Ah Cells Research Articles

Enabling Stable Operation of Lithium-Ion Batteries under Fast-Operating Conditions by Tuning the Electrolyte Chemistry.

Inferior fast-charging and low-temperature performances remain a hurdle for lithium-ion batteries. Overcoming this hurdle is extremely challenging primarily due to the low conductivity of commercial ethylene carbonate (EC)-based electrolytes and the formation of undesirable solid electrolyte interphases with poor Li+-ion diffusion kinetics. Here, a series of EC-free fast-charging electrolytes (FCEs) by incorporating a fluorinated ester, methyl trifluoroacetate (MTFA), as a special cosolvent into a practically viable LiPF6-dimethyl carbonate-fluoroethylene carbonate system, is reported. With a solvent-dominated solvation structure, MTFA facilitates the formation of thin, yet robust, interphases on both the cathode and anode. Commercial 1 Ah graphite|LiNi0.8Mn0.1Co0.1O2 pouch cells filled with the FCE exhibit ≈80% capacity retention over 3000 cycles at 3 C and 4 C (15min) charging rates in the full range of 0-100% state-of-charge. Moreover, even at a low operating temperature of -20 °C, the 1 Ah cell retains a high capacity of 0.65 Ah at a 2 C discharge rate and displays virtually no capacity fade on cycling at a C/5 rate. The work highlights the power of electrolyte design in achieving extra-fast-charging and low-temperature performances.

Thermal characterization of pouch cell using infrared thermography and electrochemical modelling for the Design of Effective Battery Thermal Management System

Lithium-ion (Li-ion) cells are the optimal choice of energy storage for battery electric vehicles. As the Li-ion cells must operate in a temperature range of 15–45 °C for optimal performance and life, thermal control of the cells is paramount. The study uses infrared imaging to investigate the temperature dynamics of two lithium-ion pouch cells with two energy capacities, 60 Ah and 20 Ah under different operational scenarios with natural convection. Experimental analysis conducted at ambient temperatures of 27 °C, 35 °C, and 40 °C reveals the necessity of cooling for the 20 Ah cell at temperatures exceeding 40 °C and C-rates beyond 1C. Similarly, thermal management is recommended for the 60 Ah cell at ambient temperatures of 35 °C and above, as temperatures surpass the 45 °C desirable threshold during charging and discharging rates of 1C and higher. Further studies are concentrated on the 60 Ah cell due to its increased cooling demands in comparison to the 20 Ah cell. The 60 Ah cell is modelled using NTGK and ECM electrochemical models and validated against experimental data, showing a good agreement within ±10% between both models and the experimental study. Finally, numerical simulations explain the efficacy of localized cooling with forced convection of liquid and performance metrics are introduced to evaluate the cooling efficiency of design configurations. Based on performance metrics, the T-shaped cold plate design, with an inlet coolant temperature of 30 °C, achieved the highest performance index of 1.13. This design notably decreased the maximum temperature and maximum temperature difference by 41.8% and 31.8%, respectively, compared to natural convection. This improvement is observed during the discharge of 60 Ah cell at 2C in a 40 °C environment, where the cell demands substantial cooling measures. Therefore, implementing localized cooling for the cell demonstrates its effectiveness in regulating temperature increase, leading to a significant decrease in the infrastructure requirements and weight of the thermal management system.

Ionblox’s SiOx-Based, High-Energy, High-Power Li-Ion Battery for Performance Electric Vehicles and Electric Aviation

Demands on land-based, high-performance electric vehicles (EVs) and electric aviation, by means of electric conventional takeoff and landing aircraft (eCTOLs) and electric vertical takeoff and landing aircraft (eVTOLs) demand more on a secondary cell chemistry than ever before. There are many secondary cells on the market that offer energy density, power density, fast-charge capability, or cycle life, but few, if any other manufacturing-ready cells, offer a combination of all four. IONBLOX has solved this by pairing it’s patented, Pre-lithiated SiOx anode with a high nickel, NMC cathode to produce cells exceeding 330 wh/kg. Herein we describe the performance of our 32 Ah cell, featuring high-energy density, high-power density, extreme fast charge capability, and good cycle life, within a package that is already in production.In particular, challenges for the eVTOL market will be addressed, which require peak power demand on the cell at low state-of-charge, without reducing the energy density. Methods for characterizing cells for such high-power applications will be further explored. DCIR pulse characterization and more customized testing like usable energy testing, which is important for identifying the applicable energy density for high-power use cases, will be demonstrated. Additionally, extreme fast charge capability is described on our large format cells with 5 min charge to >60% total cell capacity, over 1000 cycles. This shows such a cell is up to the expectations of a consumer familiar with the timing of a standard gasoline pump. Contribution from the information presented herein demonstrates the state of Si-based anode chemistry and can serve as useful guidelines to the academic community as future technologies are pursued for similar applications Figure 1

