SEI Growth Research Articles

Interfacial Engineering Constructing TFSI- Ion-Sieve Protective Umbrella Guiding Li-Ion Selective Transport and Solid SEI Growth.

A novel strategy is proposed by constructing TFSI- ion-sieve interlayer to guide Li-ion selective transport and solid SEI growth. The uniform MgF2 seeds on the fiber surface reacts rapidly with Li+ in electrolyte to form Mg and LiF dual functional sites for the first charging process. Benefiting from the high affinity of LiF, the TFSI- ions is enriched near the anode forming an ion-sieve interlayer, which acts as a protective umbrella and guides priority penetration of Li+ due to the coordination reaction with Li+ and thus homogenize the Li+ flux. While the Mg sites induce Li nucleation with its strong lithiophilicity and facilitate uniform Li plating on fiber surface. Furthermore, as raw material of LiF, the TFSI- enrichment on anode surface is contribute to increasing LiF content in SEI, achieving the stability enhancement and densification of SEI. Of greater importance, the excess Li+ can spread to the adjacent Mg sites for nucleation by means of ultralow Li+ migration barrier on LiF and Mg. The combination of the ion-sieve homogenization of Li+ flux in electrolyte and the uniformity of Li+ transport in LiF/Mg solid medium achieves the purpose of uniform Li metal plating/stripping.

Insights on SEI Growth and Properties in Na‐Ion Batteries via Physically Driven Kinetic Monte Carlo Model

Insights on SEI Growth and Properties in Na‐Ion Batteries via Physically Driven Kinetic Monte Carlo Model

Diagnosing NMC Battery Aging Modes Using Digital Twin

Traditional lithium-ion battery (LiB) modeling does not provide sufficient information to accurately verify battery performance under real-time dynamic operating conditions, particularly when considering various aging modes and mechanisms. This paper proposes a lithium-ion battery digital twin that can capture real-time data and integrate the strong coupling between SEI layer growth, anode crack propagation, drying up of Electrolytes, and lithium plating. It can be utilized to predict the degradation behavior, voltage-current profiles in dynamic aging conditions, and analyze the lithium inventory loss (LLI) of Nickel-Manganese-Cobalt-Oxide (NMC) lithium-ion batteries.Commercially available 18650 cylindrical NMC Samsung battery cells were investigated. The cathode and anode materials are LiNi0.5Co0.2Mn0.3O2 and synthetic graphite, respectively. Four dynamic aging test cases using 1C, 1.3C, MC (multistep charging), and 2C, were designed and performed at 25 °C. The reference performance test (RPT) was repeated every 100 full equivalent cycles (FECs) until the cells reached 20 % capacity fade. Figure 1 shows the real-time voltage and current profile captured and predicted by the digital twin.The model takes into account LLI induced by SEI growth and lithium plating, aligning with the LLI calibrated from the differential voltage (DV) endpoint shift (Figure 1h). Based on the model results, SEI growth is found to be the primary contributor to capacity loss before 500 FECs. SEI-induced degradation is minimal under the MC protocol, with the capacity loss varying by less than 5.22% across four test cases (Figure 1e). After 500 FECs, anode cracking becomes a non-linear accelerated aging factor. The crack propagation stabilizes in the initial 200 FECs, followed by unstable accelerated growth leading to capacity loss. Subsequently, a rapid acceleration in capacity loss occurs after 700 FECs (Figure 1f). The growth of anode cracks under the MC aging protocol has a much slower effect on capacity loss compared to the 2C and 1.3C before 500 FECs, as strongly confirmed by the post-mortem analysis. In addition, the lithium plating phenomenon triggers two orders of magnitude less capacity loss than SEI growth and cracking at 25 °C. The MC protocol demonstrates an effective reduction in lithium plating capacity loss compared to the other three traditional charging protocols (Figure 1g). This digital twin can represent a firm physical foundation for future physics-informed machine learning development to predict LiBs degradation behavior.Figure 1. Real-time voltage and current captured and predicted by our designed digital twin under (a) 1C-WLTC, (b)1.3C-WLTC, (c) MC-WLTC, and (d) 2C-WLTC aging profiles. Additionally, (f) illustrates capacity loss density for the four protocols attributed to (e) SEI film growth, (f) anode crack propagation, (g) Li plating, and (h) LLI prediction by the digital twin and DV measurement. Figure 1

