Mechanical Abuse Conditions Research Articles

Modeling state-of-charge dependent mechanical response of lithium-ion batteries with volume expansion

The behavior of lithium-ion batteries under mechanical abuse conditions has been studied extensively in recent years. Typically, characterization is performed by conducting experiments on discharged batteries to minimize the chances of thermal runaway and fire. However, studies have shown that material models calibrated at discharged state may not be as accurate at higher states of charge. In this study, a combined experimental-numerical method is proposed to simulate the stiffening of mechanical response in electrode stacks/jellyrolls of lithium-ion batteries at various states of charge and levels of confinement. Our study indicates that the mechanical properties of the jellyroll do not inherently change as a function of the state of charge, rather, the primary cause of the higher stiffness in charged batteries is the volume expansion of the jellyroll during charging. Therefore, mechanical characterization tests are conducted at the discharged state and the expansion of the jellyroll is induced in the finite element models to match the equivalent volume at the desired state of charge. In the second phase of the simulation, mechanical abuse loading is applied to validate the accuracy of simulations using the test data. This method was applied and validated for both pouch and cylindrical batteries with high accuracy.

Effects of Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolytes on the safety of hybrid solid–liquid batteries

Hybrid solid–liquid batteries (HSLBs) are emerging as promising solutions to address the safety issues of lithium-ion batteries. However, the effects of solid-state electrolytes (SSEs) on battery safety remain unclear, hindering the large-scale application of HSLBs. This paper presents a comprehensive investigation on the safety performance of HSLBs with different amounts of nano-sized Li1.3Al0.3Ti1.7(PO4)3 (LATP) SSEs in the LiNi0.9Co0.05Mn0.05O2 cathode under thermal, electrical, and mechanical abuse conditions. The HSLBs with LATP SSEs exhibit significantly enhanced tolerance to overcharge, as the battery with 5 wt% LATP does not go into thermal runaway throughout the whole overcharge process. In-depth characterizations reveal that the LATP additives experience electrochemical delithiation during overcharge and generate a protective coating layer on the cathode surface, thus effectively mitigating the cathode structural changes and cathode-electrolyte interfacial reactions. Benefiting from the coating layer, the HSLBs with LATP SSEs also exhibit reduced temperature rise rate and retarded thermal runaway during the accelerating rate calorimetry and oven tests, as well as enhanced rate performance and cycling stability. Finally, the safety, electrochemical performance, and cost of HSLBs and conventional LIBs are comprehensively compared through a radar graph, aiming to provide guidance for the rational design of high–energy density and high-safety batteries.

A comparative study on mechanical-electrical-thermal characteristics and failure mechanism of LFP/NMC/LTO batteries under mechanical abuse

Understanding the failure behaviors and failure mechanisms of lithium-ion batteries under mechanical abuse is essential for numerical reconstruction of abuse scenarios for different types of cells. This study investigates the mechanical-electrical-thermal characteristics, components tensile properties and failure mechanisms of LiFePO4 (LFP), Li(Ni0.5Mn0.3Co0.2)O2 (NMC), and Li2TiO3 (LTO) cells through indentation experiments, including ball intrusion, cylindrical intrusion, and out-of-plane compression modes at quasi-static loading rates. Additional ball intrusion experiments were conducted at varying loading rates. This study compares the effects of different material systems on battery performance under standardized mechanical abuse conditions. Post-test examinations analyze surface damage and internal component fracture morphology. Two distinct fracture modes were observed: ductile fracture and brittle fracture. The findings suggest that, under the same loading mode, LTO cells exhibit distinct failure behavior compared to NMC and LFP cells, attributed to differing material properties and resulting fracture modes during intrusion. Based on the analysis of the tensile results of the battery components, the cell fracture mode may be related to the tensile strength of the separator. The loading rate significantly impacts the mechanical-electrical-thermal performance of pouch cells, resulting in increased cell stiffness and shorter internal short circuit duration at higher loading speeds. However, the effect of loading rate is consistent across cells with different material systems.

