The QuaLiZell project (competence cluster AQua – analytics and quality assurance) is dedicated to quality assurance in the process of Lithium-ion pouch cells assembly. The aim of this project is to identify safety-relevant sources of defects in the production steps, to clarify the cause-and-effect relationships through the targeted introduction of cell defects, to quantify the tolerance and intervention limits and to develop suitable analytical in-line methods for the real-time detection of production defects. The focus of this work is on the processing steps of cutting and stacking of the electrodes as well as the separator.
The project requires a production line that allows cells to be manufactured with highly reproducible quality and industry-like characteristics, but which at the same time has a high degree of flexibility and offers possibilities to intervene in the manufacturing process in order to be able to manipulate the intermediate products and manufacturing steps in a targeted and quantifiable manner. The semi-automated manual production line for large-format pouch cells at the KIT Battery Technology Center meets these requirements and delivers cells in industrial quality, where the influence of deliberately introduced defects clearly stands out from the general quality scatter. The analysis focuses on process and material defects that can occur during the cutting and stacking process of the separator and the electrodes. The cutting quality of the electrode and separator edges, the stacking accuracy of the individual sheets and the avoidance of contamination by particles are key quality characteristics and are systematically varied for the influence analysis. Furthermore, the influence of different cutting methods as well as the quality of the cutting tool will be investigated. The analysis is carried out using optical and electrochemical methods. An end-of-line test for early detection of critical cells is developed.
Within the scope of a detailed examination of the manufacturing process and a failure mode analysis, potential failure causes are identified and evaluated with respect to their probability of occurrence. An evaluation of the influence on safety- and performance-relevant properties is carried out in initial tests on pouch cells with specifically introduced cell defects by means of electrochemical analyses (including cycling, rate tests, and determination of internal resistance) and post-mortem investigations.
The results obtained to date provide a first step towards quality assurance and allow initial conclusions to be drawn regarding tolerance and intervention limits. Transfer of the information obtained will serve to develop suitable in-line analytics and build a bridge to the competence cluster InZePro – Intelligent Battery Cell Production.