Meaning
Standardized leak measurement metrics convert the flow of a tracer gas under test conditions to an equivalent leak rate of another substance. To assess cell hermeticity, the helium equivalent leak rate translates measured helium gas flow into the corresponding rate of electrolyte loss or moisture entry. This calculation allows engineers to apply standard leak testing methods while designing for long-term cell chemistry protection.
Mathematical Conversion
The calculation accounts for the molecular weight and viscosity of helium compared to water vapor or carbonate solvents. Helium flows through micro-pores much faster than liquid electrolyte, so the measured gas flow is much higher than the actual liquid leak. Converting these rates ensures that the test sensitivity is aligned with the required service life of the battery pack.
Sourcing Specification
Procurement agreements often specify a maximum allowable leak rate to ensure cell quality over a multi-year warranty period. Suppliers must demonstrate that their manufacturing processes can consistently achieve these low leak rates. This metric provides a clear, auditable threshold for accepting or rejecting cell shipments.
Structural Limit
The conversion assumes that the flow through the leak path is governed by gas dynamics and does not change. In practice, a physical leak path can become blocked by crystallized electrolyte salts. Therefore, leak rates should be measured on dry, un-filled cell housings.
