Generally speaking, a good quality lithium battery has a protective device that will not explode, and a poor quality battery may explode.
The overwhelming majority of 18650 lithium batteries are encapsulated in steel shells. Due to the lack of protection, over-charged batteries will suddenly increase their internal pressure and explode when they exceed the withstand value. Short circuit, excessive temperature or squeezing or even puncturing the battery may cause the battery to explode.
There are many reasons for the explosion of the 18650 lithium-ion battery. The three main reasons are analyzed below.
1. Being over-charged
The 18650 lithium battery is overcharged, which is a common cause of explosion. Lithium batteries must work within the specified voltage range, otherwise there will be hidden dangers of explosion and fire. For example, the ternary lithium battery is usually 2.5V ~ 4.2V; the lithium iron phosphate battery is usually 2.0V ~ 3.65V.
When the 18650 lithium battery is charged, the lithium ions of 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 precipitation of the negative electrode, causing lithium crystals and piercing the separator. The cell is short-circuited internally, causing an explosion.
This is why, when charging a lithium ion battery, an overcharge protection circuit must be added to protect the lithium battery from overcharging. The lithium battery protection board will monitor each string voltage of the lithium battery pack. If the overcharge voltage is exceeded, the lithium battery protection board will cut off the charge and protect the lithium battery.
If the lithium battery pack is overcharged and exploded, this happens mostly because the lithium battery pack has a string of 0V voltage cell, or the protection board is abnormal and the lithium battery cannot be overcharged protection; there is also maybe the charger Use error.
For example, a 36V lithium battery pack requires 10 ternary lithium batteries connected in series. If 2 cells of the battery packs become 0V, the charger's charging voltage of 42V will directly charge the remaining 8 cells. The protection board function Abnormal, unable to provide overcharge protection function. The average voltage of 8 cells of batteries will be charged to more than 5.25V (42V / 8 cells) by the charger. This will cause the lithium battery to be overcharged, causing an explosion.
If the charger is used incorrectly, if the lithium battery pack is not charged according to the specified special charger, the lithium battery protection board will also be abnormal and the lithium battery pack will be overcharged.
For example, for a 36V lithium battery pack, the output voltage of the dedicated charger should be 42V. If a 72V lithium battery pack charger is used (charging voltage is 84V), the 84V charging voltage is directly loaded on the 36V lithium battery pack to protect The components of the board are easily damaged, and the functions are easily disabled. At this time, the lithium battery pack will be charged without protection, and the voltage of each string of cells will be charged above 8.4V (84V / 10 cells), and the full charge voltage of ternary lithium is 4.2V, the 8.4V voltage of the ternary lithium battery is more dangerous, and it is easy to cause an explosion.
Therefore, please use the lithium battery correctly, use the lithium battery protection board correctly, and use the lithium battery charger correctly.
2. Short circuit
18650 lithium battery is shorted, including internal short circuit and external short circuit, will cause 18650 battery explosion.
There are several reasons for the internal short circuit. One reason is the problem of the production process. There are residual debris inside. During the use of the lithium battery, an internal short circuit of the positive electrode and the negative electrode occurs, causing an explosion. Another reason is that external needle sticks or squeezes cause internal materials to short-circuit, causing an explosion.
The external short circuit is caused by the direct contact between the positive and negative electrodes of the lithium battery. For example, the load device is faulty, the circuit is short-circuited, and the function of the lithium battery protection board fails to cut off the circuit in time. Continued short circuit will cause the internal pressure of the lithium battery to rise, causing an explosion. The causes of external short circuits include short circuits caused by vibration, short circuits caused by squeeze collisions, and so on.
3. High temperature
If the temperature is too high, it will also cause an explosion of the 18650 lithium battery. The normal operating temperature range of lithium batteries is charging 0 ~ 45 ℃; discharging -20 ~ 65 ℃; storing 0 ~ 45 ℃.
Lithium battery protection board is generally set to charge high temperature of 50 ℃ protection; discharge high temperature of 70 ℃ protection. If there is no high temperature protection, the lithium battery continues to discharge or store, it will cause the explosion of the lithium battery.
The internal material of the lithium battery will be deteriorated above 120 ° C. Like the separator of the internal material of the battery, the material of the conventional battery separator is more common. The separator of 120 ° C or above will shrink. Direct contact with the short circuit will soon cause a high-temperature internal short circuit, which will immediately cause an explosion of the lithium battery.
Therefore, please be sure to use and store the 18650 lithium battery within the specified temperature range, otherwise the consequences will be serious.
The above is the reason for the explosion of the 18650 lithium battery. The preparation process of the 18650 lithium battery is very mature. In addition to the greatly improved performance, its safety is also very perfect. In order to avoid the explosion of the sealed metal shell, the 18650 battery will now be equipped with a safety valve on the top. The safety valve is standard for each 18650 battery and is the most important explosion-proof barrier.
