Investigation on Defects of Battery Pouch Cell Housing

Currently three relevant designs for battery cells have emerged, which are distinguished by their housing and overall shape into cylindrical, prismatic and pouch cells. The latter consist of electrode stacks encased in pouchfoil bags. These bags themselves are crafted from two half shells, which are deep drawn out of the eponymous pouchfoil. Defect patterns in the manufacturing process of these pouch foil housings have so far only been described experimentally without concrete quantification. In addition to its manufacturing process, damage to the pouch cell housing on its way between cell- and pack-assembly has also not been described. It is necessary to identify the different defect patterns and their origin and to give an estimation of their impact towards safety and service life of pouch cells. To analyze the possible damages observed in the manufacturing and handling of the housings, ISO 8785:1998 is applied which categorizes all known surface defects. An assessment, based on the risk priority number RPN, is made to determine the risk associated with these damages and the extent to which they can be classified. Such classification is exemplary presented on the wrinkles observed, which are subdivided into four categories. A leakage test specifically designed for this application is employed to identify which category of wrinkles adversely affects the sealing tightness of the cell.