arXiv subjects

Lukas Lehnert

Publications and source records attributed to Lukas Lehnert.

3 recordsLinked to original sources

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↗

arXiv2025

Combining Molecular Dynamics and Experimental Methods for the Parametrization of Binary Carbonate-Based Electrolytes

Modelling the ionic transport in battery cells requires precise parametrization of the involved electrolytes. For carbonate-based electrolytes, however, the evaluation of their parameters suffers from interphase effects between the bulk electrolyte and the Li metal electrode, commonly present in the usual electrochemical polarization experiments. In this work, we combine measurements on conductivity and concentration cells with molecular dynamic simulations, avoiding these difficulties and thus, allowing for a more accurate determination of the parameters. We determine the conductivity, the transference number, the thermodynamic factor and the salt diffusion coefficient for three different electrolytes, i.e mixtures of ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl propionate (MP), dimethyl carbonate (DMC) and propylene carbonate (PC), containing LiPF$_6$ at various concentrations and temperatures. In order to validate the simulated transference numbers, we employ electrophoretic Nuclear Magnetic Resonance spectroscopy (eNMR).

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↗