(Invited) Lifetime Predictive Model of Capacity Loss, Resistance Increase, and Irreversible Thickness Growth

We present a battery lifetime model that predicts Irreversible battery thickness change under constant pressure operation as the battery ages, along with capacity loss and resistance growth. These metrics are very important for predicting lithium-ion battery state of health (SOH) and remaining useful life due to their interdependence with battery packaging and safety. To design and operate battery storage systems safely, we must be able to predict and detect changes in all three SOH metrics over life accurately and simultaneously. Traditionally, these three SOH metrics have been modeled separately. However, we developed a single model that simultaneously predicts battery capacity, resistance, and expansion over its lifetime.In this work, battery degradation is modeled using the single particle model (SPM) framework, including mechanical damage in the electrodes, which results in loss of active material (LAM), and the side reactions for SEI growth and Li plating, which result in loss of lithium inventory (LLI). We introduce an equivalent stress and concentration dependence of stress to the mechanical damage model. Commonly used fatigue models assume symmetric cycles (zero-mean stress) [1]. To account for cycling conditions with different currents on charge and discharge, an equivalent stress that adjusts for non-zero mean stress is needed. The concentration dependency of strain and the resulting stress allows us to capture different degradation rates for cells cycled at different depths of discharge (DOD). Lithium plating at the separator interface is often described as a spatially non-uniform process using the pseudo-2D (P2D) model. This phenomenon can be captured in the SPM framework using a current-dependent dynamic term to account for spatial-nonuniformity of electrolyte dynamics at higher currents.Experimental data from cells cycling with periodic reference performance tests were used to tune the degradation model. In addition to the standard I, V, and T measurements, continuous measurements of the thickness change of the battery pouch cells were recorded. From this data, we extracted the capacity, electrode state of health (eSOH), resistance, and reversible and irreversible expansion. The test conditions were designed to excite different dominant degradation mechanisms (e.g. mechanical damage) by cycling the cells at different conditions (C-rate, temperature, preload pressure, and DOD). The tuning, which uses accelerated aging simulations [2] (to speed up the tuning process), results in a single set of parameters that predicts capacity loss, resistance growth, and irreversible thickness change as the battery ages, even for conditions that were not used for parameter tuning.The tuning is performed in two sequential steps. First, the parameters related to the electrochemical and mechanical degradation rates, which result in LLI and LAM, are tuned to match the extracted eSOH variables at each Reference Performance Test (RPT). The first tuning gives us the amount of plated Li, SEI growth, and mechanical damage in the particles. We then relate these quantities to irreversible expansion using a linear relationship in the case of SEI and mechanical damage and quadratic in the case of Li plating [3]. The same relationship is used for all cells, and this represents the 2nd tuning step. Our data set and calibration are unique in that the dominant degradation mode is the loss of lithium inventory due to the loss of active anode material. Most prior work on lifetime predictive models relied on SEI growth as the dominant degradation mode. Figure 2 shows the tuned model prediction of the three performance metrics over the cycle life of cells for various cycling conditions. The markers represent the measurement at each reference performance test, and the lines correspond to the model.

Benefit to Harm (B2H) Ratio for Bulk Vehicle to Grid (V2G) Services Using Lifetime Degradation Digital Twin: Emulating Various Dominant Degradation Mechanism

