Onset Temperature Of Thermal Runaway Research Articles

A cost-effective alternative to accelerating rate calorimetry: Analyzing thermal runaways of lithium-ion batteries through thermocouples

In order to facilitate safety of heavy-duty batteries, approaches for studying thermal runaway (TR) need to be developed. So far, these have relied on accelerating rate calorimetry as a standard technique. This method, however, is costly, generally has size limitations, and is therefore of limited use for large format batteries. In this study, we examined the TR behavior of battery cells through a thermal propagation test at module level employing 157 Ah battery cells, using simple thermocouples. This constitutes one of the largest prismatic cell format analyzed to date, while the utilization of thermocouples enables a cost-effective method to study its TR. Parameters such as TR onset temperature, maximum temperature, heat release, and trigger time of the cells were comprehensively evaluated and compared, using this method. An onset temperature for TR at around 144 °C and a maximum temperature from 757 °C to 863 °C were observed. Heat release was estimated as 1.59 MJ per battery cell, deviating within ∼1 % compared to nail penetration tests. Moreover, six distinct stages during TR could be observed, in accordance with literature. This shows that the thermal propagation test using thermocouples is able to align well with other methods such as accelerating rate calorimetry, but is considerably easier to employ.

Quantifying the Thermochemistry of Kinetic Transitions in a Solid-State Charged Li/Llzo/LCO Cell Using Differential Scanning Calorimetry

It is a general understanding that removal of combustible organic solvent with the introduction of solid-state electrolytes would make a battery safer. However, safety in solid state batteries is multifaceted and involves analysis of self-heating rates, total generated energy, thermal runaway onset temperature, maximum temperature, and thermal runaway prevention mechanisms1,2. The use of reactive lithium metal as the anode, and cathode material such as LiCoO2 that releases O2 when heated in its delithiated state, results in conditions in which the exothermic reaction 4Li+O2→2Li2O may occur if these reactants come into contact. We measure heat flow data using a differential scanning calorimeter (DSC) and hermetically sealed DSC pans to establish a reaction thermochemistry responsible for self-heating of LixCoO2|LLZO|Li metal cell, with x=0.43 (which corresponds to 4.3V vs. Li). While the main exothermic reaction is 4Li+O2→2Li2O when only Li0.43CoO2 is present in the cathode3, a practical solid-state cathode will almost certainly contain conductive carbon and a fluorinated binder. We carry out careful DSC analysis with a range of components and ratios of components to quantify the expected reaction pathway, and amount of heat released, for a cathode that contains Li0.43CoO2, carbon additive, and PVDF binder. We find that the carbon and PVDF strongly influence the reaction pathway upon heating to 500°C in our DSC experiments. Hence, the presence of even small weight fraction components in a solid-state cathode should be considered when evaluating their thermochemistry upon heating.

Quantifying the Thermochemistry of Kinetic Transitions in a Li/Llzo/Layered Metal Oxide Cathode Solid-State Battery with Varying Cathode States of Charge

The safety of solid-state battery is multifaceted and requires analysis of the thermal runaway onset temperature, total heat released, maximum heat release rate, the amount and toxicity of any gases released, and other factors1. The onset temperature of strong self-heating is particularly important, and hence quantitative analysis of exothermic reactions as a function of temperature is required. We use differential scanning calorimetry to measure heat flow for solid-state cells with a Li metal anode, an LLZO separator, and both LiCoO2 and NMC cathode sheets (which also contain a conductive additive and a binder), and quantitatively analyze the data to develop a thermochemical reaction map consisting of all major reactions that take place upon heating. This quantitative thermochemistry map can serve as a basis to assess cell safety, and in particular the rate and extent of temperature rise. We find that primary reaction that determines the total heat released is lithium reaction with oxygen from delithiated cathode decomposition (i.e., 4Li+O2→2Li2O), but other components in the cell such as conductive carbon, PVDF binder and current collectors also have significant participation in the reaction pathway. As previous studies for graphite/liquid electrolyte/metal oxide cathode cells have shown, reducing the state of charge also reduces the amount of heat released upon heating2, with implications for safe storage and operation of future cells.

