Benjamin Bold, M.Sc.

  • 76131 Karlsruhe
    Kaiserstraße 12

Benjamin Bold, M.Sc.

Area of Research:

  • Research in the production for the e-mobility
  • Calendering of electrodes
  • Investigation on the cause-effect relationships between error patterns and machine and material parame-ters for calendering


General Tasks:

  • Workshop “Working methods for mechanical Engineering” (educational course)
  • MAP Talent-Pool



  • POF III (Helmholtz)
  • PErfektZELL - Process quality improvement with an additional add-on for the calender for the processing of battery electrodes for the cell production


Test benches:


Dissertation: Optimization of calendering of electrodes for lithium-ion battery cells via compensation of the wrinkles formation


Curriculum Vitae:

since 04/2017 Research Associate at the Institute of Production Science (wbk) at Karlsruhe Institute of Technology (KIT)
04/2015 - 03/2017 Study of Mechanical Engineering (M.Sc.) at Karlsruhe Institute of Technology (KIT)
10/2011 - 04/2015 Study of Mechanical Engineering (B.Sc.) at Karlsruhe Institute of Technology (KIT)



[ 1 ] Hofmann, J.; Bold, B.; Baum, C. & Fleischer, J. (2017), "Investigations on the Tensile Force at the Multi-Wire Needle Winding Process". Proceedings of 2017 7th International Electric Drives Production Conference (EDPC), eds. IEEE, pp. 1.
The electric motor is the main component in an electrical vehicle. Its power density is directly influenced by the winding. For this reason, it is relevant to investigate the influences of coil production on the quality of the stator. The examined stator in this article is wound with the multi-wire needle winding technique. With this method, the placing of the wires can be precisely guided leading to small winding heads. To gain a high winding quality with small winding resistances, the control of the tensile force during the winding process is essential. The influence of the tensile force on the winding resistance during the winding process with the multiple needle winding technique will be presented here. To control the tensile force during the winding process, the stress on the wire during the winding process needs to be examined first. Thus a model will be presented to investigate the tensile force which realizes a coupling between the multibody dynamics simulation and the finite element methods with the software COMSOL Multiphysicsę. With the results of the simulation, a new winding-trajectory based wire tension control can be implemented. Therefore, new strategies to control the tensile force during the process using a CAD/CAM approach will be presented in this paper.

[ 2 ] Bold, B. & Fleischer, J. (2018), "Kalandrieren von Elektroden für Li-Ionen-Batterien", ZWF Zeitschrift für wirtschaftlichen Fabrikbetrieb, no. 9, pp. 571-575. 10.3139/104.111968
Die Energiedichte ist ein entscheidendes Merkmal für Lithium-Ionen- Batteriezellen und bestimmt maßgeblich die Reichweite von elektrisch angetriebenen Fahrzeugen. Ein für die Energiedichte entscheidender Prozessschritt ist das Kalandrieren. In diesem Beitrag wird der Zusammenhang zwischen den Anlagen- und Materialparametern aufgezeigt, indem die Prozessgrößen variiert und die Veränderungen der Elektrode betrachtet werden. Mit den Ergebnissen werden Handlungsfelder aufgezeigt, die für eine Optimierung notwendig sind.

[ 3 ] Bold, B.; Weinmann, H. W. & Fleischer, J. (2018), "Challenges in conveying electrodes and new approaches to quality assurance". Tagungsband zur International Battery Production Conference 2018, eds. Prof. Arno Kwade, B. L. B., pp. 56-57.
Electric mobility is gaining importance in Germany but high battery costs are still an obstacle. The production of battery cells amounts to a considerable share to the total costs and therefore efficiency must be further increased. Within the battery cell production the electrode is processed continuously as an electrode web until stack formation. In the individual process steps the material is guided via deflection rollers, including various compensation systems, which are designed to eliminate unevenness in the web tension and to align the position of the web edge. Such systems are mostly adapted from the paper or film processing industry. However, compared to paper or foil the electrode consists of a composite material consisting of active material and current collector. As a result, the electrode forms a system of complex properties since it consists of two materials with different mechanical properties. The presentation thus gives an overview over available market solutions and sets out why an adaptation is not possible without further ado. It also presents the challenges that occur within the material transport of electrodes. These include the wrap angle, roller diameter and web tension applied. With regard to the material parameters, the distortion of the electrode and the formation of folds are described. Up to now, the electrode behavior has been evaluated qualitatively as there are no measurement methods available. New approaches for optical methods are presented that enable a quantification of the electrode distortion within the electrode web. Three variants are described which show first promising results. By means of image processing and applied colored points their displacement is detected and thus how the electrode deforms in the process. Furthermore, another similar method is presented which works with a sprayed-on pattern and a software from the GOM GmbH for evaluation. Since these methods do not allow for an in-line quality evaluation a further variant is being considered in which the deformation of a laser pattern projected onto an electrode is assessed. Finally, a description of the material flexibility with respect to the measurement methods is given, as this will play an important role in the future.

