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.”
I know what you mean, Lou, it seems like there has to be an incident with serious consequences before companies improve certain aspects of their products or, in the case of the airline industry, airplanes. But in all fairness, perhaps they weren't aware that there was potential for such problems in the first place. This is where more careful and attentive design with anything, especially lithium-ion batteries, must come into play.
I made a careless mistake and paid for in seconds. The cell energetically disassembled without the slightest hint that it was aggravated with me. As if the chemical burns weren't bad enough, the freed lithium also ignited, so I had to figure out if I wanted to wash my eyes out first or put out the little fires scattered across my workbench.
Oh my gosh, that sounds horrible. I hope you are OK. I take it you have learned alot from this situation and I guess having some kind of guidelines or test to prevent such a thing in the future is something you would welcome. Take care!
I really think UL has missed the point on this one. One of the mysteries concerning L-ion cell failures is why L-ion cells short in the first place! This "indenting test" which forces a short to make it fail will NOT test to see if a cell has been designed and built to avoid shorts. All it does is to test whether a cell overheats AFTER this mysterious short. It's like UL is saying, "it's OK to have a cell which mysteriously shorts. After a forced short though, we want to ensure that it doesn't overheat." I say go after the cause, not the result.
I think it is great that someone be it UL or who ever can come up with some safety test, not just for Li Battery but for ANY battery.
From experience I also think that the entire "package" needs to be evaluated and tested, as for example I have seen more than one Golf Cart where the entire vehicle burned down, just because one battery wire was having too high a resistance and caused enough heat to not just melt a Lead-alloy post but ignite what ever was next to it, which in turn burned down the entire vehicle.
Other example may be the few Fisker cars, that burned for what ever reason, but one of them was apparently short in "cooling fan motor" that burned off entire 1/2 of front end of the car.
So NOT having easily flammable materials next to "potential" ignition source, be it extreme heat or spark, is also somthing about which engineers need to think about and design in appropriate safety.
I.e. if battery fails, for what ever reason, the device, be it computer or a car, should not be a total loss as a result !
That sounds like good advice, tekochip--in fact, it sounds a bit like a no brainer! But I guess an experienced engineer might get lazy sometimes with safety? I'm personally not an engineer and don't do a lot of work in a lab situation, so I wouldn't know, but I guess if you do something every day you might think you can slack a bit with the safety precautions. It's good to remind people not to! Glad you came out of the accident OK.
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.
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 question of whether engineers could have foreseen the shortcut maintenance procedures that led to the crash of American Airlines Flight 191 in 1979 will probably linger for as long as there is an engineering profession.
More than 35 years later, the post-mortem on one of the country’s worst engineering disasters appears to be simple. A contractor asked for a change in an original design. The change was approved by engineers, later resulting in a mammoth structural collapse that killed 114 people and injured 216 more.
If you’re an embedded systems engineer whose analog capabilities are getting a little bit rusty, then you’ll want to take note of an upcoming Design News Continuing Education Center class, “Analog Design for the Digital World,” running Monday, Nov. 17 through Friday, Nov. 21.
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