BATTERY LEAK TESTING manufacturer has developed its own strategies. We are working with them as a common team.” Eutamene notes that the major difference between solid-state and lithium-ion batteries in terms of leak testing is that there is no liquid electrolyte in a solid-state battery and therefore a detecting gas must be added. All rigid cells (coin, cylindrical, prismatic) can be helium pre-tested, which means that parts with leaks can be scrapped early rather than the leak being discovered during a final product test. For pouch cells that cannot be pre-tested with helium, it is even more important that leaks are caught in a final test, but only electrolyte testing (not pressure testing) can detect these small leaks. “It is difficult, and each OEM has developed its own solutions and methods,” says Eutamene. “It depends on packaging as well; it is easier to do with a prismatic RIGHT: Submersion testing assesses the ability of Fellten’s batteries to withstand marine applications where there is a greater risk of water ingress as well as road car use cases BELOW: The supplier does not leak test every battery it manufactures due to the associated high costs having a validated solution that can be deployed in production. “We don’t have aging data for a lot of cells and I think that’s where adding real-time monitoring comes in” Chris Hazell, chief executive officer and co-founder, Fellten aluminum casing than with a polyethylene pouch. For prismatic cells we have developed our own solution and demonstrated it in production. The leakage rate depends on the battery size and capacity, but in our case it is 2 x 10 -7 atm-cc/sec. This rate has been established based on testing with external labs on the impact of leakage on the battery lifecycle. For pouch, we aim to provide a mature system in the coming years.” As part of the development of its new system, Blue Solutions is undertaking experiments to understand the hermeticity level of the metal plastic bag and the sealed joints, but it is still a long way from Fellten – a specialist in niche, low-volume electrification applications – coolant leakage tests every pack it makes. For every new battery the company develops, it performs water ingress testing. Submersion testing ensures its batteries are especially hardy in tough environments. “So that we don’t need to do in-depth leak testing, we use custom pre-made seals, which removes the human error during production,” explains chief executive officer and co-founder Chris Hazell. “One thing to be aware of when doing leak testing is that the pressure equalization valves may allow air through but not fluids, so those need to be blocked off,” he adds. Beyond preproduction testing, some vehicle makers are integrating diagnostics equipment to detect changes in the battery chemistry, for example, that could lead to a serious incident. Hazell highlights, “We don’t have aging data for a lot of cells and I think that’s where adding real-time monitoring comes in. Even if they don’t do anything now, 10 years down the line, that’s when that sensing is going to really come up as a massive lifesaver potentially in the EV space.” Leakage is also a concern for second-life batteries. With various second-life battery initiatives in place, monitoring technology could become commonplace. Seal the deal 40 JUNE 2024 www.AutomotiveTestingTechnologyInternational.com