Custom lithium battery cells will start to produce side effects when they are overcharged to a voltage higher than 4.2V. The higher the overcharge voltage, the higher the risk. When the voltage of the custom lithium battery cell is higher than 4.2V, the amount of lithium atoms remaining in the positive electrode material is less than half, and the cell often collapses, causing the battery capacity to drop. If the charging continues, since the cell of the negative electrode is already filled with lithium atoms, the subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms grow dendrites from the surface of the negative electrode toward the direction of lithium ions. These lithium metal crystals pass through the separator paper, shorting the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs. This is because during the overcharging process, the electrolyte and other materials will crack and generate gas, causing the battery casing or pressure valve to bulge and rupture, allowing oxygen to enter and react with the lithium atoms deposited on the surface of the negative electrode. Then exploded. Therefore, when charging a lithium battery, you must set the upper voltage limit to take into account the battery life, capacity, and non-harm. The ideal charging voltage is limited to 4.2V. Lithium batteries should also have a lower voltage limit when discharging. When the cell voltage is lower than 2.4V, some materials will start to be destroyed. Since the battery will self-discharge, the voltage will be lower for the longer the discharge, so do not stop until 2.4V is discharged. During the period from the discharge of 3.0V to 2.4V, the energy released by the lithium battery is only about 3 percent of the battery capacity. Therefore, 3.0V is an ideal discharge cutoff voltage.
When charging and discharging a custom lithium battery, in addition to the voltage limit, current limitation is also necessary. When the current is too large, the custom lithium battery does not have time to enter the cell and will accumulate on the surface of the material. When these lithium ions obtain electrons, crystals of lithium atoms are generated on the surface of the material, which is dangerous as overcharge. In the event of a broken battery case, it will explode.
Therefore, the protection of the customized lithium battery must include at least three factors: the upper limit of the charging voltage, the lower limit of the discharging voltage, and the upper limit of the current. In the general custom lithium battery pack, in addition to the custom lithium battery core, there will be a protective board, which is mainly to provide 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 stability of the battery system, it is necessary to conduct a more careful analysis of the cause of the battery explosion, so as to better protect the lithium battery.
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