Comsol (United States)

The mechanical failure of NMC electrode materials is a critical factor governing various capacity degradation mechanisms in lithium-ion batteries. Conventional modelling, however, often neglects the complexity of electrode microstructure, limiting the accurate assessment of how mechanical failure impacts cell performance. This work presents a comprehensive electro-chemo-mechanical model, utilising tomography data to incorporate a realistic electrode microstructure including both active and inactive components. This enables a more precise characterisation of battery performance by resolving the inhomogeneous distribution of charge, stress, and mechanical damage within the electrode during cycling. These heterogeneities are then linked to experimentally observed spatial variations in degradation and uneven ageing.A key factor in mechanical failure is the volume change of active particles during lithium (de)-intercalation, which induces significant stress within the electrode material due to mechanical constraints from particle and binder connections. This mechanical damage disrupts charge transport, further increasing heterogeneity and contributing to capacity degradation. We assess and investigate the dominant mechanical degradation modes, particularly comparing particle cracking to the failure of inactive components. Specifically, we examine how mechanical damage deteriorates electronic conductivity by increasing contact resistance at various interfaces. Our findings reveal that while particle cracking increases surface area potentially aiding charge transfer, it simultaneously weakens electronic connectivity among fragmented particles, leading to higher overall electronic resistance. Crucially, the structure and distribution of carbon-binder (CBD) are shown to significantly impact both Li-ion transport efficiency and active particle utilization; its mechanical failure directly contributes to resistance build-up and effective capacity loss.

Wave-based room acoustic simulations require accurate modeling of sound propagation in the presence of extended (bulk) reacting porous absorbers. The sound absorption in porous media is typically addressed by means of equivalent fluid models that provide frequency-dependent effective material parameters, such as density and bulk modulus. In the time domain, these frequency dependent properties result in the computation of convolution integrals, which is effectively handled via an auxiliary differential equations (ADE) method. In this work, we apply the time-explicit discontinuous Galerkin approach to modelling of sound propagation in anisotropic porous media (with an anisotropic equivalent fluid model) together with the ADE method. We demonstrate the importance of using the extended approach for porous media, where the sound absorption depends not only on the frequency and incident angle, but also on the travelling wave direction.

CITplusVolume 23, Issue 11 p. 51-51 U3Free Access Index/Impressum First published: 05 November 2020 https://doi.org/10.1002/citp.202071128AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume23, Issue11November 2020Pages 51-51 RelatedInformation

Modelling of electrochemical impedance spectroscopy (EIS) to predict aging in lithium ion batteries is a useful tool when performing a diagnosis of the state of health (SOH) of the battery. Aging of lithium ion batteries happens in applications from electric vehicles to stationary systems and is associated to capacity fade and impedance increase [1]. By predicting the aging parameters through modeling of EIS from separated electrodes, it is possible to estimate the SOH of the full cell and therefore improve its performance. In this work NCA and graphite electrodes were harvested from cylindrical cells aged under an off-grid PV/Battery system conditions and analyzed by means of EIS to determine the causes of electrode deterioration. The NCA/graphite cylindrical cells were calendar aged and cycle-aged between SOC 20-50 %, 35-65 %, 60-90 % and 20-95 % until end of test (EOT) is reached (e.g. 1000 cycles). The impedance behavior of the calendar and cycle aged cells were measured. Each electrode is carefully harvested once reached the EOT and electrochemically characterized using symmetric cells by means of EIS. A physics-based impedance model is employed to fit the experimental EIS of symmetrical cells using a least square fitting tool in COMSOL® Multiphysics 5.4. It is based on the pseudo two-dimensional (P2D) model [2] incorporating intercalation kinetics, mass and charge transport based on concentrated solution porous electrode theory. The model additionally accounts for double layer effect and aging mechanisms. Using the model, useful aging parameters were parameterized, and the variation of the aging parameters with different aging history was validated with the support of scattered electron microscopy (SEM) technique. Among the aging mechanisms described, an increase in the local contact resistance between the active material and the conductive carbon, and decrease in particle size due to particle cracking and further film formation due to SEI are considered. The impedance model parameters from both electrodes are then linked to the aging process observed on experimental full cell. Figure 1 shows the fitting and experimental curves for graphite Nyquist plot, in which we observe a good fitting specifically at low frequencies. Although the model predicts a second semicircle in the middle requency range, the experimental curve also shows a time constant element which can be considered as a truncated semicircle in the same region. [1] T. G. Zavalis, M. Klett, M. H. Kjell, M. Behm, R. W. Lindström, G. Lindbergh, Electrochemica Acta, 110 (2013) 335-348. [2] J. Newman and W. Tiedemann, AIChE J., 21, 25–41 (1975). Figure 1

