火与冰不混合。水和电池也是如此。在电动汽车中，一小部分的水蒸气会损坏锂离子电池电池。

由于大多数电池组的外壳都集成到电动汽车的机箱中，因此它们极易受到水，泥浆，雪，冰和其他形式的水分，这些水分从路面踢起来。

To address the issue, EV suppliers and automakers must ensure that battery trays and covers are tightly sealed. Leak testing plays a critical role in the assembly of battery cells, modules and packs.

Batteries need to be leak-free and protected from humidity, water and other liquids for 10 years or more.

Reliable leak testing of battery cells is crucial because the highly flammable electrolytes they contain can spark fires. Even small amounts of humidity in a battery module can cause the system to short circuit, reduce service life and degrade performance, including a vehicle’s driving range.

“Leak tests have long been one of the most critical quality control checks performed by automakers and suppliers," says Thomas Parker, North American automotive market sales manager at Inficon Inc. “Electric-powered systems require even more precise testing.

“It’s vital to prevent electrolytes from leaking from the battery cell or coming into contact with water under any circumstances throughout the production process and life of any electric or hybrid-electric vehicle,” explains Parker. “We have been flooded with projects recently, as more OEMs and suppliers scramble to develop EVs.

“Atmospheric accumulation tests are widely used, because it’s a repeatable process that has good sensitivity and provides good metrology,” Parker points out. “As production volumes ramp up, more manufacturers are looking for automated equipment, such as robotic sniffers.”’

Lithium-ion battery cells fall into three categories: hard-cased prismatic cells, cylindrical cells and softer pouch cells. Because they are lighter in weight, pouch cells are growing in popularity with automakers, but they also are more difficult to accurately test.

According to Parker, empty hard-case battery cells currently can be checked by filling the cells with helium test gas to detect leaks in a vacuum chamber. Electrolytes are not inserted into a hard-case cell until after it has been dry tested.

氦气炸弹是另一种方法。在这种情况下，将电池电池放在真空腔中，并在压力下暴露于氦气中。氦气能够通过现有泄漏进入，然后在逃回真空室时可以测量它。

但是，两项测试方法都没有提供可靠的一致结果，以建立整个行业范围的电池电池泄漏检测标准。

“Tracer-gas test methods are the most suitable for most testing tasks for alternative drive components,” says Parker. “In fact, tracer-gas tests can detect leaks that are 1,000 times smaller than air tests currently in use.”

“Of all the EV components, battery packs pose the most challenges to leak testing,” notes Gordon Splete, global product manager at Cincinnati Test Systems Inc. “Part size is an issue, as it is more difficult to reliably test large volumes. Electric vehicle packs are prone to part expansion at unpredictable rates.

Splete解释说：“温度和大气压的变化也会影响零件的压力，从而导致测试结果的变化。”“在泄漏测试中，气球零件和柔性组件在泄漏测试中造成了重大挑战，除非选择适当的测试方法和设备以应对应用程序的独特挑战，否则可能会损害结果。”

辛辛那提测试系统的电子活动业务开发总监Chuck Hagyard补充说：“许多负责电动电动电池测试的工程师正在学习泄漏测试新设备所需的内容，以及应用程序的合理泄漏率和测试压力。”“绝大多数OEM和供应商都在寻找压力衰减或基于质量流的系统。压力衰减是一种简单，低成本的技术，可吸引许多制造商。

“A select few are using tracer gas to test their battery packs,” explains Hagyard. “The type of leak test equipment necessary is also dependent upon the size of the battery pack, its flexible nature and the leak rate.”

In-Process vs. End-of-Line Testing

Manufacturers use both in-process and end-of-line leak testing. The former tests components and subassemblies during various steps in the production cycle. The latter is the last checkpoint before a finished product leaves the factory floor. When a test correctly identifies a defective unit, it must be reworked or scrapped.

“In-process leak testing catches any quality problem early at component level before putting together a full battery module or pack,” says Anne Marie Dewailly, technical director at ATEQ Corp. “An end-of-line test guarantees that the final assembly of the cooling circuit does not leak coolant inside the battery and that the enclosure is protecting the inside of the battery against water, mud or other types of splashing moisture.

DeWailly解释说：“对于电动汽车电池，有多种解决方案，并且没有标准练习。”“组装后，整个电池组都用空气进行测试，但其组件的测试方式不同。例如，用空气测试了冷却电路，同时用示踪剂气体或电离空气方法测试了电池电池。

Dewailly指出：“需要进行进程的泄漏测试，以检查每个电池子组件，例如电池，冷却板，冷却电路，排气阀，托盘和盖子。”“过程中的泄漏测试很快，并提供有关影响泄漏的过程的即时反馈。电池内部的某些组件（例如电池）在最终组装后无法访问，必须事先进行泄漏测试。出于成本原因，您想知道电池托盘在将电池和模块放入其中之前是否泄漏。”

“In-process tests enable you to discover things such as defective electrical feedthroughs, cooling circuit piping and tubing, heat exchangers or lids,” adds Inficon’s Parker. “One type of leak test cannot replace the other. You just can’t do in-process testing on individual components and not do a final test on the finished battery pack.

