Lithium battery protection measures

　　After the lithium battery cell is overcharged to a voltage higher than 4.2V, side effects will begin to occur. The higher the overcharge voltage, the higher the risk. After the lithium cell voltage is higher than 4.2V, the number of lithium atoms remaining in the positive electrode material is less than half, and the storage cell often breaks down, so that the battery capacity is permanently reduced. If you continue to charge, because the negative cell has been filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative material. These lithium atoms will grow dendritic crystals from the negative surface in the direction of the lithium ions. These lithium metal crystals will pass through the diaphragm paper and short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs, because during the overcharge process, materials such as electrolyte will crack to produce gas, making the battery housing or pressure valve burst and crack, allowing oxygen to go in and react with lithium atoms piled on the surface of the negative electrode, and then explode. Therefore, when charging lithium batteries, it is necessary to set the upper voltage limit to take into account the life, capacity, and safety of the battery. The most ideal charging voltage is up to 4.2V. Lithium battery should also have a lower voltage limit when discharging. When the cell voltage is below 2.4V, part of the material will begin to be destroyed. And because the battery will self-discharge, the longer the voltage will be lower, therefore, it is best not to stop at 2.4V when discharging. During the period from 3.0V discharge to 2.4V, the energy released by the lithium battery only accounts for about 3% of the battery capacity. Therefore,3.0V is an ideal cut-off voltage for discharge. When charging and discharging, in addition to the limitation of voltage, the limitation of current is also necessary. When the current is too large, lithium ions have no time to enter the storage cell and will gather on the surface of the material. When these lithium ions gain electrons, they crystallize lithium atoms on the surface of the material, which, like overcharging, can be dangerous. If the battery case breaks, it will explode. Therefore, the protection of lithium-ion batteries, at least include: charging voltage upper limit, discharge voltage lower limit, and current upper limit three. In general, in the lithium battery group, in addition to the lithium battery core, there will be a protection plate, which mainly provides these three protections. However, these three protections of the protection board are obviously not enough, and the global lithium battery explosion is still frequent. To ensure the safety of the battery system, the cause of the battery explosion must be more carefully analyzed.

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