There are many reasons for the explosion of 18650 lithium-ion batteries, mainly three.
1. Overcharged
Overcharging
is a common cause of explosion of 18650 lithium-ion batteries.
Lithium-ion batteries must work within the specified voltage range,
otherwise there will be potential safety hazards of explosion and fire.
For example, the normal voltage of a ternary lithium battery is
2.5V~4.2V; the normal voltage of a lithium iron phosphate battery is
2.0V~3.65V.
When
the 18650 lithium ion battery is charged, the lithium ions of the
positive electrode move to the negative electrode and are embedded in
the network structure of the negative electrode material. If the lithium ion battery
is overcharged, it will easily cause the negative electrode lithium to
precipitate, causing lithium crystals and piercing the diaphragm. Causes
a short circuit inside the battery, which can cause an explosion.
This
is why an overcharge protection circuit is added to the lithium-ion
battery during charging to protect the lithium-ion battery from being
overcharged. The lithium-ion battery protection board monitors the
voltage of each string of the lithium-ion battery pack. If the
overcharge voltage is exceeded, the lithium-ion battery protection board
will cut off the charge to protect the lithium-ion battery.
If
the lithium-ion battery pack explodes due to overcharge, it is mostly
because the voltage of some of the lithium-ion batteries is zero, or the
protection board is abnormal, and the lithium-ion battery cannot be
overcharged. There is also a charger error.
For
example, a 36V lithium-ion battery pack requires 10 strings of ternary
lithium. If the voltage of the 2 strings of cells becomes 0V, the 42V
charging voltage of the charger will directly charge the remaining 8
strings, and the protection board will not function properly. Can not
provide overcharge protection function. The uniform voltage of the 8
strings of cells will be charged to more than 5.25V by the charger
(42V/8 strings). This can cause the lithium-ion battery to overcharge
and cause an explosion.
If
the charger is used improperly, and the lithium-ion battery pack is not
charged according to the designated special charger, the lithium-ion
battery protection board will also be abnormal, causing the lithium-ion
battery pack to overcharge.。
For
example, for a 36V lithium-ion battery pack, the output voltage of a
dedicated charger should be 42V. If a 72V lithium-ion battery pack
charger is used (charging voltage is 84V), the 84V charging voltage is
directly added to the 36V lithium-ion battery pack. On the other hand,
the components of the protection board are easily damaged and their
functions are prone to failure. At this time, the lithium-ion battery
pack will be charged without protection. The cell voltage of each string
is above 8.4V (84V/10 strings). The full charge voltage of ternary
lithium is 4.2V. The ternary lithium battery is more dangerous, and it
is easy to cause an explosion.
Therefore,
please use the lithium-ion battery correctly, use the lithium-ion
battery protection board correctly, and use the lithium-ion battery
charger correctly.
2. Short circuit
The
18650 lithium-ion battery is short-circuited, including internal
short-circuit and external short-circuit, will cause the explosion of
the 18650 battery.
There
are many reasons for internal short circuits. One of the reasons is the
problem of processing technology. There are impurities in it. During the
use of lithium-ion batteries, the internal positive and negative
electrodes are short-circuited, causing an explosion. Another reason is
that external needle sticks or squeezing cause short circuit of internal
materials, which can cause fire or explosion.
3. High temperature
If the temperature is too high, it will also cause the 18650 lithium-ion battery
to explode. The normal operating temperature range of lithium battery
is 0~45℃ for charging; -20~65℃ for discharging; 0~45℃ for storage.
Lithium-ion
battery protection board usually sets the battery charging high
temperature to 50℃ for protection; discharging high temperature 70℃ for
protection. If there is no high temperature protection, the lithium
battery will continue to be discharged or stored, which will cause the
lithium battery to explode.
The
internal raw materials of lithium batteries will deteriorate above
120°C. Like the separators of the internal materials of lithium
batteries, the internal separators of lithium-ion batteries are
generally more common. The partition will shrink above 120°C. If the
separator shrinks, the positive and negative materials will directly
contact and cause a short circuit. A short circuit will generate high
temperature, which will open the battery safety valve, release hot gas,
and cause deflagration or explosion.
BENZO Energy Technology Co.,Ltd
UFine Technology Co., Ltd
Site: www.bz-battery.com / www.benzoenergy.com
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