Common causes of lithium battery explosion and avoidance measures

Almost most of the safety accidents caused by lithium batteries are caused by short circuits.

1. Avoid short circuit and overcharge

Almost most safety accidents caused by lithium batteries are caused by short circuits.

We know that when the positive and negative electrodes of the battery are connected to each other in an abnormal path with very small resistance, which is what we often call a short circuit.

A very large current and heat will be generated inside the battery.

The heat generated and the release of too strong electrical energy will not only cause serious damage to the battery life, but also for lithium batteries made of airtight packaging.

A certain amount of pressure will be generated inside the battery, which will cause a sudden increase in the internal pressure of the battery. In addition, because the chemical properties of lithium ions are very active, the shell will eventually burst and burn.

Due to the chemical properties of lithium-ion batteries, when we overcharge the battery, the negative electrode of the lithium battery cannot be embedded with more lithium ions. And the lithium ions precipitate with lithium metal on the surface of the negative electrode, causing the phenomenon of dendrite lithium. When the dendrite lithium grows to a certain extent, it will pierce the diaphragm, causing a short circuit inside the battery. And also the dentrite lithium will damage the isolation film. Eventually, an internal short circuit will also occur, causing a safety accident.

Therefore, when we use lithium batteries in our daily lives, we should try our best to avoid short circuits or overcharges. However, for most current digital products, the internal charging circuit will be equipped with corresponding protection IC to avoid overcharging of lithium batteries. When the protection circuit detects that the lithium battery has reached full power, it will automatically cut off the charging circuit.

However, it is still not recommended to connect mobile phones or other devices to the charger in the powered state for a long time.

After all, no one wants to use their mobile phones or other devices or even personal safety to bet on a small charging protection chip.

2. Avoid Piercing Lithium Battery

Compared with short-circuiting and overcharging, piercing lithium batteries is also a very unwise approach. If the lithium battery is pierced by any hard object, the lithium ions inside it will directly react chemically with the oxygen in the air, and it will also burn violently.

When our lithium battery inevitably is swollen, it is very dangerour to pirece the battery. More details:https://www.dnkpower.com/lithium-battery-swelling/

For lithium batteries themselves or other electronic products that contain lithium batteries inside, we usually see eye-catching trash can signs. If lithium batteries are discarded at will, they will not only cause environmental pollution, but also be more prone to fire and other situations during garbage disposal.

3. Avoid High Temperature and Fire Roasting.

High temperature or fire burning can also cause the explosion and combustion of lithium batteries. Especially in the hot summer or long-term exposure to the sun in the car, the ambient temperature of the lithium battery will be higher than its normal storage temperature.

Therefore, when we use equipments with lithium-ion batteries, we should try to avoid long-term using in environments with high temperatures.

Although lithium batteries explode and burn for a relatively long time when they are directly roasted by fire, there will still be a sudden increase in their internal pressure, which is what we often call swelling.

When our mobile phone batteries or other lithium-ion batteries is swelling, the power supply should be cut off immediately and stopped to prevent further internal pressure from increasing, and replace the batteries with new ones.

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Summarize some situations of explosion in the production and use of lithium batteries:

1. Overcharge explosion

When the charging voltage to be greater than 5V which is caused by that the protection circuit or the detection cabinet are out of control, the electrolytr will decompose. Violent reactions occur inside the battery. The battery will explode because of the increasing pressure.

2.Over-current explosion(Rarely Occurs)
The protection circuit or the detection cabinet are out of control, causing the charging current to be too large, causing the lithium ions to be too late to be embedded, and the lithium metal is formed on the surface of the electrode sheet, penetrating the diaphragm, and the positive and negative electrodes are directly shorted, causing an explosion (rarely occurs).

If the protection circuit or the detection cabinet are out of control, lithium ions will be too late to embedded in cathode. And the lithium ions will form lithium on the surface of the electrode sheet. Then the metal will pierce the diaphragm. Short circuit occurs, explode.

