68 low in toxicity at the concentrations used, non-flammable, harmless to all the materials in the battery, inexpensive and plentiful. The gas had to be effectively absent from the air, while the colourchange reagent had to respond to the gas but not to the air. The gas chosen was ozone (O3), while the developer formulated its own colorimetric reagent. The one they came up with can be applied to a tape, and it changes from clear to purple permanently within seconds of exposure to low concentrations of ozone. The sensitivity of this technology depends on factors such as the volume of the system, the pressure of the challenge gas and the size of the hole through which it is leaking. The gas changes the colour of the reagent media at concentrations below the limit set by the US Occupational, Safety and Health Administration (OSHA), the manufacturer says. In tests, the time taken for the reagent to change colour varied with hole diameter – the larger the hole, the faster the colour change – but it was not influenced significantly by a small change in gas pressure. While the technology has been created to detect gas leaks, the developer notes that it is possible to formulate another colour-change reagent to interact with liquids or electrolytes, depending on their underlying chemistry. Further, the challenge gas could be added to the battery and used for continuous monitoring. Systems based on mass spectrometry can detect leaks of all gases and liquids, including electrolytes through the use of tracer gases or the final medium. The required sensitivity depends on the application, and different detectors have different sensitivities, with some capable of detecting leak rates as low as the standardised limit of 10⁻¹² atm cc/s. This means that under a pressure difference of 1 atmosphere, only one-trillionth (10⁻¹²) of a cubic centimetre of gas escapes through the leak every second. That’s a tiny leak and such sensitivity is not required in the battery industry, but it illustrates the capability of the technology. As a rule of thumb, real requirements range from a few milligrammes per year up to kilogrammes per year. Systemic needs Detection capability alone is an insufficient metric, one equipment manufacturer cautions, adding that most customers need assistance in developing a complete testing process. For example, consultations explain how to fill the test article with tracer gas, take the gas out of the part, reclaim and reuse expensive gases, and how to establish proper leak rates for their scenario. All the detectors feature digital or analogue interfaces Product focus | Battery leak testing March/April 2025 | E-Mobility Engineering Battery pack vent valves designed to support leak testing represent an important innovation. This is an Eaton valve with its compatible leak check tool (Image courtesy of Eaton) It can be applied to a tape, and it changes from clear to purple permanently within seconds of exposure
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