Internal Short Circuit Research Articles

Influence of Particle Size and Morphology on Electrochemical Properties of Glass Particle-Based Separators for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are one of the most important and common energy storage technologies for mobile devices as well as electric vehicles due to their high specific energy density [1]. However, there are still safety concerns in case of overcharge or mechanical damage. The separator as the passive safety-relevant component is placed between the two electrodes to prevent internal short-circuits. Nevertheless, accidental or inhomogeneous deposition of metallic lithium (Li plating) can lead to dendrite growth, which is one of the most common failure mechanisms. If only one dendrite penetrates the separator and forms a conductive path between the two electrodes, a short circuit in the battery leads to its failure [2].Despite the inherent rigidity of glass materials, previous studies demonstrated the successful application of glass-based separators in LIBs [3, 4]. To meet the requirements of modern battery production, a colloidal water-based system of glass particles and binder is used to manufacture flexible separators. Compared to state-of-the-art polymer-based separators, those flexible glass particle-based separators are superior in many of the required properties such as higher temperature resistance and dimensional stability up to 600 °C [3].However, the size and morphology of the utilized particles have a significant impact on the manufacturing process, e.g. affect slurry processability and separator formation, and consequently on the electrochemical performance. The effects of these parameters have already been studied for spherical or arbitrarily-shaped particles [5, 6].In the present work, platelet-shaped particles are utilized to manufacture glass-based separators. To further improve the operational safety of lithium-ion batteries, the benefit of platelet-shaped particles is compared to the use of arbitrarily-shaped particles. The use of these so-called glass flakes serves the purpose of forming an effective barrier against growing lithium dendrites by establishing a self-stabilizing structure. This barrier prevents or at least effectively delays penetration of the separator.For platelet-shaped particles, thickness and edge length of a particle differ significantly. Particles with a too high aspect ratio (edge length to thickness) block the Li+ diffusion pathway, affecting performance and stability of the final cell. Preliminary tests have shown that increasing the thickness of the glass flakes leads to a slight improvement of ionic conductivity, while increasing the edge length results in a strong reduction of ionic conductivity. However, separators containing particles with higher aspect ratio are expected to show increased piercing resistance. Thus, a trade-off between processability, electrochemical performance and safety barrier function against Li-dendrite growth and penetration is evaluated to understand the influence of particle morphology on the properties of separators using these particles.The microstructure of separators containing the different particle morphologies is examined using scanning electron microscopy (SEM) and correlated with the results of further characterization methods such as electrochemical impedance spectroscopy (EIS) and galvanostatic cycling.

Mesoporous Polyimide Thin Films as Dendrite-Suppressing Separators for Lithium-Metal Batteries.

Lithium-metal batteries require the effective suppression of lithium dendrites to guarantee both high performance and safety. Today's separators have macropores allowing lithium dendrites to traverse, leading to internal short circuits and other catastrophic results. Herein, we report a mesoporous polyimide separator for dendrite suppression. The polyimide separator exhibits mesopores of 21 nm width and a high storage modulus of 1.80 GPa. This mesoporous polyimide separator assists in the electrodeposition to form flat-top protrusions instead of sharp dendrites, therefore, allowing the safe cycling of lithium-metal batteries. This work is expected to advance the development of dendrite-suppressing strategies and contribute to the revival of lithium-metal batteries.

Needle penetration studies on automotive lithium-ion battery cells: Influence of resistance between can and positive terminal on thermal runaway

Thermal runaway (TR) can be initiated by the heat dissipated from an internal short circuit (ISC). In prismatic cells, a crucial type of ISC is located between the cell can on positive potential and the first anode layer. To enhance the safety, the potential of the can could be adjusted by increasing the ISC resistance, i.e., realizing a floating can, whereas a universal automotive prismatic cell has a can on potential in contrast. This work demonstrates that the floating can mitigates the ISC current and possibly prevents ISC from leading to TR using an advanced needle penetration test. Moreover, the ISC current was quantitatively measured, proving that there is no significant ISC current between floating can and outmost anode, while the ISC with can on potential can cause TR. To demonstrate that such difference originates only from the increased resistance, the equivalence in thermal behaviors between the two types of cans was analyzed by a heat-wait-seek test in an accelerating rate calorimeter. This work provides not only a guidance on designing a safer prismatic cell but also a prospect how the optimized needle penetration test can bring a deeper insight into the internal processes of Lithium-ion cells during mechanical abuse.