Influence of Phosphate Surface Coating on Performance of Aqueous‐Processed NMC811 Cathodes in 3 Ah Lithium‐Ion Cells

AbstractAqueous processing of state‐of‐the‐art cathode materials for lithium‐ion batteries like LiNi0.8Mn0.1Co0.1O2 (NMC811) has evolved as a more sustainable and cost‐effective alternative to the conventional 1‐methyl‐2‐pyrrolidone‐based process. However, the implementation of aqueous processing is challenging due to the water sensitivity of nickel‐rich layered oxides. This study investigates the influence of a phosphate‐based NMC811 surface coating on the performance of aqueous‐processed NMC811 cathodes in 3 Ah cells. The results show that the cells with phosphate‐coated NMC811 outperform those with uncoated NMC811, i. e., they exhibited higher initial capacity and improved capacity retention during cycling. Post‐mortem characterization techniques reveal that the phosphate coating limits the lithium loss during aqueous cathode manufacturing and further reduces side reactions during cycling, resulting in a smaller increase of cell impedance.

Making Room for Silicon: Including SiOx in a Graphite-Based Anode Formulation and Harmonization in 1 Ah Cells

Transitioning to more ambitious electrode formulations facilitates developing high-energy density cells, potentially fulfilling the demands of electric car manufacturers. In this context, the partial replacement of the prevailing anode active material in lithium-ion cells, graphite, with silicon-based materials enhances its capacity. Nevertheless, this requires adapting the rest of the components and harmonizing the electrode integration in the cell to enhance the performance of the resulting high-capacity anodes. Herein, starting from a replacement in the standard graphite anode recipe with 22% silicon suboxide at laboratory scale, the weight fraction of the electrochemically inactive materials was optimized to 2% carbon black/1% dispersant/3% binder combination before deriving an advantage from including single-wall carbon nanotubes in the formulation. In the second part, the recipe was upscaled to a semi-industrial electrode coating and cell assembly line. Then, 1 Ah lithium-ion pouch cells were filled and tested with different commercial electrolytes, aiming at studying the dependency of the Si-based electrodes on the additives included in the composition. Among all the electrolytes employed, the EL2 excelled in terms of capacity retention, obtaining a 48% increase in the number of cycles compared to the baseline electrolyte formulation above the threshold capacity retention value (80% state of health).