High-safety poly(ethylene-co-vinyl acetate)/poly(ether ether ketone)/poly(ethylene-co-vinyl acetate) composite separator with the thermal shutdown feature for lithium-ion battery

The thermal safety of lithium-ion batteries (LIBs) is a major obstacle to expanding LIBs applications. High-safety separators with a thermal shutdown feature are considered the most promising and appealing thermal protection strategy for LIBs to avoid thermal runaway. Herein, a high-safety poly (ethylene-co-vinyl acetate)/poly (ether ether ketone)/poly (ethylene-co-vinyl acetate) (EVA/PEEK/EVA) composite separator is fabricated by dip-coating and thermally induced phase separation. Once the operating temperature exceeds 80 °C inadvertently (the thermal runaway onset temperature), the EVA layers of the EVA/PEEK/EVA separator are converted into barrier membranes to cut off ion transport and prevent battery reactions. Meanwhile, the PEEK substrate remains dimensionally stable even at temperatures up to 240 °C to avoid the dangers associated with thermal inertia after shutdown. Moreover, compared to the polyolefin separator (commercially available), the EVA/PEEK/EVA separator shows an increase of 42% and 77.1% in ionic conductivity and discharge capacity at the rate of 4C, respectively. Therefore, the EVA/PEEK/EVA separator can secure the LIBs without sacrificing electrochemical performance, and further expand the application of LIBs.

A novel dual-purpose thermal runaway propagation mitigation system using a liquid cooling pipe with aperture sealed by films

Preventing thermal runaway (TR) propagation in lithium-ion battery (LIB) modules is essential for the safe application of LIBs. The current study proposes a novel dual-purpose system using a liquid cooling pipe with aperture sealed by films (LCPASF). The system can maintain the module within the desired temperature by the rapid heat dissipation of the liquid cooling during the normal operation. Once TR occurs, the film on the aperture of the pipe melts and the coolant in the pipe correspondingly releases to cool the cells to prevent the TR propagation. Induced by heater, all of the cells in the module get involved in TR without preventing measures. Systems using polyethylene (PE), biaxially oriented polypropylene (BOPP), polyimide (PI) and polytetrafluoroethylene (PTFE) films limit the TR within 0, 1, 1 and 3 cells, respectively. The melting temperature of PE is much lower than the TR onset temperature, thus the PE film melts before the TR occurrence and no cells get TR. For the film with melting temperature much higher than the TR onset temperature, increasing the aperture diameter can improve the cooling effect. This study provides critical insights for the design of thermal management and TR propagation mitigation system for LIB modules.

Quantifying the Thermochemistry of Solid-State Lithium Metal Battery Reactions Using Differential Scanning Calorimetry

It is commonly assumed that the introduction of solid-state electrolytes implies the improved safety of high-energy batteries due to the removal of the combustible organic solvents in present Li-ion cells. However, safety is a multifaceted issue that involves thermal runaway onset temperature, self-heating rates, total generated energy, maximum temperature, gas or other material releases from a cell, thermal runaway prevention mechanisms, etc.1 In addition, the use of lithium metal anodes (which melt at 180°C) for high energy density cells may introduce previously unconsidered safety issues not faced by Li-ion cells, in which no molten and reactive lithium metal is present during a thermal runaway. Quantitative heat flow data on reaction thermochemistry among solid-state battery cell components can be gathered using differential scanning calorimetry on milligram-scale samples that include the key components of a full cell stack. While a principal exothermic reaction observed in previous DSC work2 is the formation of Li2O from molten Li and O2 released upon metal oxide cathode decomposition, this work did not include current collectors or carbon and binder, which add further competing reactions such as the oxidation of binder, and lithium/current collector alloying. In addition, the measured heat flows in a DSC test that includes several cell components are critically dependent on the mass ratio of materials present in the cell, for example the electrode capacity ratio. In this talk we present our own DSC measurements on the onset temperatures, total heat release, and rate of heat release for numerous combinations of cell components (e.g., Li metal, solid electrolyte separators, cathode active materials, cathode inactive components) for prospective solid-state batteries.