Innovative fault diagnosis and early warning method based on multifeature fusion model for electric vehicles

Fault diagnostics and early warning are crucial to the safe operation of lithium-ion batteries, and despite partial progress, it is still extremely difficult to solve the problem in a high-dimensional parameter space with complex failure causes. In this article, an innovative fault diagnosis and early warning method based on multifeature fusion model is designed for quantitative and qualitative comprehensive analysis and evaluation of the battery operating state information and the complex internal safety evolution trajectory. Firstly, to form a multi-dimensional fault feature matrix, a real vehicle dataset consisting of 400 vehicles is constructed using typical vehicle fault data from the cloud platform. Then, the original data is noise-reduced and pre-processed by applying initial bias correction and anomalous signal identification methods. Moreover, based on the equivalent circuit model and data-driven algorithm, 13 features including internal short circuit internal resistance, inconsistency accumulation risk, and principal element extraction index are designed from three dimensions: threshold, statistics and model. Finally, the multiple features are combined with random forest (RF) algorithm for hybrid fusion decision to achieve better generalization ability and suppress the overfitting risk of the algorithm. The results show that the proposed feature extraction and fusion decision methods can identify abnormal states and hazard levels in a timely and accurate manner, and this RF-based classification, warning and evaluation framework shows the promise of machine learning algorithms for interpretable early warning studies of battery failures, which can use more modal features to assess the hazard levels of actual operating battery systems in end-cloud collaboration scenarios.

Ultra-thin SiO2 nanoparticle layered separators by a surface multi-functionalization strategy for Li-metal batteries: Highly enhanced Li-dendrite resistance and thermal properties

Mechanical and thermal failure of a polyolefin separator often causes the internal short-circuit of batteries, which leads to abrupt heat generation in a short time, so-called thermal runaway. For this, we introduce grafting polymer layers with cross-linking to make a superior, thin, and uniform SiO2 layer with strong chemical binding to the surface of a polypropylene separator (PPS). The surface of the PPS was modified with i) coating of double bond-contained PVDF, ii) grafting with poly(ethylene glycol) methacrylate, 3-(trimethoxysilyl)propyl methacrylate, and ethylene glycol dimethacrylate, and iii) coating with SiO2 nanoparticles via immersing (GDPS-SNPI) or casting (GDPS-SNPC) methods. The pore structure and distribution, electrolyte affinity, thermal stability, and mechanical properties were progressively improved after respective modification steps. The GDPS-SNPC cell shows excellent capacity retention of 100% at 1 C after 100 cycles and the lowest increase in the cell impedance, whereas the LFP half-cell with PPS exhibited capacity retention of 88.32%. Furthermore, it is found that the coating method for SiO2 nanoparticles substantially influences the long-term cycling stability of Li-symmetric cells. The GDPS-SNPC cell survived after cycling over 1,000 h at a current density of 1 mA cm−2, whereas the GDPS-SNPI cell died before 500 h. Post-mortem analysis of the cycled Li-metal surface shows that smooth Li-plating occurred at the GDPS-SNPC cell, presumably due to a high Li-ion transference number. This work provides a solid methodology for producing a novel and robust separator and advances the understanding of separators' impact on electrochemical and physical phenomena within the cell.

