Example of safety, lithium-ion battery protection measures and explosion reasons

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

Lithium-based battery is the fastest battery system in the past 20 years and is currently widely used in electronic products. Recent mobile phones, laptop explosion essentially battery explosion. What kind of mobile phone and laptop battery are working, how to work, why explosion, how to prevent explosion.

After the lithium ion battery core is charged to the voltage higher than 4.2V, it will begin to appear. The overcharge pressure is high, and the danger is also higher.

After the lithium battery voltage is higher than 4.2V, the remaining number of lithium atoms in the positive electrode material is less than half, and the storage gear will often fall, so that the battery capacity has a permanent decline. If it continues to charge, since the reservoir of the negative electrode is filled with a lithium atom, the subsequent lithium metal will accumulate in the surface of the negative material.

These lithium atoms will be branched crystallization from the direction of the negative surface to the lithium ion. These lithium metal crystals will pass through diaphragm paper to make positive and negative short circuits. Sometimes the battery before the short circuit will explode first because materials such as the overcharge process, the electrolyte and other materials will crack the gas, so that the battery housing or pressure valve is broken, allowing oxygen to enter the lithium atomic reaction in the negative surface, In turn explodes.

Therefore, when the lithium ion battery is charged, it must be set to set the voltage upper limit to simultaneously taking into account the life, capacity, and security of the battery. The most desirable charging voltage limit is 4.2V.

There must be a voltage limit when the lithium battery is discharged. Some materials will be destroyed when the battery voltage is below 2.4V.

Also because the battery will be self-discharge, the more long voltage is lower, so it is best not to put it until 2.4V when discharged. The lithium ion battery is discharged from 3.

0V to 2.4V, and the released energy only accounts for about 3% of the battery capacity. Therefore, 3.

0V is an ideal discharge cutoff voltage. At the time of charge and discharge, in addition to the voltage limit, the limit of current is also necessary. When the current is too large, the lithium ion does not enter the storage grid, which will aggregate on the surface of the material.

After these lithium ions are electronically, the lithium atomic crystallization occurs on the surface of the material, which is the same as the excessive charge, which can cause dangerous. In the case of cracking, it will explode. Therefore, the protection of lithium ion batteries should be included: the upper limit of the charging voltage, the discharge voltage limit, and the upper limit of current.

In general, in addition to the lithium-ion battery cell, there will be a protective plate, which is important to supply these three protection. However, the three protection of the protector is obviously not enough, and the global lithium-ion battery explosion is still biography. To ensure the safety of the battery system, you must make a more careful analysis of the battery explosion.

Explosion causes: 1, internal polarization; 2, extreme tape absorption, reactive drum with the electrolyte; 3, the quality, performance problem of the electrolyte itself; 5, the laser welding sealing performance in the assembly process is poor, leakage when the immersion is leaked; 6, dust, polar dust is first easily causing micro-short circuit; 7, the positive and negative poles are thicker than the process range, the shell is difficult; 8, note Liquid sealing problem, steel ball sealing performance is not good to cause gas drum; 9, the housing material exists thickness, the thickness of the housing deformation; 10, the outer ambient temperature is also an important cause of explosion. The type of explosion type explosion analysis of the battery core explosion can be summarized as external short circuit, internal short circuit, and three kinds of charge. The external system here refers to the outside of the battery, which includes short circuits caused by poor insulation design in the battery pack.

When a short circuit is outside the battery cell, the electronic component is not cut off, and the interior of the battery cell will have high heat, resulting in a partial electrolyte steaming, and support the battery shell. When the internal temperature of the battery is high to 135 degrees Celsius, the quality of the diaphragm is closed, the electrochemical reaction is terminated or near termination, the current is plummeted, and the temperature is slowly decreased, which in turn prevents the explosion. However, the fine hole closing rate is too poor, or the fine hole does not close the diaphragm paper, which will continue to rise, more electrolyte, and finalize the battery housing, and even increase the battery temperature to make the battery temperature燃 并 and explod.

