Lithium-ion Cells Research Articles

Electrochemical Performance of Lithium-Ion Cells with Lithium- and Manganese- Rich Oxide Cathodes

State-of the-art (SOA) lithium-ion batteries (LIBs) being developed for transportation applications contain a transition metal (TM) oxide cathode and a graphite anode; both serve as host-matrices to house lithium ions during battery operation. The cathodes typically contains Li1+xNiaCobAlcO2 (NCA) or Li1+xNiaMnbCocO2 (NMC) oxides: both oxide chemistries contain Co, which is known to preserve the layered structure during lithium extraction/insertion reactions. However, the possibility of a global Co shortage and soaring costs has galvanized the LIB community to explore sustainable cathode chemistries, while maintaining cell performance (energy/power densities), safety and cycle/calendar life. In this context the U.S. Department of Energy (DOE) initiated the Earth-Abundant Cathode Active Material (EaCAM) Program for the development of sustainable cathode chemistries, based on earth-abundant elements.Materials of particular interest to the EaCAM program are the x Li2MnO3 ● (1-x) LiMnaNibZcO2 composites; here Z refers to various elements that could be included in the oxide structure. These lithium- and manganese- rich materials are considered attractive candidates because of their high specific capacities, zero cobalt content, and lower costs compared to the SOA oxides. We have been examining the electrochemical behavior of cells with these oxides, with a particular focus on the 0.3 Li2MnO3 ● 0.7 LiMn0.5Ni0.5O2 (LMR) compound.During this presentation, we will show results from battery cells, containing LMR cathodes and either graphite or lithium-titanate anodes. In particular, the use of a microprobe reference electrode to monitor the cathode and anode potentials will be discussed. The effect of activation on cell performance and the performance loss characteristics during cycling will be highlighted. We will show how cell impedance is affected by voltage hysteresis and the voltage fade that results from cycling. Our ultimate goal is to identify constituents and mechanisms responsible for the cell performance loss and develop solutions to mitigate this degradation.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Investigating Temperature-Dependent Dynamics of SEI Growth and Battery Degradation

Several studies have contributed to the current understanding of the temperature-dependent behavior of solid-electrolyte interphase (SEI) formation in lithium-ion batteries and its impact on battery capacity and lifespan. Liu et al. developed a thermal-electrochemical model that revealed the complex interplay between diffusivity, reaction kinetics, and temperature on SEI growth1. Leng et al. presented an electrochemistry-based electrical model to examine the temperature's effect on battery aging2. Alipour et al. reviewed temperature-dependent electrochemical properties3, while Lubhani Mishra et al. provided a detailed physics-based analysis of battery degradation and temperature inhomogeneities4. These studies collectively indicate higher temperatures accelerating and promoting growth of compact and less permeable SEI structures leading to an increase in capacity loss and cell resistance, and lower temperatures resulting in slow ionic transport through the SEI also causing higher ohmic loss. In the present work, we study SEI growth and resulting effect on battery capacity fade using continuum scale modeling under the assumption of constant battery cell temperature as well as considering actual dynamically changing temperature data from experiments. SEI growth under these two considerations is compared and the comparison is used in determining scenarios where considering dynamically varying temperature is crucial for accuracy. The detailed analysis of the internal states from the simulation results contributes to the understanding of the effect of the thermal dynamics on battery cell degradation due to SEI growth. To achieve these objectives, a physics-based model, specifically the Single Particle Model (SPM), is utilized. The model uses temporal temperature data obtained from past experimental studies as well as temperature dependent properties of SEI provided in the literature as inputs for this investigation. The ultimate aim of this study is to better understand how temperature influences SEI characteristics, thereby contributing to improved battery performance and longevity across diverse thermal environments. References Liu, L., Park, J., Lin, X., Sastry, A. M., & Lu, W. (2014). A thermal-electrochemical model that gives spatial-dependent growth of solid electrolyte interphase in a Li-ion battery. Journal of power sources, 268, 482-490.Leng, F., Tan, C. M., & Pecht, M. (2015). Effect of temperature on the aging rate of Li-ion battery operating above room temperature. Scientific reports, 5(1), 12967.Alipour, M., Ziebert, C., Conte, F. V., & Kizilel, R. (2020). A review on temperature-dependent electrochemical properties, aging, and performance of lithium-ion cells. Batteries, 6(3), 35.Mishra, L., Subramaniam, A., Jang, T., Garrick, T. R., & Subramanian, V. R. (2022, October). Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries. In Electrochemical Society Meeting s 242 (No. 28, pp. 1075-1075). The Electrochemical Society, Inc.

