Large-format Li-ion Batteries Research Articles

Thermal runaway front propagation characteristics, modeling and judging criteria for multi-jelly roll prismatic lithium-ion battery applications

Large-format prismatic Li-ion batteries (LIBs) are prominent energy storage devices in electric transportation applications. However, large-format LIB induces severe thermal runaway (TR) disasters. Battery failure commonly initiates from a local point of one jelly roll and then propagates to the whole cell, called thermal runaway front (TRF) propagation. This study investigates the TRF propagation mechanism of multi-jelly roll-based LIBs through experiments, modeling, and theoretical analysis for thermal runaway propagation (TRP) mitigation. Experiments prove that battery venting changes along the jelly roll-safety valve directions during the TRF boundary movement. Besides, TRF propagation speed is found to be accelerated inside each cell (from 3.6 to 10.6 mm/s) during TRP, driven by a significant temperature gradient, chemical reactions, and gas flow along the TRP direction. The in-cell TRF acceleration behavior is more noticeable for batteries with more jelly rolls. The TRF speed-jelly roll index equations are proposed to reveal the propagation acceleration principle mathematically. Furthermore, a thermal-physical model is developed to precisely simulate in-cell TRF propagation behavior, which is validated by experimental data. Moreover, the TRF boundary temperature equation and “No TRP” judging criteria are proposed through theoretical analysis. This study proposes promising strategies for potential TRP suppression, contributing to future safe battery system design.

Distributed Thermal Monitoring for Large-Format Li-Ion Battery Under Limited Sensing

Distributed Thermal Monitoring for Large-Format Li-Ion Battery Under Limited Sensing

Co-estimation of state-of-charge and state-of-temperature for large-format lithium-ion batteries based on a novel electrothermal model

The safe and efficient operation of the electric vehicle significantly depends on the accurate state-of-charge (SOC) and state-of-temperature (SOT) of Lithium-ion (Li-ion) batteries. Given the influence of cross-interference between the two states indicated above, this study establishs a co-estimation framework of battery SOC and SOT. This framwork is based on an innovative electrothermal model and adaptive estimation algorithms. The first-order RC electric model and an innovative thermal model are components of the electrothermal model. Specifically, the thermal model includes two lumped-mass thermal submodels for two tabs and a two-dimensional (2-D) thermal resistance network (TRN) submodel for the main battery body, capable of capturing the detailed thermodynamics of large-format Li-ion batteries. Moreover, the proposed thermal model strikes an acceptable compromise between the estimation fidelity and computational complexity by representing the heat transfer processes by the thermal resistances. Besides, the adaptive estimation algorithms are composed of an adaptive unscented Kalman filter (AUKF) and an adaptive Kalman filter (AKF), which adaptively update the state and noise covariances. Regarding the estimation results, the mean absolute errors (MAEs) of SOC and SOT estimation are controlled within 1% and 0.4 ​°C at two temperatures, indicating that the co-estimation method yields superior prediction performance in a wide temperature range of 5–35 ​°C.

Optimization of LFP Pouch Cell Tab Design for Uniform Temperature Distribution

An increase in the size of large-format Li-ion batteries (LIBs) may lead to nonuniform temperature distribution, which degrades the performance and lifespan of the LIBs. To address this issue, we performed design optimization using a 3D electrochemical-thermal coupled model for 55 Ah LFP/graphite large-format pouch cells. To minimize temperature differences in Normal Tab (NT), Lateral Tab (LT), and Counter Tab (CT) types of LIBs, design optimization was performed on the width, height, and attachment position of each positive and negative Table The upper and lower limits of each design variable were set as constraints without exceeding the sum of the total area of the tabs of the initial NT type. Owing to the optimization of the NT, LT, and CT types, the temperature difference in the optimized CT type was 79.2% less than in the initial NT type. Additionally, the potential difference decreased by 37.1%, minimizing ohmic heat. Aging analysis of 2500 cycles was performed to analyze the improvement in the lifespan due to the uniform temperature distribution. Consequently, the capacity retention rate of the optimized CT type was 6.5% higher than that of the initial NT type. Thus, the temperature distribution and lifespan of LIBs were improved by design optimization.

Detection of jelly roll pressure evolution in large-format Li-ion batteries via in situ thin film flexible pressure sensors

Mechanical pressure develops in Li-ion batteries (LIBs) during operation and is critical to battery performance and safety. Detecting pressures in situ is essential to elucidate the operating mechanisms. However, the feasibility and scalability of the current methods face challenges in practical in-situ measurements given the harsh battery internal environment and shell obstruction, especially for large-format LIBs. This study develops an in-situ measurement method for the mechanical pressure of electrode stacks, referred to as jelly rolls, by using embedded thin-film flexible pressure sensors. Pressure sensors are placed inside a prismatic power LIB, and the pressure behaviors are detected. The experiments demonstrate that this method can be used to inspect the mechanical behavior of the jelly roll over a long operation time. The mechanical pressure generated by the volume expansion of the jelly roll is related to the lithiation and delithiation of the graphite cathode. Both reversible and irreversible pressures can be observed using this method, their evolution characteristics are related to spatial location, charging/discharging rate, external pressure, and electrode stack assembly. The proposed method is promising in detecting the pressure state of LIBs and assisting in the evaluation of battery engineering design, manufacturing, and operation monitoring.

