Three reasons for the explosion of 18650 lithium batteries

 1. Overcharged

Overcharging of 18650 lithium batteries is a common cause of explosions. Lithium batteries must operate within the specified voltage range, otherwise there may be a safety hazard of explosion and fire. For example, the conventional voltage for ternary lithium batteries is 2.5V~4.2V; The conventional range for lithium iron phosphate batteries is 2.0V~3.65V.

 

When charging an 18650 lithium battery, the lithium ions in the positive electrode move to the negative electrode and are embedded in the mesh structure of the negative electrode material. If the lithium ion battery is overcharged, it is easy to cause lithium deposition in the negative electrode, resulting in lithium crystallization and piercing the separator, which can cause a short circuit inside the battery cell and trigger an explosion.

 

That's why an overcharge protection circuit must be added to lithium-ion batteries during charging to provide overcharge protection. The lithium battery protection board will monitor the voltage of each string of the lithium battery pack. If it exceeds the overcharge voltage, the lithium battery protection board will cut off charging to protect the lithium battery.

 

If an overcharge explosion occurs in a lithium battery pack, it is mostly due to individual strings of lithium batteries experiencing 0V voltage or abnormal protection boards that cannot provide overcharge protection for the lithium batteries; Another issue is the incorrect use of the charger.

For example, a 36V lithium battery pack requires 10 strings of ternary lithium. If the voltage of 2 strings of cells becomes 0V, the charger's charging voltage of 42V will directly charge the remaining 8 strings. The protection board function is abnormal and cannot provide overcharge protection. The average voltage of 8 strings of battery cells will be charged by the charger to above 5.25V (42V/8 strings). This can lead to overcharging of lithium batteries, causing accidents such as explosions.

 

If the charger is used incorrectly and the lithium battery pack is not charged according to the prescribed dedicated charger, it can also cause the lithium battery protection board to malfunction and the lithium battery pack to be overcharged.

 

For example, for a 36V lithium battery pack, the output voltage of a dedicated charger should be 42V. If a 72V lithium battery pack charger (with a charging voltage of 84V) is used and the 84V charging voltage is directly loaded onto the 36V lithium battery pack, the components of the protection board are easily damaged and the function is prone to failure. At this point, the lithium battery pack will be charged without protection, and the voltage of each string of cells will be charged to above 8.4V (84V/10 strings). The full charge voltage of ternary lithium is 4.2V, and the voltage of 8.4V is relatively dangerous for ternary lithium single cells, which can easily cause explosions.

 

So, please use lithium batteries correctly, use lithium battery protection plates correctly, and use lithium battery chargers correctly.

 

2. Short circuited

Short circuits, both internal and external, can cause explosions in 18650 lithium batteries.

There are several reasons for internal short circuits, one of which is due to production process issues where impurities remain inside. During the use of lithium batteries, internal positive and negative pole short circuits occur, leading to explosions. Another reason is that external needles or pressure can cause internal material short circuits, leading to explosions.

 

The situation of external short circuit is caused by direct contact between the positive and negative electrodes of lithium batteries. For example, if the load device fails and the circuit is short circuited, and the lithium battery protection board fails to function and cannot cut off the circuit in a timely manner, continuing the short circuit will cause the internal air pressure of the lithium battery to rise, leading to an explosion.

 

The reasons for external short circuits include short circuits caused by vibration, short circuits caused by compression and collision, and so on.

The explosion and fire caused by the short circuit of 18650 lithium battery pack are more powerful, with sparks and explosions occurring simultaneously.

So, please protect the 18650 lithium battery, pay attention to each process from assembly technology, packaging and shipping, transportation, etc., to avoid short circuiting the lithium battery.

 

3. High temperature

Excessive temperature can also cause explosions in 18650 lithium batteries. The normal operating temperature range for lithium batteries is from 0 to 45 ℃ during charging; Discharge -20~65 ℃; Store at 0-45 ℃.

Lithium battery protection boards are generally set to a charging high temperature of 50 ℃ for protection; High temperature discharge protection at 70 ℃. If there is no high temperature protection, the continued discharge or storage of lithium batteries can cause explosions.

 

The internal materials of lithium batteries will deteriorate above 120 ℃, such as the separator used in the internal materials of battery cells. The materials used in the separator of conventional battery cells are relatively common. The separator will shrink above 120 ℃. Once the separator shrinks, the positive and negative electrode materials will short-circuit and directly contact each other, quickly causing a high-temperature internal short circuit and instantly triggering a lithium battery explosion.

 

So, please be sure to use and store 18650 lithium batteries within the specified temperature range, otherwise the consequences will be serious.

Above are the main reasons for the explosion of 18650 lithium batteries.