Free Standing Electrodes: From Roll Product to 41-Layer Pouch Cells

Processes to produce free standing electrodes for Lithium-Ion Batteries (LIB), using lithium iron phosphate (LFP) as active material for the cathode and artificial graphite for the anode, are being developed. The production of these electrodes is realized by using a slot die to produce a liquid film which solidifies in a precipitation bath and is wound up after moving through washing baths. This procedure consumes significantly less energy compared to conventional coating processes, as the drying needs are reduced, and the electrodes have a broader spectrum of use cases due to their high flexibility.In this work, the development process of the manufacturing procedures of pouch cells using free standing electrodes will be presented. This includes the characterization of the electrodes, usability trials with research pilot line equipment, and cycling tests of built pouch cells of up to more than 7 Ah per device.The screening of electrodes through cycling in coin cells showed a specific discharge capacity of > 120 mAhg-1 for 50 cycles at 0.2C.This innovative and sustainable electrode production process required adjustments throughout the whole production process of a LIB, starting with the slot die geometry to reduce thick edges of the released film. The electrodes’ surfaces were investigated regarding homogeneity and roughness using a digital microscope. Gas adsorptioneasurements showed the specific surface of cathodes at around 3.6 m²g-1. Challenges during calendaring of the free-standing electrodes included thickness deviations of the pristine electrodes and uneven tension throughout the width of the samples.After laminating the free-standing electrodes with current collectors, they were electrochemically and mechanically analysed. Therefore, additional adjustments had to be made to attach tabs on multiple layers of these flexible electrodes through a single ultrasonic welding spot. All electrodes were successfully processed inside a dry room (dew point < -40 °C) using industrially relevant pilot scale equipment (punching, stacking, electrolyte filling, sealing).The manufactured pouch cells all showed an initial OCV of around 400 mV and were formed prior to cycling. During three formation cycles at 0.1C, followed by a constant Voltage step, the two-layered pouch cells showed a specific discharge capacity of . These cells reached roughly 90 mAhg-1 of discharge capacity after 20 cycles at 0.2C, but higher C-rates reduced the capacity and cell life significantly. Measuring the cells’ resistance after cycling at 3.3 V using 10 measurement points at 1 kHz revealed the high inner resistance of > 2 Ohm. Post-mortem analysis revealed lithium deposition throughout the whole surface of the anode. In the following upscaling process, the number of layers was increased to 11 layers (2 Ah cells) and 41 layers (7 Ah cells). These pouch cells showed similar performances, specific discharge capacities of around 110 mAhg-1 during formation, but with decreased cycling capabilities at C-rates higher than 0.1C. The main cause for this behaviour is the high inner resistance of these cells.In this work we demonstrate that free-standing electrodes can be handled at pilot scale in a comparable manner as conventionally coated electrodes. The produced cells were all successfully cycled but showed higher inner resistances and lower capacities at high C-rates (> 0.5C). The proof-of-concept was therefore achieved, further improvement of the cell performance will be focused on in the future. Figure 1

Fast method for calibrated self-discharge measurement of lithium-ion batteries including temperature effects and comparison to modelling

The self-discharge rate is an important parameter to assess the quality of lithium-ion batteries (LIBs). This paper presents an accurate, efficient, and comprehensive method for measuring and understanding the self-discharge behaviour of LiB cells, considering factors such as temperature and cell to cell variability, as well as underlying electrochemical mechanisms. A method for precise potentiostatic self-discharge measurement (SDM) is demonstrated that is validated by measuring 21 commercial cylindrical 4.7 Ah cells at a state of charge (SoC) of 30%. The self-discharge current ranges between 3 and 6 μA at 23 °C, with an experimental noise level of 0.25 μA. At higher temperatures of 40 °C the self-discharge current increases to 97 μA. The temperature coefficient of voltage (TCV) is experimentally obtained by exposing the cells to a temperature profile with positive and negative step polarities and following the open circuit voltage (OCV) response. Observed TCVs range from +180 µV/K at 40% SoC to −320 µV/K at 0% SoC. For SDM temperature experiments, the cells were set to an SoC with a minimum TCV. From the SDM currents at different temperatures the Arrhenius kinetics and the electrochemical activation energy barrier is determined as 0.94 ± 0.14 eV, indicating chemical side reactions as source of self-discharge. For SDM modelling the electrochemical processes are coupled with a 3D temperature finite element model (FEM) and an electric circuit model resulting in a good overlap with the dynamics and time-constants of the experimental self-discharge curves. The primary challenges addressed are accurately measuring microampere (µA) discharge currents of high-quality cells, reducing measurement time, understanding the temperature dependence of self-discharge, determining activation energy, and demonstrating the applicability and generalization of SDM.

Improvement of positive plate grid corrosion resistance through two methods of boric acid addition to lead-acid battery electrolyte