Enhanced Discharge Capacity in Carbon Felt Electrodes for Aqueous Aluminium-Ion Half-Cells

Diversifying the battery technology in use is an important step in ensuring a sustainable transition to a carbon neutral society, and reducing the emissions associated with lithium-ion cell manufacture. Aluminium is an attractive material for battery applications due to its high theoretical volumetric charge storage capacity of 8046 mA h cm−3 compared to lithium’s 2061 mAh cm-3 and relative abundance in the earth’s crust (1). Aqueous Al-ion batteries are one of many metal-ion systems being investigated utilising water as the electrolyte (2). Further, there are well-established mining, processing, and recycling routes for aluminium, with Li-ion battery recycling still in its infancy (3). Using aqueous electrolytes further provides improved safety as fire risk is reduced, and manufacturing costs are also reduced (4).The substrate on which the electrode material is applied impacts how it is utilised within an electrochemical system. The substrate provides both a shape to the electrode, as well as the material itself forming part of the system, and common substrates double as current collectors e.g. thin metal foils, but carbon polymers have also been explored as a substrate (5, 6). Carbon felt is a conductive substrate, with thin fibres of 5-10 μm diameter, providing a flexible porous structure and large surface area for the active material ‘ ink’ to adhere (0.4 m2 g-1 (7)) . Carbon based electrodes have been assessed in a non-aqueous Al-ion cathodes (8), with varying performance metrics based on the structure and make-up of the electrode, however, these were not investigated as a substrate for further electrode ink. In adding the ink to the carbon felt, the electrode becomes an effective 3D-matrix electrode.This poster explores the use of such 3D-matrix electrodes in order to increase the amount of active material utilised within the aq. Al-ion battery system (9) – a key requirement in reducing the environmental impacts of the battery overall (5), and a means for increasing the capacity of an individual electrode without increasing the overall volume. The cell described in (10) has a carbon-polymer electrode substrate, anatase TiO2 negative electrode and a copper hexacyanoferrate (CuHCF) positive electrode, with the electrolyte being 1 M AlCl3 + 1 M KCl. While the CuHCF redox reaction is partially understood, the negative electrode mechanism has not been fully elucidated. A theorised surface reaction, and pseudo-capacitance of the TiO2 electrode in the aq. Al-ion battery would benefit from an increased surface area of the electrode provided by the carbon felt. Therefore, a key factor in achieving the optimum utilisation of active material is not purely an increase of TiO2 in the electrode, but an increase in the surface area in contact with the electrolyte. Key findings presented show that the lower active material loadings result in a higher discharge capacity for both the positive and negative electrodes, with values reaching an order of magnitude higher than seen for the 2D electrodes studied in the past. For the TiO2 electrode, we see 205.0 mAh g-1 @978 mA g-1 (1.81 mg cm-2 active material loading) and for the CuHCF, 259 mA h g-1 @ 1256.8 mA g-1 (2.5 mg cm-2 active material loading). Elia GA, Kravchyk KV, Kovalenko MV, Chacón J, Holland A, Wills RGA. An overview and prospective on Al and Al-ion battery technologies. Journal of Power Sources. 2021;481:228870. Wu D, Li X, Liu X, Yi J, Acevedo-Peña P, Reguera E, et al. 2022 Roadmap on aqueous batteries. Journal of Physics: Energy. 2022;4(4):041501. Baum ZJ, Bird RE, Yu X, Ma J. Lithium-ion battery recycling─ overview of techniques and trends. ACS Publications; 2022. Chao D, Zhou W, Xie F, Ye C, Li H, Jaroniec M, et al. Roadmap for advanced aqueous batteries: From design of materials to applications. Science Advances. 2020;6:eaba4098. Melzack N. Advancing battery design based on environmental impacts using an aqueous Al-ion cell as a case study. Scientific Reports. 2022;12(1):8911. Holland A, Kimpton H, Cruden A, Wills R. CuHCF as an electrode material in an aqueous dual-ion Al3+/K+ ion battery. Energy Procedia. 2018 d;151:69-73. Sigracell. Speciality Graphites for Energy Storage. 2016. McKerracher RD, Holland A, Cruden A, Wills RGA. Comparison of carbon materials as cathodes for the aluminium-ion battery. Carbon. 2019;144:333-41. Holland A, McKerracher RD, Cruden A, Wills RGA. An aluminium battery operating with an aqueous electrolyte. Journal of Applied Electrochemistry. 2018;48(3):243-50. Melzack N, Wills R, Cruden A. Cleaner Energy Storage: Cradle-to-Gate Life Cycle Assessment of Aluminum-Ion Batteries With an Aqueous Electrolyte. Frontiers in Energy Research. 2021;9(290).

