3.3 Aging & EoL Testing

Quality Testing is the final, crucial validation stage in cell finishing, ensuring every cell meets stringent performance, quality, and safety standards before it leaves the factory. After formation and any necessary degassing or resealing, cells first undergo Aging. This involves storing them, often at a controlled room or elevated temperature, for a set period (days or even weeks). Aging allows the cell's internal chemistry to further stabilize (e.g. continued refinement of the SEI layer and complete electrolyte wetting) and helps identify any early-life defects by monitoring for excessive self-discharge.

Following aging, each cell proceeds to comprehensive End-of-Line (EOL) Testing. Here, a series of precise electrical measurements (and physical checks) are performed to characterize the performance of each cell. Typical parameters measured include its actual capacity, internal resistance (both DCIR and ACIR), open-circuit voltage (OCV), and sometimes its pulse power capability. Based on these detailed test results, cells are then graded into different quality tiers or rejected if they don't meet the required specifications. This entire rigorous process is essential for guaranteeing product reliability, safety, and consistency for the end-user or for subsequent assembly into battery modules and packs.