arXiv subjects

Arnulf Latz

Publications and source records attributed to Arnulf Latz.

At least 19 recordsLinked to original sources

arXiv2026

Lattice Boltzmann Methods with Anisotropic Equilibrium Distributions

Lattice Boltzmann methods are usually derived under the assumption of isotropy. In this work, we present a derivation of a Lattice Boltzmann method for anisotropic fluid flow. Starting from an anisotropic equilibrium distribution, we show a full derivation of the resulting lattice Boltzmann method. We ensure that our method correctly reproduces macroscopic behavior via Chapman-Enskog analysis for a single-relaxation time collision operator. As a result, we are able to show that a properly discretized anisotropic Maxwell-Boltzmann equilibrium does macroscopically in fact lead to an anisotropic variation of the Navier-Stokes equations. All desired properties of lattice Boltzmann methods, such as locality of the collision operator, isotropic discrete position and velocity space, or mass and momentum conservation are retained. While it is explicitly shown in the context of fluid flow, the presented scheme is straight-forward to adopt to advection-diffusion problems.

physics.flu-dyn↗

arXiv2026

Effects of High-Temperature Preconditioning on Li Plating During Low-Temperature Cycling of the COTS LG Chem HG2 Cell

Commercial off-the-shelf~(COTS) Li ion cells offer an attractive and rechargeable power source for spacecraft applications. However, since these cells are typically designed for charging above 0\,\textdegree C, challenging sub-zero temperatures could inflict irreversible degradation and safety hazards during in-flight operation. To address these challenges, this work explores strategies affecting their low-temperature performance. Specifically, we investigate the Li plating behavior of the COTS~LG~Chem~18650~HG2 cell during galvanostatic cycling at $-20\,$\textdegree C and its dependence on prior high-temperature preconditioning protocols, involving either two-week galvanostatic cycling or storage at 30\,\textdegree C, as well as a reference case without preconditioning, i.e., direct cycling at $-20\,$\textdegree C. Experimental cycling tests reveal distinct differences in Li metal deposition between cells subjected to these conditions. To identify the origin of these discrepancies, we combine computed tomography of the electrode microstructure with three-dimensional, spatially resolved cell modeling and analyze the simulation results.

physics.chem-ph↗

arXiv2026

Structure Matters: A Scale-Resolved Numerical Operando Approach for Lithium-Sulfur Batteries

Lithium-Sulfur batteries (LSBs) are believed to have a high potential for aerospace applications due to their high gravimetric energy density. However, despite decades of research and advances, they still suffer from poor rate capability and low power output, eventually preventing their practical implementation. One particular aspect we want to shed light on is the influence of the porous cathode structure on the rate performance during discharge. Therefore, we present a scale-resolved simulation methodology involving high-performance computing (HPC), which aims to provide structural insights into the electrochemical cell behavior that are experimentally hardly accessible even for modern operando methods. Our \emph{numerical operando approach} employs scaling analysis for efficient model parametrization as well as rigorous parameter transfer between models of different dimensionality and is based on a coarse-grained continuum model. The latter is spatially discretized with a Discontinuous Galerkin (DG) method and advanced in time by an adaptive controller. The models and methods as well as HPC aspects of our toolbox will be critically discussed, finally showcasing the capabilities of our workflow to improve LSBs.

physics.comp-ph↗

arXiv2026

Physics-based modeling of cyclic and calendar aging of LIBs with Si-Gr composite anodes

Higher energy density and longer lifetime are the requirements for next-generation lithium-ion batteries. A promising anode material is silicon, which offers high specific capacity, but its significant volume change during lithiation and delithiation enormously reduces battery lifetime. A physical understanding of the processes degrading the battery is key to mitigate this effect and advance in the field. We develop a physics-based model to describe degradation during battery cycling under various protocols and storage conditions, with varying check-up (CU) frequencies. The model can disentangle basic degradation mechanisms, such as the growth of the Solid-Electrolyte Interphase (SEI), from silicon mechanisms, such as particle cracking, SEI growth on cracks, and loss of active material (LAM). We investigate the impact of CUs on the observed storage degradation and the reason behind the increased degradation in batteries, including silicon in the anode. Additionally, we relate the observed degradation to operating conditions, enabling future optimization of battery use and design.

physics.chem-ph↗

arXiv2025

Nested State and Degradation Estimation of a Satellite Battery with In-flight Data