Review of Lithium-Ion Battery Internal Changes Due to Mechanical Loading

The growth of electric vehicles (EVs) has prompted the need to enhance the technology of lithium-ion batteries (LIBs) in order to improve their response when subjected to external factors that can alter their performance, thereby affecting their safety and efficiency. Mechanical abuse has been considered one of the major sources of LIB failure due to the changes it provokes in the structural integrity of cells. Therefore, this article aims to review the main factors that aggravate the effects of mechanical loading based on the results of different laboratory tests that subjected LIBs to abusive testing. The results of different cell types tested under different mechanical loadings have been gathered in order to assess the changes in LIB properties and the main mechanisms responsible for their failure and permanent damage. The main consequences of mechanical abuse are the increase in LIB degradation and the formation of events such as internal short circuits (ISCs) and thermal runways (TRs). Then, a set of standards and regulations that evaluate the LIB under mechanical abuse conditions are also reviewed.

Critical Factors Contributing to the Thermal Runaway of Thiophosphate Solid Electrolytes for All‐Solid‐State Batteries

AbstractAlthough all‐solid‐state batteries are suggested as a means to tackle the safety concerns associated with current Li‐ion batteries, there is presently a lack of comprehensive understanding regarding their thermal safety. In this context, critical factors contributing to the thermal runaway of thiophosphate solid electrolytes with charged Li1‐xNi0.8Co0.1Mn0.1O2 (NCM) under thermal and mechanical abuse conditions are demonstrated, considering parameters such as heating rate under thermal abuse conditions and the hybridization of S atom in structure. In particular, the thermal behavior of various solid electrolytes, including thiophosphates, thioantimonates, and halides, is investigated to clarify critical elements in Li6PS5Cl (LPSCl) contributing to its thermal instability when combined with charged NCM. Various ex situ analyses, along with density functional theory calculations, reveal a correlation between the hybridization of S atoms and the thermal instability of solid electrolytes, suggesting that sulfur acts as a key element triggering the thermal runaway of sulfide‐based solid electrolytes.

Experimental study on the internal short circuit and failure mechanism of lithium-ion batteries under mechanical abuse conditions

The safety issues of lithium-ion batteries under mechanical abuse conditions have attracted widespread attention due to their high uncertainty and risk. This research takes cylindrical lithium-ion batteries as the research object and conducts three-point bending tests on cylindrical lithium-ion batteries with different states of charge (SOC), electrode thicknesses and electrode materials. The mechanical response, voltage changes, temperature changes during the loading process of the battery, and the microstructural changes of the battery's electrodes and separator after the bending test were examined. The results show that the maximum load-bearing capacity of the battery and the displacement corresponding to the short circuit decreases with the SOC of battery; the higher the battery SOC means a faster average temperature rise rate of the battery. When the SOC is higher than 60 %, the battery will experience violent thermal runaway phenomena such as explosions and spouting fire after bending tests. The mass loss rate of the battery is also greatly affected by the battery SOC and the electrode thickness, however, electrode material have almost no effect on the mass loss rate of the battery. According to the SEM images of the electrodes, it is found that short circuits cause graphite particles to break, separators to close and electrolytes oxidize on the surface of positive electrode particles. After triggering the internal short circuit, more broken particles are observed in the positive electrode material of the battery with thicker electrodes and the surface roughness of the broken particles is higher. By comparing the electrode changes of LFP and NCM, it is found that the intensity of the internal electrochemical reactions in NCM is far greater than that in LFP. The research results provide theoretical insights for understanding the electrothermal characteristics and mechanical integrity of lithium-ion batteries under mechanical abuse, which can shed light on the design and optimization of high-performance and safe lithium-ion batteries.