Vehicle-to-grid (V2G) services, utilizing electric vehicle (EV) batteries for grid support, enhance reliability and reduce peak energy demand. We present a physics-based model tuned for three different cell chemistry families and examine the influence of bulk V2G services on EV battery life. We consider various duty cycles, cell chemistries with nickel content (NMCxyz and various anode graphites), and associated dominant degradation mechanisms. To quantify the impact of offering V2G services, we introduce the V2G benefit-to-harm ratio (B2H). We define the benefit as the Ah gained with V2G and the harm as the life lost in days due to V2G, both compared to the baseline noV2G.B2H=(normalized Ah gained by 70% capacity fade) divided by (time in days reduction by the time that capacity fade has reached 70%). Note that the 70% capacity fade can be changed for various vehicle models depending on the warranty definition of the % capacity or usable battery energy (UBE) at the end of the warranty.Our findings indicate that the dominant degradation mechanism plays a crucial role in the benefit-to-harm (B2H) ratio of V2G or vehicle-to-building (V2B) [1]. Specifically, we clarify that the relative contribution of calendar aging to overall capacity loss is pivotal in determining the degradation due to V2G and possible associated benefits.Our model takes into account four degradation mechanisms based on a single-particle model. SEI growth and cathode transition metal dissolution are part of the calendar aging loss of lithium inventory (LLICal). The remaining LLI is attributed to Li-plating and mechanical degradation caused by particle cracking.We calibrate the model for three families of cell chemistries and conditions. The primary degradation mechanism for one cell family is anode mechanical degradation (LAMNeg). The second family of cells predominantly ages due to SEI layer growth, and the third family is degrading due to both mechanisms [2].We show that, in cases with a higher contribution of calendar aging to degradation (LLICal/LLI), V2G can be potentially more beneficial (in Ah gained by 70% capacity fade) than harmful (lifetime reduction in days by the time that capacity fade has reached 70%). Furthermore, we have evidence that the V2G charging pattern can have a secondary effect on the B2H ratio. For example, being a risk taker and charging the battery late or being cautious and charging it as soon as possible can lead to different degrees of degradation depending on the chemistry and conditions of the battery [3].With our multiphysics reduced order model of battery lifetime degradation, we fully explain why previous studies [4] have shown that the impact on EV battery degradation varies from inconsequential [5] to projecting a need for early battery replacement [6]. Our results clarify that battery chemistry and usage patterns are important factors in determining whether or not to utilize a vehicle for grid support, as well as the overall financial impact on the owner and OEM warranty.

Guiding the Choice of Carbon Nanotubes Conductive Additives for Silicon Anode Electrode through Microstructure Scale Analysis

Silicon anode electrodes exhibit a large microstructure design space as several carbon additives are considered to improve its conductivity and thus electrochemical performance. Investigating each combination experimentally is time-consuming. In this work, microstructure scale modeling is used to discriminate between different carbon additives to accelerate electrode development [1]. Baseline spherical C45, single wall carbon nano tube (SWCNT, cf. Fig. 1), carbon nano rods (CNR), and mixed SWCNT-CNR are considered and their respective impact on connectivity, effective conductivity, specific surface area, pore size distributions, and effective diffusivity are calculated to provide design recommendations. To do so, microstructures are numerically generated using the NREL open-source Microstructure Analysis Toolbox (MATBOX) available to the battery community* [2].Additionally, the model is used to correlate material utilization and silicon particle size, in agreement with experimental data, to further guide the selection of silicon material.Lastly, the model is used to investigate the porosity specific surface area relationship in the low porosity range, for which the analytical expression 3ε/r (with ε the particle volume fraction and r the particle radius) is no longer valid due to the packing density limit, and revealed a non-monotonic correlation. Such result is very relevant for silicon anode development as one major hindrance to this chemistry is its limited calendar life due to SEI growth, for which the specific surface area is a key parameter. *Nanotube generation new feature will be released after article [1] publication. [1] F. L. E. Usseglio-Viretta, J. H. Kim, J. Preimesberger, N. Neale, P. Weddle, A. Verma, A. M. Colclasure, Guiding the Choice of Carbon Nanotubes Conductive Additives for Silicon Anode Electrode Through Microstructure Scale Analysis, in preparation[2] F. L. E. Usseglio-Viretta, P. Patel, E. Bernhardt, A. Mistry, P. P. Mukherjee, J. Allen, S. J. Cooper, J. Laurencin, K. Smith, MATBOX: An Open-source Microstructure Analysis Toolbox for microstructure generation, segmentation, characterization, visualization, correlation, and meshing, SoftwareX, 17 (2022) 100915. Figure 1

