Analysis of explosion types of lithium-ion batteries

Explosion type analysis The types of battery cell explosion can be summarized into three types: external short circuit, internal short circuit, and overcharge. The outside here refers to the outside of the battery cell, including short circuits caused by poor internal insulation design of the battery pack. When a short circuit occurs on the outside of the battery cell and the electronic components fail to cut off the circuit, high heat will appear inside the battery, which will cause part of the electrolyte to vaporize and expand the battery shell. When the internal temperature of the battery reaches 135 degrees Celsius, a good quality diaphragm paper will close the pores, the electrochemical reaction will be terminated or almost terminated, the current will drop sharply, and the temperature will slowly drop, thus preventing an explosion. However, the pore closure rate is too poor, or the pores are not closed at all. The diaphragm paper will cause the battery temperature to continue to rise, more electrolyte will vaporize, and finally the battery shell will be broken, or even the battery temperature will be increased to The material burns and explodes. The main reason for the internal short circuit is that the burrs of the copper foil and the aluminum foil pierce the diaphragm, or the dendrites of lithium atoms pierce 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. The copper and aluminum foil burrs are caused by the production process. The observable phenomenon is that the battery leaks too fast, and most of them can be screened by the battery cell factory or the assembly factory. Moreover, due to the small burrs, they will sometimes be burned, causing the battery to return to normal. Therefore, the probability of explosion caused by burr micro-short circuit is not high. This statement can be seen from the fact that there are often bad batteries with low voltage shortly after charging in various battery cell factories, but there are few explosions, which is supported by statistics. Therefore, the explosion caused by the internal short circuit is mainly caused by overcharge. Because after overcharge, there are needle-like lithium metal crystals everywhere on the pole piece, the puncture point is everywhere, and the micro short circuit occurs everywhere. Therefore, the battery temperature will gradually rise, 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 outer shell is first broken, causing the air to enter and oxidize the lithium metal, it is an explosion. However, the 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 to burn the material and the gas is not enough to break the battery casing, the consumer will stop charging and take the mobile phone out. At this time, the heat generated by the numerous micro-short circuits gradually increased the battery temperature, and after a period of time, it exploded. The common description of consumers is that when they pick up the phone, they find that the phone is very hot, and it explodes after throwing it away. Based on the above types of explosions, we can focus on the three-way explosion protection on the prevention of overcharge, the prevention of external short circuits, and the improvement of the safety of the battery. Among them, overcharge prevention and external short circuit prevention belong to electronic protection, which has a greater relationship with battery system design and battery assembly. The focus of battery cell safety enhancement is chemical and mechanical protection, which has a greater relationship with battery cell manufacturers. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: How long will it take for the cobalt-free power lithium battery?