A Reduced-Order Model of the Coupled Venting-Thermal-Electrochemical Behavior to Predict First Venting Under External Short Circuit Conditions

Modeling abusive battery operation before thermal runaway (TR) can reduce the testing requirements and facilitate the development of effective and reliable early failure detection and fast discharge strategies [1] which require multiple types of sensor signals, including current, voltage, temperature, and pressure. We present a multi-physics model that can predict the rapidly evolving discharge behavior of cells undergoing an external short circuit, including hazards like first venting. First venting models account for gas generation due to SEI decomposition and electrolyte vaporization at high temperatures to calculate the build-up of internal cell pressure under constant-displacement conditions [2]. Modeling gas generation requires accurate temperature prediction, which subsequently requires accurate Joule heating calculated from current and voltage predictions. From the cascading chain of model input dependencies, the first challenge is managing error propagation through the submodels with appropriate parameterization. Previous modeling work parameterized a venting model for a cell undergoing an external short circuit (ESC) but did not include a thermal or electrical model [2]. The second challenge is modeling the diffusion-limited discharge behavior with currents approaching 50-80 C with a fast and accurate model that is feasible for detection and control applications. Diffusion-limited behavior occurs when the local Li concentration saturates, suddenly causing large concentration overpotentials that are observable in the terminal voltage and current (see Fig. 1) as well as numerical instability when solving the Butler-Volmer (BV) equation. Previous ESC modeling works either used the Doyle-Fuller-Newman (DFN) model with a limiting current density in the BV equation [3] or an equivalent circuit model (Eq-CM) [1]. However, solving the DFN is computationally intensive for a control application, while Eq-CMs cannot predict the diffusion-limited electrical behavior beyond the data they were parameterized on, requiring apriori experiments to be accurate. To balance the trade-offs, we instead look towards reduced-order modeling.In this work, we present a control-oriented, reduced-order, multi-physics model that captures the electrochemical, thermal, and venting behavior of four 4.6 Ah NMC pouch cells undergoing an external short circuit with different initial state-of-charge (SOC). The multi-physics model couples a first venting model with a lumped thermal model driven by Joule heating calculated through the overpotentials from the Single-Particle Model with electrolyte (SPMe). The combined model was parameterized through four experiments by fitting five key parameters in the submodels related to the SEI decomposition rate, cell thermal behavior, and solid electrode diffusion to capture the first venting timing, peak temperature, and diffusion-limited current-voltage drops. Additionally, two resistances were tuned to match the initial current and voltage with all other parameters were taken from the literature. Applying the same parameter set consisting of the average of the fitted values on all four cells, the combined multi-physics model correctly predicted that the fully-charged cells would vent and conservatively predicted the cell venting timing up to about 40 s before it occurred in the experiment. For high initial SOC cells, the SPMe also accurately predicted the current and voltage drops associated with diffusion limitations and SOC up until the cell vented. This is the first work that systematically parameterizes and couples a reduced-order, physics-based model to capture the electrical, thermal, and venting behavior under battery abuse conditions. Future work will explore applications for the model in early detection and response to critical safety events.REFERENCES[1] Tran, Vivian, Jason Siegel, and Anna Stefanopoulou. "Emergency Li-ion Battery Discharge using Nonlinear Model Predictive Control with Temperature and Venting Pressure Constraints." 2023 American Control Conference (ACC). IEEE, 2023.[2] Cai, Ting, et al. "Modeling li-ion battery first venting events before thermal runaway." IFAC-PapersOnLine 54.20 (2021): 528-533.[3] Rheinfeld, Alexander, et al. "Quasi-isothermal external short circuit tests applied to lithium-ion cells: Part ii. modeling and simulation." Journal of The Electrochemical Society 166.2 (2019): A151. Fig. 1: 15-min simulation of an external short circuit for cells at different initial SOC. Model results and experimental measurements are shown for four cells that were externally shorted. The measured current, voltage, temperature, and expansion force were measured at 10 Hz and plotted versus log time to highlight the dynamic current-voltage behavior in the first few minutes. The diffusion-limited current and voltage behavior are captured by the model. The two cells at 100% SOC, experienced venting and higher peak temperatures, which are well captured by the model. The cell venting timing was predicted to be 43 s and 7 s early for Cell 100A and 100B, respectively. The cells that were shorted at lower SOC did not vent. Figure 1

Leveraging Advanced Analytical Chemistry Techniques to Probe Thermo-Electrochemical Aging Effects in Lithium-Ion Battery Electrolytes

As lithium-ion and other battery chemistries gain market traction for grid and industrial-scale applications, pressure is mounting to develop more robust, longer lasting cells that can operate for hundreds of cycles at variable temperatures without sacrificing performance or safety. Electrolyte design is crucial to this effort and requires deep understanding of the correlated physical, chemical, and electrochemical factors that dictate long-term electrolyte performance. In this presentation, I will discuss the value of combined analytical chemistry techniques (solid- and liquid- state NMR, GCMS, and ICPMS) to resolve molecular-level impacts of thermally- and electrochemically- induced aging of lithium-ion electrolytes. In a model electrolyte, High Resolution (HR)-GCMS enables identification of subtle changes in solvent and additive chemistry while NMR reveals the formation of lithium-salt breakdown products. These findings are instructive for battery cycling as demonstrated by full chemical analysis of electrolyte extracted from aged lithium-ion cells, including evolved gas analysis, electrolyte deformulation, and SEI characterization. These cutting-edge analytical chemistry techniques are powerful and underutilized tools for detecting and mitigating failure modes in liquid electrolytes.