Quantifying multiphase SEI growth in sulfide solid electrolytes

Quantifying multiphase SEI growth in sulfide solid electrolytes

Degradation of lithium-ion batteries under automotive-like conditions: aging tests, capacity loss and q-OCP interpretation

Battery electric vehicles are spreading worldwide as a relevant solution for the decarbonization of the transportation sector, ensuring high volume and weight-based energy density, high efficiency and low cost. Nevertheless, batteries are known to age in a rather complex and conditions-dependent way. This work aims at investigating battery aging resulting from close-to-real world conditions, highlighting single stressors role. Hence, aiming at representativeness for automotive application, an extensive literature review is performed, identifying a wide set of representative conditions together with their specific variations to be investigated. Realistic driving schedules like WLTP is identified and continuously applied in cycling on commercial samples, investigating the capacity loss from a q-OCP perspective with an equilibrium model. In general, loss of lithium inventory is detected as the main degradation parameter, likely related to SEI growth. Recharge C-rate and load profile appear as poorly-affecting degradation, while a dominant role is associated with operating temperature. Interestingly, temperature and cycling-related degradation appears to be independent and their effects can be effectively superimposed. Loss of active positive electrode material seems particularly affected by cycling depth of discharge, likely having mechanical origin as particle cracking.

Boron-Silicon Alloy Nanoparticles as a Promising New Material in Lithium-Ion Battery Anodes.

Silicon's potential as a lithium-ion battery (LIB) anode is hindered by the reactivity of the lithium silicide (Li x Si) interface. This study introduces an innovative approach by alloying silicon with boron, creating boron/silicon (BSi) nanoparticles synthesized via plasma-enhanced chemical vapor deposition. These nanoparticles exhibit altered electronic structures as evidenced by optical, structural, and chemical analysis. Integrated into LIB anodes, BSi demonstrates outstanding cycle stability, surpassing 1000 lithiation and delithiation cycles with minimal capacity fade or impedance growth. Detailed electrochemical and microscopic characterization reveal very little SEI growth through 1000 cycles, which suggests that electrolyte degradation is virtually nonexistent. This unconventional strategy offers a promising avenue for high-performance LIB anodes with the potential for rapid scale-up, marking a significant advancement in silicon anode technology.

Enable superior performance of ultra-high loading electrodes through the cost-efficient solvent-free electrode manufacturing technology

This research explores an innovative solvent-free method for fabricating ultra-high loading NMC811 and graphite electrodes (∼6mAh∙cm−2), showcasing remarkable electrochemical performance enhancements compared to the electrodes prepared by the conventional slurry-casting method. The optimized microstructure with dry-printed (DP) electrodes enhanced electrolyte penetration and minimized lithium-ion diffusion tortuosity resulting in improved rate performance at high current rates. Additionally, this innovative electrode manufacturing approach enables more uniform CEI and SEI formation and growth, which effectively doubles the cycle life of single-layer pouch cells with DP electrodes. Beyond the performance enhancements, this method also offers a notable 29.2 % overall cost advantages, potentially revolutionizing future battery manufacturing. The findings presented in this work underscore the potential of solvent-free manufacturing technology as a high-loading capable and cost-efficient path for advanced battery production.

Challenges of Predicting Temperature Dependent Capacity Loss Using the Example of NMC-LMO Lithium-Ion Battery Cells

In semi-empirical aging modeling of lithium ion-batteries an Arrhenius approach is commonly applied to describe the temperature dependency of a linear capacity loss. However, this dependency can change with degradation modes which was also observed in this cyclic aging study on NMC111-LMO graphite pouch cells in a temperature range of 4 °C to 48 °C. By means of differential voltage analysis and post-mortem analysis we correlated different regimes in capacity loss to degradation modes and aging mechanisms. In the first regime, a power dependency of time was observed. A second accelerated linear regime which followed an increase in loss of active material of the positive electrode was seen for medium (∼19 °C to 25 °C) to high aging temperatures. Transition metal dissolution was suggested to cause accelerated SEI growth. An activation energy could be estimated to 0.83 eV (± 0.17 eV, 95% CI). Finally, at aging temperatures around 45 °C we propose decreased charge transfer kinetics to result in mossy dendrites on the negative electrode which cause a final knee in aging trajectory. The findings highlight the necessity of sufficient aging temperatures and testing time.