Li-ion batteries are essential for the energy supply of satellites. The accurate estimation of their states is important for the reliable and safe operation in space. This paper introduces a new algorithm for the estimation of SOC and SOH. The multi-timescale algorithm combines Kalman filters and physics-based models for batteries. We use a P2D model combined with a degradation model that describes capacity fading due to SEI growth. The state estimation algorithm combines two extended Kalman filters for the two states evolving on different timescales, with one filter nested within the other one. We test the algorithm with synthetic data as well as with in-flight data from Japanese satellite REIMEI. The algorithm adequately estimates the SOC and SOH in both cases. Furthermore it gives insight into the reliability of the chosen model.

physics.chem-ph↗

arXiv2025

Decomposing the collision operator in the lattice Boltzmann method

In transport theory, physical phenomena are well described using the Boltzmann equation, which is efficiently simulated and discretized with the lattice Boltzmann method. The collision step defines the microscopic molecules behavior, and thus the simulated physical phenomena. For complex phenomena, the collision step becomes complex as well. In this paper, we propose a framework to systematically decompose the collision step into individual collision rules. Each collision rule is easier to understand, thus a faster understanding of the whole is achieved. By inverting the process, i.e. composing multiple collision rules together, one can create novel collision steps, which can better describe the underlying complex phenomena. This framework's applications are manyfold, from both a theoretical and an application standpoint. Shown here is the decomposition of Robin boundary condition into Dirichlet and Neumann boundary conditions, extending it to a partial Robin boundary condition, and semi-permeable reactive membranes.

physics.flu-dyn↗

arXiv2025

Workflows and Principles for Collaboration and Communication in Battery Research

Interdisciplinary collaboration in battery science is required for rapid evaluation of better compositions and materials. However, diverging domain vocabulary and non-compatible experimental results slow down cooperation. We critically assess the current state-of-the-art and develop a structured data management and interpretation system to make data curation sustainable. The techniques we utilize comprise ontologies to give a structure to knowledge, database systems tenable to the FAIR principles, and software engineering to break down data processing into verifiable steps. To demonstrate our approach, we study the applicability of the Galvanostatic Intermittent Titration Technique on various electrodes. Our work is a building block in making automated material science scale beyond individual laboratories to a worldwide connected search for better battery materials.

cs.DB↗

arXiv2025

Stress-driven whisker formation in lithium metal batteries

Lithium metal batteries are promising for next-generation high-energy-density batteries, especially when lithium is directly plated on a current collector. However, lithium whiskers can form in the early stages of electroplating. These whiskers lead to low Coulombic efficiency due to isolated lithium formation during stripping. The mechanism of whisker formation is not fully understood, and different mechanisms are proposed in the literature. Herein, we computationally explore a stress-driven extrusion mechanism through cracks in the solid-electrolyte-interphase (SEI), which explains the experimentally observed root growth of lithium whiskers. We model the extrusion as a flow of a power-law Herschel-Bulkley fluid parametrized by the experimental power-law creep behavior of lithium, which results in the typical one-dimensional whisker shape. Consequently, in competition with SEI self-healing, SEI cracking determines the emergence of whiskers, giving a simple rule of thumb to avoid whisker formation in liquid electrolytes.

physics.chem-ph↗

arXiv2024

Physics-based inverse modeling of battery degradation with Bayesian methods

To further improve Lithium-ion batteries (LiBs), a profound understanding of complex battery processes is crucial. Physical models offer understanding but are difficult to validate and parameterize. Therefore, automated machine-learning methods (ML) are necessary to evaluate models with experimental data. Bayesian methods, e.g., Bayesian optimization for likelihood-free inference (EP-BOLFI), stand out as they capture uncertainties in models and data while granting meaningful parameterization. An important topic is prolonging battery lifetime, which is limited by degradation, such as the solid-electrolyte interphase (SEI) growth. As a case study, we apply EP-BOLFI to parametrize SEI growth models with synthetic and real degradation data. EP-BOLFI allows for incorporating human expertise in the form of suitable feature selection, which improves the parametrization. We show that even under impeded conditions, we achieve correct parameterization with reasonable uncertainty quantification, needing less computational effort than standard Markov chain Monte Carlo methods. Additionally, the physically reliable summary statistics show if parameters are strongly correlated and not unambiguously identifiable. Further, we investigate Bayesian alternately subsampled quadrature (BASQ), which calculates model probabilities, to confirm electron diffusion as the best theoretical model to describe SEI growth during battery storage.

physics.chem-ph↗

arXiv2024

Elliptical Silicon Nanowire Covered by the SEI in a 2D Chemo-Mechanical Simulation