High performance polyimide-based separator for 4.5V high voltage LiCoO2 battery with superior safety

Polyolefin separator has poor thermal stability which leads to short circuit and thermal runaway of lithium ion batteries(LIBs) about 100 °C. Here, we used polyimide (PI) as the core material and poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) as the shell material to prepare PI/PVDF-HFP composite separator by coaxial electrospinning. Compared with Celgard 2400, the PI/PVDF-HFP separator not only demonstrates negligible thermal shrinkage at 200 °C and excellent flame retardancy, but also shows higher porosity and electrolyte uptakes as well as superior wettability, which are conducive to reduced interfacial impedance and improved ion conductivity. The 4.5 V high-voltage LiCoO2/Li cell with PI/PVDF-HFP separator exhibits an initial discharge specific capacity of 181 mAh g−1 and a capacity retention ratio of 95% after 300 cycles, and it also shows superior C-rate capability. The accelerating rate calorimetry (ARC) test manifests that the onset temperature of thermal-runaway of the 4.5 V LiCoO2/Li cell with PI/PVDF-HFP separator is 190 °C, indicating that PI/PVDF-HFP separator possesses superior safety.

Impact of solid-electrolyte interphase layer thickness on lithium-ion battery cell surface temperature

The widely used non-destructive battery characterization techniques, such as voltage, capacity, and impedance measurements, often fail to fully characterise a discarded lithium-ion battery when reuse of spent battery is envisaged. Here we propose a tool that uses the surface temperature of a pouch cell to measure the thickness of the solid-electrolyte-interphase (SEI) layer, which is often attributed as one of the main causes of lithium-ion battery degradation at 0.1C–1C discharge rates in ambient conditions. A 2D multiphysics coupled electrochemical-thermal continuum model and a 3D thermal model have been developed to investigate the changes in the surface temperature of a lithium-ion pouch cell with varying SEI layer thicknesses. Present modelling results show that the cell surface temperature changes due to significant SEI layer heat generation at several discharge rates. Furthermore, the temperature change has also been subject to different cooling conditions and particle sizes. The present results provide a reference to making decisions on battery reuse by providing a correlation between the SEI layer thickness with the surface temperature of the cell and inform future research on thermal runaway as a thicker SEI layer can decrease the onset temperature of thermal runaway.

Chemical Characterization Using Laser-Induced Breakdown Spectroscopy of Products Released from Lithium-Ion Battery Cells at Thermal Runaway Conditions.

Laser-induced breakdown spectroscopy (LIBS) was used to characterize the ejecta released by lithium-ion (Li-ion) cells at thermal runaway conditions. Commercial AAA-size, rechargeable, 3.7 V, 350 mAh, Li-ion battery cells were heated in a N2 -atmosphere tubular chamber up to about 165 ℃ to induce thermal decomposition. Through measurements of the chamber internal temperature and LIBS emission intensities over, time the onset temperature of thermal runaway (≈143 ℃) and the duration of the cells outgassing (>40 minutes) were determined. Relatively high-intensity atomic emissions from C, F, H, Li, Na, and P were detected at different times during the heating experiments. The detection of analytes such as C and H was continuous over time. On the contrary, detection of F, Li, Na, and P was more irregular, indicating the presence of solid-phase analytes or analyte-bearing particles. A calibration scheme for estimation of the total mass/volume concentration of all carbon-based species sampled within the laser-induced plasma was developed.

