Runaway Lithium-Ion batteries
In my youth, I might have been a member of a small subset of boys who were attracted to flames. I enjoyed watching a campfire or an open flame burn. Even a burning candle was an attraction. There seemed to be something close to magic about it. At school, teachers would give all types of presentations, with seemingly no regard to the possibility that you might attempt to duplicate the demonstration at home.
In junior high (middle school for others) our science teacher wanted to demonstrate combustion. The demonstration was fairly simple, but dramatic in that it also demonstrated explosion. She took an empty, cleaned-out paint can, poked a hole about a quarter of an inch wide in the middle of the lid and in the side of the can very near the bottom, then secured the lid firmly. She used the natural gas outlet to fill the can with natural gas until she believed the contents were saturated with gas.
Next she lit the top hole to create a small candle-like flame. As time went on the flame grew smaller and smaller, along with our attention to what was going on. At some point, the flame disappeared and the lid blew off the can with a bang loud enough to startle everyone in the class. As you can imagine, this demonstration was repeated at home to the delight of the neighborhood boys. It was the unexpected bang, along with the idea that this was, for the most part, safe that entertained us.
This certainly is not the case for Lithium-Ion (Li-Ion) batteries. No one expects these batteries to be entertaining by making any kind of sound or flames. I have not spent much time ferreting out information about any accidents involving the batteries. In general, I consider these batteries to be well-behaved, given that they are treated in the manner dictated by the manufacturer. However, they have resurfaced in the news.
The last big news story for me was the Li-Ion recall in late 2006 when more than eight-million batteries were recalled. There were a few incidents of laptop batteries going into thermal runaway. The problem was traced back to metal shaving from the manufacturing process contaminating the internal battery environment. This caused these batteries to produce an internal short that raised the local battery temperature to the point of thermal runaway.
You may recall a UPS plane crash in 2011 that was thought to have occurred due to a large shipment of Li-Ion batteries onboard. If you want to know more there is a posting by Josie Garthwaite that describes a fair amount of detail about the accident.1 Another article by Matt Thurber goes into detail about the current use of Li-Ion batteries as part of the backup power system onboard aircraft.2 The Boing 787 is not the first aircraft to use this type of battery.
Matt also covers other reported events involving batteries. Some of these were certainly news to me. For example, there was an event in 2004 where a lithium battery inside a camera exploded and set a passenger seat on fire. The flight attendants put the fire out and the plane returned to the departure airport. The list of incidents is not very long and would certainly lead one to consider this technology to be safe.
So what do we know about the 787 Li-Ion battery pack incident? The only definitive information is that the batteries went into thermal runaway. Information is slowly being released. Initially the problem was described as a possible overcharge, but later this was retracted. Recently more information was given about the battery voltage dropping from 32V to 28V unexplainably. This 4V drop would certainly indicate a substantial short of a single cell. If this is the case, there would be enough energy to raise the temperature to thermal runaway.
A graph in Figure 1 shows the behavior of thermal runaway. The chart shows some of the popular cathode material (Reference 4). LiCoO2 often is used when maximum energy density is valued. However, it can be placed into thermal runaway as indicated by the chart. Just before 200°C, this cathode material releases energy that supports a runaway condition. LiFePO4 has virtually no thermal runaway potential, but it also has only about 60 percent of the energy density of LiCoO2. The aviation application has the same issues as many other applications, the demand for high-energy density and nonnegotiable safety.
Figure 1 Accelerating rate calorimetry (ARC) at 100% state-of-charge (SOC).
The big question for the Boeing 787 batteries is how the battery got to a state where thermal runaway became the outcome. This probably is the maddening part of the investigation as this rarely happens.
There may be an opportunity to detect the early stage of the problem before it becomes an emergency. The act of charging and discharging the battery does give an opportunity to analyze how the battery has changed. When in doubt, change it out!
One aspect of monitoring the activity around this problem is that you get to see very interesting pictures of batteries destroying themselves.
Please let me know your thoughts or opinions on how power can have a play in making high-density energy storage safe. You could be part of the solution in making these batteries safer! For more information about this and other power topics, visit TI’s Power House blog.
- Josie Garthwaite, “Lithium Ion Batteries Faulted for Jet Crash,” April 4, 2011
- Matt Thurber, “Lithium Fires Generate Myths and Misinformation,” Aviation International News, Oct. 2012
- Mike M. Ahlers, “Boeing can conduct Dreamliner test flights,” CNN, Feb. 8, 2013
- E. Peter Roth, Tom Wunsch, Chris Orendorff, “Sandia Battery Abuse Testing Laboratory (BATLab),” Sandia National Laboratories