Understanding the mechanical interplay between silicon anodes and their surrounding solid-electrolyte interphase (SEI) is essential to improve the next generation of lithium-ion batteries. We model and simulate a 2D elliptical silicon nanowire with SEI via a thermodynamically consistent chemo-mechanical continuum ansatz using a higher order finite element method in combination with a variable-step, variable-order time integration scheme. Considering a soft viscoplastic SEI for three half cycles, we see at the minor half-axis the largest stress magnitude at the silicon nanowire surface, leading to a concentration anomaly. This anomaly is caused by the shape of the nanowire itself and not by the SEI. Also for the tangential stress of the SEI, the largest stress magnitudes are at this point, which can lead to SEI fracture. However, for a stiff SEI, the largest stress magnitude inside the nanowire occurs at the major half-axis, causing a reduced concentration distribution in this area. The largest tangential stress of the SEI is still at the minor half-axis. In total, we demonstrate the importance of considering the mechanics of the anode and SEI in silicon anode simulations and encourage further numerical and model improvements.

physics.app-ph↗

arXiv2024

Modeling the Influence of Solvation on the Electrochemical Double Layer of Salt / Solvent Mixtures

Modelling electrolytes accurately on both a nanoscale and cell level can contribute to improving battery chemistries.[Armand and Tarascon, Nature, 2008, 451, 652-657] We previously presented a thermodynamic continuum model for electrolytes.[arXiv:2010.14915] In this paper we include solvation interactions between the ions and solvent, which alter the structure of the electochemical double layer (EDL). We are able to combine a local solvation model -- permitting examination of the interplay between electric forces and the ion-solvent binding -- with a full electrolyte model. Using this, we can investigate double layer structures for a wide range of electrolytes, especially including highly concentrated solutions. We find that some of the parameters of our model significantly affect the solvent concentration at the electrode surface, and thereby the rate of solvent decomposition. Firstly, an increased salt concentration weakens the solvation shells, making it possible to strip the solvent in the EDL before the ions reach the surface. The strength of the ion-solvent interaction also affects at which potential difference the solvation shells removed. We are therefore able to qualitatively predict EDL structures for different electrolytes based on parameters like molecule size, solvent binding energy and salt concentration.

physics.chem-ph↗

arXiv2024

Homogenized Lattice Boltzmann Model for Simulating Multi-Phase Flows in Heterogeneous Porous Media

A new homogenization approach for the simulation of multi-phase flows in heterogeneous porous media is presented. It is based on the lattice Boltzmann method and combines the grayscale with the multi-component Shan-Chen method. Thus, it mimics fluid-fluid and solid-fluid interactions also within pores that are smaller than the numerical discretization. The model is successfully tested for a broad variety of single- and two-phase flow problems. Additionally, its application to multi-scale and multi-phase flow problems in porous media is demonstrated using the electrolyte filling process of realistic 3D lithium-ion battery electrode microstructures as an example. The new method shows advantages over comparable methods from literature. The interfacial tension and wetting conditions are independent and not affected by the homogenization. Moreover, all physical properties studied here are continuous even across interfaces of porous media. The method is consistent with the original multi-component Shan-Chen method. It is accurate, efficient, easy to implement, and can be applied to many research fields, especially where multi-phase fluid flow occurs in heterogeneous and multi-scale porous media.

physics.flu-dyn↗

arXiv2024

Electro-Chemo-Mechanical Model for Polymer Electrolytes

Polymer electrolytes (PEs) are promising candidates for use in next-generation high-voltage batteries, as they possess advantageous elastic and electrochemical properties. However, PEs still suffer from low ionic conductivity and need to be operated at higher temperatures. Furthermore, the wide variety of different types of PEs and the complexity of the internal interactions constitute challenging tasks for progressing towards a systematic understanding of PEs. Here, we present a continuum transport theory which enables a straight-forward and thermodynamically consistent method to couple different aspects of PEs relevant for battery performance. Our approach combines mechanics and electrochemistry in non-equilibrium thermodynamics, and is based on modeling the free energy, which comprises all relevant bulk properties. In our model, the dynamics of the polymer-based electrolyte are formulated relative to the highly elastic structure of the polymer. For validation, we discuss a benchmark polymer electrolyte. Based on our theoretical description, we perform numerical simulations and compare the results with data from the literature. In addition, we apply our theoretical framework to a novel type of single-ion conducting PE and derive a detailed understanding of the internal dynamics.

physics.chem-ph↗

arXiv2024

Silicon Nanowires as Anodes for Lithium-Ion Batteries: Full Cell Modeling

Silicon (Si) anodes attract a lot of research attention for their potential to enable high energy density lithium-ion batteries (LIBs). Many studies focus on nanostructured Si anodes to counteract deterioration. In this work, we model LIBs with Si nanowire (NW) anodes in combination with an ionic liquid (IL) electrolyte. On the anode side, we allow for elastic deformations to reflect the large volumetric changes of Si. With physics-based continuum modeling we can provide insight into usually hardly accessible quantities like the stress distribution in the active material. For the IL electrolyte, our thermodynamically consistent transport theory includes convection as relevant transport mechanism. We present our volume-averaged 1d+1d framework and perform parameter studies to investigate the influence of the Si anode morphology on the cell performance. Our findings highlight the importance of incorporating the volumetric expansion of Si in physics-based simulations. Even for nanostructured anodes - which are said to be beneficial concerning the stresses - the expansion influences the achievable capacity of the cell. Accounting for enough pore space is important for efficient active material usage.

