Safety Of Lithium-ion Batteries Research Articles

Enhancing lithium-ion battery safety: Investigating the flame-retardant efficacy of bis(2,2,2-trifluoroethyl) carbonate during ethyl methyl carbonate combustion

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a candidate fire suppressant for lithium-ion batteries (LIBs). The high flammability of the electrolyte is the reason behind the frequent fire incidents reported with LIBs. These incidents are due to various factors, such as a default in the conception of the battery or operational abuse. The flame-retardant effectiveness of BtFEC was investigated by measuring its effect on the oxidation of ethyl methyl carbonate (EMC), a common LIB electrolyte component. Laminar flame speed (LFS) measurements for EMC-BtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (ϕ) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at ϕ = 1.1 with BtFEC addition ranging from 0.1 up to 1.4 % vol. To further understand the combustion chemistry of the EMC-BtFEC system, ignition delay times (time at the maximum peak production of the excited radical OH*) and CO time histories were measured in a shock tube with temperatures ranging from 1217 to 1732 K, at near-atmospheric pressure (1.24–1.42 atm), and for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0). These new results constitute an experimental database that was used to evaluate the performance of a model assembled for both BtFEC and EMC using previous work from our group. The updated, detailed chemical kinetics mechanism presented in this study consists of 237 species and 1630 reactions. Sensitivity, rate-of-production, and reaction pathway analyses permitted the oxidation of the BtFEC-EMC system to be described. A flame sensitivity analysis exhibited the significant effect from the reactions H + CF2O ⇆ HF + CFO and CF3 + H ⇆ CF2 + HF, which consume H radicals that are involved in the branching reaction H + O2⇆ OH + O, ultimately reducing the LFS. This study shows that improvements in the base fluorine chemistry are still necessary to obtain better agreement with the experiments, especially at the speciation level.

Multi-sensor multi-mode fault diagnosis for lithium-ion battery packs with time series and discriminative features

Sensor fault diagnosis is essential to guaranteeing the safety of lithium-ion batteries. To address the general drawbacks of the existing diagnosis methods, including the difficulty in determining the threshold, inability to handle multiple faulty sensors concurrently, and limited capacity in identifying fault modes, a multi-sensor multi-mode fault diagnosis method for lithium-ion battery packs is proposed. The proposed method utilizes time series and discriminative features to accomplish sensor-specific fault detection and fault mode identification. First, a total of 18 general time series features are extracted to characterize the measurements of each sensor during each charge–discharge cycle. Principal component analysis is then used to reduce the high-dimensional feature space to a two-dimensional space, such that fault detection can be carried out with the α-hull algorithm. For the detected faulty samples, a two-layer identification algorithm is designed based on three discriminative features, namely, correlation coefficient, impulse factor, and Hurst coefficient, to identify the specific fault modes. The diagnostics can decouple the information from different types of sensors so that the proposed method can effortlessly isolate current, voltage, and temperature sensors that are concurrently experiencing faults. Ultimately, experimental results from three scenarios, including simultaneous failure of multiple sensors, substantiate the effectiveness and feasibility of the proposed method.

Design of β-Mo2C with an appropriate intercalation potential as an anode material toward lithium ion batteries

The advancement of innovative Mo2C anode yet faces the challenge of exploring a simple, convenient and controllable synthetic route. β-Mo2C was prepared by utilizing low-cost hexamethylenetetramine and ammonium molybdate as raw materials and employing simple calcination treatment under N2 atmosphere. When applied as an anode for lithium ion batteries (LIBs), β-Mo2C delivers a satisfactory rate performance (147.0 and 103.4 mAh g−1 at 0.5 and 1.0 A g−1) and excellent cyclic stability (72.2 mAh g−1 at 2.0 A g−1 after 1500 cycles). Meanwhile, a suitable voltage plateau at ∼1.4 V for β-Mo2C also avoids the formation of lithium dendrites to improve the safety of LIBs.

