64 March/April 2025 | E-Mobility Engineering Peter Donaldson delves into the world of battery leak testing Accurate and reliable testing With the exception of old, British motorbike engines – it was said that if they’re not leaking, there’s no oil in them – leaks from anything are usually a sign of a problem. The escape of liquids such as coolant and electrolyte are undesirable, and the emission of gases can be the first warning sign of a thermal runaway. Also, intrusion of water or road debris from the vehicle’s exterior into the battery enclosure can cause corrosion, shortening battery life, generating heat and even potentially triggering a thermal runaway. Therefore, reliable and accurate leak detection is essential at every stage of an EV battery’s lifecycle. During manufacture, testing is focused on quality control. It is vital that customers define the specific failure they aim to prevent (such as electrolyte leakage rather than water ingress), as this dictates the required leak rate sensitivity, which can differ by a factor of 100 between application specifications. Automated able to handle, say, 200 parts per minute, with reliable repeatability and data tracking is critical in high-throughput production. At the dealer or vehicle repair level, inservice leak detection is possible. These systems prioritise simplicity and lower cost than those used in manufacturing due to infrequent use, which might be as little as once a month. A vehicle manufacturer is likely to have orders of magnitude fewer production lines to equip (perhaps as few as 50). At this level, slower testing is acceptable, while durability is less critical. Leak detection systems that may be built into battery packs differ from those used in production and during servicing. Sensors monitor concentrations of target substances rather than flow rates, and the distinction between them is important. Systems also have to be much cheaper, with sensors costing just a few dollars each. Relatively slow response of 30 seconds or so is acceptable, but performance must remain stable over many years. At first, battery manufacturers often focus on detection methods sensitive enough to find the smallest leaks, but matching the leak rate to the failure being prevented avoids unnecessary expense, as does matching the required testing speed to the application. Also, application context is crucial, with, for example, cell-level electrolyte testing, pack-level water ingress detection, and cooling circuit checks all needing tailored solutions. The LDS3000 helium and hydrogen leak detection system can be set to detect minimum leak sizes between 1 x 10-7 and 1 x 10-11 mbar l/sec, featuring a helium-saving EcoBoost mode (Image courtesy of INFICON)
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