The internal short circuit is important because the copper foil is pulling the membrane of the aluminum foil, or the branches of the lithium atom wear the diaphragm. These fine needles can cause micro-short circuits. Since the needle is very fine, there is a certain resistance value, therefore, the current is not necessarily.

Copper aluminum foil glue is caused by the production process. And because the glitch is small, sometimes it will be burnt, so that the battery will return to normal. Therefore, the probability of the explosion caused by burrs is not high.

In this way, it is possible to have a short battery internally charged from the interior of each of the cells. However, the explosion event has occurred, but it has been statistically supported. Therefore, the explosion caused by internal short circuits is important because of overcharge.

Because, it is a needle-shaped lithium metal crystallization, and it is a micro-short circuit. Therefore, the battery temperature will gradually increase, and finally high temperature will electrolyte gas. This situation, whether it is too high to make the material burning explosion, or the outer shell is first broken, so that the air invested in and lithium metal, it is the explosion.

However, this explosion caused by excessive internal short circuit is not necessarily occurring at the time of charging. It is possible that the battery temperature is not high to let the material burned. When the gas appears, the consumer is not enough to break the battery housing, the consumer will terminate the charging, with the mobile phone to go out.

At this time, the heat of many micro-short circuits, slowly increase the temperature of the battery, after a period of time, only explosion. The common description of the consumer is to pick up the phone and find that the phone is hot, and then exploded. Some types of explosions, we can put explosion-proof focus on prevention, external short circuit prevention, and improve battery safety three aspects.

Among them, overchalten prevention and external short circuit prevention belong to electronic protection, and have a large relationship with battery system design and battery pack. The focus of electricity safety improvement is chemical and mechanical protection, which has a big relationship with the battery core manufacturer. Safety problems of safety hazardous lithium-ion batteries are not only related to the nature of the pool materials, but also related to battery preparation technology and use.

The mobile phone battery has frequent explosion events, on the one hand, due to the failure of the protection circuit, but more importantly, there is no fundamental solution to the material. The lithium cobalt-cobaltate is a very mature system, but after the charge is filled, there is still a large amount of lithium ions to stay in the positive electrode. When it is filled, the lithium ions remaining in the positive electrode will flock to the negative electrode.

The negative electrode forming the dendride is an inevitable result of an inevitable battery with a battery of the lithium cobaltate material. Even in the normal charge and discharge process, there may be excess of lithium ion free to the negative electrode to form dendrites, and the lithium cobaltate material. Energy is more than 270 mA per gram, but in order to ensure its cycle performance, the actual use capacity is only half the theoretical capacity.

During use, due to some reason (such as damage to management system), the battery's charging voltage is too high, and a portion of the lithium remaining in the positive electrode will take out that the electrolyte is deposited in the form of a metal lithium in the form of metal. Dendritic paste the diaphragm to form an internal short circuit. The important component of the electrolyte is carbonate, the flash point is very low, the boiling point is also low, and it will burn or explode under certain conditions.

If there is an overheating of the battery, it can cause carbonates in the electrolyte to be oxidized and restored, there is a large amount of gas and more heat, such as lack of safety valve or gas is not released through the safety valve, the battery pressure will rise sharply and cause explosion. The polymer electrolyte lithium-ion battery does not fundamentally solve safety problems, and lithium cobaltate and organic electrolyte, and the electrolyte is a gel, it is not easy to leak, and more violent combustion will occur, combustion is a polymer battery safety Best problem. There are also some problems in use, and there will be a short circuit or internal short circuit in the battery.

External short-circuit time battery instant current discharge, consume a lot of energy in the internal block, huge heat. The internal short circuit forms a large current, and the temperature rise results in melting, and the short circuit area is expanded, which in turn forms a vicious circle. The lithium-ion battery is a high operating voltage of 3 to 4.