(Digital Presentation) Experimental Techniques for Parameterization of a Commercial 21700 Lithium-Ion Cell for Multiscale Battery Models

Lithium-ion batteries have gained huge attention in the past few decades. Since its commercialization, a steady improvement in cost, and performance over the last 25 years has surfaced many new applications such as EV, HEV, etc., and growing popularity for military and aerospace applications [1, 2]. However, developing a safer, longer life, high energy, power-dense, and cheaper Lithium-ion battery requires a concerted research effort from various disciplines. For a long time, research was focused on developing the chemistry, but in the recent past, the improvement in the battery performance has been realized by reengineering the manufacturing processes and model innovation that help to understand the battery performance during the charging-discharging process. Battery models employed to optimize and predict battery performance are useful tools to design and manage batteries to ensure safe and efficient utilization. To understand the underlying physical, chemical, and electrochemical properties and precisely capture the cell dynamics in EVs application, the model should be based on fundamental governing equations of diffusion and migration processes as well as the kinetics of species intercalation.The physicochemical model requires precisely evaluated model parameters for the materials under consideration. Accurately measured kinetics and transport parameters will hold the key to deriving reliable conclusions about the internal state of a Lithium-ion battery. Parameter’s quantification is a challenging and time-consuming process that requires a range of characterization and analytical methods as shown in Figure. The battery modelling community usually borrowed the parameters list from the literature, with their origins not essentially being traced [3]. In literature, parameterizations have been reported for both high-energy and high-power cells for a physicochemical model [4-7]. This work employed several characterization techniques to parametrize a commercial Lithium-ion cell model. Also, various analytical methods were employed to determine the geometrical, chemical, and electrode microstructure as suggested in Figure. To determine the thermodynamic, kinetics, and transport properties of the extracted electrode materials different electrochemical tests, e.g., galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), constant current constant voltage (CC-CV) charge and constant current (CC) discharge were employed. The parameter’s accuracy would be investigated by validating the mathematical modelling simulation results with the experimental charge-discharge curves at different currents of the commercial 21700 cell at room temperature.

Conversion Electrodes for Rechargeable Li-Sulfur, Na-Ion and Zn-Air Batteries

Rechargeable batteries are reliable and highly efficient energy storage devices providing high energy density at high voltages with the lead of the Li-ion technology since the early 1990s. Despite these promising advantages, the strongly limited abundance of Li and also that of other elements contained in a Li-ion battery (LIB) leads to the search for low-cost and more abundant alternatives. Especially for stationary storage devices alternative battery technologies are required. Alternative chemistries, such as those based on lithium conversion or alloying, can actually lead to higher energy density compared to the lithium (de)intercalation one.Among them, the lithium-sulfur (Li/S) conversion process appeared as one of the most promising candidates to achieve a lithium battery with enhanced performances compared to the state-of-art. In fact, sulfur electrode can deliver in lithium cell a theoretical capacity and energy density as high as 1675 mAh gS −1 and 2600 Wh kg−1 Unfortunately, soluble polysulfides can migrate and directly react with the lithium anode or shuttle between anode and cathode throughout a continuous process without any charge accumulation. This leads to efficiency decrease, active material loss or even to short circuits and cell failure, whilst insoluble polysulfides can precipitate into the cell and cause resistance increase and capacity fading. The characteristic electrochemical process involving at the cathode side the electro-deposition/dissolution of soluble species focused the attention on the nature of the current collector. Hence, flat and thin metal supports (e.g., bare Al current collector) may lead to poor performances due to high overall impedance of the cell and modest ability in allowing the complex multi-step reaction pathway, whilst thicker porous supports (e.g., gas diffusion layer, GDL) can enhance the cell response, reduce the impedance and actually boost the kinetics of the Li/S process, but suffer from its higher thickness, lowering down the volumetric energy density of the overall cell.In this view, graphene-based materials can actually allow the thinnest configuration of a carbon-coated metal support and hold, at the same time, a suitable Li/S process due to their characteristic morphology, mechanical stability and enhanced electronic conductivity. In regard to this, research activities are going to be presented about an exploited binder-free few layer graphene (FLG) thin carbon-coated Aluminum support for application in a Li/S cell with excellent characteristics in terms of stability, efficiency and delivered capacity.Conversion electrodes play also an important role for sodium-ion batteries (SIBs) being a promising alternative, since Na cells show similar properties to the Li analogues in many cases, while they are based on more environmentally friendly and/or more abundant materials. The use of SIBs often results slightly lower energy densities and cell voltages than those of LIBs, but they still provide significantly better values than lead-acid batteries, which are currently dominating the market in terms of annually manufactured capacity. Tin (Sn) and its compounds are well investigated alloy electrodes for SIBs as tin provides a very high theoretical specific capacity of 847 mAh g−1. Sn is an example that shows even better capacity retention when used in SIBs compared to its use in LIBs. Moreover, transition metal compounds containing phosphorus (P) and/or sulfur (S) are promising conversion electrodes as well, since these elements enable high specific volumetric and/or gravimetric capacities in LIBs and SIBs.In addition to LIBs and SIBs, zinc batteries are also attracting research interest due to their environmental friendliness and their applicability with aqueous electrolytes. However, especially zinc-air batteries are well established for use as primary cells, but when considered for use as secondary cells, they suffer from their low rechargeability. Despite great research efforts to solve these problems, no established system has yet been able to achieve reasonable rechargeability in the context of using the commonly considered alkaline electrolytes. However, Sun et al. (2021) found a promising approach using Zn(OTf)2 salt in a small amount of water as an electrolyte. This approach enables the formation of zinc peroxide (ZnO2) instead of formation the irreversible zinc oxide (ZnO) in alkaline electrolytes, which deposits on the gas diffusion layer electrode, blocking the oxygen evolution reaction. ZnO2, on the other hand, has been shown to be highly reversibly malleable. In our current project WaZABi, we are trying another approach using a freeze-cast zinc anode, which enables high porosity, and the application of a hybrid electrolyte under participance of a polymer for rechargeable high performance zinc air batteries.

