Lithium-ion batteries, the main danger is the electrolyte is active combustible, although lithium-ion electricity is currently the most widely used battery products, but the lithium-ion battery explosion-proof technology, and protection measures have never stopped research. Lithium-ion batteries according to different uses, there will be different explosion-proof protection standards, the next small analysis of the lithium-ion battery explosion-proof technology protection measures.
When a lithium-ion battery is charged, the lithium atoms at the positive electrode lose electrons and oxidize to lithium ions. Lithium ions swim to the negative electrode via the electrolyte, enter the storage compartment of the negative electrode, and gain an electron, reducing to lithium atoms. When discharging, the whole procedure is reversed. To prevent the positive and negative electrodes of the battery from directly touching and shorting out, a diaphragm paper with many fine holes is added to the battery to prevent shorting out. A good diaphragm paper can also automatically close the fine holes when the battery temperature is too high, so that lithium ions can not cross, in order to self-destruct and prevent dangerous occurrences.
Lithium-ion battery explosion-proof technology protection measures
Lithium-ion battery cell overcharge to a voltage higher than 4.2V will begin to appear after the vice use. The higher the overcharge voltage, the higher the danger will follow. After the voltage of the lithium cell is higher than 4.2V, the number of lithium atoms left in the positive electrode material is less than half, and the storage compartment will collapse, causing a permanent drop in battery capacity. If charging continues, as the storage compartment of the negative electrode is already full of lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the surface of the negative electrode in the direction of the lithium ions. These lithium metal crystals can pass through the diaphragm paper and short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs, because in the overcharge process, the electrolyte and other materials will be cracked gas, making the battery shell or pressure valve bulge rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the surface of the negative electrode, and then explode. Therefore, when charging lithium-ion batteries, it is important to set the upper voltage limit in order to take into account the battery life, capacity, and safety. The ideal charging voltage limit is 4.2 V. There is also a lower voltage limit when discharging lithium cells. When the cell voltage is below 2.4V, some materials will start to be destroyed. Because the battery will self-discharge, the longer you put the voltage will be lower, therefore, it is best not to put it to 2.4V before stopping when discharging. Lithium-ion battery from 3.0V to 2.4V discharge period, the energy released only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage.
When charging and discharging, in addition to the voltage limit, the current limit is also necessary. When the current is too high, lithium ions do not have time to enter the storage compartment and will collect on the material surface. These lithium ions gain electrons and crystallize lithium atoms on the surface of the material, which can be dangerous in the same way as overcharging. In case the battery case breaks, it can explode.
Therefore, the protection of lithium-ion batteries should include at least three items: upper limit of charging voltage, lower limit of discharging voltage, and upper limit of current. General lithium-ion battery pack, in addition to lithium-ion battery cells, there will be a protection plate, this protection plate is important to supply these three protections. However, the protection board of the three protection is obviously not enough, the global lithium-ion battery explosion is still frequently spread. To ensure the safety of the battery system, the cause of the battery explosion must be more carefully analyzed.
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