East Syracuse, New York – New high-performance batteries for electric vehicles create a variety of quality-control challenges for auto makers and their suppliers.
More than 1.3-million battery-powered electric vehicles and plug-in hybrids were in service globally at the end of 2016. Analysts expect that total to pass four million within the next five to six years.
The amount of lithium-ion battery power required to drive 4 million electric vehicles exceeds 8GW -- the equivalent of four large-scale nuclear power plants generating electricity to support the daily needs of more than 5 million people.
"The quality of individual battery packs, components and sub-assemblies will be a critical concern for car makers as the number of electric and hybrid-electric vehicles increases," says Thomas Parker, North American automotive sales manager for Inficon. "Leak-detection tests are a proven method for checking battery quality, but the auto industry has yet to establish clear-cut leak-detection guidelines."
Faulty battery systems can lead to on-road power failures, fires or even explosions Parker notes, pointing out that recent electric vehicle fires and a ban on certain Samsung mobile phones underline the need for strict quality standards as well as accurate and reliable test methods.
Leak-detection equipment is available to accurately test lithium-ion battery cells, larger battery packs and battery-cooling systems at various production stages. Vacuum and sniffer tests are the two methods Parker recommends for detecting battery component flaws.
He adds that even though battery cells or fully assembled packs may pass supplier quality checks, it's not uncommon for damage to occur during shipment to a car maker's final assembly line. Quality-control experts especially recommend the careful inspection of battery cells from overseas suppliers.
A thermal runaway in a single battery cell caused by an electrode short circuit can lead to a fire or explosion in a shipping container with temperatures reaching 1,100°C. Some transport companies today deny shipment of lithium-ion batteries due to cargo fires that have destroyed entire shipboard containers and actually downed aircraft.
Three primary types of lithium-ion battery cells currently are in production. Although different in design, each should be tested to avoid electrolyte leakage or potential water damage. The three basic types are:
- Round or cylindrical cells, used for example by Tesla, are enclosed by welds. Even a "tiny" leak could lead to a loss of electrolyte.
- Prismatic cells currently used by BMW are rectangular in shape and range from extremely small up to 70 liters in size. If sealed by a weld, the potential for an electrolyte leak also exists.
- Pouch cells are flat and soft-sided. Pouch seals are subject to leaks which can draw moist air into the pouch. The pouch also can experience pinhole-size damage as a result of post-production handling.
Parker says that all three cell types should be leak tested before they are filled with electrolyte. Cylindrical and prismatic cells can be tested in a helium vacuum chamber. The cells are filled with helium, sealed and then placed in a vacuum chamber connected to a helium leak detector. Pouch cells are filled with helium, then tested for leaks with a detector that sniffs out leaks along the seals.
Battery packs generate a considerable amount of heat and must be cooled while in operation either with a water-glycol mix or a refrigerant such as R1234yf. The cooling system should be tested to ensure that coolant doesn't leak into the battery module and cause a short circuit.
Older, more commonly used leak-detection methods such as pressure-drop or water-bath tests simply can't compete with modern high-sensitivity helium and hydrogen test-gas methodology, according to Parker.
"Adopting modern test-gas systems to assure the quality of today's new generation of batteries has become critically important as more and more electric vehicles hit the roads in North America and elsewhere around the world," Parker concludes.