Characterization of Particulate Emissions From Thermal Runaway of Lithium-Ion Cells

Abstract Over the past decade, there has been a significant acceleration in the adoption of lithium-ion (Li-ion) batteries for various applications, ranging from portable electronics to automotive, defense, and aerospace applications. Lithium-ion batteries are the most used energy storage technologies due to their high energy densities and capacities. However, this battery technology is a potential safety hazard under off-nominal conditions, which may result in thermal runaway events. Such events can release toxic gaseous and particulate emissions, posing a severe risk to human health and the environment. Particulate emissions from the failure of two different cell chemistries—lithium iron phosphate (LFP) and nickel manganese cobalt oxide (NMC)—were studied. Experiments were conducted at multiple states of charge (SOC), and three repeats were performed at each SOC for each cell chemistry to examine the repeatability/variability of these events. Particulate emissions were characterized in terms of particulate matter mass (PM2.5), black carbon, and particle number (PN)/size. Failure of a single cell led to a significant release of particulate emissions, with peak emission levels being higher at the higher SOCs. A high level of variability was observed for a specific SOC for LFP cells, while NMCs exhibited relatively less variability. In general, much higher particulate emissions were observed for NMCs compared to LFPs at each SOC. For NMCs at 100% SOC, peak PN levels were ∼2.5 × 10+09 particles/cc (part/cc), and black carbon levels were ∼60 mg/m3. For LFPs at 100% SOC, peak PN levels were ∼9.0 × 10+08 part/cc, and black carbon levels were 2.5 mg/m3.

Impact of Electrolyte on Direct-Contact Prelithiation of Silicon-Graphite Anodes in Lithium-Ion Cells with High-Nickel Cathodes.

Silicon-based anodes offer high specific capacities to enhance the energy density of lithium-ion batteries, but are severely hindered by the immense volume expansion and subsequent breakage of the solid-electrolyte-interphase (SEI) during cycling. Herein, we utilize an effective strategy, known as direct-contact prelithiation, to mitigate the challenges associated with expansion and surface instability in SiOx/graphite (SG) anodes. It involves introducing lithium into the anode via physical contact with lithium metal and electrolyte before cycling. Prelithiation of SG anodes with an advanced localized high-concentration electrolyte is shown to develop a mechanically robust artificial SEI that tolerates better the electrode volume expansion. The modified SG anode paired with the high-Ni cathode LiNi0.90Mn0.05Co0.05O2 delivers a high initial capacity of 191 mA h g-1 with 80% capacity retention over 150 cycles, compared to 46% retention with a conventional electrolyte. The bolstered SEI layer with reduced surface reactivity is due to the reduced electrolyte consumption and regulated SEI formation during cycling. Furthermore, the advanced electrolyte and fortified SG anode help reduce cathode degradation, transition-metal dissolution, and loss of active lithium. This study highlights viable prelithiation strategies to stabilize Si-based anodes for high-energy-density batteries through electrolyte design.

