Proposed Standards and Methods for Leak Testing Lithium-Ion Battery Packs Using Glycol-Based Coolant with Empirically Derived Rejection Limits

Lithium-ion battery systems are an energy source for a variety of electric-vehicle applications due to their high energy density and low discharge rates. Battery packs, whether made of prismatic, cylindrical or pouch cells, are cooled by common automotive thermal management systems. The rapid detection of battery pack coolant-system leaks during production operations is essential for meeting necessary safety and service-life requirements. Industry standards for measuring leak rates for both glycol-based and refrigerant-based cooling systems, however, currently do not exist. This presentation will discuss how leaks in water-glycol cooling circuits can be detected reliably and quantitatively through detection of escaping test gas as an indicator of ethylene glycol leaks and how the test gas leak rates correlate to the liquid leakage of the cooling liquid. Influencing variables such as leakage channel diameter, pressure difference and viscosity are considered, and go/no-go leak rates are described.