The performance of Lead-Acid Batteries (LABs) can be enhanced by the approach of incorporation of additives. In this way, boric acid (H3BO3) has been studied as an electrolyte additive as prior investigations have done. Nevertheless, the innovation provided by this work is based on the addition method employed. In fact, the H3BO3 effect on the LAB performance was measured when the addition was performed before and after the LAB formation. Firstly, a previous study was carried out in a three electrode cell to understand the effect of this additive on the positive grid. As a result, a decrease in the oxide reduction charge (23 %) and an increase in the resistance of the corrosion process were found by the addition of 0.50 wt% H3BO3. Furthermore, the research was then extended to a LAB system. Thus, 2 V/1 Ah cells were built and H3BO3 was added in different concentrations before and after the cell formation. Consequently, different effects were showed by the two addition methodologies. When the additive was introduced before the cell formation, the Cold Cranking Ampere (CCA) performance was improved (26 %). In contrast, when the additive was incorporated after the formation procedure, the Oxygen Evolution Reaction (OER) rate on the positive plate was significantly reduced (75 %). Lastly, the corrosion growth in the positive plate grid was slowed by the two methods although in different ways: 20 % reduction after 42 days of corrosion process (addition before formation) and 12 % reduction after 21 days of corrosion process (addition after formation). In addition, the prior cell performances were affected by the addition methodologies. If the additive was added to the electrolyte before the cell formation, the positive plate performance was possibly altered by the formation and growth of boric compounds in the PAM. However the cell performance was influenced by the suppression of OER on the positive plate when H3BO3 was added after the cell formation. In this way, different nuances of improvement were obtained due to the addition method applied.

Incremental capacity analysis (dQ/dV) as a tool for analysing the effect of ambient temperature and mechanical clamping on degradation

This work presents a comprehensive degradation study of two types of large lithium-ion pouch cells; 26 NMC532/Graphite (64 Ah) and 9 NMC433/Graphite (31 Ah) pouch cells. The cells were degraded under different cycling conditions and periodically characterized at room temperature. Specifically, the effect of different ambient temperatures and constraining the cells by clamping was studied. Incremental capacity analysis is an in situ, non-invasive characterization technique that allows the identification of battery degradation modes, and is a technique that does not require additional and advanced equipment. Therefore, in this study we also look into applying the analysis technique on an existing data set. This is done by combining incremental capacity analysis on a qualitative level with the tracking of features of interest in the incremental capacity curve as a function of State of Health and utilizing the simulation of different degradation modes for a more in-depth analysis. We combine simulation and experimental incremental capacity analysis with conclusions from capacity loss and resistance changes with a focus on understanding the benefit and limitations of the incremental capacity analysis for large cells. This is important, as incremental capacity analysis is a relatively fast analysis to qualify large commercial batteries for 2nd life applications. Specifically in this study, we found that degradation and capacity loss do not always correlate. For the 64 Ah Cells cycled at 15 °C and 25 °C, the rate of capacity loss appeared to be similar, although the degradation modes and mechanisms are found to be very different. The clamping was the most important factor for impeding degradation. The 31 Ah Cell cycled at low temperatures showed a very poor cycling performance, where the incremental capacity analysis revealed that Loss of Lithium Inventory from fast and irreversible plating was responsible.

Studies on Multi-step Addition of NMP in (LiNi0.80Co0.15Al0.05) (NCA) Cathode Slurry Preparation and its Rheological, Mechanical Strength and Electrochemical Properties for Li-ion Cells

For electrode stability and the electrochemical performance of the Li-ion cell, it is essential that the active ingredients and unique additives in the polymer binder be well dispersed with the solvent-based slurry. The efficient procedure used to create the slurry affects the rheological characteristics of the electrode slurry. When successively adding different steps of N-methyl-2-pyrrolidone (NMP) solvent to the cathode composition, it is evenly disseminated. The electrochemical performance of the Li-ion cells and the electrodes made with slurry formed by single step and multiple steps of addition of NMP solvent are examined. To preform rheological properties of cathode electrode slurry on Ni-rich Lithium Nickel-Cobalt-Aluminum Oxide (LiNi0.80Co0.15Al0.05) (NCA). Also, we investigate different step addition of electrode formation and mechanical strength characterization like peel strength. According to the EIS study, a multi-step electrode slurry has lower internal resistance than a single-step electrode slurry, which results in better electrical characteristics and efficiency. Further, microstructure of electrodes is obtained electrochemical performance in the 18650 cylindrical cells with targeted capacity of 1.5 Ah. The slurry of electrodes prepared by single step and multiple steps of addition of NMP solvent and its effect on the fabrication of 1.5 Ah cells. A three-step solvent addition on slurry has been found to be a lower internal resistance than a single-step electrode slurry as confirmed by the EIS analysis, yielding improved electrical properties and efficiency.