[ 4 ] Kopp, A.; Niedermaier, J.; Bold, B.; Holl, K.; Bernthaler, T. & Schneider, G. (2019), "Microstructural investigation of deformation of Al folis in cathode current collectors during compression of electrode coatings". International Battery Production Conference IBPC, eds. Technische Universität Braunschweig, pp. 18.
Highl compressed electrode folis are used to increase the capacity and the volumetric energy density in Li-ion batteries. During the calendering the microstructrue of the electrodes undergo tremendous changes. Depending on the size and morphology of the active material the particles are pushed into the Al-foil while the uncoated regions of the Al-foil reamin undefomation. This leads to the formation of wrinkles in the electrode foils which reduce the processability of the foils and are a main reason for limited compression of intermittently coated eletrodes. The microstructure is analysed to investigate the changes during compressing and get a deeper knowlegde of the wrinkle formation.

[ 5 ] Bold, B.; Weinmann, H.; Bernecker, J. & Fleischer, J. (2019), "Identifying the Impact of Calendering on Subsequent Processes Using a New Approach to Quality Assurance". Advanced Battery Power 2019, eds. Haus der Technik e.v., pp. 1.
Electric mobility is of core importance for the German automotive industry. The development of the German economy strongly depends on activities in battery production and on their integration into the process chain - from material to final battery system. On the one hand, further development of the material systems is necessary and on the other hand, progress is needed in production. Both aspects influence the energy density of the battery cell and thus determine the range of electrically driven vehicles or the available capacity for stationary applications. The aim of a high energy density can be achieved by finding the ideal material composition or by using the right manufacturing process. The decisive process step is calendering, in which the volumetric energy density is increased by compressing the active material. Residual stresses are induced into the material, which become visible at high densities through wrinkling at the boundary between the coated and uncoated areas. The characteristics of the wrinkles allow a conclusion to be drawn about the strength of the residual stresses. These effects in the electrode constitute a hindrance for further process steps and thus prevents the maximum possible density. In the single sheet stacking process, this is expressed through the tolerance of dimensional accuracy. Due to excessive residual stresses, the shape can no longer be guaranteed after cutting. First, the poster presents results that show which deviation is to be expected at what calendering degrees. Investigations into the cause of wrinkle formation are to be carried out by detecting the residual stresses induced. The residual stresses are determined by recording the distortions of the material. For this purpose, a pattern is printed on the electrode before calendering. A picture is taken before and after calendering, allowing the strain of the electrode to be known through the displacement of the color points. Therefore, results are presented which show the material behavior for different parameter settings at the calender for high volumetric densities. The described undertaking reveals which calender parameter is responsible for the wrinkle development. This in-line quality assurance forms the basis for modelling the relationships between the calender parameters and the properties of the material in particular residual stresses. In addition, it is the starting point for an additional module on the calender, which enables wrinkle-minimized processing of current and future material systems allowing for better qualities also in further process steps, as exemplified by the stacking process.

[ 6 ] Bold, B.; Kopp, A.; Denk, N.; Schneider, G. & Fleischer, J. (2019), "In-line measurement of wrinkle formation and strains for NMC 622 cathodes while calendering". International Battery Production Conference IBPC, eds. Technische Universität Braunschweig, pp. 57.
The characteristics of battery cells, such as energy density, power density and capacity, are determined by the material and influenced and adjusted during the production. Within the electrode production, calendering is an essential process step for adjusting the volumetric energy density. The higher the compaction during calendering, the higher is the achieved energy density, taking into account the limits of the material. Nevertheless a high compression leads to defect patterns which are wrinkles at the coating edge and wave formation in the coating area. This is the starting point for the presentation and it will be explained, how the wrinkles and the waves in the coating are formed during calendering and why the effects depend on the material. The main part of the presentation shows how the wrinkles and the wave formation of the electrode are detected and measured in-line while calendering. The wrinkles are described geometrically by their length, width and angle. The wave formation is determined by measuring the strains of the electrode in three-dimensional space. In relation to the parameter description, the self-designed measuring system and its evaluation algorithm based on image processing is explained. This measuring system is applied in a series of experiments within the BMBF project PErfektZELL for the investigation of NMC 622 cathodes on the industrial calender at the wbk Institute of Production Science at KIT Battery Technical Center. Therefore, the results of a statistical test planning are presented and the dependencies between the wrinkle description and the material strains to the process parameters are shown. Finally, the results lead to conceptual solutions of effective countermeasures in order to reduce the effects of wrinkles and wave formation.

