using Box–Behnken design of experiments. Regression models were developed correlating the catalyst amount, oxidizer dosing-rate, and reaction temperature with reactor pressure and N-oxide yield; good agreement with experimental data obtained in the present study and from literature was achieved. Results indicate that, even when cond...

Performance and safety protection of internal short circuit in lithium-ion battery based on a multilayer electro-thermal coupling model

Internal short-circuited lithium-ion battery can generate much heat in a short time and that leads to local high temperature or even explosion. A multilayer electro-thermal coupling model considering the interplay of current at different positions is developed to study the performance of internal short circuit and penetration before the trigger of thermal runaway. The simulation result agrees with the experiment in a certain extent. This study will serve as a guideline for protective design of internal short circuit. It concludes that penetration is not a precise method to simulate the performance of one-layer internal short circuit from view of maximum temperature and effect of cell unit layers. Temperature of large capacity battery is higher relatively when internal short occurs. A new method, in which the battery is forced to external short circuit when the internal short circuit is detected, is proposed to protect the battery from internal short circuit. The battery is within safe range if the external short circuit resistance is small enough. More, the maximum temperature increases with the decrease of battery resistance. Decreasing the resistance may increase the thermal runaway risk while increasing the battery resistance is a good protective method.

Theory of Flow Batteries with Fast Homogeneous Chemical Reactions

Redox flow batteries are widely investigated toward cost-effective storage of energy generated via intermittent renewable sources. Many redox chemistries have been proposed for flow batteries, possessing various attractive features such as low-cost reactants, fast electrochemical reaction kinetics without precious metal catalysts, negligible thermal runaway risk, and low toxicity. While all flow batteries rely on heterogeneous electrochemical reactions occurring at electrode surfaces, in a subset of chemistries homogeneous chemical reactions occur in the electrolyte. A prominent example are batteries employing halogen-based catholytes, where halogen molecules complex with halide ions in the catholyte, forming redox-active polyhalide ions. However, state-of-the-art models capturing flow battery performance for halogen systems typically neglect the presence of such homogeneous reactions and polyhalide ions. The latter assumption allows for simpler models, but at the cost of accurately predicting battery chemical state and performance. We here present a generalized flow battery theory extended to include fast homogeneous reactions, which employs a technique known as the method of families to simplify the governing equations. We then apply and solve the model for the specific case of a membraneless hydrogen-bromine flow battery, illustrating the predicted effect of the homogeneous complexation reaction in the catholyte on flow battery performance.

Experimental study on the thermal runaway of hydrogen peroxide with in-/organic impurities by a batch reactor

Hydrogen peroxide, as a very versatile reagent for many industrial processes, has caused many accidents in recent years. Therefore, understanding the thermal hazards of hydrogen peroxide with or without impurities is essential for the prevention of fire and explosion accidents. In this work, batch reactor tests were conducted to study the thermal runaway behavior of hydrogen peroxide under the contaminations of Fe3+ ion, formic/acetic acid and ethanol/acetone. Experimental results revealed that the thermal runaway risk of H2O2 increased significantly with increasing initial temperature and Fe3+ ion concentration. Comparatively, the potential risk of organic impurities on the thermal stability of hydrogen peroxide was found to be much larger, because several violent explosions were measured resulting from a series of rapid and complicated decomposition reactions. The explosion severity of H2O2 with organic matters followed acetone > ethanol > formic acid > acetic acid. In addition, a modified runaway scenario characterized as adiabatic temperature increase and time to maximum rate was briefly described to theoretically evaluate the thermal risk of H2O2 decomposition. This scenario was found to be valid to estimate thermal runaway hazards. These results improve our understanding of thermal runaway behavior and explosion risk of H2O2 with incompatible impurities.

Mechanical abuse simulation and thermal runaway risks of large-format Li-ion batteries

Abstract Internal short circuit of large-format Li-ion pouch cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ∼40% maximum compressive loading force during the pinch test. The cell was twisted about 5° to the side by horizontally pulling a wire attached to the anode tab. The combined torsion-compression force created small failure at the separator yet allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4–6 cells at each state-of-charge (SOC). Commercially available 18 Ahr LiFePO4 (LFP) and 25 Ahr Li(NiMnCo)1/3O2 (NMC) cells were tested, and a thermal runaway risk (TRR) score system was used to evaluate the safety of the cells under the same testing conditions. The aim was to provide the cell manufacturers and end users with a tool to compare different designs and safety features.