Synthesis of Sb-doped Li10P3S12I solid electrolyte and their electrochemical performance in solid-state batteries

The glass-ceramic Li10P3S12I solid electrolyte exhibited moderate ionic conductivity of ∼3 mS cm−1, but it shows low interface stability with lithium, poor moisture stability, and the electrochemical performance is not well established with respect to lithium. In this work, we enhance the ionic conductivity, interface stability, and air stability using Sb-substitution in Li10P3S12I glass-ceramic solid electrolyte using a high-energy ball milling process followed by a low heat treatment process. The ionic conductivity analysis reveals that the prepared Li10.1P2.95Sb0.05S12I glass ceramic composition shows a higher ionic conductivity of 5.9 mS cm−1 at 25 °C than Li10.1P2.95Sb0.05S12I (5.06 mS cm−1). The Li10.1P2.95Sb0.05S12I glass ceramic symmetric cell exhibits a better critical current density of 1 mA cm−2 than bare (0.7 mA cm−2). Also, it demonstrates better DC cyclability at 0.25 mA cm−2 without internal short circuits after 80 cycles. The Sb-substitution not only enhanced the ionic conductivity, also increased the moisture stability according to HSAB theory. The lithium solid-state battery is constructed using the Li10.1P2.95Sb0.05S12I electrolyte that demonstrates a high discharge capacity of 146 mAh g−1 at 0.1C rate than bare electrolyte (126 mAh g−1).

Assessment of Thermal Runaway propagation in lithium-ion battery modules with different separator materials

The current work aims to understand and model thermal runaway (TR) events in lithium-ion (LIB) 18650 cells within the context of aircraft battery applications. The primary goal is to comprehend the phenomenon and discuss strategies for mitigating its consequences during aircraft operation. TR is modeled using Arrhenius kinetic equations and is implemented in both lumped parameters (Matlab SimulinkTM), and 3D CFD simulations (Ansys FluentTM) using User Defined Functions. To validate the thermochemical model, cells are initially simulated in an oven test, where a cell is exposed to a temperature-controlled atmosphere, triggering exothermic reactions. With a strong correlation between lumped parameters and 3D models, the latter is simulated under battery module installation conditions. An internal short-circuit is then implemented within the cell to observe how thermal runaway is triggered by an internal heat source. The trigger cell is subsequently placed in a battery module assembly to assess the dominant heat transfer modes and the likelihood of TR induction from one cell to its neighbors. This work’s main objective and innovation are to compare different materials in which cells are immersed while observing the main heat transfer parameters for each material. Three conditions are tested: ceramic paper fiber and G7 as solid separators, and no separator material, where air fills the gaps between cells. The analysis of heat transfer modes reveals radiation’s dominance in the case of air interstice, suggesting the possibility of using a special coating to reduce the cell surface emissivity as an alternative to decrease the likelihood of TR propagation. Thus, two values of surface emissivity were tested in the case of air. Considering a cell triggered by an internal short-circuit, a thermal runaway temperature spike is not observed in any of the four cases. However, the air interstice case with regular emissivity is the most critical one, with the closest cell reaching peak temperatures as high as 136 °C in 490 s. The ceramic paper fiber is considered the best separator material, as it postpones the temperature increase in the closest cell while also being lighter than G7. The results and discussions concerning heat propagation presented herein can serve as guidelines for developing strategies to mitigate thermal runaway in battery modules.

Temperature enhanced early detection of internal short circuits in lithium-ion batteries using an extended Kalman filter

Fuel shortages and environmental concerns primarily drive the recent growth in electrification. Lithium-ion batteries are the preferred power source for electric vehicles and other applications due to their high energy and power densities. Among potential issues that can affect Li-ion batteries, thermal runaway is a significant concern, believed to be primarily caused by internal short circuits. Therefore, early internal short circuit detection has become a critical task for any Li-ion battery-powered engineering system prioritizing safety. This paper presents a novel online internal short circuit detection method based on the state vector augmentation of an extended Kalman filter with: (i) voltage and surface temperature observations, (ii) a hysteresis state, and (iii) a state related to the internal short circuit. The proposed method is assessed numerically, mimicking an electrical vehicle battery working cycle. The framework allows for an online estimation of the internal short circuit state while remaining computationally lean, thus potentially allowing for implementation into commercial BMSs, and it is proven to capture the internal short circuit occurrence within safety limits. Additionally, the advantages of including both voltage and surface temperature observations have been highlighted. Future work envisaged towards field implementation of the technique in BMS is eventually and briefly discussed.