Comparative study on the influence of incident heat flux on thermal runaway fire development of large-format lithium-ion batteries

In response to the growing demand for higher energy density in various applications, large-format batteries have gained popularity. However, the larger size of these batteries also increases their exposed area, which may lead to more severe thermal events. This study aims to understand the influence of incident heat flux on the occurrence and progression patterns of fires in large-format lithium-ion batteries. Two representative large-format lithium-ion batteries, 38 Ah LiNi0.3Co0.3Mn0.3O2 prismatic cell and 78 Ah LiNi0.8Co0.1Mn0.1O2 pouch cell, were investigated. To evaluate the thermal hazard to the environment, the heat release rates (HRR) of the lithium-ion battery fire were measured under incident heat fluxes ranging from 10 to 50 kW∙m−2, using the oxygen consumption principle. The results highlight significant differences in thermal runaway and fire development between the 38 Ah and 78 Ah cells, attributable to variations in structure and materials, and scale effect. The 38 Ah cell exhibited an evident venting stage, characterized by an unignited jet on the verge of ignition, followed by a transition from momentum-driven jet fire to buoyancy-driven jet fire. In contrast, the 78 Ah cell experienced direct ignition, accompanied by strong air entrainment, overflow flame, and flame sinking phenomena as the fire progressed. Notably, unlike the 38 Ah cell, the peak HRR, THR, and burning time of the 78 Ah cell were minimally sensitivity to the incident heat flux. Furthermore, a generalized relationship model between the incident heat flux and the ignition time was established and validated based on the energy conservation equation during the ignition stage of the cell. This model enhances our understanding of the interplay between incident heat flux and ignition time, contributing to the development of strategies for fire prevention and mitigation in large-format lithium-ion batteries.

Failure analysis of lead‐acid batteries at extreme operating temperatures

AbstractThe lead‐acid battery system is designed to perform optimally at ambient temperature (25°C) in terms of capacity and cyclability. However, varying climate zones enforce harsher conditions on automotive lead‐acid batteries. Hence, they aged faster and showed lower performance when operated at extremity of the optimum ambient conditions. In this work, a systematic study was conducted to analyze the effect of varying temperatures (−10°C, 0°C, 25°C, and 40°C) on the sealed lead acid. Enersys® Cyclon (2 V, 5 Ah) cells were cycled at C/10 rate using a battery testing system. Environmental aging results in shorter cycle life due to the degradation of electrode and grid materials at higher temperatures (25°C and 40°C), while at lower temperatures (−10°C and 0°C), negligible degradation was observed due to slower kinetics and reduced available capacity. Electrochemical impedance spectroscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy analysis were used to evaluate the degradation mechanism and chemical and morphological changes.

The impact of osmotic stresses on the biofilm formation, immunodetection, and morphology of Aeromonas hydrophila

Aeromonas hydrophila (Ah) is a zoonotic pathogen of great importance to aquaculture and human health. This study systematically evaluated the impact of salinity, sugar, ammonia nitrogen, and nitric nitrogen levels on the fitness of Ah by using Luria-Bertani (LB) broth supplemented with different concentrations of NaCl, sucrose, NH4Cl, urea, NaNO2 or NaNO3. Results showed that the static biofilm formation of Ah was higher at 28 °C compared to 37 °C (P < 0.05). At 28 °C, as the NaCl (>1 %) and sucrose levels increased, the Ah biofilm formation and the binding between Ah cells and monoclonal antibodies (mAbs, for immunodetection) decreased. Elevated ammonia nitrogen and nitric nitrogen levels generated no significant impact on Ah biofilm formation or immunodetection (P > 0.05). The expression of mAbs-targeted Omp remained unchanged under high NaCl or sucrose conditions. Further analysis showed that high sucrose conditions led to the over-expression of the extracellular polysaccharides (PS) and promoted the formation of capsule-like structures. These over-expressed PS and capsule structures might be one reason explaining the inhibited immunodetection efficacy. Results generated from this study provide crucial insights for the design of recovery and detection protocols for Ah present in food or environmental samples.