Multi-Length Scale X-Ray CT and Thermal Analysis for Battery Safety Assessment

Lithium-ion battery failure occurs across multiple length and time scales. This work presents the properties of thermal and mechanical failure in batteries of cylindrical, pouch and coin cell format by using a combination of Accelerating Rate Calorimetry (ARC) and X-ray Computed Tomography (CT) at various length scales; from whole cell (macro) to bulk electrode (micro) to particle (nano).Typical features of a thermal runaway (TR) sequence in a commercial 18650 cell, such as the onset temperature of TR, the order of and rate of heat generation from cell component breakdown, such as SEI layer deformation, are shown using a heat-wait-search protocol in an ARC. Alongside this, pre- and post-mortem X-ray CT images reveal the effects of thermal failure on the bulk electrode structure within the cell, such as deformations due to gas formation and release. Electrode material characteristics, such as porosity, particle size distribution, tortuosity, and particle cracking, are also quantified and compared before and after cell failure in the bulk electrode (micro–X-ray CT) and individual particles (nano-X-ray CT)[1].A novel X-ray CT scanning protocol is also demonstrated for characterising bespoke pouch cells (single and multi-layer) with sufficient resolution to reconcile electrode morphology, for example to evaluate the morphology changes during thermal abuse by nail penetration.Furthermore, this work investigates the sequence of reactions leading up to thermal runaway using a novel coin cell Differential Scanning Calorimeter (DSC). Heat flux signals are used to quantify the contribution of various exothermic and endothermic reactions to the overall heat generated by a cell as it undergoes failure. Some key features of early-stage TR reactions, such as the decomposition of the SEI layer are revealed for NMC111, NMC622 and NMC811. Some of the typical thermal characteristics of cells as they undergo ‘normal’ charge and discharge are also shown and compared to abnormal operating conditions such as, temperatures up to 60 °C, high C-rates, and cycle numbers.[1] D. Patel, J. B. Robinson, S. Ball, D. J. L. Brett, and P. R. Shearing, J. Electrochem. Soc., 167, 090511 (2020). Figure 1

Reliable and Early Warning of Lithium-Ion Battery Thermal Runaway Based on Electrochemical Impedance Spectrum

Lithium ion battery thermal runaway constitutes a severe inhibitor for the spread and application of electric vehicles and widespread adoption of renewable energy. Reliable and early warning of thermal runaway calls for a technique capable of detecting abnormal response well in advance of the critical event and being effective to the module when a single cell in it has safety issues. In this study, electrochemical impedance spectrum (EIS) dependence on cell temperature and deformation is exploited to generate a two-staged warning method with three indicators in three frequency ranges. Specifically, the first stage utilizes the high sensitivity of EIS at the intermediate-frequency range to abnormal cell internal temperature rise, which is before self-heating temperature, as an early indicator for safety issues. The second stage utilizes the abrupt changes in EIS behaviors due to cell deformation in high- and low-frequency ranges, which are more sensitive than cell voltage change, as indicators for the thermal runaway onset temperature. The potential and issues of such an EIS-based method for both reliable and early warning of thermal runaway in field application, including measurement feasibility, versatility in various scenarios and the difference between the experimental and actual situation, are discussed.

Investigating the thermal runaway features of lithium-ion batteries using a thermal resistance network model

Accurate measurement of the characteristic temperatures of thermal runaway, which are affected by many factors, is important for battery safety evaluation. A one-dimensional thermal resistance network model is built in this study to investigate the influences of various factors on the thermal runaway features of lithium-ion batteries. In the model, the battery is divided into four independent components in the thickness direction, with thermal resistances connecting different nodes. The gas thermal resistance is added to simulate swelling and rupture of the battery. The model can effectively fit the battery thermal runaway behavior under both adiabatic thermal runaway and oven test conditions. Model-based analyses show that the thermal runaway features and characteristic temperatures are significantly affected by the test conditions, thermocouple positions, and battery thickness. The onset temperature of thermal runaway (T2) obtained in the oven test is 48.1 °C lower than that obtained in the adiabatic thermal runaway test. The measured T2 varies at different positions, and the difference can exceed 20% when the battery thickness increases to 10 cm. Moreover, the maximum thermal runaway temperature (T3) at the surface is approximately half that at the other positions. Finally, several suggestions for reasonable thermocouple placement are proposed, which can provide useful guidance for accurately evaluating battery thermal runaway performance.

Safer lithium-ion battery anode based on Ti3C2Tz MXene with thermal safety mechanistic elucidation

Thermal safety concerns of lithium ion batteries (LIBs) need to be solved urgently to facilitate their large-scale applications. Introducing safer anode materials can suppress the thermal runaway initiation but is usually compromising the cell performance due to their induced lower energy density. In this work, Ti3C2Tz MXene with tailored surface terminating groups is identified to be a safer LIB anode with improved capacity and lower operational potential. Calorimetric analyses demonstrate its significantly reduced heat generation (204 J g−1) with electrolyte compared to conventional graphite anode (995 J g−1). Detailed characterizations and thermal analyses reveal the great dependence of its thermal behavior on the lithiation states, surface morphology, and surface-terminating functional groups. Modifying the Ti3C2Tz surface functional groups via annealing can eliminate the irreversible lithium metal plating, which mitigates the parasitic exothermic reactions during thermal runaway and enhances the anode initial coulombic efficiency and cycling stability. The in-situ thermal analyses of LIB full cells demonstrate the obviously improved onset temperature of thermal runaway (195 °C) from the modified Ti3C2Tz-lithium cobalt oxide (LCO) full cell than the graphite-LCO full cell (169 °C), indicating a much safer LIB developed.

