Researchers at INFICON, a Switzerland-based supplier of automotive leak-detection systems, have determined that lithium-ion batteries used in hybrid and full-electric vehicles require better quality control testing to avoid performance issues and safety hazards down the line.
Results of tests run by the researchers showed that tracer-gas leak tests are simpler and detect leaks up to 1,000 times smaller than currently used pressure decay and mass flow tests. Dr. Daniel Wetzig, head of leak-detection research, and development at INFICON says to ensure optimal battery usage throughout its lifetime, closer scrutiny is needed during production.
Pressure decay tests are the most common examination used today given their ease of automation and integration into assembly lines and processes. It works by injecting a small amount of pressure into an area — in this case a battery encasement — until it reaches target pressure, and the loss of pressure is measured over a set period.
Mass flow testing using similar methods but measures the passage of a substance (liquid or gas) as it flows past a set point in a given period. Tiny leaks can cause dramatic inefficiencies, where severe cases can short-circuit the electrical system or 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 meter 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 too time consuming and can damage the battery.
Tests conducted at INFICON’s facilities in Cologne, Germany, established that water ingress tests require relatively low specifications to pass, and proved gas leak testing reliably detects these leaks and more.
For the tests, glass capillaries were used to check leak channels with various diameters, lengths, and inlet/outlet pressures for the amount of water penetrating through the openings and correlated them to a helium leak rate by measuring the same glass capillaries with a helium leak detector.
The results are detailed in an SAE International paper, “New Leak Detection Methodology to Protect Against Microscopic Leaks and Water Ingress in Battery Cells, Battery Packs, and ADAS Sensors,” and was co-authored by Wetzig and Marc Blaufauss, an application engineer for leak-detection tools at INFICON.