Detailed analysis of the principle of the 3 situations of lithium battery explosion

　　The types of battery cell explosion can be classified 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 cell and the electronic components fail to cut off the circuit, high heat will be generated inside the cell, which will cause part of the electrolyte to vaporize and expand the battery shell. When the internal temperature of the battery is as high as 135°C, the 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 avoiding an explosion. However, the pore closure rate is too poor, or the pores are not closed at all, the battery temperature will continue to rise, more electrolyte will vaporize, and finally the battery shell will be broken, and the battery temperature will even be increased. The material burns and explodes.

　　The internal short circuit is mainly caused by the burrs of the copper foil and aluminum foil piercing the diaphragm, or the dendritic crystals 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. The copper and aluminum foil burrs are caused during the production process. The observable phenomenon is that the battery leaks too fast, which 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 verified 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. Therefore, the explosion caused by an internal short circuit is mainly caused by overcharging. Because, after overcharging, 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 vaporize the electrolyte. 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. Let's take a mobile phone battery as an example. It is possible that when the temperature of the battery is not high enough to burn the material and the gas generated is not enough to break the battery casing, consumers will stop charging. At this time, the heat generated by the numerous micro-short circuits slowly raises the temperature of the battery, and it explodes after a period of time. 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 preventing overcharge, preventing external short circuits, and improving battery cell safety. Among them, the prevention of overcharging and the prevention of external short circuits belong to electronic protection, which has a greater relationship with battery system design and battery assembly. The focus of battery cell safety improvement is chemical and mechanical protection, which has a greater relationship with battery cell manufacturers.

　　Lithium-ion battery (LIB) has become the main energy storage solution in modern social life. Among them, lithium iron phosphate batteries are a perfect replacement for lead-acid batteries, and they are the first choice for grid-connected peak shaving, off-grid energy storage, photovoltaic energy storage, UPS, data center and other industries.