New insight into the interaction between maleic anhydride grafted polypropylene and aluminum foil converted with trivalent chromate: An experimental and DFT study

The good adhesion between layers of aluminum (Al)/polymer composite is necessary for the safety of lithium-ion batteries. The Al foil was converted with environmentally friendly trivalent chromate [Cr(III)] to enhance its adhesive strength with the inner adhesive layer. The morphology, composition and adhesive strength with maleic anhydride grafted polypropylene (mPP) of different Cr-converted Al foils were studied. The Cr conversion coating mainly consists of metal oxides and hydroxides and the interfacial adhesion strength is enhanced by 93 % through Cr(III) conversion treatment. The effect of Cr conversion on the acid-base characteristics on the Al was determined through contact angle measurement. The results reveal that Cr conversion increases the acidity of the Al surface. The bonding mechanism at the interface was further studied fundamentally. To study the reaction at the interface mPP/Al foils, a coating-evaporation technique was utilized to fabricate a nano-thick mPP layer on the Al foils. The morphology and thickness of the mPP coating on the substrate were analyzed using atomic force microscopy and the interfacial reaction was characterized through attenuated total reflection-Fourier Transform Infrared Spectroscopy. The bonding mechanism at the molecular level was further investigated by quantum chemical calculations based on density function theory. The results of theoretical calculations further indicate that the strength of the interfacial interaction between mPP and Cr oxides and hydroxides is stronger than that between mPP and Al oxides and hydroxides.

Heat Generation Mechanisms of 18650 Lithium-Ion Battery Cells: An in-Depth Analysis

Lithium-ion batteries are known for their exceptional properties such as high energy density and long-life cycle, making them popular in various applications, including electric vehicles and energy storage systems. However, the growing concern over the safety of lithium-ion batteries in hot environments with limited cooling has prompted an in-depth analysis of their heat generation mechanisms.To address this concern, it is important to understand the heat generation mechanisms of lithium-ion batteries. In this study, we conducted an in-depth analysis of the heat generation mechanisms of 18650 lithium-ion battery cells. We investigated the impact of temperature on the primary aging mechanisms of the batteries, such as capacity fade and impedance growth. We also studied the thermal behavior of the batteries, including the heat generation and thermal stability.Our analysis involved the disassembly of both fresh and aged 18650 lithium-ion battery cells, followed by a physico-chemical analysis on the electrodes at the microscale level to investigate the chemical and physical changes in the electrodes. We used advanced techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to analyze the cells.Our results showed that high temperatures can accelerate the chemical reactions within the battery, leading to an increase in heat generation. We also found that the aged battery cells had a higher degree of degradation in the electrodes compared to the fresh cells, which affected the battery's overall performance. Our analysis revealed changes in the surface morphology of the electrodes, which could impact the thermal behavior of the battery.During the presentation, I will delve into the specific findings of our analysis of the 18650 lithium-ion battery cells. I will provide a more detailed explanation of the state of health, capacity fade, and impedance growth of the batteries, including how these aging mechanisms were affected by the high temperatures. Additionally, I will discuss the specific changes observed in the electrodes, such as the changes in the surface morphology, and how they impacted the battery's overall performance.Overall, the presentation will provide a comprehensive overview of our study's findings and their significance for the future of lithium-ion batteries in high-temperature environments.

Swelling of Polypropylene Separators and Its Effect on the Lithium-Ion Battery Performance

