Lithium-ion battery explosion causes:
1. Large internal polarization;
2. The pole piece absorbs water and reacts with the electrolyte gas drum;
3. The quality and performance of the electrolyte itself;
4. The amount of liquid injection does not meet the process requirements;
5. Poor sealing performance of laser welding in the assembly process and air leakage when measuring air leakage;
6. Dust, pole piece dust is easy to lead to micro-short circuit in the first place;
7. Positive and negative pole pieces are thicker than the process range, and it is difficult to enter the shell;
8. Liquid injection sealing problem, steel ball sealing performance is not good leading to gas drum;
9. Shell incoming shell wall thickness, shell deformation affects the thickness;
10. Outside the high ambient temperature is also an important cause of the explosion.
Protective measures taken by the battery:
Lithium-ion battery cells are overcharged to a voltage higher than 4.2V and will begin to show side effects. The higher the overcharge voltage, the higher the danger. When the voltage of a lithium cell is higher than 4.2V, less than half of the lithium atoms remain in the positive electrode material, and the storage compartment often collapses, causing a permanent drop in battery capacity. If charging is continued, as the storage compartment of the negative electrode is already full of 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 anode 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, this is because in the overcharging process, the electrolyte and other materials will be cracked to appear gas, making the battery shell or pressure valve bulge rupture, so that the oxygen into the reaction with the accumulation of lithium atoms on the surface of the negative electrode, and then explode.
Therefore, when charging lithium-ion batteries, the upper voltage limit must be set in order to take into account the life, capacity, and safety of the battery at the same time. The ideal upper limit of charging voltage is 4.2 V. There should also be a lower voltage limit when discharging lithium cells. When the cell voltage falls below 2.4V, some of the materials will begin to be destroyed. And because the battery will self-discharge, the longer you put the lower the voltage will be, therefore, it is best not to discharge to 2.4V before stopping. The energy released during the period from 3.0V to 2.4V only accounts for about 3% of the capacity of a lithium-ion battery. Therefore, 3.0V is an ideal cut-off voltage for discharge. When charging and discharging, in addition to voltage limitation, current limitation is also necessary. When the current is too high, the lithium ions do not have time to enter the storage compartment and will collect on the surface of the material.
These lithium ions gain electrons and crystallize lithium atoms on the surface of the material, which is the same as overcharging and can be dangerous. In case of a rupture of the battery case, it will explode. Therefore, the protection of lithium-ion batteries should include at least three items: the upper limit of charging voltage, the lower limit of discharging voltage, and the upper limit of current. General lithium-ion battery packs, in addition to lithium-ion battery cells, there will be a protective plate, this protective plate is important to supply these three protection.
Post time: Dec-07-2023