To the right is a clip from one of our tests, where the cell was intentionally overcharged, demonstrating what can occur when no overcharge protection is included in Lithium Battery Packs.
As the cell reaches full charge, continued application of charging power causes the lithium ions in solution to plate out on the anode in elemental metallic form, rendering the cell highly reactive & unstable.
As the charge is continued, more lithium plates out, and the cell heats up. This heat, along with the reaction of the now metallic lithium with the flammable electrolyte causes further heating. At this point the delithiated cathode is also beginning to react with the electrolyte, releasing various gases. Both chemical processes are extremely exothermic, and the cell ruptures from the combination of heat damage & internal gas pressure.
As the electrode material breakdown continues, driven by thermal runaway & the continuing charge current, the cell vents the resulting breakdown products. Further heating as a result of the combination of chemical/electrochemical processes eventually reaches the autoignition point, and the cell explodes, spewing flames.