Investigation of The Failure Mechanisms of Li-Ion Pouch Cells with Si/Graphite Composite Negative Electrodes and Single Wall Carbon Nanotube Conducting Additive

Silicon-Graphite composite electrodes are a rapidly developing area of research and commercialization. Increasing the energy density of current Li-ion battery technology can be done by simply creating silicon-graphite composite electrodes. It is well known that the failure of these silicon-graphite composite electrodes stems from the expansion of the silicon during cycling that causes mechanical degradation, excessive SEI formation, and electrode shift loss. Here we explore the use and capacity loss mechanisms of a silicon-graphite composite anode employing CMC/SBR binder used in conjunction with single wall carbon nanotubes. These nanotubes are thought to be effective in increasing mechanical resiliency of the electrodes and increase the electrical connectivity between particles within the formed electrode. When the Si/graphite electrode cycles, it is believed that the SWCNTs help keep the active particles electrically connected and, hence, electrochemically active. Through dV/dQ analysis and in situ pressure monitoring, the pouch cells studied here are shown to exhibit minimal loss of active mass in the positive and negative electrodes but experience capacity loss due to continued negative electrode SEI growth leading to lithium inventory or shift loss.

Aging Mechanism For Calendar Aging of Li-Ion Cells With Si/Graphite Anodes

Calendar aging of Li-ion batteries with Si/graphite electrodes was investigated within this study. A total of 121 single-layer pouch full cells with either graphite or Si/graphite (3.0 wt−%, 5.8 wt−% and 20.8 wt−% Si) anodes and NMC622 cathodes with the same N/P ratio were built on pilot-scale. Calendar aging was studied at SoC 30%, 60%, and 100%, as well as temperature (25 °C, 45 °C, 60 °C) and time dependence. The aging data was analyzed in terms of capacity fade and a square-root behavior was observed. Differential voltage analysis (DVA) has been performed as a function of aging time. The observed temperature and time dependence is best described by time dependent, 3D Arrhenius plots. Post-Mortem analysis (SEM, EDX, GD-OES) is applied to investigate the changes on electrode and material level. Conclusions are drawn on the main aging mechanisms for calendar aging of Li-ion cells with Si/graphite anodes and differences between Si/graphite and pure graphite anodes are discussed. The Si-containing cells show a combination of lithium inventory loss and a loss of accessible Si active material, both caused by SEI growth.

The Study of High-Energy Lithium Polymer Cells for Second-Life Applications

The environmental impact of lithium-ion batteries (LiBs) depends directly on their useful lifetime. Doubling the useful lifetime cuts the environmental impact per functional unit in half. However, if the cell is insufficient for one application it can still be sufficient for another. The beneficial operational value of LiBs between various applications presents a prospective solution to environmental sustainability. However, the capacity and power of the LiBs tend to degrade over time, which is a major concern for its application. The investigation and identification of the several key battery aging mechanisms are essential to its second life application. This paper is focused on the experimental analysis performed on XALT 31 Ah high-energy lithium polymer cells with NMC 433 as active electrode material. Characterization and cycling tests were performed on new cells and the data obtained was compared to equal cells cycled 7 years ago. The tests were carried out with the same temperatures (25 and 45 degrees Celsius) for both new and old batteries, respectively. The internal resistance diminishes after 100 cycles for both new and old batteries at 25oC. It does however decrease more for the new batteries, than the old ones. The decrease in resistance can be due to an increase in capacity and it is normal to see in the BoL of a cell. In addition, the temperature during cycling is assumed to be higher than the storage temperature, which also can decrease internal resistance. Since both the new and old batteries behave the same way, it is argued that this is the natural development of resistance in this cell type. When cycled at 45oC, the cell resistance increased after 100 cycles. Even though resistance diminishes with increasing temperature. Other ageing mechanisms such as SEI growth and lithium plating are activated by higher temperatures, resulting in an increase in internal resistance at 45 degrees. For the new and old batteries, the dQdV curves at the BoL are very similar after 100 cycles, it is difficult to know if the trend would continue as the cells age further. Based on this study findings, new approaches can be developed for more accurate and reliable prediction on the aging degradation of high energy lithium batteries.

