5
Thermal Events
A thermal event is one where excessive heat in or around the cell destroys it immediately. Proper battery pack
design is essential to allow the thermal safety features of A123’s cells to function as designed. A123 cell design
includes a safety feature that allows over-overheated cells to relieve dangerous pressure buildup by venting and
dispersing the gases into the environment. However, an improperly designed battery pack can prevent the gases
from safely dispersing.
For example, if the cell vents are blocked when a cell overheats, pressure within the cell can cause the overheated
cell to rapidly disassemble and damage a poorly designed enclosure or other battery pack components. This
document highlights some recommendations on the pack’s physical and electrical design, which when followed,
can mitigate these dangers.
Adding an ignition source to vented gases can create a dangerous thermal event.
The battery pack
must
ventilate these expelled gases to the environment after the gases
are vented from the cell itself.
Short Circuits
Because A123 cells have relatively little internal resistance, an improperly designed
battery pack may allow short circuits with dangerous levels of current.
Arc Flashes
A poor battery pack design may increase the chances of an arc flash. An arc flash caused
by a short circuit involving both high voltage and high current, emits extremely high
intensity visible and ultra violet light with the potential to damage property and cause
blindness and burns to personnel.
High Voltage
Assembling a battery pack involves combining cells in series or parallel to achieve higher
voltages and currents, respectively. As the voltage and current increase, so does the
danger to personnel assembling the battery pack. Without the proper training,
experience, tools and personal protective equipment (PPE), handling high voltage
battery packs will result in injury or death.