1.Insufficient of negative electrode capacity:
The following is the thermal runaway process if negative electrode capacity is insufficient
When the capacity of the negative electrode opposite the positive electrode part is insufficient, or there is no capacity at all, some or all of the lithium generated during charging cannot be inserted into the inter layer structure of the negative electrode graphite.
Then lithium will settle on the surface of the negative electrode, forming a protruding “dendrite”. The next time, when battery is charged, this protruding part is more likely to generate lithium.
After dozens to hundreds of cycles of charging and discharging, the “dendrite” will grow.
Finally, “dendrite” will pierce the diaphragm paper and cause a short circuit inside.
The battery discharges sharply which will generate a lot of heat.
The heat will burn out the diaphragm, and cause a greater short circuit.
The high temperature will decompose the electrolyte into gas, and the negative carbon and the diaphragm paper will burn, causing excessive internal pressure. When the shell of the battery cannot withstand this pressure, the battery will explode.
2.High moisture content
Moisture can react with the electrolyte in the battery to produce gas. When charging, it can react with the generated lithium to generate lithium oxide, which causes the capacity of the battery to be lost. It is easy to overcharge the battery and generate gas. The decomposition voltage of moisture is low, and it is easy to decompose to generate gas when charging. When this series of generated gases will increase the internal pressure of the battery, and when the shell of the battery cannot withstand it, the battery will explode.
3. Internal short circuit
Due to the internal short-circuit phenomenon, the battery discharges at a high current, generating a lot of heat, burning out the diaphragm, and causing a greater short-circuit phenomenon. In this way, the battery will produce high temperature, causing the electrolyte to decompose into gas, causing excessive internal pressure. When the shell of the battery cannot withstand this pressure, the battery will explode.
During laser welding, heat is transmitted through the housing to the positive electrode ear, so that the temperature of the positive electrode ear is high. If the upper adhesive paper does not separate the positive electrode ear and the diaphragm, the hot positive electrode ear will burn out or shrink the diaphragm paper, causing an internal short circuit and an explosion.
4. External short circuit
The external short circuit may be caused by improper operation or misuse. Due to the external short circuit, the battery discharge current is very large, which will cause the battery to heat up. The high temperature will shrink or completely damage the diaphragm inside the battery, causing an internal short circuit and thus an explosion.
5.High temperature adhesive paper wraps the negative electrode ear
During spot welding of the negative electrode ear, heat is transmitted to the negative electrode ear. If the high-temperature adhesive paper is not affixed, the heat on the negative electrode ear will burn out the diaphragm, causing an internal short circuit and an explosion.
6. The bottom glue is not completely wrapped around the bottom
When the customer spot welds at the bottom of the aluminum-nickel composite belt, a lot of heat will be generated on the bottom shell wall, and the bottom of the conduction pole core. If the high-temperature adhesive paper does not completely wrap the diaphragm, it will burn out the diaphragm, causing an internal short circuit and an explosion.
When the battery is overcharged, the excessive release of lithium from the positive electrode will cause the structure of the positive electrode to change, and the excessive release of lithium will easily fail to be inserted into the negative electrode, which will also easily cause lithium to be analyzed on the surface of the negative electrode. Moreover, when the voltage reaches above 4.5V, the electrolyte will decompose to produce a large amount of gas. All of the above may cause an explosion.