Experimental analysis and safety assessment of thermal runaway behavior in lithium iron phosphate batteries under mechanical abuse

Mechanical abuse can lead to internal short circuits and thermal runaway in lithium-ion batteries, causing severe harm. Therefore, this paper systematically investigates the thermal runaway behavior and safety assessment of lithium iron phosphate (LFP) batteries under mechanical abuse through experimental research. Mechanical abuse experiments are conducted under different conditions and battery state of charge (SOC), capturing force, voltage, and temperature responses during failure. Subsequently, characteristic parameters of thermal runaway behavior are extracted. Further, mechanical abuse conditions are quantified, and the relationship between experimental conditions and battery characteristic parameters is analyzed. Finally, regression models for battery safety boundaries and the degree of thermal runaway risk are established. The research results indicate that the extracted characteristic parameters effectively reflect internal short circuit (ISC) and thermal runaway behaviors, and the regression models provide a robust description of the battery's safety boundaries and thermal runaway risk degree. This work sheds light on understanding thermal runaway behavior and safety assessment methods for lithium-ion cells under mechanical abuse.

Assessment of the complete chain evolution process of LIBs from micro internal short circuit failure to thermal runaway under mechanical abuse conditions

Lithium-ion batteries (LIBs) are widely used in various devices, ranging from mobile phones and laptop computers to electric vehicles and energy storage systems. However, internal short circuits (ISCs) can occur for a variety of reasons, such as internal foreign matter, overcharging, and mechanical abuse. Micro short circuit (MSC) usually shows a long incubation period and is hard to detect, which leads to many thermal runaway (TR) accidents of LIBs. For mobile phone batteries, bending is a very common abuse condition that may be encountered in daily use. This paper explores the microstructural changes, electrochemical performance, thermal behavior, and the critical point of TR under three-point bending abuse test. Key findings include the impact of bending on the ion diffusion coefficient, the correlation between bending degree and heat generation during charge-discharge cycles, and the identification of a critical angle for TR at 60°. A competing relationship between irreversible heat due to bending and Joule heat from ISC was found, where there exists a critical point of bending angle, after which the total heat generated will be higher than that of normal batteries.

(Invited) Benchmarking and Predicting the Risks of Commercial Li-Ion Cells Undergoing Thermal Runaway

The performance of commercial Li-ion batteries increases year after year. New mechanical designs of cells as well as changing electrolyte and active material compositions continually push performance boundaries forward. With such changes, the risks associated with thermal runaway of cells change too and a challenge persists in recording and benchmarking risks to determine whether increased performance comes at the expense of increased risk in the event of thermal runaway. The Battery Failure Databank provides a record of thermal and mass ejection behaviors of past and present commercial cells and provides a valuable resource for benchmarking behaviors and determining the predictability of risks associated with thermal runaway.A Fractional Thermal Runaway Calorimeter (FTRC), developed by the NASA Johnson Space Center in collaboration with the National Renewable Energy Laboratory (NREL), distinctly measures heat emitted from the body of commercial cells and heat that is ejected from the cell. The FTRC also facilitates in-situ high-speed radiography to link phenomena occurring inside the cell with external thermal measurements. The FTRC was used for all tests recorded in the Battery Failure Databank and high-speed radiographs accompany each thermal dataset. Having thermal, mass ejection, and internal dynamics behaviors from hundreds commercial cells under mechanical and thermal abuse conditions facilitates statistical analyses of cell behaviors and evaluation of the efficacy of machine learning methods for predicting risks associated with thermal runaway.Using data from the Battery Failure Databank, the following three topics will be covered in this talk: Correlations between heat generation and mass ejection: The total heat output from cells showed a strong correlation with the quantity of material ejected. An explanation for this based on distinct heat measurements from ejected and non-ejected materials will be discussed. Potential causes of outlier cells that produce exceptionally high heat: Upon conducting numerous repeat tests for each cell, outlier cells that produce exceptionally high quantities of heat were observed. High-speed radiography data revealed that internal dynamic phenomena can lead to extreme variations in thermal and ejection behavior observed externally. The predictability of thermal runaway outcomes using machine learning methods and limited data: With limited data on thermal behavior, mass ejection, and cell specifications, the accuracy of zero- and one-shot approaches to predicting the variation and distribution of heat output during thermal runaway of a new cell type, based on training data in the Battery Failure Databank, will be discussed. The analyses and open-access resources provided with this work are expected to provide a foundation for benchmarking the behavior and predictability of risks associated with thermal runaway of past and present commercial Li-ion cells. In addition to providing a valuable resource for designing safe battery systems, it is expected that this data will be imperative as we evaluate next generation cell designs and assess their respective failure mechanisms and associated risks.