The safety of lithium-ion batteries (LIBs) depends on separators -- porous materials providing ionic transport between the electrodes while preventing them from direct contact. Many commercial separator materials are polymers, e.g., polypropylene. Polypropylene has a non-polar structure, so it tends to interact favorably with non-polar solvents, such as carbonates used in LIBs as electrolyte solvents. These favorable interactions result in two effects: separator plasticization (softening) [1] and swelling [2]. Both swelling and plasticization affect the battery performance and cause safety concerns.Here we present a model which predicts the swelling of a porous polymer separator based on the molecular structures of the polymer and the solvent. The model is based on Flory's theory of polymer solutions and the Flory–Huggins parameter for polymer–solvent interactions. We introduced two additional parameters to Flory's theory, taking into account the complex structure of the porous polymers. These two parameters can be obtained from experimental data on two solvents. The Flory–Huggins parameter is calculated based on the UNIFAC-FV group contribution method for a given polymer–solvent pair. Our model predicts swelling of polypropylene separators in various solvents, matching the experimental data [3] quite well. By relating the swelling of the separator to the change in its porosity and tortuosity, we estimated the increase of cell impedance as a result of the swelling.Finally, the plasticization of the separator makes it less persistent to mechanical impacts, increasing the chances of failure. Since the solvent-induced plasticization of the separator is correlated with its swelling [3], our model can also be utilized to assess this effect. Therefore, our model can be used to quickly evaluate various polymer–solvent pairs for application in lithium-ion batteries.1. Sheidaei, A.; Xiao, X.; Huang, X.; Hitt, J. Mechanical behavior of a battery separator in electrolyte solutions. J. Power Sources 2011, 196, 8728−8734.2. Cannarella, J.; Liu, X. Y.; Leng, C.; Sinko, P.; Gor, G. Y.; Arnold, C. B. Mechanical properties of a battery separator under compression and tension. J. Electrochem. Soc. 2014, 161, F3117−F3122.3. Gor, G. Y.; Cannarella, J.; Leng, C. Z.; Vishnyakov, A.; Arnold, C. B. Swelling and softening of lithium-ion battery separators in electrolyte solvents. J. Power Sources 2015, 294, 167−172.4. Maksimov, A. V.; Molina, M.; Maksimova, O. G.; Gor, G. Y. Prediction of Swelling of Polypropylene Separators and Its Effect on the Lithium-Ion Battery Performance. ACS Appl. Polym. Mater. 2023, 5(3), 2026-2031.

Carbon: A Ubiquitous Electrode Material for Lithium-Based Rechargeable Batteries

In recent times, research has been directed to develop high-capacity anodes along with high-energy-density (high capacity and high voltage) and safe Lithium-ion battery (LIB) cathodes to power electric vehicles (EV’s). State-of-the-art lithium-ion cells use layered transition metal oxides (LiCoO2, LiNi1/3Mn1/3Co1/3 or LiNi0.8Co0.15Al0.15O2), or Phosphates (LiFePO4), Mn-based spinels (LiMn2O4) as cathodes and graphitic carbon as anode [1-2]. The nominal capacities of most of these cathodes range between 140-180 mAh g-1 when cycled up to 4.2 V. This is only half the specific capacity of graphite anode (372 mAh g-1). Thus, there has been intense research activity in the last decade to develop high-capacity anodes or high energy (high capacity and high voltage) and safe cathodes for lithium-ion batteries (LIBs) [1-2].Eliminating binders and carbon diluents and replacing carbon fiber-based 3D electrode architectures can improve the capacity utilization and C-rate performance, thereby improving energy density, cycle life, and safety of LIBs. The presentation will be focused on the development of organic binder and conducting diluent-free carbon fiber-based 3D electrodes architectures for LIBs, where the conventional copper (Cu) and aluminum foil (Al) foil current collectors are replaced with highly conductive carbon fibers (CFs). In this approach, the petroleum pitch (P-pitch) is used as a binder that adequately coats between the CFs and active nanoparticles (NPs) at high temperatures to form a uniform continuous layer of carbon coating along the exterior surfaces of NPs and 3D CFs. As a result, the electrodes assembly delivers superior electrochemical performances than conventional electrode fabrications. 3D electrode architecture of LiFePO4, FeF3, Li2MnSiO4 cathodes, and Si-C anodes will be presented [3-5].Dual carbon batteries (DCBs) based on LIB electrolytes have been evolving in recent times [5]. In DCBs, both electrodes consist of carbonaceous materials, and the ions from the electrolyte intercalate and deintercalate into the electrode matrix. During the charge, the cations and anions get inserted into the anode and cathode, respectively, and during discharge, the process is reversed. A DCB based on the 3D electrode architecture of carbon (zero transition metal ion) will be discussed. A DCB based on fully graphitic carbon fiber can have a nominal voltage of 4.65 V and can deliver energy densities of 92.7, and 110.9 Wh kg−1 at a power density of 114 W kg−1 for the cells cycled at 3.0–5.0 and 3.0–5.2 V, respectively. It is believed that the study presented here may contribute to the future development of carbon fiber-based dual-carbon and lithium-ion batteries.

