Five causes of fire in lithium-ion batteries
Ⅰ. External short circuit
External short circuit caused by improper operation or misuse. Due to external short circuit, the battery discharge current is very large, which will make the battery cell heat up. High temperature will make the diaphragm inside the battery cell shrink or completely break down, resulting in internal short circuit and fire.
Ⅱ. Internal short circuit
Because of the short-circuit phenomenon inside, the battery cell discharges with high current, and lot of heat burns the diaphragm, resulting in a greater short-circuit phenomenon. In this way, the battery cell will have high temperature, which will decompose the electrolyte into gas, resulting in excessive internal pressure. When the battery cell shell can't bear this pressure, the battery cell will catch fire.
Ⅲ. Overcharging
When the battery is overcharged, the excessive discharge of lithium from the positive electrode will change the structure of the positive electrode, and too much discharged lithium will easily be unable to insert into the negative electrode, which will also easily lead to lithium precipitation on the surface of the negative electrode. Moreover, when the voltage reaches above 4.5V, the electrolyte will decompose and produce a large amount of gas. All of the above can cause a fire.
Ⅳ. Too high water content
Water can react with the electrolyte in the battery cell to produce gas. When charging, it can react with the generated lithium to generate lithium oxide, which makes the battery cell lose its capacity and is easy to overcharge and generate gas. The decomposition voltage of water is low, and it is easy to decompose to generate gas when charging. When this series of generated gases increases the internal pressure of the battery cell, the battery cell will explode when the battery cell shell can't bear it.
Ⅴ. 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, some or all of the lithium during charging cannot be inserted into the interlayer structure of the negative electrode graphite, and will precipitate on the surface of the negative electrode, forming a protruding dendrite, which is more likely to precipitate lithium during the next charging. After dozens to hundreds of cycles of charging and discharging, the dendrite will grow up, and finally it will pierce the separator paper, resulting in short circuit inside.