How to better protect customized lithium batteries

After the customized 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. When the cell voltage of customized lithium battery is higher than 4.2V, the number of lithium atoms left in the cathode material is less than half. At this time, the storage cell often collapses, reducing the battery capacity. If you continue to charge, since the storage cell of the negative electrode has been filled with lithium atoms, the 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 lithium ions. These lithium metal crystals will pass through the diaphragm paper and short circuit the positive and negative electrodes. Sometimes the battery will explode before the short circuit occurs, because in the overcharge process, electrolyte and other materials will crack to produce gas, which makes the battery shell or pressure valve swell and crack, allowing oxygen to enter and react with lithium atoms accumulated on the surface of the negative electrode, and then explode. Therefore, when charging lithium battery, the upper voltage limit must be set to take into account the service life, capacity and non harmfulness of the battery at the same time. The ideal upper limit of charging voltage is 4.2V. There should also be a lower voltage limit when the lithium battery cell is discharged. When the cell voltage is lower than 2.4V, some materials will begin to be damaged. Because the battery will discharge itself, the longer it is discharged, the lower the voltage will be. Therefore, do not stop at 2.4V during discharge. During the period from 3.0V to 2.4V, the energy released by lithium battery accounts for only about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage.

When charging and discharging custom lithium batteries, in addition to voltage limitation, current limitation is also necessary. When the current is too high, the customized lithium battery will gather on the surface of the material without time to enter the storage cell. After these lithium ions obtain electrons, lithium atoms will crystallize on the surface of the material, which, like overcharge, will cause danger. If the battery shell breaks, it will explode.

Therefore, the protection of customized lithium batteries should include at least three items: 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. Lithium battery explosions are still frequent all over the world. To ensure the stability of the battery system, we need to analyze the causes of battery explosion more carefully, so as to better protect the lithium battery and play its role.