In daily life, lithium-ion batteries can be seen 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 thing is the explosion and fire of lithium-ion batteries. Then the common causes of fire in lithium-ion batteries are mainly as follows.
1. Insufficient negative electrode capacity
When the capacity of the negative electrode opposite to the positive electrode is insufficient, or there is no capacity at all, part or all of the lithium that appears during charging cannot be inserted into the interlayer structure of the negative electrode graphite, and will precipitate on the surface of the negative electrode to form protruding dendrites. , And the next charge, this protruding part is more likely to cause the precipitation of lithium, after tens to hundreds of cycles of charge and discharge, dendrites will grow up, and finally pierce the diaphragm paper, causing internal short circuits. The battery cell discharges rapidly, a large amount of heat occurs, which burns the diaphragm and causes a greater short-circuit phenomenon. The high temperature will decompose the electrolyte into gas, and the negative carbon and diaphragm paper will burn, resulting in excessive internal pressure. When subjected to this pressure, the battery cell will explode.
2. The moisture content is too high
Moisture can react with the electrolyte in the battery cell to process gas. When charging, it can react with the generated lithium to generate lithium oxide, which causes the capacity of the battery cell to be lost. It is easy to overcharge the battery to generate gas and decompose the water. The voltage is low, and it is easy to decompose and generate gas when charging. When this series of generated gas will increase the internal pressure of the battery, when the outer shell of the battery cannot withstand it, the battery will explode.
3. Internal short circuit
Due to the internal short-circuit phenomenon, the large current discharge of the cell will cause a lot of heat, which will burn the diaphragm and cause a greater short-circuit phenomenon. In this way, the cell will have a high temperature, which will decompose the electrolyte into gas and cause excessive internal pressure. When the shell of the battery cell cannot withstand this pressure, the battery cell will explode.
When the battery cell is overcharged, the excessive release of lithium in the positive electrode will change the structure of the positive electrode. If too much lithium is released, it is easy to be unable to be inserted into the negative electrode. It is also easy to cause lithium deposition on the surface of the negative electrode. Moreover, when the voltage reaches 4.5V or more, The electrolyte will decompose and process a large amount of gas. All of the above may cause an explosion.
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