Inspired by recent overheating incidents, Underwriters Laboratories Inc. (UL) has developed a new testing methodology, along with guidelines and standards aimed at making lithium-ion battery applications safer.
An online journal for engineers published by the organization features articles and insights based on the new procedures.
In the journal, UL explained that the need for better methods became evident in the past year.
Since March 2012, the Consumer Product Safety Commission documented 467 reported incidents that identified lithium-ion cells as the battery type involved, with 353 of those being incidents involving fire/burn hazards,” UL wrote. “Further, in 2013 there were two reported incidents related to lithium-ion batteries employed in the Boeing 787 aircraft in which flames were seen coming from an auxiliary power unit battery and/or odd smells were detected in the cockpit and cabin.
As was the case with the Boeing batteries, many of the incidents have been linked to internal short circuits, UL told Design News. “It’s been written about many times,” John Drengenberg, consumer safety director at UL, said. “It’s mainly the quality control of the separator that gets implicated in many of these incidents.”
To help engineers deal with the challenges of the chemistry, UL teamed with NASA and Oak Ridge Laboratories to develop new tests, including an indentation test that induces an internal short circuit. In the test set-up, the cell is placed in a holder, then pressed from above by an “indenter.” As the indenter pushes against the battery casing, layers of the separator, anode, and cathode are deformed, potentially causing separator failure and overheating.
”For some cells, seconds after a measured drop in open circuit voltage, there is a rapid increase in cell temperature (as high as 700°C) with an outcome involving explosive release of gases and generation of flames,” the organization wrote.
The test helps engineers to know if the construction of their lithium-ion batteries -- whether cylindrical or prismatic -- is safe from overheating caused by separator failure.
Although UL doesn’t tell engineers how to build their battery packs, the organization believes it can potentially save product developers time and money, especially when dealing with such a new and highly energetic chemistry.
To date, UL has provided certification for smaller lithium-ion batteries in other applications, such as cell phones and laptops. Monolithic batteries, such as those used in autos and aircraft, have been less likely to have UL certification. Drengenberg stressed, however, that all lithium-ion applications can benefit from third-party consultation. ”Consumers are demanding more and more power in smaller packages. That’s easy to say, but for engineers, it’s very difficult to do.”
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Funny you should mention that. I picked up the phrase while in a technical writing class in college. The professor had us study the Three Mile Island accident report which had colorful euphemisms like "energetic disassembly" for explosion and "rapid oxidation" for fire.
@Dr Bob and tekochip: in my past I taught High school English and would have been proud to use your examples as how the language can be perfectly manipulated to hide what is being said. Not quite as good as collateral damage when referring to dead people, but still great examples.
I seem to remember some years ago that a UPS aircraft either crashed or made an emergency landing because a bulk delivery of LiOn batteries overheated. I believe the FAA banned bulk shipment of lithium ion batteries as a result. Also reading about this technology for marine use has led me to believe that every battery cell needs to have a temperature and voltage monitor in order to regulate charge/discharge rate to prevent fires. In other articles it has been explained that the separators are made of a plastic which is thermally sensitive. I suspect UL has been reluctant to offer a test that would suggest that this technology is "Safe". The subject test only appears to demonstrate that when stressed in a particular fashion, the battery will not energiticaly disassemble. There is an awful lot of energy packed into any storage battery. None will survive having all that energy escape in seconds.
Great post Charles. Years ago I was selected by my company to be the "agency" engineer; working with UL, IEC, ETL and AGA (now CSA). It was a definite learning experience and I quickly found both UL and CSA were extremely knowledgeable and very forward leaning relative to standards and safety. The professionalism displayed by UL was very refreshing and I came to rely on their years of experience for design guidance in several areas. I think the "marriage" between NASA, Oak Ridge and UL will be extremely beneficial in mitigating safety issues with Lithium-Ion batteries.
As I always say, we've got smart readers around here. I had never heard of "rupture with extreme prejudice" nor "spontaneous diassembly with report." But I know those phrases now. Thank you for adding to my collection of engineering stoicisms.
The indentation tests used by UL bring to mind the GM battery solution of 2012. After a post-crash fire, GM beefed up the vehicle, adding a cross-bar structure and longitudinally-oriented members around the battery. They did this, despite the fact that the Volt fire was actually caused by spilling of coolant on a circuit board, not by indentation. Many people scratched their heads and asked why GM was beefing up the battery so much. Maybe the UL indentation test provides us a glimpse of their thinking.
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