3. Explosion when ultrasonic welding plastic shell

When ultrasonic welding the plastic shell, the ultrasonic energy is transferred to the battery cell due to equipment reasons. The ultrasonic energy is very large. The internal diaphragm of the battery melts, and the positive and negative electrodes are directly shorted, resulting in an explosion.

4. Explosion during spot welding

During spot welding, if the current is too large, will cause a serious internal short circuit to explode. In addition, the positive electrode connecting piece is directly connected with the negative electrode during spot welding which will cause the positive and negative electrodes to explode after a direct short circuit.

5. Over-discahrge explosion

When battery be in stare of over-charging or over-discharging with the C-rate at 3C, it is easily for negative electrode copper to dissolve and deposite on thte diaphragm. This will cause short circuit and explode.

Do not worry. This phenomenon is rarely occur in our daily life.

6. Explosion in vibration and falls

When the battery vibrates violently or falls, the internal pole piece of the battery is misplaced, and it is directly severely shorted and explodes (rarely occurs).

After the lithium battery cell is overcharged to a voltage higher than 4.2V, side effects will begin to occur. The higher the overcharge voltage, the higher the danger. After the voltage of the lithium battery cell is higher than 4.2V, the number of lithium atoms remaining in the cathode material is less than half.

At this time, the storage cell often collapses, causing a permanent decrease in battery capacity. Since the storage cell of the negative electrode is already filled with lithium atoms, if charging continues, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the surface of the negative electrode in the direction where the lithium ions come.

These lithium metal crystals will pierce the diaphragm, shorting the positive and negative electrodes. Sometimes the battery explodes before a short circuit occurs. This is because during the overcharge process, the electrolyte and other materials will crack to produce gas which will cause the battery shell or pressure valve to bulge and break. It also allows oxygen to enter and react with the lithium atoms accumulated on the surface of the negative electrode, and then explode.

Therefore, when charging lithium batteries, the upper voltage limit must be set. So that the battery life, capacity, and safety can be taken into account at the same time. The ideal upper limit of the charging voltage is 4.2V. There must also be a lower voltage limit when the lithium battery is discharged. When the cell voltage is lower than 2.4V, part of the material will begin to be destroyed.

Because the battery will self-discharge, the longer it is put on, the lower the voltage will be. Therefore, it is best not to charge it before 2.4V. During the period when the lithium battery is discharged from 3.0V to 2.4V, the energy released only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage.

During charging and discharging processes, the current limit is also necessary. When the current is too high, the lithium ions will not have time to enter the storage cell and will gather on the surface of the material.

After these lithium ions obtain electrons, they will crystallize lithium atoms on the surface of the material, which is the same as overcharging and can cause danger. In case the battery shell breaks, it will explode. Therefore, the protection of lithium-ion batteries must include at least three items: the upper limit of the charging voltage, the lower limit of the discharge voltage, and the upper limit of the current.

Generally, in lithium battery packs, in addition to lithium battery cells, there will be a protection board. This protection board mainly provides these three protections. However, these three protections of the protection board are obviously not enough, and lithium battery explosions are still frequent around the world.

Conduct a more careful analysis of the causes of the battery explosion, and list some:

1. Large internal polarization;
2. The pole absorbs water and reacts with the electrolyte. Battery swells because of gas generated by reaction.
3. The quality and performance of the electrolyte itself;
4. When injecting liquid, the amount of liquid injected does not meet the process requirements.;
5. The sealing performance of laser welding in the assembly process is poor, and the air leaks when the air leaks are detected.;
6. Dust and pole piece dust can easily cause micro-short circuits in the first place.;
7. The positive and negative electrode pieces are thicker than the process range, making it difficult to enter the shell.;
8. The problem of liquid injection sealing, the poor sealing performance of the steel ball leads to the air bulge;
9. The incoming material of the shell has a thick shell wall, and the deformation of the shell affects the thickness.;
10.The external ambient temperature is too high, which is also the main cause of the explosion.

 

 

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