As a very important invention in history, the emergence of batteries has indeed solved many problems, and the 18650 battery is the oldest but commonly seen Type. Since 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. But First, Let’s take a closer look at the Charging and discharging of 18650 lithium battery.
Why Explain charging and discharging process and principle first?
Because 18650 Battery explosion happens when it’s charging and discharging.
1 18650 Lithium Battery Charging Process.
18650 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(CV) 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.
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/CV 0.5 c and left standing for a while (It is usually 12 hours).
Discharge with 0.2 C current and discharge to 3.0 v (there is also another standard of 2.75 V, but the impact is not significant, since from 3v to 2.75 v, the battery will drop soon and not much capacity will be lost), the value of the released capacity , due to a certain number of batteries must have an individual.
The difference is the actual discharge 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.
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.
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.
4 Choose Branded 18650 Battery Charger
From consumers end, One of the important things we can do to avoid possible 18650 battery explosion is to buy high-quality battery charger?
The Easier way? Buy Branded chargers.
Some chargers that customer buy are made using inexpensive charging Chips/Designs and are not good enough in sending out accurate current, which can easily cause abnormal battery charging and even damage the battery. When choosing the charger, try to choose the top brand of 18650 lithium-ion battery charger, they have good quality control, and after-sales service, and thus can extend your battery life.
Branded 18650 battery charger has four basic protections: short-circuit protection, over-current protection, over-voltage protection, and battery reverse protection.
Over-Charge Protection: When the charger overcharges the lithium-ion battery, it needs to terminate the charging state immediately to prevent the possible internal pressure from rising since the internal battery temperature will rise if the battery is charged full already.
For this reason, It’s also suggested that a protection IC on the BMS of the battery is required 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.
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.
5. 3 Storage Tips for 18650 Battery
The most important storage condition of 18650 lithium battery is temperature and humidity. Generally, room temperature has little effect on the performance of lithium battery, but there should be no direct sunlight. High temperature can easily cause the model lithium battery to bulge or explode.
Here are some storage suggestions:
1. Do not put the 18650 lithium battery into the water, or use the battery in a humid environment; do not store the battery when the ambient temperature is higher than 65 °C.
2, the best charging environment for lithium batteries is at 20 ~ 26 ° C, please do not charge outdoor high temperature in the summer noon and low temperature outdoor charging in winter night. If the temperature is too high, it is easy to overcharge. If the temperature is too low, it will easily lead to low voltage, which will have a bad effect on the performance and use of the lithium battery.
3. If the lithium battery is not used for a long time, please take out the lithium battery and put it in a cool and dry place. If it is stored for a long time, charge the battery to 40% and store it.
6. 4 Tips for 18650 Battery Manufacturer and Engineers
The safety problem of 18650 lithium-ion battery is burning or even exploding. The root cause of these problems lies in the thermal runaway inside the battery. In addition, some external factors such as overcharge, fire source, extrusion, puncture, short circuit, etc. Will cause the battery to explode.
We here come up with some tips for battery manufacturers and enigineers.
1, 18650 lithium battery electrolyte and positive and negative electrodes have high reactivity, especially at high temperatures, in order to improve the safety of the battery, improve the safety of the electrolyte is one of the more effective methods. The safety hazard of the electrolyte can be effectively solved by adding functional additives, using new lithium salts and utility model solvents.
2. For the 18650 lithium battery anode material, since the surface is often the most prone to thermal chemical decomposition and exotherm in the lithium ion battery, improving the thermal stability of the SEI film is the key method to improve the safety of the anode material.
3, the installation of battery safety valve, thermal fuse, series with positive temperature coefficient components, the use of heat-sealed diaphragm, loading special protection circuit, dedicated battery management system, etc., will also enhance the safety of 18650 battery.
4. Lithium batteries will release heat during work. If they are too late to release, they will spontaneously ignite and explode. It can be managed by a battery thermal management system, which is a subsystem in the battery management system that enables the battery to cool when the temperature is too high, while the temperature is low. Then preheating is performed, thereby better exerting the performance of the battery.
With the advancement of the times, the development and manufacturing of lithium battery materials technology will continue to improve. It can be foreseen that under the continuous development of battery technology, lithium batteries will become more and more secure, and consumers do not need to worry too much about safety.
Why 18650 Battery would Explode and How to Avoid that
This article will Explain from 18650 Lithium Battery Charging and Discharging Process to Actual Explosion Case, and Most importantly, What Consumers can do to Avoid that.