“The biggest benefit of end-of-line leak testing is keeping defective product away from the consumer,” says Parker. “If you don’t do a good final test, the next testing station is going to be at the dealership. Consumers are already weary of EVs, because of range anxiety and fire risks. If you don’t catch a problem in the plant, the end users will catch it at their dealership or in their garage.”

Typically, two leak tests are done on battery packs. First, the cooling circuit is tested before the battery modules are inserted into the tray. The second test is done after the cover or lid is attached.

辛辛那提测试系统的Hagyard说：“冷却液测试通常为1至5 SCCM（标准立方厘米每分钟），周期时间在180至200秒范围内。”“电池组测试的规格范围从低至10 SCCM到500 SCCM。电池组测试的周期时间在15至500秒范围内，具体取决于电池的大小和泄漏速率。

Hagyard解释说：“过程中的测试是必不可少的，因为在执行盖子泄漏测试时不会捕获冷却液电路的泄漏。”“这两个测试对于验证电池组组件过程的完整性至关重要。”

“In-process testing allows easier repair and replacement of leaking components prior to the completion of a final assembly and finds leaks before more value is added into the product,” adds Splete. “Final assembly testing may still require non-water leak rates, which become more challenging as the assembly is larger than subassembly testing.”

Testing Battery Trays and Lids

Battery pack housings and enclosures are typically rectangular- or T-shaped and made of aluminum, plastic or steel. Many housings are made out of extruded steel or aluminum profiles. They are assembled with either fasteners, structural adhesives or welded joints.

Traditionally, a metal battery enclosure features about 40 parts. While most enclosures appear similar, designs vary among automakers. For instance, one leading supplier currently produces more than 30 different battery box covers for different OEMs.

“Battery packs can often be as big as a queen-sized mattress and don’t tolerate a high change of pressure,” says Parker. Depending on the vehicle class, housing lengths and widths can be well over 2,000 or 1,500 millimeters, respectively.

“装配式后,托盘是检查pty before battery modules and thermal management systems are installed,” explains Daniel Seikaly, product manager for assembly and leak test equipment at Marposs Corp. “The trays are heavy, so it is difficult to position parts.

“Because these boxes have a lot of volume and are quite flexible, leak testing can be quite a challenge,” warns Seikaly. “Battery trays move and expand, which makes it difficult to get a reliable reading. And, because each tray is different, we must take a different approach from customer to customer.”

The housing can be leak-tested empty or full using the pressure decay, accumulation or sniffing method. The latter approach involves filling the housing with helium and scanning a sniffer probe (attached to a helium leak detector) over the part to measure out-leakage at suspect locations. Production volume typically determines whether a person or a robot manipulates the sniffer probe.

“The large, bulky size of battery trays and lids often creates challenges with leak testing cycle times,” notes Hagyard. “Unique characteristics, such as the flexible nature of battery enclosures, which are typically made out of thin sheet metal or aluminum, can cause deflection. For instance, just the influence of barometric pressure change in a factory can cause deflection that is significant enough to cause variation in the measurement results.”

但是，不同的材料具有独特的刚性水平。这可能会影响泄漏测试，因为较少的刚性材料倾向于弯曲和偏转。

To address lightweighting demands, suppliers such as Continental Structural Plastics Inc. and Magna International Inc. are developing battery enclosures made out of mixed materials, including composites. These alternatives appeal to engineers because they reduce weight, improve strength and stiffness, and improve vehicle safety.

“Battery trays and covers made from composite materials have some fundamental differences compared to metallic enclosures,” says Seikaly. “Welding is not possible, so components are bonded instead. These new materials may not transfer heat as readily as metallic counterparts and this could be an advantage for air leak test systems.”

“Lighter weight and thinner materials are good for EV automakers, because they help improve battery range,” notes Splete. “But, it makes it more challenging from a testing perspective, due to lower leak rates. As a rule of thumb, the thinner or shorter the leak path, the lower the leak rate. The thicker or longer the leak path, the higher the leak rate.”

However, no matter what type of material battery enclosures are made out of, most observers agree that tighter leak testing specs and standards will be needed in the future.

“Right now, standards are inconsistent,” claims Hagyard. “Everyone refers to the IP67 water ingress test requirement, but how OEMs and suppliers interpret that and set their specs can vary from company to company.

“There’s no commonality from one OEM to another when it comes to how they test battery pack cooling circuits and trays,” explains Hagyard. “There’s a broad range of specifications from one company to the next, even among Asian, European and North American manufacturers.”