Lithium battery forced internal short circuit test

　　The mandatory internal short circuit test was first proposed by relevant Japanese authorities. In 2019, a laptop battery produced by a Japanese company caught fire. After a detailed study and analysis of the cause of the battery fire, relevant parties believed that it was due to the mixing of small metal particles inside the lithium battery during the production process. These particles pierced the separator between the positive and negative electrodes, causing an internal short circuit in the battery and resulting in the battery fire. Forced internal short circuit test

　　Analogous to the situation where metal particles puncture the diaphragm and cause an internal short circuit, the experiment examines the internal short circuit from two positions: between the positive electrode active substance and the negative electrode active substance; Positive aluminum foil - negative active material. During the experiment, the fully charged battery cells are first decomposed in an environment with a dew point lower than -25 ℃. Then, small nickel sheets are placed in the upper and lower positions, rolled back into the battery, and placed in sealed polyethylene bags. They are placed under the conditions of upper (lower) test temperature plus (minus) 5 ℃ for 45 minutes. Then, under the upper and lower test temperature conditions, a standard pressurization tool is used to apply pressure at a speed of 0.1mm/s to the position where the nickel sheets are placed until an internal short circuit is observed causing a voltage drop of 50mV or the pressure reaches the requirement (circular battery 800N, square battery 400N). The pressure is maintained for 30 seconds before being released. Require the battery to not ignite or explode in the event of an internal short circuit.

　　The forced internal short circuit test has received a lot of controversy, mainly due to the damage to the electrochemical environment of the battery during disassembly. Although the disassembly process requires an environment with a dew point lower than -25 ℃, it still cannot fully guarantee that the battery maintains its original state. There is still some controversy about whether the rolled back cells can effectively simulate the internal short circuit of a normal battery.

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