Advances in Direct Electrolyte Leak Testing of Pouch and Hard Case Lithium-Ion Battery Cells

Summary:

Direct electrolyte leak testing is a key technology for reliable and traceable leak detection for quality control in battery production processes. The interest of quality control is manifold from reduction of maintenance or warranty costs to sustainable battery production with long-living batteries. Most important is to ensure the distribution of only safe and secure batteries. Pouch battery cells are advantageous due to their minor thickness, adjustable size and reduced weight as compared to common hard case cells. That allows an increased capacity related to the footprint and weight of battery cells making them interesting for various applications. That includes Pouch cells as single cells for mobile devices or as part of battery modules for EV (electric vehicle) batteries.
We previously presented the ELT3000 Electrolyte Leak Detector equipped with small rigid chamber. The diversity of cell types and sizes – from small coin cells to larger prismatic cells – and especially the increased demand for Pouch cells necessitates the choice of a well-suited test chamber. Prerequisite for direct electrolyte leak detection is reversing the driving force for the leak with electrolyte escaping from the battery cell. Therefore the pressure in the surrounding atmosphere is reduced to a value even lower than the inner cell pressure. Due to the thin foil covering the cell, a Pouch cell is usually not withstanding huge pressure differences and possibly expanding and bursting in standard vacuum chambers. Therefore we developed a flexible test chamber in which the Pouch cell is placed between two membrane layers. That allows the application of a vacuum while simultaneously supporting the battery cell and avoiding its expansion.
We herein present the working principle and first application data of the ELT3000 with flexible test chamber and its benefits such as application flexibility, short cycle times and highly sensitive non-destructive testing. While the small rigid chamber is well suited for coin cell applications, a larger chamber (12 L) enables leak testing of cylindrical and prismatic cells. With the gathered data for different electrolyte solvents (DMC, DEC, EMC) an approximation of measurement capabilities (e.g. sensitivity and cycle times) for even larger customized chambers is possible. Short cycle times are maintained by use of an additional pump reducing the chamber evacuation time.
The integration of leak detection within battery production can be carried out after electrolyte filling to avoid risks and costs due to formation of leaky cells or after formation to ensure that only leak-free cells are leaving the facility. First ELT3000 systems installed at customer sites are used at manual working places. To meet the requirements for battery production lines progress is made co-working with system integrators on automation of the leak detection part.