Author ：Iflowpower – Portable Power Station Supplier
First, lithium ion battery characteristics 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 produce a fierce oxidation reaction with oxygen and explod. 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 classes are not allowed to prevent the lithium atoms to avoid 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 protective measure of the lithium battery core will begin to generate side effects 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 degene will often be collapsed, so that the battery capacity has a permanent drop.
If the charging is continued, 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 electrode 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 lysis generating gas, so that the battery housing or pressure valve is broken, allowing oxygen to enter the lithium atomic response to the surface of the negative surface. In turn explodes. Therefore, when the lithium battery is charged, it must be set to set the voltage limit to simultaneously take 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 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 obtain electron, the lithium atomic crystallization is produced on the surface of the material, which is the same as overcharges.
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 the general lithium battery pack, in addition to the lithium battery core, there will be a protective plate, which is mainly to provide these three protection.
However, the three protection of the protector is obviously insufficient, and the global lithium battery explosion is still transmitted. To ensure the safety of the battery system, you must make a more careful analysis of the battery explosion. Second, the battery explosion cause: 1: The internal polarization is large! 2: Take the absorbent, reactor with the electrolyte.
3: The quality and performance of the electrolyte itself. 4: The amount of liquid is not until the process. 5: Laser welding in the assembly process is poor, leakage, leakage, gas leakage test.
6: dust, polar dust is first easily causing micro-short circuit, specific reasons unknown. 7: The positive and negative plate is thick, the process is thick, and the shell is difficult. 8: Nipple sealing problem, steel ball sealing performance is not good.
9: The housing material exists thickness, and the thickness of the housing deformation. Third, the explosion type analysis of the type of 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 internal cell can generate high heat, resulting in a partial electrolyte steaming, and support the battery housing. 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, and the explosion occurs. 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 mainly because the copper foil is pulling the membrane, or the branch crystal of the lithium atom is caused by 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, mainly 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 has not been high enough to combust to the material, and the generated gas is not enough to break the battery case, the consumer will terminate the charging, with the mobile phone to go out. At this time, the heat generated by many micro-short circuits slowly increases the battery temperature.
After a period of time, explosion occurs. 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. Fourth, design specifications 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 provide two safety protection, the failure rate of each protection is one-third, and the failure rate can be reduced 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. Text block: Adapter AC variable DC text block: Charging controller limited flow limited text square: charger text square: protective board over charge, overcharges and other protective text square: battery pack text square: limited flow film text square: 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 overcharged. 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 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, it is generally designed to provide the first to protection, and the protective plate on the battery pack provides a second protection. When the electronic product detects that the supply voltage is below 3.
0V, it should be automatically shut down. If the product is not designed when the product is 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, it must provide two electronic protection for overcharge, over, and overcurrent. Among them, the protective board is the second protection. Take the protective plate after charging, if the battery explodes, represents poor design.
Although the above method provides 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 a solution as shown 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 If the protection of electronics failed, the last line of defense is to be provided 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 the internal lithium atom is stacked in the surface of the material, the explosion power 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.
Aluminum-shell batches and steel shell battery safety compare aluminum shells with high security advantages relative to the steel shell. .
Copyright © 2023 iFlowpower - Guangzhou Quanqiuhui Network Technique Co., Ltd.