2V to a single battery. It is necessary to take an anterior solution having a decomposition voltage greater than 2V, and an organic electrolyte will be electrolyte under high current and high temperature, and a gas is generated. Resulting in elevated internal pressure, severely breaking the housing.

Overcharge may precipitate metal lithium, in the case of cracking in the housing, direct contact with air, resulting in combustion, and incorporate electrolyte, a strong flame, rapid expansion, explosion. In addition, there is a battery short circuit due to improper use of improper use, such as squeezing, impact and water, etc., which can cause battery short circuit, exotherm in discharge or charging process.

Safety of lithium-ion batteries: To prevent battery over-discharge or overcharge due to improper use, a triple protection mechanism is provided in a monomer lithium ion battery. First, the switching element is used. When the temperature in the battery rises, its resistance increases, when the temperature is too high, the power is automatically stopped; the second is to select the appropriate partition material, when the temperature rises to a certain value, The microphone microphone on the partition will be automatically dissolved, so that the lithium ion cannot pass, the internal reaction is stopped; the third is to provide a safety valve (that is, the inner pressure of the battery rises to a certain value, the safety valve Automatically open to ensure the safety of the battery.

Sometimes, although the battery itself has safety control measures, because some reasons causing the failure, the lack of safety valves or gas is not as follows through the safety valve release, the compressor in the battery will rise sharply and cause explosion. In general, the total energy and safety of the lithium ion battery are inversely ratio, with the new battery capacity, the battery volume is also increased, its heat dissipation performance is deteriorated, and the possibility of accidents will increase significantly. About lithium-ion batteries for mobile phones, basic requirements are one of the probability of safety accidents, which is also a minimum standard that the public can accept.

About large-capacity lithium-ion batteries, especially automobiles, etc., forced heat dissipation, especially important. Choose a safer electrode material, select the lithium manganate material, and ensure that the lithium ion of the positive electrode is completely embedded in the negative electrode carbon aperture in the full power state.

At the same time, there is a solid structure of lithium manganate, so that its oxidative properties are much lower than lithium cobaltate, and the decomposition temperature exceeds lithium cobaltate 100 ° C, even because the internal short circuit (acupuncture), external short circuit, when it is fully charged, it is fully capable Prevent the risk of burn, explosion due to precipitated metal lithium. In addition, the lithium manganate material can also be greatly reduced. Improve the performance of existing safety control technology, first improve the safety performance of lithium-ion battery cores, this is especially important for large-capacity batteries.

Selecting a diaphragm with a good thermal shutdown performance, the use of the diaphragm is to pass through the positive and negative electrode of the battery, allowing the passage of lithium ions. When the temperature rises, it is closed before the diaphragm is melted, thereby rising the internal resistance to 2000 ohms, so that the internal reaction stops. When the internal pressure or temperature reaches the preset criteria, the explosion-proof valve will open, start to perform a pressure, and the internal gas is too tired, the deformation, eventually causes the housing to burst.

Improve control sensitivity, select more sensitive control parameters and joint control with multiple parameters (this is especially important for large-capacity batteries). Regarding the large-capacity lithium-ion battery pack is a string / parallel-linked, such as the laptop has a voltage of 10V, the capacity is large, and the voltage requirements can be satisfied with 3 to 4 unit cells, and then 2 ~ 3 series of battery packs are parallel to ensure large capacity. The large-capacity battery pack itself must set more complete protection, but also consider two circuit board modules: protection circuit board module and SmartBatteryGaugeboard module.

The entire set of battery protection includes: Level 1 Protection IC (Preventing Battery Overcharge, Over-Press, Short Circuit), Level 2 Protection IC (Preventing 2nd Overstall), Fuse, LED Indication, Temperature Adjustment. Under the multi-level protection mechanism, even in the case of an abnormality in the power charger, the laptop has an abnormality, the laptop battery can only be converted to automatic protection, if the situation is not serious, often work properly after re-plugging, no Explosion. .

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