Improved leak-detection tests are needed for lithium-ion batteries used in electric and hybrid-electric vehicles currently on the road, according to researchers at INFICON, a leading supplier of automotive leak-detection systems.
Recent tests conducted by INFICON show that tracer-gas leak tests are significantly better than current methods in use for checking battery packs and components for water ingress. INFICON has proven that, to prevent water ingress, tests are needed for leak rates that cannot be found reliably with air tests. Tracer-gas tests, for example, can detect leaks that are 1,000 times smaller than what is possible through air tests.
Closer scrutiny of electric vehicle (EV) battery components during production is needed to ensure that safety, performance and quality levels are maintained throughout the life of each battery, according to Dr. Daniel Wetzig, head of leak-detection research and development at INFICON.
“Today’s pressure-decay methods are either too slow or unreliable, and allow significant leaks to go unnoticed,” Wetzig says.
He points out that even tiny leaks can dramatically shorten battery life, negatively impact performance and increase warranty costs. Severe cases can short-circuit the electrical system or even cause fires.
EV battery packs are expected to meet the International Electrotechnical Commission’s IP67 standard (or the European EN 60529 equivalent), which require that components are capable of being immersed in one metre of water for 30 minutes without suffering any ‘harmful quantity’ of water ingress or negative effect on performance.
In practice, however, alternative test methods are used because water-bath testing is time consuming and can damage the battery.
Lab tests conducted in 2020 at INFICON’s facilities in Cologne, Germany, established that to safely protect against water ingress, leak rate specifications need to be rather low. The lab tests also proved empirically that the required leak rates can be detected by tracer gas leak testing with high confidence.
For its Cologne tests, INFICON used glass capillaries to check leak channels with various diameters, lengths and inlet/outlet pressures for the amount of water penetrating through these well-defined openings, and correlated them to a helium leak rate by measuring the same glass capillaries with a helium leak detector.
Study results are detailed in an SAE International paper titled ‘New Leak Detection Methodology to Protect Against Microscopic Leaks and Water Ingress in Battery Cells, Battery Packs and ADAS Sensors’. The paper is co-authored by Wetzig and Marc Blaufuss, an INFICON application engineer for leak-detection tools.
The authors found that gas-based test methods can be used to accurately detect potential water and other liquid leak channels in various battery-housing materials. Similar tests are effective for leak testing sensors used for automated driving systems.
The latest lab tests demonstrate the accuracy and effectiveness of INFICON’s gas-based leak-detection systems, according to Thomas Parker, the company’s North American automotive sales manager. He claims that INFICON customers are conducting validation tests for gas-based leak-detection systems on their own production lines.
“Our research and customer studies provide hard data and scientific proof that gas-based leak detection is needed to meet IP67 standards,” Parker adds. “Using equipment with such high sensitivity rates will ensure batteries operate as intended, help increase consumer confidence in EVs and drive growth in coming years.”
INFICON offers multiple types of gas-based systems, including industry-first mass-spectrometer technology that enables testing of batteries filled with electrolytes instead of ‘dry’ units, to leak test all types of lithium-ion battery cells, providing quantifiable and repeatable results with extremely high sensitivity rates.