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.”