Forming Artificial Solid-Electrolyte-Interfaces between Lithium Metal Anodes and Halide and Sulfide Solid Electrolytes in All-Solid-State-Batteries Via Spatial-Atomic-Layer-Deposition

Increasing need in energy density and safety of current lithium-ion batteries has resulted in a search for next generation battery technologies1,2. All-solid-state-batteries (ASSBs) could answer these needs owing to the use electrode materials with higher capacities and potential difference, and by replacing flammable liquid electrolytes with solid electrolytes3,4. ASSBs using inorganic sulfide and halide solid electrolytes in particular have drawn a lot of attention as the electrolytes have very high RT ionic conductivities (>10-3 S.cm-1)5–7. Nevertheless, they suffer from issues related to electro-chemical and chemo-mechanical stabilities at electrode – electrolyte interfaces7,8. One promising approach to mitigate this issue is depositing an artificial solid-electrolyte-interface (SEI) layer via atomic-layer-deposition (ALD)9–11. In this work, we deposited a variety of artificial layers with different thicknesses and chemistries on the lithium metal anode using spatial ALD. We characterized the bonding within the thin film layer using X-ray photoelectron spectroscopy, and evaluated the stabilizing effect of the artificial SEI layer using electrochemical impedance spectroscopy and galvanostatic lithium plating and stripping methods. We compared the growth of lithium dendrites within the solid electrolyte pellets post-mortem analysis via scanning electron microscopy. J. Janek and W. G. Zeier, Nat. Energy (2023) https://www.nature.com/articles/s41560-023-01208-9.Q. Wang, L. Jiang, Y. Yu, and J. Sun, Nano Energy, 55, 93–114 (2019) https://doi.org/10.1016/j.nanoen.2018.10.035.J. B. Goodenough and M. H. Braga, Dalt. Trans. (2017) http://xlink.rsc.org/?DOI=C7DT03026F.J. Janek and W. G. Zeier, Nat. Energy, 1, 16141 (2016) http://www.nature.com/articles/nenergy2016141.R. Schlem et al., Adv. Energy Mater., 11, 2101022 (2021) https://onlinelibrary.wiley.com/doi/10.1002/aenm.202101022.S. Ohno et al., Prog. Energy, 2, 022001 (2020) https://iopscience.iop.org/article/10.1088/2516-1083/ab73dd.T. Koç, F. Marchini, G. Rousse, R. Dugas, and J. M. Tarascon, ACS Appl. Energy Mater., 4, 13575–13585 (2021).Y. He, C. Lu, S. Liu, W. Zheng, and J. Luo, Adv. Energy Mater., 9, 1–40 (2019).L. Han, C. Te Hsieh, B. Chandra Mallick, J. Li, and Y. Ashraf Gandomi, Nanoscale Adv., 3, 2728–2740 (2021).J. Liu and X. Sun, Nanotechnology, 26, 24001 (2015) http://dx.doi.org/10.1088/0957-4484/26/2/024001.Y. Jiang et al., Energy Storage Mater., 28, 17–26 (2020) https://doi.org/10.1016/j.ensm.2020.01.019.

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.

Increasing Battery Safety of Lithium-Ion Batteries by Using Cell-Internal Glass Fiber Sensors for in-Situ Temperature Monitoring