Li pre-doping technique using perforated electrodes for the cells with a rubber-derived sulfur composite cathode

We attempted to develop a disassembly- and reassembly-free Li pre-doping technique using perforated electrodes in order to develop Li-ion batteries containing a rubber-derived sulfur composite cathode. The Li pre-doping of the anodes was performed using perforated electrodes by external shorting between the anodes and Li metal electrodes provided on both end parts of the stacked electrodes within the cell, in which the degree of the Li pre-doping could be determined by the open circuit voltage measurement between the anodes and Li metal electrodes. The Li pre-doping of the graphite anodes in the cell composed of rubber-derived sulfur composite cathodes and graphite anodes was successfully conducted using this technique without disassembly and reassembly of the cell. After the Li pre-doping treatment, a stable charge-discharge was achieved between the rubber-derived sulfur composite cathodes and Li pre-doped graphite anodes. The Li pre-doping technique using the perforated electrodes was demonstrated to be applied even for practical 5 Ah cell. Furthermore, the Li pre-doping of the SiO anodes could be achieved in the cell composed of the perforated rubber-derived sulfur composite cathodes and SiO anodes, in which the cell showed a stable cycling performance and excellent charge-discharge rate performance.

Optimal and systematic design of large-scale electrodes for practical Li–air batteries

The battery market to enable the broad uses of electric vehicles and renewable energy sources is undergoing a rapid expansion given the requirements of light, safe, and low-cost materials. Li–air batteries are considered suitable candidates that can overcome the existing challenges in this field. Continuous progress in performance improvements triggered by the structure and design evolution of battery electrodes is essential to utilize Li–air batteries in future applications. In this study, an optimal design process is devised for the practical application of Li–air batteries with large-scale area and capacity levels. The primary difficulty in the large-scale design for practical use originates from the design complexity caused by the one-side (air cathode) open-cell structure for the proper air flow. To examine problems related to practical cell manufacturing, we attempted to explore the large-scale electrode on the charge/discharge performance with two current collectors, specifically Ni foam and a gas diffusion layer (GDL), in single and stacked Li–air cells. A large-scale stacked 1.07 Ah cell was manufactured using commercial carbon mixtures with tabless current collector of Ni foam. The single-cell capacity of tabless Ni foam presented approximately 440 mAh at full-depth scan, showing that the cell-specific gravimetric and volumetric energy densities were 385 Wh/kg and 428 Wh/L, respectively. In the case of tabless GDL, the cell capacity was 630 mAh at full-depth scan. The cell-specific gravimetric and volumetric energy densities of tabless GDL were 680 Wh/kg and 756 Wh/L, respectively. However, the use of a GDL current collector resulted in structural deformation during the charge/discharge reaction due to a self-reaction in spite of the 1.56 times higher energy density than that of Ni foam. Although the GDL helps to enhance the reactivity and performance by increasing the capacity when used with an active material, the extended cycle stability of the Li–air cell is hindered due to the self-reaction of the current collector. These results present case‐based evidence that extends our knowledge about the trade‐offs between capacity enhancements and long-cycle stability regarding the choices of materials for the manufacturing of Li-air cells, thus proving practical insights with regard to the fabrication of large-scale Li–air cells for commercialization.

Experimental study of cell integrated heat pipe cooling with a lithium-ion cell emulator

Novel switchable cells challenge conventional thermal management approaches in battery electric vehicles. The study introduces a novel hybrid cooling approach based on liquid bottom cooling and cell integrated heat pipes. For the experimental investigation a thermal cell emulator is developed and the environmental conditions of a cell in an automotive battery system are reproduced. The validation of the cell emulator reveals almost similar behavior compared to a real prismatic 25 Ah cell with additional access to the internal temperature distribution. Thus, a flexible research tool is introduced for thermal investigations of lithium-ion cells. The subsequent investigation of the cell integrated heat pipes is performed for a switchable cell as an essential part of novel intelligent battery systems. As a result of the experimental investigation a reduction of the core temperature of 2 K during 3C cycling is found using integrated heat pipes. Furthermore, in a case study for fast charging the heat pipes enable consistent temperatures within the cell core, while the charging time is decreased by 12%.