Anion-exchange membrane fuel cells (AEMFC) are promising mainly due to the possibility to use none-PGM catalysts in the alkaline media [1]. However, before elaborating with alternative catalysts a better understanding is needed on which electrode is limiting and what the limitations are for the reference Pt/C catalyst. In fact, the rate constants for the ORR and HOR are not determined in the in the fuel cell [2]. On top of this the influence of water on the kinetics and water transport in and between the electrodes is debated [3]. In this study we have measured the influence of partial pressure in both a symmetrical H2/H2cell a H2/O2cell. Experimental I-V and impedance data has been modelled by two separate physic-based models. The experimental results show that the hydrogen reaction has two separate time-constants in the impedance spectra for the symmetrical cell, indicating a two-step reaction at the anode (see Figure below). From the O2/H2cell the ORR is found to be the limiting reaction at low currents densities, while the HOR has a greater impact at high currents densities. From the model, a limiting current is observed at the anode. The level of humidity is likely not determining the direct catalytic reaction kinetics but may affect indirectly through its impact on ionomer conductivity and swelling. Fig. Nyqvist plots of H2/H2symmetrical cell at OCP at different H2mixtures in Ar at 50°C, 95% RH, 125 ml/min. MEA: 0.4 mg/cm2Pt/C, AS4 ionomer and A201 Tokuyama membrane [4]. [1] D. R. Dekel. Journal of Power Sources, 375:158–169, 2018. [2] E. S. Davydova, S. Mukerjee, F. Jaouen, D. R. Dekel, ACS Catal. 8 , 665-6690, 2018. [3] B. Eriksson, H. Grimler, A. Carlson, H. Ekström, R. Wreland Lindström, G. Lindbergh, C. Lagergren, Int. J. Hydrognen Energy 44, 4930-4939, 2019. [4] A. CarlsonShapturenka, B. Eriksson, G. Lindbergh, C. Lagergren, R. Wreland Lindström, Electrochimica Acta 277 (2018) 151-160

Matured syntheses of inorganic nanocolloids today have allowed production of diverse asymmertic nanoparticles (NP) and even more complex assemblies, introducing a variety of nanomaterials with unique properties. Chirality is one of most intriguing symmetry groups in field of material science due to the optical rotatory power of chiral substances. Strong optical activity of inorganic nanoparticles (NPs) afford photosynthetic routes to chiral superstructures using circularly polarized photons (1). Although plasmonic NPs are promising candidates for such synthetic routes due to the strong rotatory power of highly delocalized plasmonic states (2), realization of light- driven synthesis of chiral nanostructures has been more challenging for plasmonic NPs than for the semiconductor due to the short lifetime of the plasmonic states. The process also can be difficult to recognize, and therefore requires unconventional approaches for the quantification of chiral products. Here, we demonstrate that illumination of Au precursors in the presence of citric acid with right- (left-) handed circularly polarized light (CPL) induces the formation of chiral Au nanostructures. Despite seemingly irregular shape of the particles, the resulted colloids showed distinctive mirror-imaged opposite circular dichroism (CD) bands according to the handedness of illuminated CPL. Circular dichroic response and geometric chirality from these seemingly achiral structures were successfully demonstrated and quantified by implementing three-dimensional (3D) electron tomography (e-tomo) into computational model. The mechanism of the light-driven assembly of chiral nanostructures is based on the asymmetric displacement of NPs in dynamic assemblies by plasmonic fields fol-lowed by particle-to-particle attachment. The ability of Au nanostructures to retain the polarization information of incident photons can be applicable to light absorbing materials, thus to create a variety of chiral nanomaterials. Similar examination of seemingly irregular NP through suggested chirality measure can also elucidate previously puzzling optical response from unclear geometric asymmetry of nanomaterials.

Understanding limitations in an operating AEMFC is essential to enhance the technology. Here the electrode processes are studied experimentally as well as by two physics-based models taking the porosity of the electrodes into account. The aim is to use the models to determine kinetic parameters specific for in-situ operation. The models can also be used to explain the experimental behavior. From the impedance model of a symmetric H2/H2 cell it is shown that the hydrogen oxidation reaction (HOR) proceeds through the Tafel-Volmer reaction pathway, with the hydrogen adsorption as the slower reaction step. Based on the HOR model a steady-state model of an O2/H2 cell is used to evaluate data from 14 experimental I-V curves, obtained for different gas partial pressures and catalyst loadings, in order to study the effects of the oxygen reduction reaction and overall cell limitations. The results show that the oxygen reduction reaction kinetics limit the cell performance for low current densities. However, at higher currents the uneven current distribution and locally low hydrogen adsorption at the anode increasingly affect the overall performance. Uneven current distribution is also observed at the cathode and likely caused by insufficient effective ionomer conductivity