Lithium-ion batteries (LIB), featuring high energy density and power density, are used in a wide range of applications. One of the most important requirements for their application is to ensure their safety and continuous performance under different operating conditions. In order to ensure the afore mentioned factors, in-situ monitoring of internal cell parameters, such as temperature, state-of-charge, and state-of-health of LIB is essential. The cell temperature is a critical factor for both the safety and the LIB’s health. Not only the average temperature, but also the temperature distribution within the cell must be considered. However, common battery management systems mostly rely on monitoring the surface temperature of the cells, while neglecting changes of the internal parameters. This is where the integration of optical glass fiber sensors into battery cells, which allow direct monitoring of internal temperature changes during operation, makes a significant contribution.In this work, different approaches for the integration of optical glass fiber sensors into battery cells have been evaluated. The focus was set on the complete integration of the glass fiber at specific positions within the LIB, while ensuring that both, the glass fiber, and the battery components remain intact. Furthermore, the influence of the integrated glass fibers on the performance of the LIB was investigated. Finally, their functionality as temperature sensors was evaluated.In a second step, temperature measurements were performed on LIB during operation, using both internal and external sensors. The results obtained clearly reveal an early detection of temperature changes by internal glass fibers compared to external sensors. This not only confirms the efficiency of the internal sensors, but also leads the path to improved battery safety by early detection of critical temperatures within the cell.

Towards Safer Batteries- 4D Imaging of Abuse Mechanisms in Lithium-Ion Batteries Using Synchrotron X-Ray Computed Tomography

Higher energy density materials are being pushed by the research community to make lithium-ion batteries a better competitor to chemical fossil fuels for transport applications. This increases potential risk of lithium-ion batteries and therefore safety investigations are highly important for application purposes. Operando Computer Tomography provides a non-destructive investigation method of different abuse mechanisms.Application of X-ray computed tomography (XCT) for studying lithium-ion batteries has gained interest among the research community especially in the past decade [1]. This technique is widely used for ex-situ samples to measure porosity and tortuosity [2], particle size and volume distribution [3] in the graphite anode as well as different cathode materials such as LiCoOx and NiMnCoOx. [4]. In situ measurements of commercial batteries are also often carried out to detect defects induced in a cell by a safety abuse test or manufacturing process [5]. Operando CT of large cells (for example 18650 form factor) is conducted at synchrotron facilities with high flux of high energy photons, however at a cost of details due to the large field of view [6].Thanks to their high brilliance, synchrotron beam facilitates us to do a full Computed Tomography in a short time. This enables us to measure batteries while being cycled with a reasonable time resolution to record morphological changes. In this presentation we illustrate how one can utilize this ability to investigate abuse mechanisms on an actual commercially available lithium-ion battery from cell level to electrode level.In this work, lab-based and synchrotron X-ray computed tomography is applied to commercial lithium-ion batteries. It is shown how to find most suitable imaging settings to study available lithium-ion batteries on different size scales, from cell level to particle level. We also demonstrate how to optimize contrast as well as both temporal and spatial resolutions to study in-situ and operando processes in a commercial battery using attenuation and phase contrast SXCT. Manufacturing defects and inconsistencies on cell level as well as the electrode and microstructure on material level are shown in our study.Using the presented methodic, some abuse conditions are induced and imaged in operando on a commercially available li-ion battery. In this work, deep discharge mechanism is visualized and quantified in detail for the first time in 4 dimensions.This oral presentation is aimed to present SXCT and lab XCT imaging as an important tool for studying state of safety of lithium-ion batteries from cell level down to particle level. It is shown how to find most suitable imaging settings to study available lithium-ion batteries on different size scales. We also demonstrate how to optimize contrast as well as both temporal and spatial resolutions to study in-situ and operando processes in a commercial battery using attenuation and phase contrast SXCT. Manufacturing defects and inconsistencies on cell level as well as the electrode and microstructure on material level are shown in our study. Moreover, some abuse conditions are imaged in operando in a commercially available li-ion battery. Le Houx, J. and D. Kramer, X-ray tomography for lithium ion battery electrode characterisation — A review. Energy Reports, 2021. 7: p. 9-14. Eastwood, D.S., et al., The application of phase contrast X-ray techniques for imaging Li-ion battery electrodes. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014. 324: p. 118-123. Finegan, D.P., et al., Investigating lithium-ion battery materials during overcharge-induced thermal runaway: an operando and multi-scale X-ray CT study. Phys Chem Chem Phys, 2016. 18(45): p. 30912-30919. Ebner, M., et al., Tortuosity Anisotropy in Lithium-Ion Battery Electrodes. Advanced Energy Materials, 2014. 4(5). Patel, D., et al., Thermal Runaway of a Li-Ion Battery Studied by Combined ARC and Multi-Length Scale X-ray CT. Journal of The Electrochemical Society, 2020. 167(9). Finegan, D.P., et al., In-operando high-speed tomography of lithium-ion batteries during thermal runaway. Nat Commun, 2015. 6: p. 6924.