(Invited) Quantitative Measurement of the Safety Performance of Li-Ion Batteries

Safety is one of the essential requirements that should be taken into account and prioritized in the course of the development phases of lithium secondary batteries for any commercial applications. Even though different safety test standards exist to simulate the electric, mechanical, and thermal abuse conditions, there are only limited methods that can be used to quantify the safety performance of the cell.This study aims to compare the quantitative measurement techniques of safety evaluation and identify the methods to define the design parameters influencing the eventual safety performance of the full cells. The nail penetration, hot box, ARC (Accelerated Rate Calorimeter) and overcharging test are performed using the pouch cells (1-3 Ah) with different cell designs and aging conditions.It is found that hot box and nail penetration results are well correlated with the OCV (open circuit voltage) of the cells, suggesting that the OCV threshold can be used as a new quantitative indicator of the safety performance. Using this indicator, the cells having different P/E (power-to-energy ratio) designs and different electrolyte formulations are compared to identify the conditions to promote the safety performance of the cells. Figure 1

Comprehensive analysis of thermal runaway and rupture of lithium-ion batteries under mechanical abuse conditions

Sidewall rupture of lithium-ion batteries plays an important role in thermal runaway (TR) propagation because flame burst from the side of cell can directly heat adjacent cells. However, the understanding of sidewall rupture in high specific energy cells under mechanical abuse conditions remains limited. In this work, nail penetration is adopted as a trigger method of TR of 21700-format cylindrical cells with high specific energy (257.0 W∙h/kg). The effects of test parameters including nail diameter, nail speed, penetrating location, penetrating depth, and state of charge on likelihood and severity of thermal runaway and sidewall rupture behaviour were investigated. A series of equipment including high-definition cameras, thermal imaging camera, X-ray computed tomography (CT), cycler and electronic balance were adopted to reveal the behaviour and the mechanism of TR and sidewall rupture. Discussion on CT scan and fire behaviour provides new perspectives for understanding sidewall rupture and TR mechanisms in high specific energy cells. The results show that the mean mass loss ratio of the cell with 100% SoC is greater than 45% under each test condition, and the maximum of them is as high as 62.5% when penetrating off-centre from the cell bottom and with a penetrating depth of 10 mm. The likelihood of sidewall rupture increases with the increasing nail speed, nail diameter, penetrating depth and state of charge when penetrating from the top cover of the cell, but it is little affected by the penetrating depth and nail diameter for penetrating from the bottom of the cell. For the first time such a relationship is presented. The root-cause analysis for the sidewall rupture of the cell has been discussed, which highlights the three key factors, including the casing strength, the internal pressure, and the opening area of the venting disk.

Numerical Study on the Use of Emergency Cooling During the Process of Lithium-Ion Battery Thermal Runaway

Abstract The thermal runaway process limits the development and wide application of lithium-ion batteries. More and more researchers are paying attention to how to suppress thermal runaway caused by thermal, electrical, mechanical, and other abuse conditions. Temperature is an important indicator in the process of battery thermal runaway. Using large heat dissipation flow to cool the battery to a safe temperature range can achieve a good thermal runaway suppression effect. This paper discusses the influence of heat dissipation flow on the thermal runaway through combining simulation and experiment. First, a simulation model is established and shows good agreement with the experiment. Both the simulated and experimental results found that an application with a short duration and large heat dissipation flow can achieve a better cooling effect at a suitable battery temperature. Then, we discussed the minimum heat dissipation coefficient required to suppress battery thermal runaway by applying emergency cooling at different battery temperatures. When the trigger temperature rises from 166 °C to 178 °C, the minimum heat dissipation flow required increases from 72 W/m2 to 1391 W/m2. At last, the relationship between trigger temperature and minimum heat dissipation flow was obtained. This provides a reference for emergency cooling of battery thermal runaway.