The high demand on specific capacity and occasionally harsh environment in electric vehicles has detrimental effects on electrochemical, mechanical and thermal properties of NMC/graphite Li-ion batteries. The battery lifetime is reduced at high voltage and high temperature, both in terms of capacity fade and impedance increase. At the graphite electrode, the notion of SEI layer formation and growth leading to battery aging is widely accepted. On the other hand, aging effects on the NMC electrode needs to be investigated more thoroughly. Xiong et al. [1] reported that Li-ion cells could experience rapid failure due to impedance rise at the NMC electrode when cycled at an elevated temperature or a cut-off voltage above 4.2 V. A surface film formation for transition metal oxides, the growth of which accelerates upon high temperature and charge voltages, has been reported [2,3]. Literature also shows that the interaction between the positive and negative electrodes in full lithium-ion cells contribute to declined cell performance [4]. However, these aging mechanisms are not independently distinguishable. Therefore, it is important to be able to quantify each contribution and to decouple different aging mechanisms occurring on each electrode at different temperatures under high voltage condition. This study focuses on impedance behavior of commercial NMC111 (LiNi1/3Mn1/3Co1/3O2) and graphite electrodes in a small laboratory pouch cells. The NMC111/graphite in full-cell configuration are calendar aged and cycle aged between +3.8 V and +4.6 V vs. Li at 25 °C and 40 °C until 50% capacity fade is reached. Capacity and impedance behavior of the full cells are measured periodically in order to track the performance changes with aging. Each electrode is harvested at specific intervals of cycling stages and electrochemically characterized in symmetric cells by means of electrochemical impedance spectroscopy (EIS). A physics-based model is employed to parameterize aging parameters by fitting the EIS results from the symmetric cells using a least square fitting tool in COMSOL Multiphysics. The pseudo two-dimensional (P2D) model is an extension to the work of Doyle et al. [5] incorporating intercalation kinetics, mass and charge transport based on concentrated solution porous electrode theory. From the preliminary EIS results on NMC111 symmetric cells in Fig. 1, impedance increases at a small magnitude at 25 °C at the end of life (EOL) compared to the beginning of life (BOL). At 40 °C, however, large impedance rise at EOL is seen. On the other hand, it had been shown that capacity fade occurs at both temperatures during slow cycling on half-cells. The model optimization is firstly done for cells at BOL to deduce the aging-independent parameters. Towards EOL, the quantification of intrinsic physical aging properties such as the particle sizes, porosity, local contact resistance and surface film resistance which are the causes of impedance rise or capacity fade can be made. The potential effects of calendar aging on cell degradation is separated from the effects of cycle aging. The comparison with experimental capacity loss and impedance rise will further validate the model. The extraction of the parameters from the model enables deduction of different aging-induced mechanisms at each electrode. This quantitative analysis of aging behavior will contribute to improved lifetime predictive model for NMC111/graphite lithium-ion batteries. [1] D. J. Xiong, R. Petibon, M. Nie, L. Ma, J. Xia, J.R. Dahn, J. Electrochem. Soc. 163 (2016), 3, A546-A551 [2] P. Niehoff, M. Winter, Langmuir 29 (2013), 51, 15813-15821 [3] M. Wohlfahrt-Mehrens, C. Vogler, J. Garche, J. Power Sources 127 (2004) 58-64 [4] K. Xu, Chem. Rev. 114 (2014) 11503-11618 [5] M. Doyle, J. Newman, A. C. Gozdz, C. N. Schmutz, J.-M. Tarascon, J. Electrochem. Soc. 143 (1996) 1890–1903. Figure 1

Abstract This paper presents a model‐based analysis of a proton exchange membrane fuel cell (PEMFC) with a planar design as the power supply for portable applications.The cell is operated with hydrogen and consists of an open cathode side allowing for passive, self‐breathing, operation. This planar fuel cell is fabricated using printed circuit board (PCB) technology. Long‐term stability of this type of fuel cell has been demonstrated.A stationary, two‐dimensional, isothermal, mathematical model of the planar fuel cell is developed. Fickian diffusion of the gaseous components (O2, H2, H2O) in the gas diffusion layers and the catalyst layers is accounted for. The transport of water is considered in the gaseous phase only. The electrochemical reactions are described by the Tafel equation. The potential and current balance equations are solved separately for protons and electrons. The resulting system of partial differential equations is solved by a finite element method using FEMLAB (COMSOL Inc.) software.Three different cathode opening ratios are realized and the corresponding polarization curves are measured. The measurements are compared to numerical simulation results. The model reproduces the shape of the measured polarization curves and comparable limiting current density values, due to mass transport limitation, are obtained.The simulated distribution of gaseous water shows that an increase of the water concentration under the rib occurs. It is concluded that liquid water may condense under the rib leading to a reduction of the open pore space accessible for gas transport. Thus, a broad rib not only hinders the oxygen supply itself, but may also cause additional mass transport problems due to the condensation of water.