Designing High Energy Density Batteries for Abuse Tolerance

Every month or so there is a news article announcing a recall of a product due to overheating and thermal runaway of the battery pack. This has occurred more frequently as the energy density of battery cells has increased. Here we present a method to greatly improve the tolerance of a cell to internal shorting and nail penetration that is uniquely enabled by Enovix LiB cells.A higher energy density results in less mass to absorb the energy released and less surface area to dissipate the heat. Frequently the failure has been identified as being initiated by an internal short between anode and cathode current collectors within a cell. These internal shorts have been associated with mechanical damage to the cell container, anode-separator-cathode alignment, and lithium dendrite breaches of the separator.External short circuits are most likely to be controlled by the battery management system before damage to the cell. In the event of an external short circuit that bypasses the BMS the power released uniformly heats the entire cell. A safe landing of the cell is reliant on the separator or electrolyte increasing resistance to the point that heat transfer from the surface of the cell can maintain the temperature below thermal run away.Shorts created by an internal short or mechanical penetration of a cell are more dangerous than external shorts. The short typically occurs at a point such that power is dissipated non-uniformly in a very small volume of material. This volume rapidly heats beyond thermal run away before the remaining cell increases significantly in temperature such that separator shutdown or electrolyte shutdown can not be relied upon to prevent thermal runaway. A thermal runaway event due to an internal short can be prevented by reducing the energy released at the point of the short.Internal shorts are difficult to create purposefully without modifying the cell. Frequently an internal short is simulated by mechanically penetrating the cell with a nail. The nail breaches the cell container and penetrates the current collector(s) and separator. Penetration of the cell is typically done perpendicular to the plane of the current collector which produces a parallel connection between all layers of anode and cathode current collectors with out much mixing of anode and cathode active materials. Penetration parallel to the current collectors tends to crush the separator and current collectors, mixes a larger volume of active materials, and connects few layers of the current collectors. The larger volume of active material mixing and fewer parallel short locations results in a more challenging test of the cell.Enovix battery architecture is designed for those systems that require a significant pressure between anode and cathode layers. A feature of this design is the segmentation of the cell into small area sub cells that are connected to a bus. Each sub cell bus connection can be designed to limit the current from the remainder of the cell in case of a short in the sub cell. We present abuse testing results of 3.4 AH cells with sub-cell protection that enable survival of nail penetration testing even when penetrated parallel to the current collector surface.

Insights into the Electrochemical Performance of 1.8 Ah Pouch and 18650 Cylindrical NMC:LFP|Si:C Blend Li-ion Cells

Silicon has become an integral negative electrode component for lithium-ion batteries in numerous applications including electric vehicles and renewable energy sources. However, its high capacity and low cycling stability represent a significant trade-off that limits its widespread implementation in high fractions in the negative electrode. Herein, we assembled high-capacity (1.8 Ah) cells using a nanoparticulate silicon–graphite (1:7.1) blend as the negative electrode material and a LiFePO4–LiNi0.5Mn0.3Co0.2O2 (1:1) blend as the positive electrode. Two types of cells were constructed: cylindrical 18650 and pouch cells. These cells were subjected both to calendar and cycling aging, the latter exploring different working voltage windows (2.5–3.6 V, 3.6–4.5 V, and 2.5–4.5 V). In addition, one cell was opened and characterised at its end of life by means of X-ray diffraction, scanning electron microscopy, and further electrochemical tests of the aged electrodes. Si degradation was identified as the primary cause of capacity fade of the cells. This work highlights the need to develop novel strategies to mitigate the issues associated with the excessive volumetric changes of Si.

(Digital Presentation) Recycled Cathode Materials Enabled Superior Performance for Lithium-Ion Batteries

