In the context of the global energy transition, electrochemical energy storage technologies are considered to be a key factor for the development and establishment of electromobility and stationary energy storage to advance renewable energy sources. Today, due to their outstanding properties, lithium-ion batteries (LIBs) are the most important storage technology for mobile applications, and have also gained high interest for stationary applications. This is why the development and production of high quality and high performance LIB cells is an essential task for industry, especially for countries whose economies rely on car manufacturing. In the past six years, great efforts have been made in German academic research in the field of battery cell production. In 2016, the German Ministry of Education and Research built and funded a competence cluster on cell production named ProZell, in order to establish a sustainable, competitive and internationally leading battery cell production industry in Europe. The research results of this cluster are intended as a scientific backbone for future European Giga Factories, which are already partly under construction. The focus of the ProZell cluster is on the investigation and improvement of the mass production of battery cells, the development of new innovative process technologies, the evaluation of process parameter influence on cell performance and product development costs, and on the further development of the knowledge gained for new battery generations. Therefore, in ProZell investigation and development along the entire LIB process chain are carried out by different academic pilot lines for cell production together with further research institutions. The research results of the first funding phase of ProZell were successfully published in a Special Issue of Energy Technology in 2020 (Special Issue: Advances in Battery Cell Production) https://onlinelibrary.wiley.com/toc/21944296/2020/8/2. In the just expiring second funding phase of ProZell, which started in 2019, the focus is on new, more sustainable processes, which enable cost savings and reduction of the environmental impact. Within the competence cluster, seventeen research projects composed of 36 German research institutions have combined their knowledge and are working together to advance German research on battery cell production. The remarkable research results of the second ProZell-phase are presented in this Special Issue of Energy Technology. In addition, this Special Issue contains the results of the joint research project on data mining and application in the production of lithium-ion battery cells, DaLion4.0, funded by the German Ministry for Economic Affairs and Climate Action. All projects of the ProZell competence cluster focus on the establishment of deep process and production knowledge along the entire process chain of LIBs, by employing simulation and setting up process-structure-property relationships, among others. In this Special Issue, this deep knowledge and the model relationships are presented with the focus on dry mixing (Asylbekov et al. and Lischka et al.), dispersing (Weber et al.), slot-die coating (Spiegel et al.), drying (Altvater et al., Lippke et al.), calendering (Tran et al., Schreiner et al. and Strzelczyk et al.), post-drying (Heckmann et al.), stacking (Kollenda et al., von Böselager et al., Husseini et al. and Olowinsky et al.), electrolyte wetting (Frankenberger et al. and Hagemeister et al.) and cell formation and performance (Drees et al., Peschel et al. and Waldmann et al.). Some contributions concentrate on the material and microstructure of electrodes, such as investigating mechanical structuring of electrodes (Keilhofer et al.), reconstruction of the carbon-binder domain in electrodes (Prifling et al.), different binders for anodes (Jagau et al.), Nickel-rich NCM based cathodes (Heck et al.) or the solid-electrolyte interphase growth during cell formation (Schomburg et al.). Strategies to increase the energy density of electrodes are also developed, such as using two-layer, hard carbon containing Silicon anodes (Gottschalk et al.) or ultra-thick cathodes (Hoffman et al.). In addition, further contributions focus on techniques for quality control, such as using ultrasound propagation (Gold et al.) or studying the influence of electrode corrugation after calendering (Mayer et al.). Last but not least, several contributions concentrate on digitalization of battery cell production (Ventura Silva et al., Karaki et al. and Mutz et al.) or life cycle assessment (von Drachenfels et al.). As the process chain for LIBs consists of many different process steps, there are a multitude of process parameters that influence the resulting cell performance and quality. Therefore, a large amount of process and intermediate product data needs to be recorded to provide reliable battery cell production. Within the project DaLion4.0 data acquisition and mining, as well as model development was established. Several electrode and cell production campaigns were conducted, focusing on intense dry mixing for high energy anodes (Weber et al.), electrochemical approaches for quality determination of the wetting process (Grundmeier et al.), traceability in battery production (Wessel et al.), as well as establishing spectrophotometry for quality control (Weber et al.). There have been many advancements in the field of battery cell production in recent years, as demonstrated by the works presented in this Special Issue. The deep process and production knowledge generated during the course of the competence cluster ProZell and the project DaLion4.0 provides an outstanding foundation for future European Giga Factories and the establishment of a sustainable, internationally leading and competitive battery cell production industry in Europe. Arno Kwade After finishing his doctorate in 1996, Arno Kwade worked for nine years as a process engineer in leading industrial positions. In 2005, he was appointed as professor and director of the Institute for Particle Technology (iPAT) at Technische Universität Braunschweig. His research focusses on processes in which particles are mechanically stressed and formulated, ranging from milling over powder mixing, handling and characterization to production of drug products and battery electrodes. Since 2011, he is speaker of the Battery LabFactory Braunschweig (BLB), since 2016 of the German competence cluster ProZell on battery cell production, and since 2018 vice spokesman of the Board of Battery Research Germany.