Solid-State NMR Revealing the Impact of Polymer Additives on Li-Ion Motions in Plastic-Crystalline Succinonitrile Electrolytes

To enhance the safety of lithium-ion batteries (LIBs), alternatives to liquid electrolytes are widely studied. One of them is the plastic-crystal succinonitrile (SN) which can solvate various Li salts.[1] This system can be further extended by inserting polymers, bringing additional advantages such as higher melting points and the possibility of adjusting thermo-mechanical and electrochemical properties.[2]The plastic-crystalline electrolyte consisting of the Li salt lithium bis(trifluoro-methanesulfonyl)imide (LiTFSI) dissolved in SN was extended by adding various thermoplastic polymers, namely, polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polyethylene carbonate (PEC), and polyvinylpyrrolidone (PVP). Even small amounts (10 wt %) of added polymer to the SN-base were found to impact the Li-ion mobility. Variable temperature investigations on structure and ion dynamics were performed using static and magic angle spinning (MAS) solid-state NMR and various relaxometry measurements. Influence of the Li-concentration and the polymers’ functional groups on the structure of SN and the resulting Li-ion mobility was elaborated. Activation energies and jump rates of the Li-ions were determined.As a result, the PAN containing system stands out to be a promising candidate for application in future LIBs as it shows high ion mobility, low activation energy, and a high potential for further modifications. Solid-state NMR turned out to be a reliable method and a good alternative to impedance spectroscopy measurements for investigating ion mobility behaviour providing even more information.[3]Literature:[1] S. Long, D. R. MacFarlane, M. Forsyth, Solid State Ionics 2004, 175, 733.[2] N. Voigt, L. van Wüllen, Solid State Ionics 2014, 260, 65.[3] J. Möller, V. van Laack, K. Koschek, P. Bottke, M. Wark, J. Phys. Chem. C 2023, 127, 1464.

Needle Penetration Studies on the Dynamics during Internal Short Circuits in Automotive Lithium-Ion Cells: Measurement of Internal Temperature and Short Circuit Current

Lithium-ion batteries (LIBs) have been widely applied in consumer electronic devices and electric vehicles for energy storage. Especially for the battery electric vehicles (BEVs), it is desirable to increase the volumetric energy density of LIB cells due to the limitation of a further volumetric expansion of the battery pack, which amounts to currently 220-400 L depending on the size of the BEV [1]. As an example, the capacity of the Li-ion battery pack in BMW i3s has been improved from 60 Ah over 94 Ah to 120 Ah over the course of a few years. Along with this trend of increasing energy density, however, the reactivity of the cells is increasing. Therefore, the potential safety issues are becoming more important. Between 2015 and 2018, a total of 15 fire incidents of BEVs were reported in Europe. In 2019, 113 fire incidents took place only within China [2]. Considering the decision by the European Union to ban the sale of new petrol and diesel vehicles from 2035, this concern with regards to the safety of LIBs would be growing progressively with the accelerated switch to BEVs.One of the main causes for a thermal runaway is an internal short circuit (ISC) [1,3]. Under many different abuse scenarios, ISC appears to trigger the thermal runaway (TR); (i) mechanical abuse (deformation of separator leading to ISC),(ii) electrical abuse (separator pierced by dendrite resulting to ISC) or iii) thermal abuse (shrinkage or melting of separator causing ISC) [1]. Nail penetration tests have been widely used to reproduce ISCs. Only the temperature on the cell surface and the cell voltage are measured in a conventional nail penetration test. However, there is also a challenge to understand the internal dynamics in a Li-ion cell in which an ISC takes place [4]. This study introduces an advanced needle penetration test that enables the measurement of both the internal temperature and the ISC current.As seen in Figure 1 (a), the amount of ISC current can be measured indirectly by replenishing the lost cell capacity from ISC with a power supply that is set to constant voltage mode (in this case, 4.2 V) and connected to the cell via a shunt. Additionally, the internal temperature can be measured using a thermocouple which is embedded in a specially crafted probe. The needle penetrates Li-ion cells with a slow penetration speed of 0.01 mm/s to understand the effect of piercing individual layers on the ISC with regard to electrical and thermal behaviour.Figure 1 (b) presents the ISC current and the internal temperature measured using this method. In the unstable ISC current signal, sharp periodical peaks are detectable. It is assumed that the ISC current is constantly increasing by several layer-to-layer shorts adding up and that its periodically decreasing profile originates from the increasing contact resistance by cell layers melting or being ruptured. Since thermal energy emerges from the ISC current, the internal temperature fluctuates dynamically corresponding to the ISC current profile, while surface temperature signals do not show any changes. This advanced needle penetration test offers the great research possibility to understand the internal dynamics of ISC that has been barely studied and to determine the internal onset cell temperature for TR.[1] X. Feng et al Energy Storage Mater., 10, 246 (2018).[2] Y.S. Duh et al J. Energy Storage, 41, 102888 (2021).[3] D.P. Finegan et al J. Electrochem. Soc., 164 , A3285 (2017).[4] S. Huang et al J. Electrochem. Soc., 167, 90526 (2020). Figure 1

Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries with Enhanced Safety and High-Temperature Performance

Lithium-ion batteries (LIBs) have become dominant power sources for various applications such as mobile electronics, electric vehicles and energy storage systems. However, liquid electrolytes currently used in LIBs have critical drawbacks such as flammability and leakage problem. In this regard, various electrolyte systems have been developed to enhance the battery safety while maintaining cycling performance. Among them, the chemically cross-linked gel polymer electrolytes (GPEs) can enhance the thermal safety of LIBs by effectively encapsulating organic solvents in the polymer matrix. However, they usually contain large amounts of organic solvents to achieve high ionic conductivity, making GPE be still flammable. To solve these problems, we designed and synthesized a novel phosphorus-based cross-linking agent with excellent flame retardancy. GPE was prepared by in-situ thermal curing of gel precursor containing liquid electrolyte and phosphorus-based cross-linking agent. The obtained GPE exhibited high ionic conductivity and nonflammability. The GPE was applied to lithium-ion cells composed of graphite anode and LiNi0.6Co0.2Mn0.2O2 cathode. Our results revealed that the lithium-ion cell employing GPE exhibited enhanced safety and improved high-temperature cycling performance compared to the cell with the liquid electrolyte.

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium-Ion Batteries with Enhanced Cycle Life and Thermal Safety.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8 Co0.1 Mn0.1 O2 /SiOx -graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6 -carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium‐Ion Batteries with Enhanced Cycle Life and Thermal Safety

AbstractHigh energy density lithium‐ion batteries (LIBs) adopting high‐nickel layered oxide cathodes and silicon‐based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano‐groups (−CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2‐dihydroxyethane‐1,1,2,2‐tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8Co0.1Mn0.1O2/SiOx‐graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6‐carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat‐resistant cyano‐enriched CEI layer as well as a stable LiF‐enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal‐induced gassing and total heat‐releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high‐nickel NCMxyz cathode and silicon‐based composite anode.

Aligned NMC811 electrodes by functionalized conductive graphite flakes for fast-charging Li-ion battery

In recent years, the demand for high capacity, long cycle life, fast charging, and increased safety lithium-ion batteries has become increasingly urgent, especially in the electric vehicle industry. The specific capacity of Li-ion batteries is growing steadily under the great efforts of researchers. However, fast charging, as one of the key technologies of lithium-ion batteries, is still not fully and efficiently resolved. Electric vehicles now have a sufficient driving range, but they take too long to refill compared to traditional vehicles. Here, we aligned polycrystalline NMC 811 microparticles by functionalized graphitic flakes (conductive graphite KS6) under a rotating magnetic field by 2 steps in the cathode fabrication process and constructed an effective and fast conducting three-dimensional conductive network for both electron and ion transport in the cathode system of a high-rate performance Li-ion battery. We successfully regulate and control the tortuosity and porosity of the NMC811 cathode on the electrode level. The new electrode structure has higher ionic conductivity and higher specific capacity. The specific capacity of the electrode with the new electrode structure is about four times and five times the reference electrode at 5 C and at 10 C, respectively. And, the half-cell of the electrode can be fed with 70 % SOC in a 6-min charge at 5 C.

