Causes of explosion: Insufficient negative electrode capacity, excessive moisture content, internal short circuit, aging and failure of protection circuit, overcharging, over-discharging, external short circuit.
Insufficient negative electrode capacity
When the capacity of the negative electrode opposite the positive electrode is insufficient, or even nonexistent, some or all of the lithium produced during charging cannot insert into the interlayer structure of the negative electrode graphite. Instead, it deposits on the surface of the negative electrode, forming protruding dendrites. During the next charge, these protrusions are more likely to cause lithium deposition. After dozens to hundreds of charge-discharge cycles, the dendrites grow and eventually pierce the separator paper, causing an internal short circuit. Rapid discharge of the cell generates a large amount of heat, burning the separator and causing an even larger short circuit. The high temperature causes the electrolyte to decompose into gas, and the negative electrode carbon and separator paper to burn, resulting in excessive internal pressure. When the cell casing cannot withstand this pressure, the cell explodes.
Excessive moisture content
Moisture can react with the electrolyte in the battery cell to produce gas. During charging, it can react with the generated lithium to form lithium oxide, causing capacity loss in the battery cell and making it prone to overcharging and gas generation. Moisture has a low decomposition voltage, so it easily decomposes and generates gas during charging. When this series of generated gases increases the internal pressure of the battery cell, the battery cell will explode when the outer casing cannot withstand it.
Internal short circuit
Due to an internal short circuit, the battery cell discharges a large current, generating a lot of heat that burns the diaphragm, causing an even larger short circuit. This results in the battery cell reaching high temperatures, causing the electrolyte to decompose into gas and creating excessive internal pressure. When the battery cell's casing can no longer withstand this pressure, the battery cell will explode.
During laser welding, heat is conducted through the shell to the positive electrode tab, causing the positive electrode tab to reach a high temperature. If the upper adhesive tape does not separate the positive electrode tab from the diaphragm, the hot positive electrode tab will cause the diaphragm paper to burn or shrink, resulting in an internal short circuit and an explosion.
High-temperature adhesive tape wrapped around the negative electrode ear
When the customer is spot welding the negative electrode tab, heat is conducted to the negative electrode tab. If the high-temperature adhesive tape is not properly applied, the heat on the negative electrode tab will burn the diaphragm, causing an internal short circuit and potentially leading to an explosion.
The adhesive on the bottom did not completely cover the bottom.
When customers spot weld the bottom aluminum-nickel composite strip, a lot of heat will be generated on the bottom shell wall, which will conduct heat to the bottom of the electrode core. If the high-temperature adhesive tape does not completely cover the diaphragm, it will burn the diaphragm, causing an internal short circuit and an explosion.
overcharge
When a battery cell is overcharged, excessive lithium release from the positive electrode can alter its structure. Excessive lithium release can also prevent it from inserting into the negative electrode, leading to lithium deposition on the negative electrode surface. Furthermore, when the voltage reaches 4.5V or higher, the electrolyte decomposes, producing a large amount of gas. All of these factors can potentially cause an explosion.
External short circuit
External short circuits may be caused by improper operation or misuse. Due to an external short circuit, the battery discharge current is very large, which will cause the battery cell to heat up. The high temperature will cause the diaphragm inside the battery cell to shrink or completely break down, resulting in an internal short circuit and thus an explosion.