Modeling strategy for progressive failure prediction in lithium-ion batteries under mechanical abuse

The prediction for the internal failure of lithium-ion batteries (LIBs) under external mechanical abuse loading remains a challenge for safe design. This paper systematically studies the modeling approach for progressive failure simulation and short-circuit prediction. Hemispherical indentation experiments are conducted on a battery specimen containing 5 representative sandwich (RS) layers to examine the deformation and progressive failure behavior of battery components. Three different models, viz, a high-fidelity detailed model, an intermediate homogenized model and a fully homogenized model, are developed and employed to simulate the progressive failure in a multi-layer battery specimen. The simulation results obtained using the three models all correlate well with experimental phenomena, capturing the overall stress-strain response and ultimate failure of the battery structure. The numerical results can help us understand the failure behavior and the mechanism for mechanical abuse-induced short circuit in LIBs. The feasibility of the three models for use in progressive failure prediction is compared by analyzing the capability of the models in predicting the critical failure events, the computational efficiency of the models, and the feasibility to implement coupled mechanical-electrochemical-thermal simulations. The results of this work provide useful insights on practical choices for the modeling strategy and safety design of LIBs under mechanical abuse conditions. • Models of different precision level for mechanical abuse of LIBs are established. • Detailed model and intermediate model show good accuracy in failure predicting. • Fully homogenized model shows high efficiency and reasonable accuracy. • Modeling methods for short-circuit prediction are systematically discussed.

High-efficiency multiphysics coupling framework for cylindrical lithium-ion battery under mechanical abuse

The emergence of electric vehicles equipped with lithium-ion batteries has largely alleviated the environmental crisis, however, the safety and sustainable development of lithium-ion batteries under mechanical abuse conditions is increasingly becoming an obstacle for the promotion of electric vehicles. Lithium-ion batteries exhibit mechanical, electrical, thermal and other multiphysics coupling response behaviors when suffering from mechanical abuse such as compression. In this paper, two high-efficiency multiphysics coupling frameworks and strategies (calculation process) are proposed innovatively. Three abuse tests, flat plate test, rigid rod test and hemispherical punch test under the quasi-static condition are carried out to create mechanical abuse conditions. The geometric-level multiphysics coupling model couples the 3D mechanical model, the 3D thermal model, the 0D battery electrical model and the 0D short-circuit model to provide visual simulation results for battery failure analysis. The simulation results show that the geometric-level multiphysics coupling model can accurately explain the battery failure behavior under a variety of operating conditions, with a calculation time of no more than 1 h on a universal computation platform. The lumped-parameter high-efficiency multiphysics coupling model adopts the lumped-parameter mechanical model and the lumped-parameter thermal model, avoids the finite element calculation process, and can provide efficient and accurate semi-quantitative calculation results for battery safety analysis in the absence of a high-performance computing platform. The calculation time on the universal computation platform is no more than 5 s. The two high-efficiency multiphysics coupling frameworks can adapt to different computational analysis scenarios, helping to analyze the failure mechanism of lithium-ion batteries, improve the safety and maintain the sustainable development of lithium-ion batteries.

Probing of Internal Short Circuit in Lithium-Ion Pouch Cells by Electrochemical Impedance Spectroscopy under Mechanical Abusive Conditions

Though lithium-ion batteries (LIB) are becoming prevalent energy storage systems for electrifying vehicles, their high energy density often makes them susceptible to various thermal instability problems. Also, due to the battery abuse that can barely be avoided and as LIBs are exposed to many accidents, mechanical damage of different intensities often facilitates internal short-circuiting of the components and leads to thermal runaway events. Herein, we demonstrate resistance measurement by electrochemical impedance spectroscopy (EIS) as a tool for the detection of an internal short circuit (ISC) and health monitoring in LIBs. The changes in the EIS at different mechanical deformation levels are evaluated through a proper equivalent circuit model. The fitted results reveal that the cathode-electrolyte interface resistance can be used to predict the onset of ISC due to the mechanical abusive conditions. Changes in the EIS are traced to the battery deformation levels or local strain changes due to the internal damage leading to ISC. The obtained results demonstrate that impedance spectroscopy provides information about the emergence of ISC and battery health.

