Why 18650 Battery Would Explode
As a very important invention in history, the emergence of batteries has indeed solved many problems, and the 18650 battery is the oldest Type. As a lithium battery still widely used at present, its safety is particularly important. This article will introduce the knowledge of the 18650 battery and explain why there is an explosion.
Charging and discharging of 18650 lithium battery.
According to lithium batteries industry standards, the nominal capacity is generally the minimum capacity. This capacity is determined At room temperature of 25 degrees, it is first filled with cc/cv0.5 c and left standing for a while (It is usually 12 hours). Discharge with 0.2 C current and constant current discharge to 3.0 v (there is also a standard of 2.75 V, but the impact is not significant, 3v to 2.75 v drop soon no much capacity), the value of the released capacity, due to a certain number of batteries must have an individual. The difference is the actual discharge of the capacity value of the battery with the lowest capacity. That is, the actual capacity of any battery in this batch should be greater than or equal to the nominal capacity.
18650 battery cell
1, 18650 lithium battery charging process.
Some chargers are implemented using inexpensive solutions and are not good enough in control accuracy, which can easily cause abnormal battery charging and even damage the battery. When choosing the charger, try to choose the big brand of 18650 lithium-ion battery charger, quality and after-sale guarantee, extend battery life.
The brand-protected 18650 lithium-ion battery charger has four protections: short-circuit protection, over-current protection, over-voltage protection, and battery reverse protection. Over-charging protection: When the charger overcharges the lithium-ion battery, it needs to terminate the charging state to prevent the internal pressure from rising due to temperature rise.
For this reason, the protection device needs to monitor the battery voltage. When it reaches the battery overcharge voltage, it activates the overcharge protection function and stops charging. Over-discharge protection: In order to prevent the over-discharge status of the lithium-ion battery, when the lithium-ion battery voltage is lower than its over-discharge voltage detection point, over-discharge protection is activated, the discharge is stopped, and the battery is maintained in a low quiescent current standby mode. Over-current and short-circuit protection: When the lithium-ion battery discharge current is too large or a short circuit condition occurs, the protection device will activate the over-current protection function.
Lithium battery charge control is divided into two phases. The first phase is constant current charging. When the battery voltage is lower than 4.2 V, the charger will charge with a constant current. The second stage is the constant voltage charging stage.
When the battery voltage reaches 4.2 V, due to the characteristics of the lithium battery, if the voltage is high, it will be damaged, the charger will fix the voltage at 4.2 V, and the charging current will gradually decrease when the current When it is reduced to a certain value (usually when 1/10 sets the current), the charging circuit is cut off, the charging completion indicator is on, and charging is completed.
Overcharge and discharge of lithium-ion batteries will cause permanent damage to the positive and negative electrodes. Excessive discharge leads to the collapse of the negative carbon layer structure, and the collapse will cause the insertion of lithium ions in the charging process; overcharging will cause too much lithium ions to be inserted into the negative carbon structure, causing some of the lithium ions to no longer be released.
2, 18650 lithium battery charging principle.
The working principle of lithium-ion battery refers to its charge and discharge principle. When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as a negative electrode has a layered structure, and it has many micropores, and lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are embedded, the higher the charging capacity.
In the same way, when the battery is discharged (ie, we use the battery), the lithium ions embedded in the carbon layer of the negative electrode escape and move back to the positive electrode. The more lithium ions returning to the positive electrode, the higher the discharge capacity. The battery capacity we usually refer to is the discharge capacity.
It is not difficult to see that during the charge and discharge of a lithium-ion battery, lithium ions move from the positive electrode → negative electrode → positive electrode. If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like a good sportsman, running back and forth on both ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a cute name rocking chair battery.
3, 18650 lithium battery why so many explosion in history.
The vast majority of 18650 batteries are housed in a steel case, and batteries with poor quality, due to their lack of protection, can cause their internal pressure to suddenly increase when overcharged (overcharging), and explode when they exceed the acceptable value. Problems such as short circuit, high temperature, or deformation or even puncture of the battery may cause the battery to explode.
In normal use, the 18650 batteries that get explosion are generally inferior batteries. The safety of regular lithium-ion batteries is actually quite good. The main reason that can cause the lithium battery to explode is that the battery with poor quality is prone to the internal short circuit during use. When an internal short circuit occurs, it will generate high temperature and high-pressure gas in a short period of time, which is too late to be released through the exhaust valve. An explosion will occur.
After 30 years of development, the 18650 battery preparation process has been very mature, in addition to the performance has been greatly improved, its safety is also very perfect. In order to avoid the explosion of the sealed metal enclosure, the 18650 battery is now equipped with a safety valve at the top.
The safety valve is standard for every 18650 battery and is the most important explosion protection barrier. When the internal pressure of the battery is too high, the top safety valve will open the exhaust decompression to avoid the explosion.
However, when the safety valve is opened, chemical substances leaked into the battery will react with oxygen in the air under high-temperature conditions, and there is still the possibility of fire. In addition, some 18650 batteries are now equipped with protection board, with overcharge and over-discharge and short circuit protection and other functions, safety performance is very high.
For lithium batteries, the reason for the explosion will be understandable, after all, in the past, the stability of the grass will not be so severe, but the 18650 as a very high-performance lithium battery, its application is certainly Will become more and more extensive, after all, in terms of such indispensable batteries, 18650 lithium battery is the best choice.