Lithium battery explosion type analysis.27A battery

　　The type of battery cell explosion can be summarized as external short circuit, internal short circuit, and overcharge. The outside here refers to the outside of the cell, including the short circuit caused by the poor insulation design of the battery group. When there is a short circuit outside the cell, and the electronic component fails to cut off the circuit, high heat will be generated inside the cell, causing part of the electrolyte to vaporize, and the cell shell will be extended. When the internal temperature of the battery is high to 135 degrees Celsius, the good quality diaphragm paper will close the fine hole, the electrochemical reaction will end or nearly end, the current will drop sharply, and the temperature will slowly drop, thus avoiding the explosion. However, the closing rate of the fine hole is too poor, or the diaphragm paper that the fine hole will not close at all will allow the battery temperature to continue to rise, more electrolyte vaporization, and finally the battery shell will burst, and even raise the battery temperature to make the material burn and explode.

　　The internal short circuit is mainly caused by the burr of copper foil and aluminum foil through the diaphragm, or the dendritic crystals of lithium atoms through the diaphragm. These tiny, needle-like pieces of metal can cause micro-short circuits. Because the needle is very thin and has a certain resistance value, the current is not necessarily very large. Aluminum foil burrs are caused in the production process, and the observable phenomenon is that the battery leakage is too fast, and most of them can be screened out by the battery plant or the assembly plant. Moreover, because the burrs are small, they can sometimes be burned off, making the battery return to normal. Therefore, the probability of explosion caused by the burr micro-short circuit is not high. This can be said from the inside of each cell factory, there are often bad batteries with low voltage shortly after charging, but there are few explosion incidents, which are statistically supported. Therefore, the explosion caused by the internal short circuit is mainly caused by overcharge.

　　Because, after overcharging, the pole plate is full of needle-like lithium metal crystals, the puncture point is everywhere, and micro-short circuits are occurring everywhere. Therefore, the temperature of the battery will gradually increase, and finally the high temperature will electrolysis the liquid gas. In this case, whether the temperature is too high to make the material burn and explode, or the shell is first burst, so that the air goes into the lithium metal to undergo intense oxidation, it is an explosion. However, this explosion caused by an internal short circuit caused by overcharge does not necessarily occur at the time of charging. It is possible that when the temperature of the battery is not high enough for the material to burn and the gas produced is not enough to burst the battery case, the consumer will stop charging and take the phone out. At this time, the heat generated by many micro-short circuits slowly increases the temperature of the battery, and after a period of time, an explosion occurs. The common description of consumers is that when they pick up the phone, they find the phone is very hot, and it explodes after throwing it away. Based on the above types of explosion, we can focus on the prevention of overcharge, the prevention of external short circuit, and the three-way explosion-proof focus on the surface to improve the safety of the battery cell. Among them, overcharge prevention and external short circuit prevention belong to electronic protection, which is closely related to battery system design and battery pack installation. The focus of cell safety improvement is chemical and mechanical protection, which has a great relationship with the battery cell manufacturer.

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