Semi-batch reactors: Thermal runaway risk

The paper deals with the thermal safety and the runaway risk evaluation for semi-batch reactors (SBR). The main contributions consist in:-Construction of a new boundary diagram which describes the reaction temperature vs. target temperature and maximum allowable temperature in order to define the critical conditions for the thermal runaway;-Identification of the most important governing parameters;-Evaluation of the risk of accident by a probabilistic description of the prior cooling problem, the appropriate combination of the critical conditions and the assessment of occurrence probability of the thermal runaway accident.A heterogeneous liquid-liquid reacting system is considered as a case study. A sensitivity analysis is then performed in order to investigate the influence of cooling temperature on the maximum reaction temperature. Monte Carlo simulations are also used in order to calculate the probability of accidents.

Numerical investigation and dimensional analysis of reaction runaway evaluation for thermal polymerization

Reaction runaway has always been the most dangerous issue for bulk thermal polymerization, especially in large scale industrial production. For highly exothermic reactions, improperly controlled reaction leads to thermal runaway and even explosion. Continuous dropping reaction method is considered to have advantages over the commonly used batch reaction method on thermal management since the energy release rate can be delicately controlled by reactant feeding rate. Reliable modeling is a key tool to get high productivity for thicker and larger products with a lower thermal runaway risk. In this study, a model of one-dimensional heat transfer is constructed and numerically solved though the finite difference method to investigate reaction runaway. Lab scale fabrication of cross-linked polystyrene proves the accuracy of the numerical model. The validated model has been applied to investigate the roles of most important factors for large scale production, including product size, temperature and feeding rate. It was found that the reaction layer thickness is the key factor for explosive reaction. Smaller product size, higher temperature and smaller feeding rare can ensure safe production. A non-dimensional analysis based on energy analysis is thereafter proposed for evaluating the reaction runaway risk during thermal polymerization.

Failure analysis of pinch–torsion tests as a thermal runaway risk evaluation method of Li-ion cells

Recently a pinch–torsion test is developed for safety testing of Li-ion batteries. It has been demonstrated that this test can generate small internal short-circuit spots in the separator in a controllable and repeatable manner. In the current research, the failure mechanism is examined by numerical simulations and comparisons to experimental observations. Finite element models are developed to evaluate the deformation of the separators under both pure pinch and pinch–torsion loading conditions. It is discovered that the addition of the torsion component significantly increased the maximum first principal strain, which is believed to induce the internal short circuit. In addition, the applied load in the pinch–torsion test is significantly less than in the pure pinch test, thus dramatically improving the applicability of this method to ultra-thick batteries which otherwise require heavy load in excess of machine capability. It is further found that the separator failure is achieved in the early stage of torsion (within a few degree of rotation). Effect of coefficient of friction on the maximum first principal strain is also examined.

Thermal runaway risk evaluation of Li-ion cells using a pinch–torsion test

Internal short circuit (ISCr) can lead to failure of Li-ion cells and sometimes result in thermal runaway. Understanding the behavior of Li-ion cells in ISCr condition is thus critical to evaluate the safety of these energy storage devices. In the current work, a pinch–torsion test is developed to simulate ISCr in a controlled manner. It is demonstrated that the torsional component superimposed on compression loading can reduce the axial load required to induce ISCr with smaller short spot size. Using this pinch–torsion test, two types of commercial Li-ion pouch cells were tested under different state of charge (SOC). Based on the severity of the cell damage, a series of thermal runaway risk scores were used to rate the thermal stability of these cells. One of the cell types showed significantly increased hazard as the SOC increased while the other type exhibited relative uniform behavior among different SOC. Therefore, this novel pinch–torsion test seems to be an attractive candidate for safety testing of Li-ion cells due to its abilities to consistently create small ISCr spots and to differentiate cell stability in a wide range of SOC.