Lithium Battery Explosion Type

Explosion type analysis The types of battery cell explosion can be summarized into three types: external short circuit, internal short circuit, and overcharge. The external refers to the external part of the battery cell, including short circuits caused by poor insulation design inside the battery pack. When a short circuit occurs outside the battery core and the electronic components fail to cut off the circuit, high heat will be generated inside the battery core, causing some of the electrolyte to vaporize, which will expand the battery shell. When the internal temperature of the battery reaches 135 degrees Celsius, high-quality membrane paper will close the pores, terminate or nearly terminate the electrochemical reaction, and the current will suddenly drop, causing the temperature to slowly drop, thereby avoiding an explosion. However, membrane paper with poor pore closure rates, or with pores that do not close at all, can cause the battery temperature to continue to rise, causing more electrolyte to vaporize, eventually breaking the battery shell, and even increasing the battery temperature to cause the material to burn and explode. The internal short circuit is mainly caused by the burr of copper and aluminum foils penetrating the membrane, or the dendritic crystal of lithium atoms penetrating the membrane.
These tiny needle shaped metals can cause micro short circuits. Because the needle is very thin and has a certain resistance value, the current may not be very large. Burrs in copper and aluminum foil are caused during the production process. The observed phenomenon is that battery leakage is too fast, and most of them can be screened out by the core factory or assembly factory. Moreover, due to the fine burrs, they can sometimes be burned off, making the battery return to normal. Therefore, the probability of explosion caused by micro short circuit of burrs is not high. This statement can be seen from the inside of each battery factory that there are often defective batteries that have a low voltage shortly after charging, but there are very few explosions that receive statistical support. Therefore, the explosion caused by internal short circuit is mainly caused by overcharge.
Because, after overcharge, needle like lithium metal crystals are everywhere on the electrode sheet, puncture points are everywhere, and micro short circuits are occurring everywhere. Therefore, the battery temperature will gradually increase, and finally the high temperature will cause the electrolyte to gas. In this case, whether the temperature is too high to cause the material to burn and explode, or the shell is first broken, causing air to enter and undergo intense oxidation of lithium metal, it is an explosion ending. However, this 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 shell, the consumer will terminate charging and take the phone out of the house. At this time, the heat generated by numerous micro short circuits slowly increases the battery temperature, and after a period of time, an explosion occurs. The common description of consumers is that when they pick up the phone, they find it very hot, and it explodes after being thrown away.
Based on the above explosion types, we can focus on preventing overcharge, preventing external short circuits, and improving the safety of the electrical core. Among them, overcharge prevention and external short circuit prevention belong to electronic protection, which are greatly related to battery system design and battery assembly. The key to improving the safety of battery cells is chemical and mechanical protection, which is closely related to battery cell manufacturers.