Flame retardant encapsulation in MOFs: A promising universal approach for enhancing battery performance

As one of the key components in a lithium-ion battery, separator plays an important role in guaranteeing the battery safety in practical application. However, polyolefin-based battery separators are prone to causing safety problems, such as internal short circuit and thermal runaway, due to their poor thermal stability, low melting point and flammable nature. In this work, a unique capsule structure with a zeolitic imidazolate framework-8 (ZIF-8) as the shell and flame retardant (FR) as the core was designed by a one-step in-situ growth method. The porous ZIF-8 shell can successfully prevent the flame retardant, i.e., hexachlorocyclotriphosphazene (HCCP) from decomposing into electrolyte, therefore, retaining the electrochemical performance. When fire accident occurs, the ZIF-8 shell collapses and releases the HCCP before further damage could take place to the battery. The results show that ZIF-8/FR-50@PP keeps 98 % area retention rate at 190 °C, and the self-extinguishing time (SET) is 2 s. The Li//NCM-811 cells based on ZIF-8/FR-50@PP deliver a remarkable discharge capacity of 50 mAh·g−1 even at 10C, and a high capacity retention of 68 % at 1C over 300 cycles. This work provides a new design strategy for high safety and good performance battery.

Study of temperature cycling of commercial rechargeable lithium-ion batteries

Lithium-ion batteries, a popular electric energy storage device, have high energy density and impressive working performance. However, the temperature affects its life cycle, capacity, and performance. Different effects are generated inside the battery for the different temperature conditions. It is necessary to study their thermal and electric characteristics in various thermal conditions since electric energy storage devices are used in various applications at low or high temperatures. In this study, the experimental analysis was performed to observe how a battery cell behaves above room temperature for a different 18650 cylindrical battery cell with a capacity of 5200 mAh. The testing temperature for this experiment was at 28˚C, 50˚C, 60˚C, 70˚C, and 100˚C. It is noted that the capacity of the battery cell fades drastically at high temperatures compared to low temperatures due to internal short circuits occurring at high temperatures.

Application of Theoretical Computational Simulations in Lithium Metal Batteries

In the area of high energy density batteries, lithium metal has attracted a lot of interest as an electrode material. But since lithium is so reactive, lithium metal batteries frequently have safety problems like thermal runaway, particularly under conditions such as overcharging, over-discharging, high temperatures, and mechanical impact. These safety issues can lead to dangerous situations such as battery explosion and fire. Furthermore, lithium-metal batteries are prone to dendrite development during the cycling process, which can pierce the separator and result in internal short-circuits, shortening the battery's cycle life. Lithium-metal battery use is strongly constrained by these important problems. To overcome these challenges, researchers are exploring various strategies, such as developing new electrolytes and additives, designing new battery structures, and exploring new anode materials. Computational simulations have emerged as a powerful tool to aid in this research. This review summarizes the recent applications of computational simulations in lithium metal batteries. Specifically, molecular dynamics (MD) and first-principles calculations have been widely employed to study key issues such as interface reactions, ion transport, and dendrite formation in lithium batteries. Additionally, this review discusses recent research directions in new types of ion electrolytes that can effectively address the safety concerns of lithium batteries and increase energy density, while still facing challenges in interface resistance and conductivity. The discussion of potential avenues for future research that will be pursued finishes this paper. These possibilities include multiscale simulations, the creation and manufacturing of new electrolyte materials, and the functional modification of lithium-metal anode surfaces.

