Most fire accidents in various products using lithium-ion batteries, including electric vehicles, occur while charging. The main reason for this is that the negative electrode material (graphite or mixed silicon) continues to inflate (Figure 1) after repeated charging cycles, shortening the distance between the positive and negative electrodes. This results in the effective distance between these electrodes becoming shorter than the original design due to electrode burrs or metal particles, increasing the risk of an internal short circuit.
Figure 1 Height changes of graphite anode material during charging and discharging
of a lithium-ion battery(Furukawa Electric Review, No. 134 2015-1)
Therefore, from a fire protection perspective, insulation tests of lithium-ion battery cells should check the distance between electrodes, rather than measure the…