Heat Transfer and Thermal Performance of Large-Format Li-ion Battery Modules Employing PCM with Airgap/Aluminum under Extreme Conditions

For optimum performance of battery modules in electric vehicles (EVs), the temperature of the batteries must be well managed and maintained within a definite range. In this paper, a passive thermal management with phase change material (PCM) is evaluated for prismatic Li-ion battery modules under abusive conditions. The proposed model aims to analyse the thermal performance of battery modules in circumstances the PCM content is reduced due to a leakage and some part of the batteries are exposed to ambient. Two different configurations are considered: one with the top of the batteries exposed to open medium with free air convection, and the other with the top of the batteries exposed to close medium with no air circulation. Comparing the two configurations, the former decreases the maximum temperature in the module by 1.17 K, 1.39 K, 1.63 K and 1.86 K for 2, 4, 6 and 8 mm PCM shrink levels. The effects of aluminum sheet (Al) placed at the top of the battery modules and charge/discharge cycles were also studied.

Development of electrochemical-thermal modelling for large-format Li-ion battery

Considering the non-homogeneous microstructure due to materials and fabrication process of large-format lithium-ion batteries, an effective electrochemical-thermal model is necessary for modern Li-ion battery (LIB) industry. In this work we developed a simplified model by using parallel method to study large-format Li-ion batteries. In particular, an approach in a combination of Maxwell-Cattaneo-Vernotte theory and Marcus-Hush-Chidsey kinetics was developed to determine the effect of lithium ion transport inertia and electron transfer behavior within 3D electrodes. To clearly verify the effectiveness of the developed model, temperature distribution measurements of a 155 Ah prismatic-type Li-ion batteries were carried out by using four built-in temperature sensors during charge and discharge process at different current densities. The simulation error of the studied model is only within 1.7 °C at 1.0C discharge, for 2.0C discharge, the error is 3.9 °C, which provide very strong verifications. We found that the hottest zone inside the battery is around the positive connector. The simulation studies also found that the internal currents of large-format batteries are unstable during constant current discharge process. During a discharge process at 2.0C, local internal current in some areas even reached 6.0C and negative current is also detected as well. This means that the local redox direction can be significantly changed in a large-format LIB. This phenomenon can be explained by the nonuniform distribution of reactant concentration and temperature inside the studied batteries. This work introduced an effective approach to establish a model for LIB industry, which can be used as a fast and accurate diagnosis method to design optimal parameters for large-format LIB batteries.

Amount of Free Liquid Electrolyte in Commercial Large Format Prismatic Li-Ion Battery Cells

The amount of free liquid electrolyte contained in commercial large format prismatic Li-ion battery cells was measured for both fresh and aged cells. Results show that cells can contain free liquid electrolyte in significant amounts - maximum average amount reaching ca. 18 g (>15 ml) in fresh cells of some well-established manufacturers and ca. 39 g (ca. 35 ml) in fresh cells of less-well established manufacturers. Cycle-aged cells were found to contain significantly lower amount of free electrolyte at the end of their life in an electric vehicle (EV) compared to the fresh cells of the same type. Preliminary results suggest that calendar ageing does not seem to noticeably reduce the amount of free liquid electrolyte in Li-ion battery cells. Comparing our findings to our previously published quantitative evaluation of the toxicity of Li-ion battery electrolytes, it can be concluded that an accidental release of the free liquid electrolyte from a single large format Li-ion battery cell can be sufficient for the formation of potentially toxic atmosphere in enclosed spaces.

A Reduced-Order Multi-Scale, Multi-Dimensional Model for Performance Prediction of Large-Format Li-Ion Cells

In this paper, a reduced-order, Multi-Scale, Multi-Dimensional (MSMD) model is developed to achieve accurate and fast simulation of the 2D distribution of thermal and electrochemical properties across the surface of a large-format Li-ion battery cell. Since the proposed model aims at supporting long-term simulation, virtual design and optimization studies, minimization of the computational complexity is achieved through analytical Model Order Reduction (MOR) based on a Galerkin projection method. The model is then verified against experimental data and a high-fidelity numerical model at various input current conditions. Results show that the computational complexity of the MSMD model is significantly reduced without sacrificing the accuracy in characterizing the distribution of the electrochemical and thermal properties. Finally, the impact of the applied current and thermal boundary conditions on the distribution of transverse current density is also evaluated.