Plasma-strengthened ionic conducting network enabling highly safety separator toward all-climate lithium metal batteries

Lithium metal batteries (LMBs) have been a promising candidate for high-energy–density energy storage system due to its high theoretical capacity and low density of metallic lithium (Li) anode, yet it still faces high risk of internal short circuits induced by thermal shrinkage and dendrite puncture of conventional polypropylene (PP) separators. To address these issues, an artificial interface, namely “plasma-strengthened ionic conducting network”, is constructed on the commercial PP separator, integrating high thermal/mechanical advantages of superionic Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and chemical regulation of plasma-introduced F-contained groups (F-LAGP@PP). The high safety F-LAGP@PP can reduce risk of the short circuit of LMBs. Time-of-flight Secondary Ion Mass Spectrometry (Tof-SIMS) indicates the plasma-introduced F-contained groups can react with Li anode to generate a LiF-rich interphase to promote a high chemical stability of LAGP. Consequently, this easy-to-commercialize fabrication separator enables both LMBs and Li-ion full pouch cells to achieve high safety and appreciable electrochemical performance in a wide temperature range (–20–120 °C), highlighting its application prospect for advanced energy storage systems.

Multifunctional Asymmetric Separator Constructed by Polyacrylonitrile-Derived Nanofibers for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries hold great promise as next-generation high-energy storage devices owing to the high theoretical specific capacity of sulfur, but polysulfide shuttling and lithium dendrite growth remain key challenges limiting cycling life. In this work, we propose a polyacrylonitrile-derived asymmetric (PDA) separator to enhance Li-S battery performance by accelerating sulfur redox kinetics and guiding lithium plating and stripping. A PDA separator was constructed from two layers: the cathode-facing side consists of polyacrylonitrile nanofibers carbonized at 800 °C and doped with titanium nitride, which can achieve rapid polysulfide conversion via electrocatalysis to suppress their shuttling; the anode-facing side consists of polyacrylonitrile oxidized at 280 °C, on which the abundant electronegative groups guide uniform lithium ion plating and stripping. Li-S batteries assembled with the PDA separator exhibited enhanced rate performance, cycling stability, and sulfur utilization, retaining 426 mA h g-1 capacity at 1 C over 1000 cycles and 632 mA h g-1 at 4 C over 200 cycles. Attractively, the PDA separator showed high thermal stability, which could mitigate the risk of internal short circuits and thermal runaway. This work demonstrates an original path to addressing the most critical issues with Li-S batteries.

Thermal runaway chain reaction determination and mechanism model establishment of NCA-graphite battery based on the internal temperature

The measurement of battery internal temperature directly affects the determination of the sequence of thermal runaway chain reaction and the choice of model heat sources, and the optimal combination identification of kinetic parameters corresponding to each heat source is the premise of establishing model. This paper focuses on the Lix(Ni0.8Co0.15Al0.05)O2-graphite pouch battery with built-in thermocouple. Based on the stage division of thermal runaway behavior and the decoupling of irreversible exothermic reaction between battery components, the thermal runaway mechanism is determined. Then, the optimal combination of kinetic parameters is determined by combining the DSC tests under variant heating rates, the Kissinger's method and the genetic algorithm. Furthermore, a thermal runaway model considering hierarchical properties is established, and the thermal contribution of six exothermic reactions at each stage of thermal runaway is quantified. Anode+electrolyte and cathode+anode contribute 53.8% and 18.7% respectively to the heat accumulation before thermal runaway. Internal short circuit accounts for 27.5%, and the heat is released instantaneously, directly triggering thermal runaway. This work has important reference significance for the design of battery safety warning system and the battery modification strategy.

