While lithium batteries are generally very safe, they occasionally catch fire or explode. We often see a variety of safety accidents caused by lithium batteries. The most impressive phenomenon is the explosion and fire caused by lithium batteries.
Are lithium batteries prone to explosion?
Lithium battery from the birth to now has been developed for decades. Most mobile phones on the market are also built in lithium battery. Although decades of development, but lithium battery still can not guarantee 100% safety, in some specific environment, even explosion.
Lithium is outstanding in terms of reserves. When released as a trickle, it powers your phone for an entire day. But when it's released all at once, the battery explodes. Most lithium-ion battery fires and explosions are caused by a short circuit. This happens when the plastic separator fails, leaving the anode and cathode in direct contact. Once these poles come together, the battery starts to overheat.
With lithium batteries, there's always a risk of explosion, but it's a very small risk. But once it explodes, the explosive power of lithium-ion batteries with larger capacity is unimaginable.
There are two important causes of lithium battery explosion, one is short circuit, the other is overcharge. Short circuit is easy to understand, is direct contact between the positive and negative terminals of the battery. First, the heat generated by the short circuit in a small area in a normal short time is actually very small. This will not cause thermal control. The cell itself is designed with an explosion-proof valve. Which means that when the internal pressure of the cell exceeds a certain value, the explosion-proof valve will be opened and the heat will dissipate quickly. The second is that the normal use of battery charging equipment are anti-overcharge protection. When the battery voltage reaches a certain value will stop charging. The third cell itself is a steel shell, with good protection.
How powerful are lithium batteries?
Calculate that a fully charged 2.6AH 18650 ternary lithium battery carries 2.63.653.6=34.164 kilojoules of energy. A joule is equivalent to the amount of work done when a force of 1 Newton moves an object 1 meter in the direction of the force. So it can easily kill an enemy within 50 meters of the pistol. Consider that a Tesla uses more than 7,000 3.4-ah 18650 lithium batteries.
The shell is aluminum alloy, the size is 20120300 (mm), the battery is extremely lithium manganese acid capacity of 50AH battery has been tested when the explosion: 3 meters high roof blackened, from the battery about half a meter wall burst through a hole (the wall is brick or sandwich plate forget), Windows and doors glass broken. It's a good thing there was no one there.
Do not recharge, dismantle, extrude, heat beyond 212°F or incinerate lithium batteries.
Lithium battery explosion generally has the following situations
The overcharge explosion
The protection line is out of control or the detection cabinet is out of control, so that the charging voltage is greater than 5V. This results in the decomposition of the electrolyte, violent reaction in the battery. It also leads to rapid rise in the battery pressure, lithium battery explosion.
Over current explosion
The protection line is out of control or the detection cabinet is out of control. The charging current is too large to embed lithium ions, and the lithium metal is formed on the surface of the pole sheet. It penetrates the diaphragm and directly short-circuit the positive and negative poles, resulting in explosion.
Exploded when the plastic shell was welded by ultrasound
When ultrasonic welding plastic shell, the ultrasonic energy is transferred to the battery core due to equipment reasons. The ultrasonic energy is very ambassador of the battery internal diaphragm melting, positive and negative poles directly short circuit, resulting in explosion.
Explosion during spot welding
In spot welding, excessive current causes serious internal short circuit and explosion. In addition, when spot welding, the positive electrode connecting piece is directly connected with the negative electrode, so that the positive and negative electrodes directly short circuit and explosion.
Overdischarge or overdischarge of lithium battery (3C or above) is easy to dissolve the anode copper foil and deposit on the diaphragm so that the anode and cathode directly short-circuit and produce an explosion (rarely).
It explodes when the vibration falls
When the cell is in violent vibration or fall, the internal pole piece of the cell dislocation, direct serious short circuit and explosion.
Why lithium battery explosion and fire
Lithium battery negative capacity is insufficient
When the capacity of the negative part of the positive part of the lithium battery is insufficient, the lithium atoms generated during charging can not be inserted into the interlayer structure of the graphite of the negative electrode, and will be separated on the surface of the negative electrode, forming crystallization. Long term crystallization in lithium batteries will lead to short circuit, when the cell discharge rapidly, will produce a lot of heat, burn out the diaphragm. High temperatures cause the electrolyte to break down into gases, and when the pressure is too high, the cell explodes.
Water content is too high
Charging, water can react and lithium, lithium oxide, make batteries capacity loss, easy to make batteries overcharge and gas production, water with low breakdown voltage, charging is easy to decompose generated gas, when the series of the generated gas can make the batteries of internal pressure, when batteries shell cannot afford, batteries would explode.
Internal short circuit
Internal cell short circuit caused by large current discharge, produce a lot of heat, burn out the diaphragm, and cause a greater short circuit phenomenon, will make the electrolyte decomposition into gas, internal pressure is too large, the cell will explode.
Lithium battery overcharge
When the cell is overcharged, the excessive release of positive lithium will change the structure of the positive electrode, and the release of too much lithium is easy to insert into the negative electrode, it is also easy to cause lithium-ion on the surface of the negative electrode, and, when the voltage reaches more than 4.5V, the electrolyte will decompose and produce a lot of gas. Any of these could cause an explosion.
External short circuit
External short circuit may be caused by the wrong connection between positive and negative poles, due to external short circuit, battery discharge current is very large, will make the cell heat, high temperature will make the diaphragm inside the cell shrink or completely bad, causing internal short circuit, and explosion.
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