With the widely equipped Lithium-ion batteries (LIBs) in electronics and electric vehicles, proper handle spent LIBs has been the subject of increasing concern. Significantly raised concerns about resource constraints and environmental issues are brought by spent LIBs. Therefore, properly handling spent LIBs is urgent and necessary.[1] However, until now, getting manufacturers to recruit recycled materials has been a hard sell because recycled materials are deemed as inferior to commercial materials, which limits the development of recycling. Although previous publications stated that their recovered materials had a comparable performance as commercial materials, the results, based on coin cells and low electrode loading, cannot convince manufacturers to employ recycled materials in the new LIBs.[2] Here, we demonstrate that recycled cathode materials with optimized microstructure have the best industrial relevant testing results (up to 11Ah cells) so far and compare them with state-of-the-art commercial equivalent. Interestingly, the recycled materials not only pass all the aggressive industrial plug-in hybrid electric vehicle (PHEV) battery tests, but also outperform control counterparts in some tests. Specifically, 1 Ah cells with the recycled LiNi1/3Mn1/3Co1/3O2 have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% capacity retention, which is 33% and 53% better than the state-of-the-art, commercial LiNi1/3Mn1/3Co1/3O2. Meanwhile, its rate performance is 88.6% better than commercial powders at 5C. Through detailed experimental and modeling analysis of pristine and cycled materials, we discover that the unique porous and larger inside void microstructure enables the superior rate and cycle performance and less phase transformation. Compared with the control sample, the surface area of the recycled LiNi1/3Mn1/3Co1/3O2 is 82.14% larger and the cumulative pore volume is 61.25% larger. Even some recycled particles have an outer diameter of the void space equal to 40% to 60% of the particle diameter. The unique microstructure can reduce 16% hoop stress during the discharge/charge process compared to control materials, and improve the lithium chemical diffusion coefficient, enabling the superior performance of cycle life and rate performance and less phase transformation. The results pave the way to re-introduce recycled materials into new batteries.[3] [1] M. Chen, X. Ma, B. Chen, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycling End-of-Life Electric Vehicle Lithium-Ion Batteries, Joule 2019, 3, 2622.10.1016/j.joule.2019.09.014[2] X. Ma, L. Azhari, Y. Wang, Li-ion battery recycling challenges, Chem 2021.10.1016/j.chempr.2021.09.013[3] X. Ma, M. Chen, Z. Zheng, D. Bullen, J. Wang, C. Harrison, E. Gratz, Y. Lin, Z. Yang, Y. Zhang, F. Wang, D. Robertson, S.-B. Son, I. Bloom, J. Wen, M. Ge, X. Xiao, W.-K. Lee, M. Tang, Q. Wang, J. Fu, Y. Zhang, B. C. Sousa, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycled cathode materials enabled superior performance for lithium-ion batteries, Joule 2021.10.1016/j.joule.2021.09.005

Mechanical Effects Occurring inside Large Format 94 Ah Prismatic Lithium-Ion Cells at Different Bracing during Aging

One of the biggest obstacles to the widespread adoption of fully electrified vehicles is the limited volumetric/gravimetric energy density of lithium-ion batteries to achieve driving ranges comparable to vehicles with internal combustion engines. Electrode thicknesses are being increased to enhance the energy density of the battery cells. Furthermore, the space within the confinements of the cell housing is utilized as much as possible. Today’s state-of-the-art (SoA) electrode materials exhibit volume and Young’s modulus change during formation and cycling, e.g. a volume change up to ~10% for graphite [1] and a threefold increase of the Young’s modulus of the graphite active particles [2]. This leads to a pressure build up within the cells due to reversible and irreversible volume changes, especially of the anode materials, during cycling. The optimized packing for SoA electrodes and the volume changes of the electrodes result in increased electrochemical/mechanical interactions that leads to stress inside the cells.In this work, the interactions between mechanical bracing and aging are studied for large format prismatic 94 Ah lithium-ion battery cells [3]. The impact of external bracing is shown for lithium-ion cells cycled up to over 7000 cycles with 100% depth of discharge (Figure 1 (a)), where the braced cells show an enhanced performance in the region of 80% state of health (SOH). The braced cells reach this threshold around 900 cycles later compared to the unbraced cells. Furthermore, the unbraced cells have a thickness change of around 17.5% after more than 7000 cycles (Figure 1 (b)). After cycling, the cells are examined with post-mortem analysis, showing significantly increased aging phenomena (e.g. lithium plating) in the unbraced cell compared to the braced cell. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses confirm these assumptions (Figure 1 (c) + (d)). In contrary to the enhanced lithium plating on the anode of the unbraced cell, X-Ray diffraction (XRD) show that bracing leads to an increased structural cathode degradation compared to the unbraced cells. Those ex-situ post-mortem experiments were also confirmed by electrochemical tests in laboratory cells, showing only small capacity fading of the aged anodes of the braced cell compared to unaged reference anode cells. Nevertheless the main factor for capacity loss inside the prismatic 94 Ah cells is the loss of lithium inventory.External pressure on cells is beneficial to guarantee sufficient contact of the components within an electrode stack and hence decreased aging phenomena mainly on the anode. The downside of the increased pressure on the cells are the significantly increased morphological and structural degradation of the cathode, which, however, plays a minor role in the overall cell degradation. The external bracing results in a more ‘homogeneous’ aging over the entire cell with only little locally different degradation characteristics.