[ 7 ] Bold, B. & Fleischer, J. (2020), "In-Line Messung beim Kalandrieren von NMC 622 Kathoden zur Detektion von wrinkles und Dehnungen zur Erweiterung des Prozessverständnisses". Abstracts Batterieforum 2020, eds. Lithium-Ionen-Batterien (KLiB) e. V., pp. 14.
Die Eigenschaften von Batteriezellen, wie Energiedichte, Leistungsdichte und Kapazität, werden durch das Material bestimmt und bei der Produktion beeinflusst und angepasst. Innerhalb der Elektrodenproduktion ist das Kalandrieren ein wesentlicher Prozessschritt zur Einstellung der volumetrischen Energiedichte. Je höher die Verdichtung beim Kalandrieren, desto höher ist die erreichte Energiedichte, wobei die Materialgrenzen berücksichtig werden müssen. Eine hohe, von der Industrie geforderte, Verdichtung führt zu Fehlerbildern, die sich durch Falten an der Beschichtungskante, den „wrinkles“, und einer Wellenbildung, auch „Schüsseln“ genannt, innerhalb der Beschichtung ausdrückt. Das Poster erläutert umfänglich die Ursachen der Falten- und Wellenbildung beim Kalandrieren und den Zusammenhang der Fehlerbilder mit den Anlagenparametern. Vorgestellt wird ein eigens entwickeltes und aufgebautes Messsystem, das die Falten und die Wellen der Elektrode beim Kalandrieren erkennt und inline erfasst. Die Falten werden geometrisch durch ihre Länge, Breite und einen Winkel beschrieben. Die Wellenbildung wird durch Messung der Dehnungen der Elektrode im dreidimensionalen Raum bestimmt. Das Messsystem ist ein Stereokamerasystem und verarbeitet die Aufnahmen über einen eigenen Algorithmus. Die Ergebnisse einer statistischen Versuchsplanung werden vorgestellt und die Abhängigkeiten zwischen der Faltenbeschreibung und den Materialdehnungen zu den Prozessparametern dargestellt. Der Aufbau und die Anwendung des Messsystems werden im Rahmen des BMBF-Projekts PErfektZELL durchgeführt. Die Untersuchung der NMC 622 Kathoden erfolgt auf dem Industriekalender des wbk Institut für Produktionstechnik im KIT Batterietechnikum. Die Ergebnisse werden in konzeptionelle Lösungen effektiver Gegenmaßnahmen überführt, um die Auswirkungen von Falten und Wellenbildung zu reduzieren.

[ 8 ] Hofmann, J.; Wurba, A.; Bold, B.; Maliha, S.; Schollmeyer, P.; Fleischer, J.; Klemens, J.; Scharfer, P. & Schabel, W. (2020), "Investigation of Parameters Influencing the Producibility of Anodes for Sodium-Ion Battery Cells". Production at the leading edge of technology, eds. Behrens, B.; Brosius, A.; Hintze, W.; Ihlenfeldt, S. & Wulfsberg, J. P., Springer, Berlin, Heidelberg, pp. 171-181.
Lithium-ion battery cells will dominate the market in the next 10 years. However, the use of certain materials as cobalt is a critical issue today and is constantly being reduced. Sodium-ion batteries are an alternative, which has already been researched on a laboratory scale. Increasing of the individual production steps are serious bottlenecks for bringing basic cell concepts into application. Within this paper a systematic investigation of parameters influencing the producibility for sodium-ion battery cells will be taken into account. For this purpose, the characteristic process variables and challenges along the production chain are presented along the process chain of lithium-ion battery cells. The influence of various process-machine interactions on the properties of the electrode is illustrated using the anode of sodium-ion batteries as an example. First conclusions whether the production technology can be adapted to the cell chemistry of the future at an early stage will be made.