When the customized lithium battery cell is overcharged to a voltage higher than 4.2V, it will start to produce side effects. The higher the overcharge voltage, the higher the danger. When the cell voltage of customized lithium battery is higher than 4.2V, the number of remaining lithium atoms in the positive material is less than half. At this time, the storage cell often collapses, causing the battery capacity to decline. If charging is continued, because the storage cell of the negative electrode is full of lithium atoms, the subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendrites from the negative surface to the direction of lithium ions. These crystals of lithium metal will pass through the separator paper, shorting the positive and negative poles. Sometimes the battery will explode before the short circuit occurs, because in the overcharge process, the electrolyte and other materials will crack to produce gas, which causes the battery shell or pressure valve to swell and crack, allowing oxygen to enter and react with the lithium atom stacked on the negative electrode surface, and then explode. Therefore, when the lithium battery is charged, the upper limit of voltage must be set, so that the battery life, capacity and non harmfulness can be considered at the same time. The ideal upper limit of charging voltage is 4.2V. When lithium battery is discharged, there should be a lower voltage limit. When the core voltage is lower than 2.4V, some materials will be destroyed. And because the battery will discharge itself, the longer it is discharged, the lower the voltage will be. Therefore, do not put it at 2.4V to stop discharging. During the period from 3.0V to 2.4V, the energy released by lithium battery only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage.

In addition to the limitation of voltage, the limitation of current is also necessary to customize the charging and discharging of lithium battery. When the current is too high, the customized lithium battery will gather on the material surface before entering the storage cell. When these lithium ions obtain electrons, they will produce lithium atom crystal on the surface of the material, which is just as dangerous as overcharge. If the battery case breaks, it will explode.

Therefore, the protection of customized lithium battery should at least include: upper limit of charging voltage, lower limit of discharging voltage and upper limit of current. Generally, in the customized lithium battery pack, in addition to the customized lithium battery cell, there will be a protective 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 stability of the battery system, we need to analyze the cause of the battery explosion more carefully, so that we can better protect the lithium battery to play its role.