Safety of A123 battery cellNovember 11, 2007
With all the conversation about lithium ion battery safety, I decided to do a little 5-minute, hands-on experiment of my own to see what’s what.
The test subject: an A123 M1 cell. It was at about 30-40% state of charge before the test, unlike some other lithium battery tests where the cells have been basically dead. That’s about the lower limit of SOC that will be encountered in production vehicles.
The test: a fine point drill bit sent straight into the side of the battery, followed by being cut in half with a hacksaw.
After drilling a few millimeters into the battery, the drilling point suddenly glowed BRIGHT red hot for about 5 seconds, and there was a strong smell(stink!) of electrolyte. The heat lit a small spot of the battery’s cardboard sleeve on fire, and it continued to burn a very small, calm, steady flame, probably fueled by the electrolyte as well as the cardboard. However, there was no continuous, escalating thermal reaction or any more glowing from battery itself. I blew the flame out after about a minute. The battery case was hot to the touch, although not uncomfortably so. A slight, almost unnoticable “crinkling” sound could be heard from the battery.
The dark gray plastic cap on the anode end turned a much lighter gray – almost white.
Drilling into the battery again – both from the original point, and a new one – produced no noticeable reaction whatsoever.
Cutting the battery in half with a hacksaw across the original drill point did not produce any subsequent reaction either. The smell of electrolyte did increase somewhat. The condition of the battery material at the point of short circuit was not noticeably different from other points, apart from having a hole in it.
-Drilling into the battery created a brief but intense short circuit with highly localized effects (apart from the whole cell getting warm). This would have probably happened with any battery.
-A small area on the cardboard/paper sleeve (directly adjacent to the drill point) caught fire, indicating the temperature was at least 451º F (~233ºC).
-Most importantly, the cell itself did not explode, rupture, or provide fuel for the initial fire, although the electrolyte (which is flammable) may have contributed to the burning of the sleeve.
I plan on repeating this experiment at some point without the sleeve present, and also with a fully charged battery.