Author ：Iflowpower – Portable Power Station Supplier
Lithium is the minimum and most active metal in the chemical cycle table. Small size, high capacity density, popular with consumer and engineers. However, chemical properties are too lively, bringing extremely high dangers.
When the lithium metal is exposed to air, it will explode with a fierce oxidation reaction with oxygen. In order to improve safety and voltage, scientists invented materials such as graphite and lithium cobaltate to store lithium atoms. The molecular structure of these materials, forms a small storage lattice of the nanometric level, which can be used to store lithium atoms.
In this way, even if the battery housing is broken, oxygen is entered, and the oxygen molecules will not be too large, and these small storage grids can not be contacted with oxygen to prevent explosion. This principle of lithium-ion batteries makes people achieve their safety while obtaining its high capacity density. When the lithium ion battery is charged, the lithium atom of the positive electrode will lose electrons, oxidized to lithium ions.
Lithium ions go to the negative electrode via the electrolytic liquid, enter the reservoir of the negative electrode, and obtain an electron, reducing the lithium atom. When discharged, the entire program fell. In order to prevent the positive and negative electrode of the battery, the battery will add a diaphragm paper with numerous fine holes to prevent short circuits.
Good diaphragm paper can also automatically turn off the fine holes when the battery temperature is too high, so that lithium ions cannot cross, to prevent danger,. The lithium-ion battery core will begin with a coupling after the voltage is higher than 4.2V.
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. Battery explosion caused 1. The internal polarization is large!.
3, the quality, performance problem of the electrolyte itself. 4, the amount of liquidation is not reached by the process. 5, the laser welding in the assembly process is poor, leaking, leakage, leakage test.
6, dust, very film dust is first easy to lead to micro-short circuits, specific reasons unknown. 7, the positive and negative plate is thick, the process is thick, and it is difficult to enter the shell. 8, the problem of nipple, steel ball sealing performance is not good.
9, the housing material exists having a thick shell wall, the thickness of the housing deformation. The type of explosion analysis of the battery core explosion can be summarized as external short circuit, internal short circuit and over 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 Material burning and exploding.
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. Because the needle is very fine, there is a certain resistance value, so the current is not necessarily.
Copper aluminum foil glue is caused by the production process. Moreover, since 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. Design norms have hundreds of millions of mobile phones, and the failure rate of safety protection must be less than 100 million.
Because, the failure rate of the circuit board is generally much higher than one hundred million. Therefore, when the battery system is designed, there must be two security lines. Common error design is to charge the battery directly with charger (Adaptor).
This will overcharge the protection of the protection, completely handle the protective plate on the battery pack. Although the failure rate of the protector is not high, even if the fault rate is low, the global is still a explosion accident in the world. If the battery system can supply two safety protection, the overcurrent, the overcurrent is supplied, and the failure rate of each protection is, if it is one tenth, two protective can reduce the failure rate to 100 million.
The common battery charging system is as follows, including two parts of the charger and battery pack. The charger also includes two parts: AdapTOR and the charging controller. The adapter converts AC power to direct current, and the charging controller limits the maximum current and maximum voltage of DC.
The battery pack contains two parts of the protective plate and the battery core, and a PTC to limit the maximum current. The battery cell is used as an example. The overchard protection system is set to 4.
2V using the charger output voltage to achieve the first defense, so that the battery is not overturned even if the protective board on the battery pack Hazard. The second protection is the overter protection function on the protective board, generally set to 4.3V.
In this way, the protective board can usually do not have to be responsible for cutting the charging current, only when the charger voltage is extremely high,. Overcurrent protection is responsible by the protective board and the current limiting film, which is also two protection, prevent overcurrent and external short circuit. Since over-discharge will only occur in the process of electronics being used.
Therefore, generally designed is a wire board of the electronic product to supply first to protection, and the protective plate on the battery pack supplies the second protection. When the electronic product detects that the supply voltage is below 3.0V, it should be automatically shut down.
If this feature is not designed, the protective board will turn off the discharge loop when the voltage is low to 2.4V. In short, when the battery system is designed, the two electronic protection must be supplied to overcharge, over, and overcurrent.
Among them, the protective board is the second protection. Remove the protector, if the battery will explode, represent poor design. Although the above method supplies two protection, since the consumer will often buy a non-original charger to charge, and the charger industry, based on cost consideration, often take the charging controller to reduce costs.
As a result, there is a lot of inferior chargers in the market. This makes the full-charge protection lose the first way is also the most important defense line. And over charge is the most important factor in which the battery explosion is caused.
Therefore, the inferior charger can be called the fierce of the battery explosion. Of course, not all battery systems use methods as described above. In some cases, there will also be a design of the charging controller in the battery pack.
For example: many battery sticks of many notebooks, there is a charging controller. This is because notebooks generally do charging controllers in the computer, only give consumers an adapter. Therefore, the extra battery pack of the notebook computer must have a charging controller to ensure that the external battery pack is safe when charging the adapter.
In addition, the product is charged using the car cigarette lighter, and the charging controller is sometimes done within the battery pack. The final line of defense, if electronic protective measures have failed, the last line of defense, will be supplied by the battery. The safety level of the battery can be based on whether the battery can pass the external short circuit and overcharge.
Because the battery explosion, if there is a lithium atom in the inside, the power of the explosion will be larger. Moreover, over-charge protection often only has a defense line due to consumers, so the ability of the battery anti-overcharge than anti-external short circuit is more important.
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