1. Overcharge explosion
If the protection circuit or the detection cabinet malfunctions, causing the charging voltage to exceed 5V, the electrolyte will decompose, a violent reaction will occur inside the battery, the internal pressure of the battery will rise rapidly, and the battery will explode.
2. Overcurrent explosion
If the protection circuit or the detection cabinet malfunctions, the charging current may be too large, causing lithium ions to not have time to intercalate and instead form lithium metal on the electrode surface. This lithium metal can penetrate the separator, causing a direct short circuit between the positive and negative electrodes and resulting in an explosion (which is rare).
3. Explosion during ultrasonic welding of plastic casing
During ultrasonic welding of the plastic casing, due to equipment malfunctions, the ultrasonic energy was transferred to the battery cell. The high ultrasonic energy caused the internal separator of the battery to melt, resulting in a direct short circuit between the positive and negative electrodes and an explosion.
4. Explosion during spot welding
Excessive current during spot welding caused a severe internal short circuit, leading to an explosion. Additionally, the positive electrode connector was directly connected to the negative electrode during spot welding, causing a direct short circuit between the positive and negative electrodes, which resulted in an explosion.
5. Over-explosion explosion
Over-discharge or overcurrent discharge (above 3C) of a battery can easily cause the copper foil on the negative electrode to dissolve and deposit on the separator, resulting in a direct short circuit between the positive and negative electrodes and an explosion (which rarely occurs).
6. Explosion upon vibration and drop
When a battery cell is subjected to severe vibration or a drop, the internal electrode plates may become misaligned, causing a direct and serious short circuit and resulting in an explosion (this is rare).
When a lithium-ion battery cell is overcharged to a voltage exceeding 4.2V, it begins to exhibit adverse effects. The higher the overcharge voltage, the greater the danger. When the voltage of a lithium-ion battery cell exceeds 4.2V, less than half of the lithium atoms remain in the positive electrode material. At this point, the storage cells often collapse, causing a permanent decrease in battery capacity. If charging continues, since the negative electrode storage cells are already full of lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow into dendritic crystals from the negative electrode surface in the direction from which the lithium ions originated. These lithium metal crystals can penetrate the separator paper, causing a short circuit between the positive and negative electrodes. Sometimes, the battery explodes before the short circuit occurs. This is because during overcharging, materials such as the electrolyte decompose, releasing gas. This gas causes the battery casing or pressure valve to bulge and rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the negative electrode surface, leading to an explosion.
