PPRuNe Forums - View Single Post - Four injured on United after lithium battery catches fire
Old 6th Mar 2023, 18:50
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henra
 
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Originally Posted by pilotmike
Perhaps counter-intuitively, some lithium chemistry (lithium Ion, I believe) batteries can be at significant risk of catching fire when deeply discharged.
That is not exactly correct. As long as they are deeply discharged nothing can happen. The problem with deep- discharging is that it damages the separator inside the cell. There are chemical processes which happen when a LiPo/LiIon cell drops beneath 3,0V per cell. These processes decrease the internal resistance between the active layers. When after such a deep- discharge the battery is charged again, the risk of a fire are extremely increased due to this internal short- circuit. The cell heats up, the polymer separator foil melts and a full- blown short circuit will happen at some stage. That is what happens in a so called Thermal Runaway. That is why deep- discharging is considered a fire hazard with LiPos/LiIons. As long as the cells are completely empty you can drive a screw driver through a cell and nothing will happe. Do that with a cell >~60% charge state and have a nice fireworks.
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