The increased focus on electromobility in European countries is closely linked to the establishment of local lithium‐ion battery (LIB) mass production facilities, such as Tesla's Gigafactory 1 in Nevada. While extensive knowledge in LIB lab‐scale assembly already exists, the transfer to industry‐scale production is an area of challenge that is tackled through intense production research. Slurries of nickel‐rich NMC811 that is sensitive to environmental conditions, and therefore more difficult to process, are successfully up‐scaled to 65 kg industry‐scale batches and investigated through rheological measurements. Defect‐free, double‐side‐coated electrodes with ≈400 m in length are obtained via slot‐die coating and assembled into large‐scale PHEV‐1 cells with graphite as the counter electrode. Possible production‐induced defects are examined through computed tomography (CT). The obtained qualified, automotive cells are investigated through galvanostatic charge/discharge testing that confirms excellent cycling performance with discharge capacities of 26.3 Ah (1st cycle) and 25.4 Ah (300th cycle), which corresponds to a capacity retention of 96.6%. These results are compared with NMC811‐containing cells from lab‐scale/literature, and large‐scale products (slurries, electrodes, and PHEV‐1 cells) containing the predecessor material NMC622. The scalability of slurry preparation, electrode production, and cell assembly with special emphasis on differences between lab‐scale and industry‐scale production is discussed.
Li-ion cells of the industrially-relevant formats PHEV1 (prismatic), multi-layer pouch, and 21700 (cylindrical) are directly compared by experiments for the first time. All three cell formats were reproducibly built on pilot-scale with the same anode (graphite), cathode (NMC622), separator, and electrolyte allowing a direct comparison. The main differences between these formats are their capacities (24.6 Ah, 2.2 Ah, 2.3 Ah), volume/surface ratios, as well as tab and the jellyroll/stack configurations (flat-wound, stacked, wound). The comparison involves voltage curves during formation (0.1 C), discharge rate capability (0.5 C−3 C), heating behaviour, cell impedances, geometrical properties such as electrode curvatures and tab configurations, as well as comparison with coin half cells with anode and cathode vs Li counter electrode. The data are put into context with commercial and pilot-line built cells from other studies.
Despite intensive research activities on lithium‐ion technology, particularly in the past five decades, the technological background for automotive lithium‐ion battery mass production in Europe is rather young and not yet ready to meet requirements of automobile manufacturers. In light of the strong increase in electromobility, bridging this gap between fundamental research and industrial production is mandatory to keep the value chain of automobile manufacture in European countries. Challenges in know‐how transfer from lab scale to industry scale arise from different product configurations and objectives. Lab scale focuses primarily on material development and screening, utilizes small‐sized half‐cell or single‐layered designs with one‐side‐coated electrodes, and applies manually operated, discontinuous equipment, whereas industry focuses on optimized trade‐offs between throughput, quality, and costs. Market‐relevant cells contain usually double‐side‐coated electrodes with comparatively higher areal capacities, assembled into multilayered configurations. Mass production is conducted through automated, continuous processes including roll‐to‐roll manufacturing and consecutive pick‐and‐place operations. Inevitably, standard laboratory conditions do not allow for prediction of either optimized mass‐production process parameters nor physicochemical characteristics of final products. Hence, this Review aims to identify challenges in transferring lab‐scale results to industry with special focus on pilot lines as intermediate step between the different technological levels.
During the production process of lithium‐ion battery cells, the filling, which consists of dosing and wetting steps, of the cell and its components with an electrolyte liquid is important for the quality and costs of the final product. The cell format as a combination of housing and cell arrangement not only determines the type of filling process but also influences the distribution of the electrolyte within the cell. The cell format also has an influence on the wetting state as a function of time. Herein, in situ neutron radiography is used to analyze the filling process of two different cell types – pouch cells with a z‐folded stack and hardcase cells with a flat wound roll. The results are then analyzed and transferred to other common cell formats to identify a fillable cell design and format‐dependent process improvement possibilities to enable faster processing.
Abstract. In this work, various Lithium-ion (Li-ion) battery models are evaluated according to their accuracy, complexity and physical interpretability. An initial classification into physical, empirical and abstract models is introduced. Also known as "white", "black" and "grey" boxes, respectively, the nature and characteristics of these model types are compared. Since the Li-ion battery cell is a thermo-electrochemical system, the models are either in the thermal or in the electrochemical state-space. Physical models attempt to capture key features of the physical process inside the cell. Empirical models describe the system with empirical parameters offering poor analytical, whereas abstract models provide an alternative representation.In addition, a model selection guideline is proposed based on applications and design requirements. A complex model with a detailed analytical insight is of use for battery designers but impractical for real-time applications and in situ diagnosis. In automotive applications, an abstract model reproducing the battery behavior in an equivalent but more practical form, mainly as an equivalent circuit diagram, is recommended for the purpose of battery management. As a general rule, a trade-off should be reached between the high fidelity and the computational feasibility. Especially if the model is embedded in a real-time monitoring unit such as a microprocessor or a FPGA, the calculation time and memory requirements rise dramatically with a higher number of parameters.Moreover, examples of equivalent circuit models of Lithium-ion batteries are covered. Equivalent circuit topologies are introduced and compared according to the previously introduced criteria. An experimental sequence to model a 20 Ah cell is presented and the results are used for the purposes of powerline communication.
Herein, two techniques to optimize the production process of large‐format lithium‐ion cells for plug‐in hybrid electric vehicles using data‐driven methods are introduced and demonstrated. The first approach uses standard settings of the quality influencing factors to maximize the number of produced electrode sheets that meet predefined quality specifications. The second approach uses statistical methods to determine the levels of the quality influencing factors of a certain process that optimizes all quality parameters of the corresponding product jointly.
For the economical production of high‐quality lithium‐ion batteries, a comprehensive understanding of all processing steps under real production conditions, especially in the electrode‐manufacturing step, is mandatory. It has been shown that calendering of the cathode has a significant impact on the electrode quality and hence affects their subsequent processability in the battery production. Undesirable electrode deformation induced by the calendering process may lead to unnecessary wastage during the roll‐to‐roll process. To increase the yield rate of high‐energy electrode production under industrial‐oriented conditions, an extensive recipe evaluation by applying mixture design methods has been carried out on the lab scale. It has been shown that the inactive carbon black/PVDF phase as well as the amount of SFG6L in the electrode formulation plays an important role in the calendering processability of the high‐energy NMC622 cathode. From the statistical data analysis, an optimized recipe has been proposed and afterward validated at the research production line under industry‐relevant conditions. A significant reduction of the scrap rate caused by the calendering process is observed after optimizing the recipe due to its better calenderability.
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