arXiv subjects

Lukas Köbbing

Publications and source records attributed to Lukas Köbbing.

6 recordsLinked to original sources

arXiv2026

Poly(1,4-anthraquinone) as an Organic Cathode Material: Simulation of Observable Bonding Properties to Li, Na, Mg, and Ca

Poly(1,4-anthraquinone) (P14AQ) has emerged as a promising cathode material, offering high capacity and good cycling stability, yet the atomic-scale mechanisms governing metal-ion binding and electrochemical behavior remain poorly understood. To address this, we investigate the binding mechanisms of Li, Na, Mg, and Ca to P14AQ using quantum mechanical methods, particularly DFT and DFTB. A key challenge lies in the material's structural complexity: multiple conformers of P14AQ are energetically similar but kinetically isolated due to significant energy barriers. To account for this, we develop an automated method to generate all unique P14AQ conformers for a periodic polymer chain without rotational duplicates through an orientation labeling scheme. For each conformer, we systematically place a metal atom adjacent to every oxygen site, enabling a complete exploration of binding configurations. We observe two structural motifs: a single metal-oxygen bond and coordination to two opposite oxygen atoms. While Li and Na exhibit continuous energy distributions, Mg and Ca show an energy gap between the two motifs, with a strong preference for the two-oxygen binding configuration. Galvanostatic measurements support these findings by showing lower gravimetric capacities for Ca and Mg than for Li and Na. For Na, the different numbers of metal-oxygen bonds are reflected in the two voltage plateaus observed experimentally. Overall, the combined computational and experimental results explain the higher capacity of monovalent ions in P14AQ: divalent ions cannot bind efficiently to a single oxygen site due to unfavorable energetics, and the conformational distribution of the polymer chain prevents optimal coordination.

physics.chem-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↗

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

Slow Voltage Relaxation of Silicon Nanoparticles with a Chemo-Mechanical Core-Shell Model

Silicon presents itself as a high-capacity anode material for lithium-ion batteries with a promising future. The high ability for lithiation comes along with massive volume changes and a problematic voltage hysteresis, causing reduced efficiency, detrimental heat generation, and a complicated state-of-charge estimation. During slow cycling, amorphous silicon nanoparticles show a larger voltage hysteresis than after relaxation periods. Interestingly, the voltage relaxes for at least several days, which has not been physically explained so far. We apply a chemo-mechanical continuum model in a core-shell geometry interpreted as a silicon particle covered by the solid-electrolyte interphase to account for the hysteresis phenomena. The silicon core (de)lithiates during every cycle while the covering shell is chemically inactive. The visco-elastoplastic behavior of the shell explains the voltage hysteresis during cycling and after relaxation. We identify a logarithmic voltage relaxation, which fits with the established Garofalo law for viscosity. Our chemo-mechanical model describes the observed voltage hysteresis phenomena and outperforms the empirical Plett model. In addition to our full model, we present a reduced model to allow for easy voltage profile estimations. The presented results support the mechanical explanation of the silicon voltage hysteresis with a core-shell model and encourage further efforts into the investigation of the silicon anode mechanics.

cond-mat.mtrl-sci↗

arXiv2023

Voltage Hysteresis of Silicon Nanoparticles: Chemo-Mechanical Particle-SEI Model

Silicon is a promising anode material for next-generation lithium-ion batteries. However, the volume change and the voltage hysteresis during lithiation and delithiation are two substantial drawbacks to their lifetime and performance. We investigate the reason for the voltage hysteresis in amorphous silicon nanoparticles covered by a solid-electrolyte interphase (SEI). Concentration gradients inside the nanoscale silicon can not produce the massive stresses necessary to cause the reported voltage hysteresis. Our chemo-mechanical model shows that plastic deformation of the stiff, inorganic SEI during lithiation and delithiation reproduces the observed silicon open-circuit voltage hysteresis. Additionally, the viscous behavior of the SEI explains the difference between the voltage hysteresis observed at low currents and after relaxation. We conclude that the visco-elastoplastic behavior of the SEI is the origin of the voltage hysteresis in silicon nanoparticle anodes. Thus, consideration of the SEI mechanics is crucial for further improvements.

physics.chem-ph↗

arXiv2022

Growth of the Solid-Electrolyte Interphase: Electron Diffusion versus Solvent Diffusion

The solid-electrolyte interphase (SEI) substantially influences the lifetime of lithium-ion batteries. Nevertheless, the transport mechanism responsible for the long-term growth of the SEI remains controversial. This study aims at discussing the characteristic time and state-of-charge dependence of SEI growth mediated by electron diffusion versus solvent diffusion. We describe both transport mechanisms with continuum models and compare them to experimental results. We show that electron diffusion can explain both the observed state-of-charge dependence and the time dependence. In contrast, we demonstrate that solvent diffusion can reproduce either the state-of-charge dependence or the time dependence of capacity fade. There is no intermediate regime where solvent diffusion can explain both dependencies simultaneously. Furthermore, we emphasize the crucial role of anode voltage and state-of-charge on SEI growth in general. Due to self-discharge, this dependence can explain deviations from the typical square-root behavior in the time domain. We conclude that electron diffusion is the relevant process leading to the state-of-charge dependent SEI growth. Further experiments are needed to investigate the reason for contributions to the capacity fade that are independent of the state-of-charge.

physics.chem-ph↗