Electrochemical Impedance Studies of Internal Short Circuits of Lithium-Ion Batteries Under Mechanical Abusive Conditions

Due to the high energy density and long lifetime, lithium-ion batteries (LIB) become ubiquitous energy storage systems for electric vehicle operations1. However, a higher energy density frequently results in a developed risk of thermal instability issues, where a series of heat-producing reactions can quickly occur, leading to fire and even explosions2. Due to the prevalent utilization in electric vehicles, battery abuse can hardly be avoided as LIB is exposed to many accidents, and mechanical abuse of various degrees of intensity often paves the way for internal short-circuiting of components through rupturing of separators3-4. Such battery failure induced by mechanical damage can lead to electrical and chemical hazards together with fire, which can result in danger to life, the environment, and the infrastructure and should therefore not occur in the field. The origin of such thermal-induced battery degradation certainly caused by short-circuiting of battery components mostly by direct contact of anode and cathode electrodes. To mitigate these issues and caution the electric vehicle drivers about thermal runaway events, the development of a diagnostic method to identify the damage mechanism under mechanical deformation and corresponding electrical behavior is essential.The onset of short circuits often characterized by a sharp increase in current, temperature, and rapid drop in voltage and set pass criteria as the absence of these potentially dangerous events as which may be enough for regular safety testing. Such events detected by a range of techniques including electrochemical impedance, incremental capacity-differential voltage, infra-red, tomography, etc5-7. However, it is challenging to design repeatable experiments that can emulate early-stage incubation of field ISC failure. Herein, we demonstrate resistance measurement by electrochemical impedance spectroscopy as an indicator for the detection of an internal short circuit of LIBs. The occurrence of ISC at different mechanical deformative conditions is evaluated through proper equivalent circuit model with multi-frequency and alternating voltage or current signal. The fitted results reveal that cathode-electrolyte interface resistance can be used to predict the onset of ISC due to mechanical abusive conditions. The obtained results demonstrate that impedance spectroscopy, together with a precise modeling parameter, provides information about the emergence of ISC and battery lifetime. Scrosati, B.; Garche, J., Lithium batteries: Status, prospects and future. Journal of power sources 2010, 195 (9), 2419-2430.Feng, X.; Ouyang, M.; Liu, X.; Lu, L.; Xia, Y.; He, X., Thermal runaway mechanism of lithium ion battery for electric vehicles: A review. Energy Storage Materials 2018, 10, 246-267.Wang, Q.; Ping, P.; Zhao, X.; Chu, G.; Sun, J.; Chen, C., Thermal runaway caused fire and explosion of lithium ion battery. Journal of Power Sources 2012, 208, 210-224.Zhu, X.; Wang, H.; Wang, X.; Gao, Y.; Allu, S.; Cakmak, E.; Wang, Z., Internal short circuit and failure mechanisms of lithium-ion pouch cells under mechanical indentation abuse conditions：An experimental study. Journal of Power Sources 2020, 455, 227939.Xiong, R.; Ma, S.; Li, H.; Sun, F.; Li, J., Toward a Safer Battery Management System: A Critical Review on Diagnosis and Prognosis of Battery Short Circuit. iScience 2020, 23 (4), 101010.Spielbauer, M.; Berg, P.; Ringat, M.; Bohlen, O.; Jossen, A., Experimental study of the impedance behavior of 18650 lithium-ion battery cells under deforming mechanical abuse. Journal of Energy Storage 2019, 26, 101039.Barai, A.; Uddin, K.; Dubarry, M.; Somerville, L.; McGordon, A.; Jennings, P.; Bloom, I., A comparison of methodologies for the non-invasive characterisation of commercial Li-ion cells. Progress in Energy and Combustion Science 2019, 72, 1-31.

