Ralf Benger

Swelling in lithium-ion cells can translate into non-uniform deformation inside mechanically constrained multi-cell assemblies, but quantitative, spatially resolved characterization at the assembly scale remains limited. Here, we present an X-ray computed tomography (CT)-based workflow to quantify aging-induced geometric change and geometric inhomogeneity in an 8-cell prismatic lithium iron phosphate (LFP) module operated under mechanical constraint. The module was scanned at the beginning of life and in an aged state, corresponding to a module state of health of 86.58\,\% based on discharge capacity, under matched conditions of 30\,\% state of charge and 25\,\degree C. From the reconstructed CT volumes, spatial fields of cell thickness and inter-cell gaps were extracted using an edge-based image-processing workflow and summarized using statistical descriptors (mean, standard deviation, interquartile range). After cycling, all cells exhibited net thickening and all inter-cell gaps decreased, while the overall stack thickness changed only marginally, indicating that swelling was largely accommodated by compression of the interleaved pads. The extracted thickness fields further revealed increased within-cell heterogeneity and enhanced cell-to-cell dispersion. These geometric dispersion trends corresponded to increased electrochemical dispersion observed during capacity determination. The proposed workflow provides non-destructive, spatially resolved metrics for evaluating deformation accommodation in constrained battery stacks and for generating quantitative reference data for model validation and design assessment.

As a result of the ongoing energy revolution, the development of new battery types with new cell chemistries gained a lot of attention in the last five to ten years. This evolution is on one side triggered due to the gap between demand and supply of required resources like lithium, nickel, and cobalt. This gap led to a huge cost-rally of the raw materials, e.g. the price of lithium was very volatile within the last 5 years.^{1, 2} The search for other cheap, reusable, and above all, safe sustainable cell chemistries led. among other things, to the development of rechargeable sodium-ion batteries (SIBs). Other cell chemistries that show promising properties are zinc-ion batteries (ZIBs) and potassium-ion batteries (KIBs) but these are not commercialized yet. One of the raising stars that gained attention in the last few years is the so-called aluminum-graphite-dual-ion battery (AGDIB). The active materials are aluminum as inexpensive anode and natural graphite as cathode material. During charging, chloroaluminate anions intercalate into the graphite host-matrix, while at the anode, metallic aluminum from the electrolyte is deposited. Typical electrolytes, which are in research focus, are the so-called ionic liquids made of 1-ethyl-3-methyl-imidazoliumchloride [EMIm]Cl and AlCl₃ or triethylamine hydrochloride [TEA]Cl and AlCl₃.^{3, 4} Other electrolytes belong to the group of so-called deep-eutectic solvents e.g., a mixture of urea and AlCl₃.⁵ Thus, less toxic than common electrolytes in other chemistries. Beside the mentioned advantages (cheap raw materials and urea-based electrolytes), the AGDIB can be operated with extraordinary high-power densities up to as shown in laboratory-scaled battery cells.⁶ Thus, together with an extraordinary long cycle-life >25.000 cycles in lab test cells, the AGDIB might be a game-changer for high-power applications. To push the technical-readiness-level (TRL), we focused on upscaling processes aiming at higher loadings & multilayered pouch cells. This involved optimization of selected pouch cell casing materials as well as a detailed study on adjusting the effective graphite loading, evaluating binders and slurry recipes together with a controlled porosity of the prepared electrodes. We increased the active graphite loading from to employing a sodium alginate binder, while the prepared electrodes showed a mean capacity up to 80-100 mAh for a 2-layered cell. The results are supported by in-depth electrochemical characterization like cyclic voltammetry (CV), U/I-curves and electrochemical impedance spectroscopy (EIS). To allow further upscaling, the specifics of cells in the ampere-hour range have been determined. To enhance the kinetics of electrochemical Al-plating and stripping mechanism, as suggested by other groups⁷, we analyzed commercially available Al-alloys by CV, chronopotentiometry (CP) and EIS to push the high-power properties of the developed AGDIB. Those new pouch cells show an extraordinary cycling stability above 3,000 cycles at 10C while increasing the energy efficiency and rate capability. For the first time the AGDIB is also tested with a typical power-profile for grid-stabilization. In addition, the AGDIB was evaluated for a potential application that matches the performance characteristics - the provision of instantaneous reserve. This profile consists of short, highly dynamic pulse loads over several hours and has been used at 20 °C and 30 °C and scaled to 1 and 5C. Simulation of these tests with a parameterized model completed the evaluation The results confirm the applicability of AGDIB for dynamic grid-stabilization and thus their possible contribution in providing a stable energy supply employing renewable, yet fluctuating energy sources. The data obtained are of fundamental importance for increasing the TRL and represent the first step towards a possible commercially usable rechargeable AGDIB.