FEM Model of the Lithium Ion Battery Nail Test

Internal short-circuit is the most dangerous abusive condition for Li-ion batteries and has been the root cause for several catastrophic accidents involving Li-ion batteries in recent years. Large-format Li-ion batteries are particularly vulnerable to internal short-circuits because of high energy content. Nail penetration test is commonly used to study the internal short-circuits, but the test results usually have poor reproducibility and offer limited insight. This paper deals with a possibility of numerical simulation of internal short circuit test using FEM.

Exploring an Interesting Si Source from Photovoltaic Industry Waste and Engineering It as a Li-Ion Battery High-Capacity Anode

Low cost electrode materials are essential for the expansion of the applications of large-format Li-ion batteries (LIBs). Kerf-loss (KL) Si waste from the photovoltaic industry represents a low cost, high-purity Si source for the production of high capacity anodes of LIBs. Producing an energy storage device from solar-panel industry waste is a potential environment-friendly energy development. This study addressed the challenges of employing KL Si as high-capacity LIB anode. The abrasive SiC particle impurities in KL waste powder were used not only as a milling agent to reduce silicon particle size but also as mechanically and electrochemically robust pillars that resist microstructural degradation of the electrode caused by the expansion of Si during lithiation. High energy ball milling of Si with rigid SiC produced fused nanosilicon particles that were supported on micrometer-sized SiC; this resulted in substantially mitigated capacity fading. In addition, an effective conducting network was formed by i...

Influence of memory effect on the state-of-charge estimation of large-format Li-ion batteries based on LiFePO4 cathode

In this work, we systematically investigated the influence of the memory effect of LiFePO4 cathodes in large-format full batteries. The electrochemical performance of the electrodes used in these batteries was also investigated separately in half-cells to reveal their intrinsic properties. We noticed that the memory effect of LiFePO4/graphite cells depends not only on the maximum state of charge reached during the memory writing process, but is also affected by the depth of discharge reached during the memory writing process. In addition, the voltage deviation in a LiFePO4/graphite full battery is more complex than in a LiFePO4/Li half-cell, especially for a large-format battery, which exhibits a significant current variation in the region near its terminals. Therefore, the memory effect should be taken into account in advanced battery management systems to further extend the long-term cycling stabilities of Li-ion batteries using LiFePO4 cathodes.

A dynamic capacity degradation model and its applications considering varying load for a large format Li-ion battery

The capacity degradation of the lithium ion battery should be well predicted during battery system design. Therefore, high-fidelity capacity degradation models that are suitable for the task of capacity prediction are required. This paper proposes a novel capacity degradation model that can simulate the degradation dynamics under varying working conditions for large-format lithium ion batteries. The degradation model is built based on a mechanistic and prognostic model (MPM) whose parameters are closely linked with the degradation mechanisms of lithium ion batteries. Chemical kinetics was set to drive the parameters of the MPM to change as capacity degradation continues. With the dynamic parameters of the MPM, the capacity predicted by the degradation model decreases as the cycle continues. Accelerated aging tests were conducted on three types of commercial lithium ion batteries to calibrate the capacity degradation model. The good fit with the experimental data indicates that the model can capture the degradation mechanisms well for different types of commercial lithium ion batteries. Furthermore, the calibrated model can be used to (1) evaluate the longevity of a battery system under a specific working load and (2) predict the evolution of cell variations within a battery pack when different cell works at different conditions. Correlated applications are discussed using the calibrated degradation model.

Controlling Factors of Cell Design on Large-Format Li-Ion Battery Safety during Nail Penetration

In this paper we investigate the controlling design parameters of large-format Li-ion batteries on safety while undergoing nail penetration. We have identified three critical design parameters that control the safety during the nail penetration process: nail diameter, single sheet foil area, and cell capacity.Using commercial AutoLion software, we have investigated two typical design problems related to the selection of cell thickness and aspect ratio, namely: (1) the safety ramifications of increasing cell capacity via greater cell thickness for a fixed footprint, and (2) the effect of aspect ratio, or single sheet foil size, on safety at a given capacity. For a fixed footprint, our results indicate that the safety of the cell can be predicted by (Qcell Dnail^-0.5). For a given cell capacity, our results indicate that typically a larger single sheet foil area leads to a greater likelihood for thermal runaway due to its effect of making the heating more local in nature; however, for small cells (~ 5Ah) and large nails (~ 20mm), the greater aspect ratio can lead to a safer cell, as the greater surface area strongly cools the global heating of the cell.