Parametric Study on the Safety Behavior of Mechanically Induced Short Circuit for Lithium-Ion Pouch Batteries

Abstract Safety issues of lithium-ion batteries under mechanical abuse have attracted worldwide attention due to its high uncertainty and high risks, following by the rapid increase of market share for lithium-ion battery-driven smart products. In this work, the safety behavior of a pouch battery under mechanical abuse conditions is numerically investigated using a simultaneously coupled mechanical–electrochemical–thermal model. The short-circuit and electrochemical–thermal responses of lithium-ion batteries under various mechanical abuse conditions are successfully predicted and compared. The main impact factors, including the state of charge (SOC), indenter shape and size, and loading displacement, are systematically studied and analyzed. The comprehensive parametric studies show that the battery is in a more dangerous state under higher SOC, identify the critical distinction of the short-circuit behavior between sharp indenter and blunt indenters for battery, and explain the discrepancies in the repeated mechanical abuse tests. These conclusions provide theoretical insights for understanding the failure mechanism of lithium-ion batteries under mechanical abuse, and technical support for the safety design of battery packs.

A combined experimental and simulation approach for short circuit prediction of 18650 lithium-ion battery under mechanical abuse conditions

Abstract Lithium-ion batteries are considered an efficient energy source for current electric vehicles (EVs); however, the safety of these batteries is vital when it comes to large-scale deployment. Short circuit of batteries is one of the concerns as it can spread quickly within the battery module or pack if not controlled at the cell level. In this paper, single lithium-ion battery cell is investigated where mechanical abuse conditions are applied to investigate short circuits and propagation of failures due to short circuits. The numerical simulation tool LS-DYNA is used for the battery-layered model, each layer thickness is considered 0.3 mm, and concentrically layered formation is used for this purpose. An improved element size of 0.5 mm is used for steel casing and 1 mm for all other layers. A total of 27 layers are simulated in a single cell and the innermost radius is considered 1 mm. Displacement at short circuit, mean temperature at the short circuit, and mean maximum temperature change criterion are used to understand short circuit and propagation of failures. Simulation models are developed for quasi-static load analysis to understand the severity of failures, which can be used to reduce the risk of sequential failure of batteries in the battery pack.

Internal short circuit and failure mechanisms of lithium-ion pouch cells under mechanical indentation abuse conditions：An experimental study

Electromechanical structural integrity and thermal stability dictate the safety performance of lithium-ion batteries. Progressive deformation and failure across microscopic and macroscopic lengths scales that are responsible for internal short circuit (ISC) in lithium-ion cells under mechanical abuse conditions remains elusive. In this study, a series of indentation tests were conducted on lithium-ion cells with different capacities up to the occurrence of ISC. The external response and internal configuration of these cells were investigated. It is discovered that cells with different capacities and state of charges exhibited different behaviors. Maximum temperature, which is often regarded as the most important parameter related to thermal runaway (TR), varied considerably due to the complicated contact configurations. X-ray computed tomography (XCT) showed that ISC was a collective result of shear band or other strain-localization modes in the electrode assembly, shear offsets in the granular coatings of electrodes, and the accompanying ductile fracture in the metal foils. We believe that the irregular strain-localization modes (kinks, cusps, and buckles), radical mismatches in mechanical properties of different layers, and geometric features of the indenter eventually lead to the tearing/puncture of cell separator at various locations. The results could provide useful guidance for the micromechanical modeling of lithium-ion cells.

Battery Safety: Data-Driven Prediction of Failure

Accurate prediction of battery failure, both online and offline, facilitates design of safer battery systems through informed-engineering and on-line adaption to unfavorable scenarios. With the wide range of batteries available and frequently evolving pack designs, accurate prediction of cell behavior under different conditions is very challenging and extremely time consuming. In this issue of Joule, Li et al. 1 used data from a previously reported finite-element model to train machine learning algorithms to predict whether a cell will undergo an internal short circuit when exposed to a selection of mechanical abuse conditions. The presented approach aims to alleviate, and yet is still limited by, a common challenge facing data-driven prediction methods: access to robust, plentiful, high-quality, and relevant experimental data.