Research on internal short circuit detection method for lithium-ion batteries based on battery expansion characteristics

Short circuits are a major contributor to thermal runaway in lithium-ion batteries, but present detection techniques cannot distinguish different forms of short circuits. Therefore, the paper provides a detection method for internal short circuits (ISCs) based on coupled mechanical stress that can determine the type of short circuit. Firstly, cathode-anode (Ca-An) short-circuit batteries with a controllable triggering time and measurable internal temperature and electrode potential are designed. Secondly, the performance evolution of fault batteries under coupled mechanical stress conditions is investigated, along with the impact of faults on the battery's safety performance. Additionally, the influence of battery expansion characteristics on the contact pressure at the short circuit location and the correlation between short circuit resistance and mechanical stress are analyzed. The results show, except for self-discharge, no significant differences between Ca-An short-circuit and normal batteries, and there are no mutable features observed, but the faults can exacerbate internal-external temperature differences during charging. The different reasons for thermal runaway during sustained pressurization between short-circuit and normal batteries are revealed. Finally, a method for detecting ISC based on the differences in short-circuit resistance at different states of charge is proposed. Overall, the paper provides a basis for fault classification in lithium-ion batteries.

Research on Electromagnetic Damage Effects in Navigation Receiver by PCI Testing

The EMP couples with electronic devices via cables, inducing electromagnetic damage effects. This paper elucidates the operational principles of a navigation receiver and simplifies the study by focusing on the radio frequency front-end module. Many PCI tests were conducted on its signal input port, yielding the damage threshold of the navigation receiver. An analysis of the output waveforms of the modules that incurred damage was also performed. Through infrared research, it was discovered that the damaged LNA experiences a rapid temperature rise to around 73°C during operation with applied power. The electromagnetic damage effect in the LNA primarily stems from internal MOS transistor short circuits. The BPF protects the subsequent circuit stages but is also susceptible to damage.

An aging- and load-insensitive method for quantitatively detecting the battery internal-short-circuit resistance

Early-stage detection of the battery internal short circuit (ISC) can effectively prevent batteries from fire-related accidents. However, it is technically challenging because the current leakage signals at the beginning stage of the ISC could be submerged by the joint effect of battery aging, battery balancing, measurement noise, and highly dynamic charging/discharging behaviors. Aiming at these issues, we here propose an equalization-based method to quantitatively calculate short circuit resistance for pack applications. The relationship between the balanced capacity and short circuit resistance is mathematically derived and unified for both passive and active equalization systems. Battery-in-the-loop experiments show that when the short-circuit resistance changes from 55 to 330 Ω, the error of our prediction can be well-bounded within ±2%, outperforming most existing algorithms. Further, the computational burden of the proposed method is similar to that of the Ah-counting method, requiring no additional information on the batteries’ aging status. Since our method supports arbitrary load profiles, it can be used in a wide range of applications such as electrified vehicles and renewable energy storage systems.

Thermally stable 3D cross-linked fluorinated polyimide/PVDF-HFP hybrid separator for lithium battery applications

Commercial Celgard 2325 separators suffer from poor flexibility, poor electrolyte wettability, and thermal instability, which can cause internal short circuits and thermal runaway in lithium rechargeable batteries. A novel 3D cross-linked and thermotolerant fluorinated polyimide (PI) / PVDF-HFP (PV) hybrid nanofiber separator rich in polar functional groups was fabricated using an electrospinning technique. PI and PV polymers are joined by a hydrogen bond through their exposed amide (–NH) and fluorinated (-CF) functional groups to build a supramolecular polymer cross-linked system. The separator exhibited high porosity (75 %), outstanding electrolyte uptake ability (775 %), strong mechanical properties (15.7 MPa), excellent thermal stability, and flexibility. As a result, the separator showed excellent Li+-conductivity (3.3 mS cm−1) and high Li+-transference number (tLi+ = 0.7) and maintained a proper-contacted electrolyte/electrode interaction for stable Li plating/stripping. Furthermore, when the PI/PV hybrid separator was applied in anode-free Li-metal batteries (a protocol of Cu/NMC cell), or Li-ion (MCMB /NMC) batteries, the cells achieved a high capacity and long lifetime. Remarkably, the Cu/NMC cell fabricated with a PI/PV hybrid separator is more robust and continues to function even after being heated at a high temperature of 140 °C for 1 h.