Comprehensive Analysis of Performance Evolution and Failure Mechanisms for Commercial Large-Format NMC-Gr Lithium-Ion Pouch Cells

With the accelerating adoption of lithium-ion battery systems, careful analysis of the performance evolution and failure mechanisms of commercially produced batteries is crucial for predicting the lifetime of battery systems, estimating operating and maintenance costs, and ensuring safe operation. Here, we present the results of a 2-year aging study conducted on large-format NMC-Gr pouch cells from a large battery manufacturer. Calendar and cycle aging tests were conducted on 23 cells, with calendar aging conducted at varying temperature and state-of-charge, and cycle aging conducted at varying temperatures, average voltage, voltage window, charge-discharge rates, using both constant-current cycling and drive cycles.The evolution of cell performance throughout aging was observed using electrochemical characterization tests. DC pulses show a general trend of decreasing then increasing resistance, while EIS measurements are used to deconvolute resistance evolution modes. Capacity checks show decreasing capacity throughout life for all cells. Fitting of C/20 charge and discharge curves using half-cell voltage data is used to quantify loss of lithium inventory and loss of active material degradation modes, as well as reveal the de/lithiation window experienced by electrodes throughout aging.While cell performance evolution is often neatly explained by a few key degradation modes, cell failures observed during testing were often the result of several interacting degradation mechanisms. Degradation mechanisms were identified by a variety of physical, electrochemical, and microstructural characterizations. Key degradation mechanisms observed were SEI growth at graphite/electrolyte interfaces, electrolyte decomposition and gassing leading, NMC particle cracking, Li plating, and electrode dry-out. Degradation mechanisms observable in early life often initiate new failure mechanism that lead to cell failure or safety concerns through physical or electrochemical interactions. The findings demonstrate the multi-faceted challenge of cell lifetime and failure prediction in real-world systems.

SEI growth on Lithium metal anodes in solid-state batteries quantified with coulometric titration time analysis

Lithium-metal batteries with a solid electrolyte separator are promising for advanced battery applications, however, most electrolytes show parasitic side reactions at the low potential of lithium metal. Therefore, it is essential to understand how much (and how fast) charge is consumed in these parasitic reactions. In this study, a new electrochemical method is presented for the characterization of electrolyte side reactions occurring on active metal electrode surfaces. The viability of this new method is demonstrated in a so-called anode-free stainless steel ∣ Li6PS5Cl ∣ Li cell. The method also holds promise for investigating dendritic lithium growth (and dead lithium formation), as well as for analyzing various electrolytes and current collectors. The experimental setup allows easy electrode removal for post-mortem analysis, and the SEI’s heterogeneous/layered microstructure is revealed through complementary analytical techniques. We expect this method to become a valuable tool in the future for solid-state lithium metal batteries and potentially other cell chemistries.

Modeling Battery Formation: Boosted SEI Growth, Multi-Species Reactions, and Irreversible Expansion

This work proposes a semi-empirical model for the SEI growth process during the early stages of lithium-ion battery formation cycling and aging. By combining a full-cell model which tracks half-cell equilibrium potentials, a zero-dimensional model of SEI growth kinetics, and a semi-empirical description of cell thickness expansion, the resulting model replicated experimental trends measured on a 2.5 Ah pouch cell, including the calculated first-cycle efficiency, measured cell thickness changes, and electrolyte reduction peaks during the first charge dQ/dV signal. This work also introduces an SEI growth boosting formalism that enables a unified description of SEI growth during both cycling and aging. This feature can enable future applications for modeling path-dependent aging over a cell’s life. The model further provides a homogenized representation of multiple SEI reactions enabling the study of both solvent and additive consumption during formation. This work bridges the gap between electrochemical descriptions of SEI growth and applications toward improving industrial battery manufacturing process control where battery formation is an essential but time-consuming final step. We envision that the formation model can be used to predict the impact of formation protocols and electrolyte systems on SEI passivation and resulting battery lifetime.