Electrochemical performance and thermal stability of lithium ion batteries after immersion

In this work, electrochemical performance, aging mechanisms and thermal stability of LIBs after immersion were analyzed. The results show that corrosion increases with the increasing electric potential, NaCl concentration and immersion time. Moreover, capacity fading occurs after immersion, decreasing the lifespan of the battery. This effect is mainly caused by the loss of active material (LAM). With increasing NaCl concentration, capacity fading increases and battery lifespan decreases. The activation barriers (Ea) and the onset temperature of exothermic reactions (TOER) of cells initially increases and then decreases. The thermal stability of cells dramatically decreases after immersion in highly-concentrated NaCl solutions, which has higher onset temperature of thermal runaway (TOTR) and lower maximum temperature (TMax). With the increasing immersion time, the TOER initially decreases and then increases, TOTR increases, while TMax and Ea decrease.

Investigation on Thermal Runaway of Li-Ion Cells Based on LiNi1/3Mn1/3Co1/3O2

Abstract The thermal runaway behavior of lithium-ion cells plays a crucial role in the safety management of the powertrain in electric vehicles. In this study, the effect of states of charge (SOC) on the thermal runaway behavior of commercial LiNi1/3Mn1/3Co1/3O2 (NMC)-based pouch cells is investigated using accelerating rate calorimetry (ARC) and ex-situ X-ray diffraction. By studying the differences in the onset temperature of self-heating (T1) and the onset temperature of thermal runaway (T2) along with the mass loss between the different SOCs, we observed that higher SOC led to a decrease in the T2. However, T1 initially increased and then decreased with increasing SOC. These trends were attributed to the phase change of cathode material and separator. The ARC results also indicated the occurrence of endothermic reactions during the self-heating accumulation period. The findings in this study are helpful for thermal safety management of battery powertrain for electric vehicles.

An experimental investigation of the degradation and combustion behaviors associated with lithium ion batteries after different aging treatments

Lithium ion cells are one of the most promising solutions for energy storage. However, inevitable aging during the actual application will influence its thermal safety. This work intends to study the effect of aging on thermal behaviors of cells under external heating abuse. It was clearly shown that both fresh and aged cells were revealed to undergo thermal runaway and be ignited to fire. The venting flow was characterized firstly by a laser visualization technique, and the different structures in the presence of venting were discussed. After aging, the onset temperature of thermal runaway increased, while the temperature rise rate and maximum surface temperature decreased. Besides, the flame temperature as well as flame shape and flame height, were analyzed. The aged cells gave a forked flame with lower maximum flame temperature and flame height than fresh cells. The total mass loss of aged cells was less than that of fresh cells. Note that the aging way also affected the thermal stability of cells. These results indicate that the aged cells have a lower hazard of safety in current study. However, aging condition and thermal stability of both on cell and material level deserve to be studied in future work.

Probing the Thermal Safety of Li Metal Batteries

Li metal batteries (LMBs) with high energy density electrodes have emerged as the primary candidate for next-generation batteries owing to its superiority over conventional Li-ion technology. However, the safe operation of these systems under thermal abuse conditions remains primary concern regardless of the tremendous efforts to prevent short circuits through dendrite formation. In this context, we employ differential scanning calorimetry technique to investigate the thermal stability of Li-S and Li-NMC532 metal batteries. The calorimetric measurements identify separator melting together with anode-centric thermal degradation reactions as the primary mechanism of thermal runaway. Separator with poor thermal stability (low melting point), could instigate an internal short circuit that leads to exponential temperature rise due to the rapid release of electrical energy. An in-house physics-based modeling technique utilizes the knowledge of thermal stability at the materials level to predict the thermal safety of LMBs for pouch cell configuration. Simulations reveal that the thermal stability of the separator and parasitic reactions at the anode (Li metal) dictate the critical onset temperature of thermal runaway in Li metal batteries. The severity of thermal runaway can be modulated by carefully designing (capacity loading ratio (N/P)) the thickness of metal anode and advanced separator with better thermal stability.

