Explosion type analysis The type of battery core explosion can be summarized as external short circuit, internal short circuit, and overcharge. The external part here refers to the outside of the cell, and it contains a short circuit caused by poor insulation design inside the battery pack. When a short circuit occurs outside the cell, and the electronic component fails to cut off the circuit, high heat is generated inside the cell, causing some of the electrolyte to vaporize and the battery case is enlarged. When the internal temperature of the battery is as high as 135 ° C, the good quality separator paper will close the pores, the electrochemical reaction will be terminated or nearly terminated, the current will drop suddenly, and the temperature will gradually drop, thus avoiding the explosion. However, the pore closing rate is too poor, or the separator paper, which does not close the pores at all, will cause the battery temperature to continue to rise, more electrolyte vaporizes, and finally the battery casing is broken, and the battery temperature is raised even to The material burns and explodes. The internal short circuit is mainly caused by the burr of the copper foil and the aluminum foil piercing the diaphragm, or the dendrite of lithium atoms piercing the diaphragm.
These tiny needle-like metals can cause micro short circuits. Since the needle is very thin and has a certain resistance value, the current is not necessarily large. Copper and aluminum foil burrs are caused during the production process. The observed phenomenon is that the battery leaks too quickly, and most of them can be screened by the battery factory or assembly plant. Moreover, since the burrs are small, they are sometimes blown off, and the battery returns to normal. Therefore, the probability of an explosion caused by a burr micro-short circuit is not high. In this way, it is possible to get a bad battery with a low voltage shortly after charging in each battery factory, but there are few explosion events and statistical support. Therefore, the explosion caused by the internal short circuit is mainly caused by overcharge.
Because, after overcharging, the lenticular lithium metal crystals are everywhere on the pole piece, and the piercing point is everywhere, and micro short circuits occur everywhere. Therefore, the battery temperature will gradually increase, and finally the high temperature will electrolyze the liquid gas. In this case, whether the temperature is too high, the material burns and explodes, or the outer shell is broken first, so that the air enters and the lithium metal is violently oxidized, which is the end of the explosion. However, such an explosion caused by an internal short circuit caused by overcharging does not necessarily occur at the time of charging. It is possible that when the battery temperature is not high enough for the material to burn and the gas generated is not enough to break the battery casing, the consumer terminates charging and takes the mobile phone out. At this time, the heat generated by the numerous micro short circuits slowly increases the temperature of the battery, and after a certain period of time, the explosion occurs. The common description of consumers is that when the phone is picked up, the phone is found to be very hot, and it will explode after being thrown away.
In combination with the types of explosions above, we can focus on the prevention of overcharge, the prevention of external short circuits, and the safety of battery cells. Among them, overcharge prevention and external short circuit prevention are electronic protection, which has a great relationship with battery system design and battery assembly. The focus of battery safety improvement is chemical and mechanical protection, which has a great relationship with battery manufacturers.