Amorphization of Inorganic Solid Electrolyte Interphase Components and Its Impact on Enhancing Their Transport and Mechanical Properties.

The safety and cycle life of lithium-ion batteries (LIBs) are largely determined by the solid electrolyte interphase (SEI) formed on the surface of the anode. However, there is still a lack of understanding regarding the structure and properties of the individual SEI components. Among others, lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium fluoride (LiF) are known to be the main components of the inorganic SEI layer in conventional LIBs, but their intrinsic protective roles remain controversial. Herein, we present the transformational effects of their amorphous phase on the mechanical and transport characteristics, based on first-principles calculations. Our studies clearly demonstrate that their amorphous phases exhibit significantly improved Li-ion conductivity when compared to the crystalline structures. Additionally, among them, amorphous LiF emerges as a frontrunner for fast Li+ ion transportation, reversing the conventionally understood hierarchy. Under ambient conditions, the amorphous phases of LiF, Li2O, and Li2CO3 are thermodynamically unstable and tend to undergo recrystallization. However, this work highlights that exceptionally ductile and resilient amorphous phases can form if SEI formation and growth would involve some admixing of lithiophilic impurities like nitrogen (N) within the host matrices.

A Thermal-Ball-Valve Structure Separator for Highly Safe Lithium-Ion Batteries.

The separator located between the positive and negative electrodes not only provides a lithium-ion transmission channel but also prevents short circuits for direct contact of electrodes. The inferior dimension thermostability of commercial polyolefin separators intensifies the thermal runaway of batteries under abuse such as short circuits, overcharge, and so on. a polyvinylidene fluoride/polyether imide (PVDF/PEI) separator with high thermal stability in which the high thermostable PEI microspheres are evenly dispersed in the PVDF film matrix and also located in the micro holes of the PVDF film is developed. They not only function as strong skeleton that enables the rare shrink of the separator at 200°C avoiding short circuit but also act as ball valve that blocks the lithium ion transmission channel at 150°C interrupting the further heat aggregation. Thus, the LiNi0.6Co0.2Mn0.2O2/Li batteries exhibit high cycle stability of 96.5% capacity retention after 100 cycles at 0.2C and 80°C. Further, the LiNi0.6Co0.2Mn0.2O2/graphite pouch cells are constructed and deliver good safety performance without smoke release and catching fire after the nail penetration test.

Li-Ion Battery Immersed Heat Pipe Cooling Technology for Electric Vehicles

Lithium-ion batteries, crucial in powering Battery Electric Vehicles (BEVs), face critical challenges in maintaining safety and efficiency. The quest for an effective Battery Thermal Management System (BTMS) arises from critical concerns over the safety and efficiency of lithium-ion batteries, particularly in Battery Electric Vehicles (BEVs). This study introduces a pioneering BTMS solution merging a two-phase immersion cooling system with heat pipes. Notably, the integration of NovecTM 649 as the dielectric fluid substantially mitigates thermal runaway-induced fire risks without requiring an additional power source. Comprehensive 1-D modeling, validated against AMESim (Advanced Modeling Environment for Simulation of Engineering Systems) simulations and experiments, investigates diverse design variable impacts on thermal resistance and evaporator temperature. At 10 W, 15 W, and 20 W heat inputs, the BTMS consistently maintained lithium-ion battery temperatures within the optimal range (approximately 27–34 °C). Optimized porosity (60%) and filling ratios (30–40%) minimized thermal resistance to 0.3848–0.4549 °C/W. This innovative system not only enhances safety but also improves energy efficiency by reducing weight, affirming its potential to revolutionize lithium-ion battery performance and address critical challenges in the field.