A Basic Study on the Diagnosis Method of Internal Short Circuit based on Feature Extraction and Separation Technique

Lithium-ion batteries are widely used in energy storage systems (ESS) and electric vehicles due to superior performance. However, most safety problems in the use process of the lithium-ion battery are attributed to internal short circuits, there are a lot of factors leading to the internal short circuit. Short circuit in the lithium-ion battery affects the electrochemical reaction and then generating a larger short circuit current. Besides, the thermal runaway is the result of a failure of the separator inside Li-ion batteries, small discharge pulses of a few mV were detected at the time of separator damages. Therefore, the fault diagnosis by internal short circuit of lithium batteries has attracted more attention to prevent the fire accidents. This paper aimed to suggest a diagnostic model for separator of LFP (Lithium iron phosphate) pouch cell as a basic research work using continuous pulse analysis method such as feature extraction and separation technique of pulse source for timely diagnose the short circuit fault. In other words, this paper provided a method that can identify the separator failure before thermal runaway in the aspect of a potential explosion and fire prevention. The internal short circuit signal for diagnosis of LFP pouch cell was investigated by forming artificial defects at the separator part compared with normal battery. To investigate the short circuit signal, artificial defect specimens are prepared as a pouch type, pulse signal was analyzed in terms of pulse waveshape (Skewness) and frequency (Fast Fourier Transform, FFT) compared with normal battery and artificial defect pouch cell. To calculate the continuous acquisition pulse signal, python code was developed. As a result, it is found that the pulse signal of artificial defect specimen shown high frequency and low skewness characteristics. Whereas, in the case of a normal battery, it showed characteristics of relatively low frequency and high or middle skewness. From our research work, the results revealed that the pulse shape and feature contain useful information which can help to understand degradation behavior of the LFP pouch cells. This result is expected to be applicable various batteries with presence a defect at the separator of battery

Triggering and Characterisation of Realistic Internal Short Circuits in Lithium-Ion Pouch Cells—A New Approach Using Precise Needle Penetration

The internal short circuit (ISC) in lithium-ion batteries is a serious problem since it is probably the most common cause of a thermal runaway (TR) that still presents many open questions, even though it has been intensively investigated. Therefore, this article focusses on the generation and characterisation of the local single-layer ISC, which is typically caused by cell-internal impurity particles that cannot be completely eliminated in the cell production. A new, very promising method of precise and slow (1 μm s−1) needle penetration made it possible to generate the most safety-critical reliable short-circuit type—the contact between the Al-Collector and the graphite active material of the anode—as demonstrated on a 10 Ah Graphite/NMC pouch cell. The special efforts in achieving high reproducibility as well as the detailed analysis of the initiated internal short-circuit conditions led to more reliable and meaningful results. A comprehensive approach to characterisation has been made by detailed measurement of the dynamic short-circuit evolution and a subsequent post-characterisation, which included the application of different electrochemical measurement techniques as well as a post-abuse analysis. It was shown that the cells demonstrated a very individual and difficult-to-predict behaviour, which is a major challenge for early failure detection and risk assessment of cells with an existing or former ISC. On the one hand, it is found that despite high local temperatures of over 1260 ∘C and significant damage to the cell-internal structure, the cell did not develop a TR even with further cycling. On the other hand, it was observed that the TR occurs spontaneously without any previous abnormalities. Based on the overall test results, it was shown that at the high state of charge (SOC = 100%), even small, dynamically developing voltage drops (<10 mV) must be classified as safety-critical for the cell. For reliable and early failure detection, the first voltage drops of the ISC must already be detected.