What circumstance can make a Li-ion battery explode?

In daily life, Li-ion battery is used everywhere, including electrical vehicles and computer backup battery. Li-ion battery becomes part of our life. There are many accidents caused by Li-ion battery, especially explosion and fire breakout.

Avoid short-circuit and over-charge

Most of the Li-ion battery accidents caused by short-circuit. When the anode and cathode of the battery connect each other under really small resistance (short- circuit), there will be very strong current and high heat inside the battery, which not only shortens the cycle life, but also produces strong pressure inside the battery, and finally, leads to outer explosion and fire breakout. Based on the chemical character of Li-ion battery, during over-discharging, the cathode cannot keep more Li ion, so that they become lithium metal (dendrite lithium). The dendrite lithium may pierce the separator, result in short-circuit and bring out accident. So try to prevent short-circuit or overcharge in daily life. Luckily, most of the digital products recently have relevant protection IC to avoid overcharging. When the protection circuit finds out that the Li-ion battery is fully charged, it will cut off the circuit. However, it’s better not to connect the mobile phone or other devices with the charger on. It is no need to compete your life with a charging chip.

It is very dangerous to pierce the battery.

Compared with short-circuit and overcharge, it is unwise to pierce the battery. The Li ion inside the battery will have chemical reaction with oxygen after breakage, and blaze fiercely. We can easily realize the trash bin label on the outer of Li-ion battery or any other devices with Li-ion battery. Littering the Li-ion battery not only pollutes the environment, but also easily causes conflagration.

High temperature environment, heating without touching and direct fire will lead to Li-ion battery explosion and conflagration.

Hot summer or car under the blazing sun will make the Li-ion battery in a higher temperature environment than usual. Try not to use devices with Li-ion battery for a long time under high temperature environment. Although it may take longer time to lead in explosion and heat without touching the battery, the Li-ion battery still strengthens the inside pressure (so called bump). Cut off the power and stop using the battery, in order to prevent strengthening the inside pressure. Then replace a new battery.

The following circumstances will lead to battery explosion:

Overcharge

Protection circuit losing control or battery testing cabinet losing control make the charging voltage over 5V, disintegrate electrolyte, fierce reaction inside the battery, pressure increases rapidly, and finally, explosion.

Over current

Protection circuit lose control or battery testing cabinet lose control, Li-ion fails to inset and becomes lithium metal on the surface of pole piece going through the separator. Short circuit between anode and cathode causes explosion (seldom happen).

Ultrasonic welds plastic outer

When ultrasonic welds the plastic outer, the equipment transmits ultrasonic energy to the cell. Ultrasonic energy melts the separator inside the battery. Short circuit between anode and cathode causes explosion.

Spot welding

Strong current during spot welding makes short circuit inside. Anode connecting cathode directly makes short circuit. Both of them can lead to explosion.

Over discharge

Over discharge or over current discharge (over 3C) can easily melt the copper foil and deposit to the separator. Short circuit between anode and cathode leads to explosion (seldom happen).

Vibrate and fall into the ground

Vibrating fiercely or falling into the ground makes pole piece dislocation inside the cell. Short circuit leads to explosion (seldom happen).

After voltage over 4.2 V, side-effect begins to work. The higher overcharging is, the more dangerous it is. The number of Li-ion will be less than a half within the anode material after the voltage over 4.2V. At this moment, the storage system is destroyed and the capacity of battery will decrease forever. If continue charging, the Lithium metal will stick on the surface of cathode material because the storage cell of cathode is full of Li-ion. These Li atom will extend to dendrite from the surface of cathode to Li-ion coming direction and pierce the separator paper, leading to short circuit between anode and cathode. Sometimes it may explode before short circuit. It is because electrolyte etc. material will break out and produce gas, which makes breakage on battery outer or pressure valve. Oxygen gets into the battery and has chemical reaction with the Li-ion on the surface of the cathode. Finally, explosion happens.

Therefore, setting up upper limit of the voltage during charging can make sure cycle life, capacity and safety of the battery. The theoretical upper limit of charging voltage is 4.2V. Lower limit is also needed during discharging. Part of the material will be destroyed when the voltage is lower than 2.4V. Do not discharge the battery until 2.4V because the battery can discharge itself and the voltage will be lower as time passes. During the period of discharging from 3.0V to 2.4V, the discharging energy can only reach 3% of the capacity, so 3.0V is a theoretical discharging cut-off voltage. Besides, control the current during charging and discharging process is also necessary. The Li-ion will stick on the surface of the material but not get into the storage cell when overcurrent.

When the Li-ion gets electron, Li atomic crystal is founded on the surface of the material. It is as dangerous as overcharging. In case the outer is broken, the battery will explode. Therefore, the protection of the Li-ion battery at least includes: upper limit of charging voltage, lower limit of discharging voltage and upper limit of current. Generally, there is a protection board inside except the cell in battery pack, which provides with the protection above. However, it is not enough to only protect by the protection board. Global Li-ion battery explosive accident still happens. To make sure the security of battery system, we must have deeper analysis of the reasons of the explosion.

Large internal polarization

The pole piece sops up, has chemical reaction with electrolyte and produces gas balloon.

Quality, performance issue of electrolyte

The volume of injecting liquid cannot reach the technological requirements.

Poor sealing performance of laser welding during assembly process, there is air leakage during gas leakage test.

Dust, dust on the pole piece will result in micro short circuit.

Positive and negative pole pieces are thicker than processing scope, so that it’s difficult to put into the outer.

Due to sealing issue of liquid injection, poor sealing performance of the steel ball generates gas balloon.

The outer material is too thick to fix the normal thickness.

Overheated environment is also the major reason of explosion.