Modeling Nail Penetration Process in Large-Format Li-Ion Cells

Internal short-circuit is the most dangerous abusive condition for Li-ion batteries and has been the root cause for several catastrophic accidents involving Li-ion batteries in recent years. Large-format Li-ion batteries are particularly vulnerable to internal short-circuits because of high energy content. Nail penetration test is commonly used to study the internal short-circuits, but the test results usually have poor reproducibility and offer limited insight. In this work, a 3 D multiscale electrochemical-thermal coupled model is used to investigate the nail penetration process in a large-format Li-ion cell. A parametric study is carried out and the results reveal strong coupling of the cell thermal response and electrochemical behaviour, which is influenced substantially by key parameters including shorting resistance, nail diameter, nail thermal conductivity, and cell capacity. The present study provides some insight that will help design more reliable experimental internal short-circuit testing protocols and improve the abuse tolerance of Li-ion cells.

Cell- and Pack-Level Simulation of Large-Format Li-Ion Battery Safety Events

Owing to their unsurpassed energy density, lithium ion batteries have been adopted for hybridized vehicles, such as the Chevy Volt and the Nissan Leaf, in the aerospace industry, and in stationary energy storage applications. However, as highlighted by several recent high profile safety events, significant challenges remain for the widespread adoption of Li-ion technology in automotive and aerospace applications. These documented safety incidents have been driven by both cell-level and pack level events, and as such, accurate simulation of safety events on both the cell and pack level is needed for fundamental understanding of the underlying physics and safety-conscious design. [1,2,3,4].In this work, using commercially available AutoLion™ software, we demonstrate cell- and pack-level electrochemical/thermal coupled simulation of various types of safety events, including nail penetration, external short, and internal short. Figures 1 and 2 highlight two types of such safety simulations performed. Figure 1 gives the peak temperature of all four cells in a four-cell pack nail penetration; this simulation highlighting the hotter temperature of the interior cells during multi-cell short. Figure 2 illustrates the voltage and current response of an externally-shorted 25Ah L-ion ion cell. In our presentation, we elucidate on the physics of these shorts on both the cell- and pack-level, and demonstrate how simulation can be used to screen various cell and pack designs for safe implementation of safe Li-ion battery technologies. Acknowledgements Partial support of this work by DOE CAEBAT2 program is greatly acknowledged.

Effect of tab design on large-format Li-ion cell performance

Large-format Li-ion batteries are essential for vehicle and grid energy storage. Today, scale-up of Li-ion cells has not maximized the potential of available battery materials, leading to much lower energy density than their coin cell benchmarks. In this work, a 3D computational methodology based on physical and electrochemical principles underlying Li-ion cells is developed for the design of large cells. We show a significant increase in the cell's usable energy density by minimizing voltage losses and maximizing the utilization of active materials in a large cell. Specifically, a class of designs using multiple current-collecting tabs are presented to minimize in-plane electron transport losses through long electrodes, thereby achieving nearly the same energy density in large-capacity cells as would be expected from battery materials used. We also develop a quantitative relation between the current density non-uniformity in a large-format cell and the cell's usable energy density, for the first time, in the literature.

Effects of Non-Uniform Current Distribution on Energy Density of Li-Ion Cells

To quantify the impact of non-uniform current distribution in a large-format Li-ion cell on its overall energy density, five cell configurations with different positive tab numbers and locations were developed. This was enabled by a specially designed segmented cell with reconfigurable positive tabs on the outside. Current distribution and overall discharge performance were measured and correlated with each other for all five cell configurations. It is shown that tab number and location have significant effects on the performance and current distribution of a Li-ion battery cell. Fewer tabs typically cause lower performance but excessive tabs do not help. The 1-tab-co-located configuration causes both very non-uniform current distribution and very low overall discharge performance, and should be avoided in tab design for cells bigger than ∼2.4Ah. The effects of tab configuration on overall performance can be attributed to and explained by current distribution. Discharge energy of the experimental cell decreases almost linearly with a current density non-uniformity factor. Non-uniform current distribution results in non-uniform utilization of active materials, reducing energy density, and likely also accelerating degradation of the Li-ion cell. Future research on diagnosing and improving current density uniformity in large format Li-ion batteries that enable vehicle- and grid-energy storage is highly warranted.

Understand Degradation of Large Format Li-Ion Battery by In Situ Neutron Diffraction at SNS

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The electrochemical insertion and safety properties of the low-cost Li-ion active material, Li 2FeS 2

The electrochemical insertion properties and safety characteristics of the alternative Li-ion positive electrode material, lithium iron sulfide (Li 2FeS 2) are presented. The active material is synthesized by a low cost, proprietary solid-state method. In terms of specific energy, the Li 2FeS 2 material offers a significant advantage over conventional lithium-ion positive electrode materials. The fully de-lithiated (charged) Li 2− x FeS 2 phase also demonstrates outstanding thermal stability suggesting that it may represent an excellent choice for safe, large format Li-ion battery applications.