Quantitative measurement of thermal performance of a cylindrical lithium-ion battery

Measuring the thermal performance of lithium-ion battery cells is a critical task in the thermal design of electric vehicle battery packs. This study introduces a quantitative method to assess the thermal performance of cylindrical 21,700 cells considering heat loss, under conditions of both high and low temperature-rises. By supervising the cell’s outgoing heat-flux (heat loss), we thoroughly analyzed the differences in cell heat generation rates between high temperature-rise (HTR) and low temperature-rise (LTR) conditions. The results show that under LTR conditions, the cell heat generation exhibits a “fast-slow-fast” increasing trend, while under HTR conditions, it displays a U-shaped pattern. Notably, the mean cell heat generation rate increases with decreasing temperatures and increasing discharge rates, especially under LTR conditions, where it significantly outperforms that under HTR conditions. This method provides valuable insights for optimizing the thermal design of battery packs.

Nonflammable All-Fluorinated Electrolyte Enabling High-Voltage and High-Safety Lithium-Ion Cells.

In this study, a nonflammable all-fluorinated electrolyte for lithium-ion cells with a Li(Ni0.8Mn0.1Co0.1)O2 cathode is investigated under high voltages. This electrolyte, named FT46, consists of fluoroethylene carbonate (FEC) and bis(2,2,2-trifluoroethyl) carbonate (TFEC) in a mass ratio of 4:6. Compared to a commercially available electrolyte and several other fluorinated electrolytes, cells containing FT46 demonstrate significantly better cycling performances under high voltage (3.0-4.5 V). This result may be ascribed to the generation of a stable, smooth, and thin passivation layer and the improved solvation structure formed by FT46. The LiF-rich passivation layer strengthens the electrode/electrolyte interface, inhibits the degradation of the electrode, and suppresses side reactions between the electrodes and electrolytes under high voltage. The solvation structure formed by FT46 is derived from anions, enabling an enhanced Li+ migration rate and inhibiting lithium plating generation. Additionally, due to the nonflammability of the electrolyte and the stable passivation layers, FT46 cells also demonstrate promising safety characteristics when exposed to typical abusive conditions, such as thermal abuse, mechanical abuse, and electrical abuse.

A device for real-time detection of gas generated from commercial lithium-ion cell

Abstract Lithium-ion batteries generate a large amount of flammable and toxic gases under abuse conditions. Research on the detection methods of gas generation from batteries is of great significance for understanding the reaction mechanism of batteries under abuse conditions, assessing the impact of gas generation on the health of occupants, and developing safer battery products. However, there is a lack of research reports on the real-time gas production behavior of commercial batteries. In this paper, a device for real-time detecting the gas component of the cylindrical lithium-ion cell is designed. Combined with a gas mass spectrometer can implement the real-time detection of the gas component of the lithium-ion cell. The device is used to explore the gas generation characteristics of lithium-ion cells in the overcharged state, and the influence of the material system and the degree of aging on the results are analyzed, verifying the feasibility of the device.

Corrosion of Lithium-ion Battery Cylindrical Cell Hardware: Understanding the Mechanisms and Exploring Effective Solutions

We present a detailed examination of Ni corrosion in lithium-ion battery Ni-coated steel cylindrical cell hardware, focusing on LiPF6-based electrolytes contaminated with water. The corrosion potential of the cell hardware is predominantly controlled by the iron component of the cylindrical can which cathodically protects the Ni coating. Despite the presence of cathodic protection, the Ni coating still experiences significant crevice corrosion, as confirmed through chemical aging tests. Mechanistic investigations on pure Ni metal reveal two distinct corrosion pathways depending on the presence or absence of oxygen in the electrolyte. The pathway involving oxygen proves to be more detrimental, as it oxidizes Ni in conjunction with acid, leading to the generation of water and the regeneration of corrosive species. This pathway exhibits corrosion rates two orders of magnitude higher than the alternative pathway. The dissolved Ni species predominantly exist in the +2 oxidation state and forms highly soluble F-rich compounds, comprising a mixture of associated species denoted by the formula Ni(PxOyFz)w. Finally, several suggestions for effectively mitigating Ni corrosion have been proposed, with alloying with chromium being the most effective.

Coupled Electrochemical-Thermal Runaway Model of Lithium-Ion Cells Operating Under High Ambient Temperatures

The risk of thermal runaway (TR) in high energy density Lithium-ion batteries (LIBs), which may initiate at around 90 °C, is a critical safety concern, particularly in regions where summer temperatures can reach nearly 50 °C. While multiple exothermic reactions that cause TR and modeled using Arrhenius equations lead to good predictions in controlled oven tests, their use in practical applications is questionable as these do not consider internal electrochemical processes that cause temperature rise and trigger exothermic reactions. Further, limited literature focuses on coupling electrochemical thermal models with exothermic reactions. This study demonstrates a method to couple the electrochemical and thermal runaway models for a commercial cylindrical Lithium-ion cell. The proposed model averages pseudo-2D electrochemical heat and couples it to a two-dimensional, axisymmetric heat transfer model of 18650-type Lithium-ion cell. The jellyroll structure is approximated as a homogeneous and anisotropic domain for electrochemical and exothermic heating. Simulations are performed through several, uninterrupted charge-discharge cycles at different ambient temperatures and C-rates. We show that while cycling rate is critical in instigating and accelerating TR, parameters like ambient temperature, particle radii and initial electrolyte concentration also play a role in determining the core temperature and its rate of growth in the cell.