physics.chem-ph↗

arXiv2024

Challenges in Measuring Transport Parameters of Carbonate-based Electrolytes

Numerical simulations are a powerful tool for the development and improvement of Li-ion batteries. Modeling the mass transport of the involved electrolytic solutions requires precise determination of the corresponding electrolyte parameters. In this work, we attempt to measure the conductivity, the diffusion coefficient, the transference number and the thermodynamic factor for a system of 0.5$\,$M LiPF$_6$ dissolved in a blend of ethylene carbonate and ethyl methyl carbonate (EC:EMC, 3:7 weight) at 20$\,$°C and 50$\,$°C. Applying galvanostatic polarization experiments to symmetrical metal Li | electrolyte + separator | Li metal cells reveals, however, a potential response qualitatively deviating from theoretical expectations. Impeded diffusion processes indicate the presence of additional, undesired porous structures on the Li electrodes, preventing a reliable evaluation of the electrolyte parameters. To spectrally resolve the diffusive processes, we conduct very-low-frequency impedance spectroscopy. The impedance in fact exhibits multiple interfering diffusive features. In our measurements, an explicit identification of the impedance for the sole diffusion through the separator is however not feasible. Therefore, the authors doubt that polarizing experiments using Li metal electrodes yield accurate parameters for electrolytes.

physics.chem-ph↗

arXiv2023

High-Performance Computing in Battery Development: From Pore Scale to Continuum

An application for high-performance computing (HPC) is shown that is relevant in the field of battery development. Simulations of electrolyte wetting and flow are conducted using pore network models (PNM) and the lattice Boltzmann method (LBM), while electrochemical simulations are conducted using the tool BEST. All aforementioned software packages show an appropriate scaling behavior. A workflow for optimizing battery performance by improving the filling of battery components is presented. A special focus is given to the unwanted side effect of gas entrapment encountered during filling. It is also known to adversely affect the electrochemical performance of batteries and can be partially prevented by appropriate microstructure design such as electrode perforation.

cs.CE↗

arXiv2023

Influence of Electrode Structuring Techniques on the Performance of All-Solid-State Batteries

All-solid-state batteries (ASSBs) offer a promising route to safer batteries with superior energy density compared to conventional Li-ion batteries (LIBs). However, the design of the composite cathode and optimization of the underlying microstructure is one of the aspects requiring intensive research. Achieving both high energy and power density remains challenging due to limitations in ionic conductivity and active material loading. Using structure-resolved simulations, we investigate the potential of perforated and layered electrode designs to enhance ASSB performance. Design strategies showing significant performance increase in LIBs are evaluated regarding their application to ASSBs. Composite cathodes with solid electrolyte channels in the structure do not significantly increase cell performance compared to unstructured electrodes. However, the design with a two-layer cathode proves promising. The layered structure effectively balances improved ionic transport due to increased solid electrolyte fraction at the separator side and substantial active material loading through increased active material fraction at the current collector side of the cathode. Our research highlights key challenges in ASSB development and provides a clear direction for future studies in the field.

cond-mat.mtrl-sci↗

arXiv2023

A Volume-based Description of Transport in Incompressible Liquid Electrolytes and its Application to Ionic Liquids

Transference numbers play an important role for understanding the dynamics of electrolytes and assessing their performance in batteries. Unfortunately, these transport parameters are difficult to measure in highly concentrated, liquid electrolytes such as ionic liquids. Also, the interpretation of their sign and magnitude has provoked an ongoing debate in the literature further complicated by the use of different language. In this work, we highlight the role of the reference frame for the interpretation of transport parameters using our novel thermodynamically consistent theory for highly correlated electrolytes. We argue that local volume conservation is a key principle in incompressible liquid electrolytes and use the volume-based drift velocity as reference. We apply our general framework to electrophoretic NMR experiments. For ionic liquid based electrolytes, we find that the results of the eNMR measurements can be best described using this volume-based description. This highlights the limitations of the widely used center-of-mass reference frame which for example forms the basis for molecular dynamics simulations - a standard tool for the theoretical calculation of transport parameters. It shows that the assumption of local momentum conservation is incorrect in those systems on the macroscopic scale.

physics.chem-ph↗