Hazard analysis of thermally abused lithium-ion batteries at different state of charges

Abstract Temperature response, thermal decomposition, and gas generation are important metrics for evaluating thermal runaway hazards of lithium-ion batteries. In this paper, the hazards associated with thermally abused LiNi1/3Co1/3Mn1/3O2/graphite batteries at different state of charges (SOCs) are experimentally assessed. The results show that the maximum temperature of the battery during thermal runaway increases linearly with SOC, which is also accompanied by a linear decrease of the thermal runaway onset temperature. In addition, %%both the 90% and the 100% SOC batteries experienced some degree of gas deflagration and particle ejection that generated 1.22 g and 2.57 g of powders, respectively. While these powders are mostly contributed by the decomposition of battery cathodes, the gas deflagration can be mainly attributed to sparks that ignited the flammable gases released from the thermally abused batteries. Furthermore, this research also establishes a complete list of gas components observed at different SOCs, and the flammable ones are mainly carbon oxides, hydrocarbons, C2H4O2, and C2H6O. It is also observed that an increasing number of gas types will be generated at higher SOCs%, and some of these new components such as benzene can be harmful and toxic to the environment. Finally, this complete list of gas components can be used to identify characteristic gas types for an early warning mechanism of thermal runaway, which can be accomplished by installing appropriate gas sensors and monitoring their volume concentrations.

Multi-scale thermal stability study of commercial lithium-ion batteries as a function of cathode chemistry and state-of-charge

This paper takes a critical look at the materials aspects of thermal runaway of lithium-ion batteries and correlates contributions from individual cell components to thermal runaway trends.An accelerating rate calorimeter (ARC) was used to evaluate commercial lithium-ion cells based on LiCoO2 (LCO), LiFePO4 (LFP), and LiNixCoyAl1-x-yO2 (NCA) at various states of charge (SOC). Cells were disassembled and the component properties were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and temperature-resolved X-ray diffraction (TR-XRD).The whole cell thermal runaway onset temperature decreases and peak heating rate increases with SOC due to cathode destabilization. LCO and NCA cathodes are metastable, with NCA cells exhibiting the highest thermal runaway rates. By contrast, the LFP cathode is stable to >500 °C, even when charged. For anodes, the decomposition and whole cell self-heating onset temperature is generally independent of SOC. DSC exotherm onset temperatures of the anodes were generally within 10 °C of the onset of self-heating in whole cell ARC. However, onset temperatures of the cathodes were typically observed above the ARC onset of whole cell runaway. This systematic evaluation of component to whole cell degradation provides a scientific basis for future thermal modeling and design of safer cells.

Thermal runaway and fire behaviors of large-scale lithium ion batteries with different heating methods.

The thermal runaway and fire of batteries under different heating methods were characterized for fully charged 50 Ah LiNixCoyMn1-x-yO2/graphite batteries. The batteries were heated using cylindrical heater and electric furnace. The influence of three key parameters (heating position, area and power) was especially investigated. Thermal runaway induced by different heating methods can be divided into three stages. More sparks and gas/white smoke ejection could be observed for the battery heated with a cylindrical heater, while the battery heated with an electric furnace produced a larger explosion and more jet fire. The onset temperature of thermal runaway for the battery heated with a cylindrical heater was lower than for the battery heated with an electric furnace. Thermal runaway can be avoided by heat dissipation before temperature beyond 126.5-132.5 ℃. The heat release, CO2 production, and mass loss were found increase as the increasing heating power or heating area. In contrast, the impact of heating position on battery burning was less obvious compared with heating power and heating area. In conclusion, a battery presents a high thermal abuse hazard under the heating method with higher heating power or larger heating area, namely, the tested electric furnace conditions in this paper.