Capacity and Resistance Diagnosis of Batteries with Voltage-Controlled Models

Capacity and internal resistance are key properties of batteries determining energy content and power capability. We present a novel algorithm for estimating the absolute values of capacity and internal resistance from voltage and current data. The algorithm is based on voltage-controlled models. Experimentally-measured voltage is used as an input variable to an equivalent circuit model. The simulation gives current as output, which is compared to the experimentally-measured current. We show that capacity loss and resistance increase lead to characteristic fingerprints in the current output of the simulation. In order to exploit these fingerprints, a theory is developed for calculating capacity and resistance from the difference between simulated and measured current. The findings are cast into an algorithm for operando diagnosis of batteries operated with arbitrary load profiles. The algorithm is demonstrated using cycling data from lithium-ion pouch cells operated on full cycles, shallow cycles, and dynamic cycles typical for electric vehicles. Capacity and internal resistance of a “fresh” cell was estimated with high accuracy (mean absolute errors of 0.9% and 1.8%, respectively). For an “aged” cell, the algorithm required adaptation of the model’s open-circuit voltage curve to obtain high accuracies.

Effects of Non-Uniform Temperature Distribution on the Degradation of Liquid-Cooled Parallel-Connected Lithium-Ion Cells

Our previous work on an air-cooled stack of five pouch-format lithium-ion (Li-ion) cells showed that non-uniform temperature can cause accelerated degradation, especially of the middle cell. In this work, a stack of five similar cells was cycled at a higher C-rate and water-cooled to create a larger temperature gradient for comparison with the air-cooled stack. It was hypothesized that the larger temperature gradient in the water-cooled stack would exacerbate the degradation of the middle cell. However, the results showed that the middle cell degraded slightly slower than the side cells in the water-cooled stack. This trend is opposite to that in the air-cooled stack. This difference could be attributed to the combined effects of a smaller temperature rise and larger temperature gradient in the water-cooled stack than in the air-cooled stack. Post-mortem analysis of cycled cells and a fresh cell showed that the degradation mainly came from the anode. Increased lithium plating and decreased porosity in the side cells are possible mechanisms for the faster degradation compared with the middle cell. It was also found that all the cells in the water-cooled stack experienced a phenomenon of capacity drop and recovery after a low C-rate reference performance test and extended rest. This phenomenon can be attributed to lithium diffusion between the anode active area and the anode overhang area.

One stone, three birds: Cu2+-substituted chloride electrolyte for high-performance all-solid-state lithium batteries

Emerging solid electrolytes, represented by Li2ZrCl6 (LZC), hold great potential due to their lower costs and superior electrochemical stability compared to sulfide SEs (e.g. Li5.4PS4.4Cl1.6). However, challenges such as relatively low ionic conductivity and instability with lithium hinder its widespread application. This work develops a cost-effective strategy by substituting Cu2+ for Zr4+ in LZC electrolyte. The evolution of electrolyte structure at varying substitution levels is comprehensively investigated by synchrotron X-ray diffraction and Raman spectroscopy. The optimized Cu2+-substituted LZC achieves a notable ionic conductivity of 0.75 mS cm−1 due to a reduced energy barrier for Li+ migration confirmed by first-principles calculations. Symmetric lithium cells with the Cu2+-substituted LZC exhibit enhanced inhibition to lithium dendrites than those with Li5.4PS4.4Cl1.6. X-ray photoelectron spectroscopy unveils the key role of Cu2+ reduction in the inhibition of the lithium dendrite, enabling the cell to stably cycle at 0.5 mA cm−2. Moreover, the Cu2+-substituted LZC exhibits improved electrochemical stability, marked by small anodic current exceeding 4 V, reduced polarization, and rapid lithium-ion diffusion kinetics. All-solid-state batteries fabricated with the Cu2+-substituted LZC and Li/LiNi0.8Mn0.1Co0.1O2 electrodes present a high reversible capacity of 139.2 mAh g−1 with retention rate of 96.9 % after 200 cycles at 0.5 C.

A Weakly Solvating Ether Electrolyte Enables Fast-Charging and Wide-Temperature Lithium-Ion Pouch Cells.

