In daily life, lithium-ion batteries can be found almost everywhere, from electric cars to computer motherboard batteries. Lithium-ion batteries have become an indispensable part of people. We often see various safety accidents caused by lithium-ion batteries. The most impressive is the explosion and fire of lithium-ion batteries. The common causes of fires in lithium-ion batteries are as follows.
1. Insufficient negative electrode capacity
When the capacity of the negative electrode opposite to the positive electrode is insufficient or has no capacity at all, part or all of the lithium present during charging cannot be inserted into the interlayer structure of the negative electrode graphite, and will precipitate to form prominent dendrites on the surface of the negative electrode, And the next charge, this protruding part is more likely to cause the precipitation of lithium, after tens to hundreds of charge and discharge cycles, dendrites will grow up, and finally pierce the diaphragm paper, causing internal short circuits. The cell discharges quickly, generates a lot of heat, burns the diaphragm, and causes a large short circuit. High temperature will decompose the electrolyte into gas, and the negative electrode carbon and diaphragm paper will burn, resulting in excessive internal pressure. When the shell of the battery cell cannot withstand this pressure, the battery will explode.
2. The moisture content is too high
The moisture reacts with the electrolyte in the battery cell to generate gas. When charging, it will react with the generated lithium to generate lithium oxide, which will cause the loss of battery cell capacity, which will easily cause the battery to overcharge and produce gas to decompose water. The decomposition voltage of water is low, and it is easy to decompose to produce gas when charging. When this series of generated gases will increase the internal pressure of the battery, the battery will explode when the battery casing cannot withstand it.
3. Internal short circuit
Due to the internal short-circuit phenomenon, the large current discharge of the battery cell generates a lot of heat, which burns the diaphragm and causes a greater short-circuit phenomenon. In this way, the battery core will have a high temperature and the electrolyte will be decomposed into gas, resulting in excessive internal pressure. When the shell of the battery cell cannot withstand this pressure, the battery cell will explode.
When the battery is overcharged, the positive electrode will release too much lithium, which will change the structure of the positive electrode. In addition, too much lithium is released, it is difficult to be inserted into the negative electrode, and it is easy to cause lithium to be deposited on the surface of the negative electrode. Moreover, when the voltage reaches 4.5V or higher, the electrolyte will decompose and process a large amount of gas. All of the above reasons can cause an explosion.