Lithium-ion batteries play a vital role in modern energy storage systems, being widely utilized in devices such as mobile phones, electric vehicles, and stationary energy units. One of the critical challenges with their use is the thermal runaway (TR), typically characterized by a sharp increase in internal pressure. A thorough understanding and accurate prediction of this behavior are crucial for improving the safety and reliability of these batteries. To achieve this, two new combined models were developed: one to simulate the thermal runaway and another to simulate the internal cell pressure. The thermal model tracks a chain of decomposition reactions that eventually lead to TR. At the same time, the pressure model simulates the proportional increase in pressure due to the evaporation of the electrolyte and the gases produced from the decomposition reactions. What sets this work apart is the validation of the pressure model through experimental data, specifically for prismatic lithium-ion cells using NMC chemistries with varying stoichiometries—NMC111 and NMC811. While the majority of the literature focuses on the simulation of temperature and pressure for cylindrical cells, studies addressing these aspects in prismatic cells are much less common. This article addresses this gap by conducting pressure validation experiments, which are hardly documented in the existing studies. Furthermore, the model’s accuracy and flexibility are tested through two experiments, conducted under diverse conditions to ensure robust and adaptive predictions of cell behavior during failure scenarios.

The authors wish to make the following corrections to their paper

The increasing adoption of lithium-ion battery cells in contemporary energy storage applications has raised concerns regarding their potential hazards. Ensuring the safety of compact and modern energy storage systems over their operational lifespans necessitates precise and dependable monitoring techniques. This research introduces a novel method for the cell-specific surveillance of prismatic lithium-ion cells, with a focus on detecting pressure increases through the surface application of a fiber Bragg grating (FBG) sensor on a rupture disc. Commercially available prismatic cells, commonly used in the automotive sector, are employed as test specimens and equipped with proven pressure and innovative FBG sensors. Encompassing the analysis capacity, internal resistance, and pressure (under elevated ambient temperatures of up to 120 °C), this investigation explores the thermal degradation effects. The applied FBG sensor on the rupture disc exhibits reversible and irreversible state changes in the cells, offering a highly sensitive and reliable monitoring solution for the early detection of abuse and post-abuse cell condition analysis. This innovative approach represents a practical implementation of fiber optic sensor technology that is designed for strain-based monitoring of prismatic lithium-ion cells, thereby enabling customized solutions through which to address safety challenges in prismatic cell applications. In alignment with the ongoing exploration of lithium-ion batteries, this research offers a customizable addition to battery monitoring and fault detection.

Various methods published in recent years for reliable detection of battery faults (mainly internal short circuit (ISC)) raise the question of comparability and cross-method evaluation, which cannot yet be answered due to significant differences in training data and boundary conditions. This paper provides a Monte Carlo-like simulation approach to generate a reproducible, comprehensible and large dataset based on an extensive literature search on common assumptions and simulation parameters. In some cases, these assumptions are quite different from field data, as shown by comparison with experimentally determined values. Two relatively simple ISC detection methods are tested on the generated dataset and their performance is evaluated to illustrate the proposed approach. The evaluation of the detection performance by quantitative measures such as the Youden-index shows a high divergence with respect to internal and external parameters such as threshold level and cell-to-cell variations (CtCV), respectively. These results underline the importance of quantitative evaluations based on identical test data. The proposed approach is able to support this task by providing cost-effective test data generation with incorporation of known factors affecting detection quality.

A possible contamination with impurities or material weak points generated in cell production of lithium-ion batteries increases the risk of spontaneous internal short circuits (ISC). An ISC can lead to a sudden thermal runaway (TR) of the cell, thereby making these faults especially dangerous. Evaluation regarding the criticality of an ISC, the development of detection methods for timely fault warning and possible protection concepts require a realistic failure replication for general validation. Various trigger methods are currently discussed to reproduce these ISC failure cases, but without considering a valid basis for the practice-relevant particle properties. In order to provide such a basis for the evaluation and further development of trigger methods, in this paper, the possibilities of detecting impurity particles in production were reviewed and real particles from pouch cells of an established cell manufacturer were analysed. The results indicate that several metallic particles with a significant size up to 1 mm × 1.7 mm could be found between the cell layers. This evidence shows that contamination with impurity particles cannot be completely prevented in cell production, as a result of which particle-induced ISC must be expected and the need for an application-oriented triggering method currently exists. The cause of TR events in the field often cannot be identified. However, it is noticeable that such faults often occur during the charging process. A new interesting hypothesis for this so-far unexplained phenomenon is presented here. Based on all findings, the current trigger methods for replicating an external particle-induced ISC were evaluated in significant detail and specific improvements are identified. Here, it is shown that all current trigger methods for ISC replication exhibit weaknesses regarding reproducibility, which results mainly from the scattering random ISC contact resistance.