Graphite-based lithium-ion batteries have succeeded greatly in the electric vehicle market. However, they suffer from performance deterioration, especially at fast charging and low temperatures. Traditional electrolytes based on carbonated esters have sluggish desolvation kinetics, recognized as the rate-determining step. Here, a weakly solvating ether electrolyte with tetrahydropyran (THP) as the solvent is designed to enable reversible and fast lithium-ion (Li+) intercalation in the graphite anode. Unlike traditional ether-based electrolytes which easily cointercalate into the graphite layers, the THP-based electrolyte shows fast desolvation ability and can match well with the graphite anode. In addition, the weak interconnection between Li+ and THP allows more anions to come into the solvating shell of Li+, inducing an inorganic-rich interface and thus suppressing the side reactions. As a result, the lithium iron phosphate/graphite pouch cell (3 Ah) with the THP electrolyte shows a capacity retention of 80.3% after 500 cycles at 2 C charging, much higher than that of the ester electrolyte system (7.6% after 200 cycles). At 4 C charging, the discharging capacity is increased from 2.29 Ah of esters to 2.96 Ah of THP. Furthermore, the cell can work normally over wide working temperatures (-20 to 60 °C). Our electrolyte design provides some understanding of lithium-ion batteries at fast charging and wide temperatures.

An all-fluorinated electrolyte with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether as co-solvent for lithium-ion cells with advanced electrochemical and safety properties at high voltage

To enable high-performance lithium-ion cells at high voltage, this work proposes a series of all-fluorinated electrolytes with fluoroethylene carbonate (FEC), bis (2,2,2-trifluoroethyl) carbonate (TFEC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) as co-solvents. It is found that a moderate increase in lithium salt concentration within the FEC-TFEC-TTE solvent enhances the long-term cycling performance of cells at high voltage, while excessive lithium salt cannot further improve the cells' performance but leads to high cost and viscosity and harms the cells’ high-temperature property. Thus, the blend named FTT1.5, i.e., 1.5 M lithium hexafluorophosphate (LiPF6) in FEC, TFEC and TTE with a ratio of 2:6:2, is selected, which outperforms not only the commercial electrolyte (EE) but another all-fluorinated electrolyte, i.e., 1.5 M LiPF6 in FEC, methyl (2,2,2-trifluoroethyl) carbonate (FEMC), and TTE with a ratio of 2:6:2, implying that TFEC cooperates better with FEC and TTE than FEMC. This mainly results from the low binding energy between TFEC and Li+ and the enhanced solvation structure that enables fast Li+ desolvation, reduces lithium plating, and suppresses parasitic reactions at high voltage. The strengthened combination between FEC and TTE with Li+ attributes to the improvement of the anode stability and the generation of reliable and thin passivation layers rich in lithium fluoride. As a result, side reactions at high voltage are successfully restrained, to further obtain high-voltage cells with promising electrochemical performance. Besides this, both the all-fluorinated electrolyte and the system utilizing this electrolyte demonstrate more advanced safety properties when subjected to typical abusing scenarios, with no thermal runaway.

Green Polymer Electrolytes Prepared by a Cost-Effective Approach.

The preparation of solid polymer electrolytes (SPEs) using poly(ethylene oxide) (PEO) typically involves incorporating fillers or undergoing chemical modifications to reduce crystallinity and enhance conductivity. PEO with a lower molecular weight, known as polyethylene glycol (PEG), exhibits higher conductivity, despite weaker mechanical strength. It is commonly employed as a plasticizer to improve the conductivity of SPEs or to fabricate PEG-based gel polymer electrolytes (GPEs). In this study, we use a straightforward approach to create innovative SPEs by blending liquid polymer electrolytes (LPEs), particularly low-molecular-weight polyethylene glycol (PEG), with a molecular weight of 400 g/mol, and sustainable poly(l-lactide) (PLLA). Solid PEG/PLLA forms are achieved by introducing 30 wt % of PLLA. Subsequently, the addition of lithium salts results in the development of novel PEG/PLLA SPEs. Another focal point of this study involves incorporating 1,3:2,4-dibenzylidene sorbitol (DBS) into these PEG/PLLA systems. DBS, an organic gelator derived from natural sugars, demonstrates self-assembly, leading to the formation of a nanofibrillar network structure. Leveraging DBS's ability to form organogels in liquid organic environments, we facilitate the transformation of low PLLA content LPEs into innovative solvent-free GPEs. Our prepared PEG/PLLA SPEs exhibited a maximum conductivity value of 4.39 × 10-5 S/cm, approximately five times higher than that of neat PEG (10000 g/mol) SPEs. The ionic conductivity exhibited a declining trend as the content of PLLA and DBS increased. However, there was an improvement in electrochemical stability. Furthermore, the incorporation of PLLA and DBS into electrolytes contributed to enhanced mechanical support and stability within the electrolyte layer. This, in turn, mitigated capacity decay and improved the cycling performance of assembled lithium-ion cells.