Using Reference Electrodes to Validate Parameterization of Individual Electrode Soh in the Single Particle Model with Electrolyte

Most model parametrization techniques for reduced order physics-based Lithium-ion battery models like the single particle model rely on minimizing the error in the measured and predicted cell terminal voltage. The battery terminal voltage is the difference between the voltages of the positive and negative electrode solid phase potentials. If the individual contribution of each electrode overpotential to the terminal voltage, is not measured, there could be multiple combinations of parameters that provide similar RMSE for voltage prediction, yielding non-unique solutions and local minima. Misattributing the parameters for kinetics and diffusion in each electrode could result in increased plating or over-conservative designs at higher operating currents.Adding a reference electrode to the battery allows us to measure the individual electrode potentials experimentally. Using this extra measurement, we can parametrize the kinetic and diffusion reactions in positive and negative electrodes with better confidence [1], and validate the electrode-specific state of health parameterization, specifically the increased resistances due to SEI growth and shift in the stoichiometric window as the cell ages [2,3]. In our experiments, we used a pouch cell manufactured in the U of M Battery Lab with Targray NMC 622 Single Crystal cathode powder, Superior SLC 1520-T anode powder, and a custom fabricated Lithium Iron Phosphate (LFP) reference electrode deposited on a porous electrode layer. Further details of the reference electrode are given in [4]. The model was parametrized using discharge data at different C-rates and a modified Hybrid Pulse Power Characterization test. Finally, the RMSE for both the modeled negative and positive electrode potentials are calculated for the validation data set which uses the US06 Drive cycle.

Transient Self-Discharge after Formation in Lithium-Ion Cells: Impact of State-of-Charge and Anode Overhang

A fast determination of cell quality after formation is challenging due to transient effects in the self-discharge measurement. This work investigated the self-discharge of NMC622/graphite single-layer pouch cells with varying anode dimensions to differentiate between SEI growth and anode overhang equalization processes. The transient self-discharge was measured directly after formation via voltage decay and for 20 weeks of calendar storage at three states-of-charge (SOC), 10%, 30%, and 50%. The transient behavior persisted for the entire measurement duration, even at a low SOC. Still, the low SOC minimized the impact of SEI growth and anode overhang equalization compared to moderate SOCs. Evaluating the coulombic efficiency from cycle aging showed a distinct capacity loss for the first cycle after storage, indicating further SEI growth, which stabilized in subsequent cycles. The aged capacity after cycling showed no significant dependence on the calendar storage, which further promotes fast self-discharge characterization at low SOC.

Exploring the Influence of Temperature on Anode Degradation in Cycling-Aged Commercial Cylindrical Graphite-Si|NCA Cells

The degradation mechanisms of commercial graphite–SiOx/NCA battery related to the aging process in full cell under cycling conditions at three different temperatures, namely, 10 °C, 25 °C, and 45 °C, have been studied via post-mortem analysis, emphasizing the high energy density graphite–SiOx anode behaviour. The aging process of the full battery has been studied by non-destructive electrochemical methods. Then, to gain more understanding on the mechanisms that govern the graphite–SiOx degradation, full cells are disassembled, and the anodes are studied by physicochemical analysis techniques, electron microscopy techniques, and electrochemical characterizations. The battery cycled at 25 °C, between 2.5 and 4.2 V, shows higher cyclability than those cycled at 45 °C and 10 °C, at SoH 80%. Under these conditions, the structural and morphological changes undergo by graphite–SiOx and SiOx particles, respectively, and the loss of active material, together with the SEI growth explain the anode degradation.