Lithium Battery Expansion Damage

Shell characteristics
Lithium, with atomic number 3 and atomic weight of 6.941, is the lightest alkali metal element. In order to improve safety and voltage, scientists have invented materials such as graphite and lithium cobalt oxide to store lithium atoms. The molecular structure of these materials forms nano-scale tiny storage grids that can be used to store lithium atoms. In this way, even if the battery shell is broken and oxygen enters, the oxygen molecules are too large to enter these tiny storage grids, so that the lithium atoms will not come into contact with oxygen and avoid explosion.
Protection measures
When 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 danger. When the lithium battery 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 grid often collapses at this time, causing the battery to have permanent capacity loss. If charging continues, since the storage grid of the negative electrode is already full of lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendrites from the negative electrode surface to the direction of lithium ions. These lithium metal crystals will pass through the diaphragm and short-circuit 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 decompose and produce gas, causing the battery shell or pressure valve to swell and rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the surface of the negative electrode, and then explode.
Therefore, when charging lithium batteries, it is necessary to set an upper voltage limit to take into account the battery life, capacity, and safety at the same time. The most ideal upper limit of charging voltage is 4.2V. There is also a lower voltage limit when discharging lithium batteries. When the battery voltage is lower than 2.4V, some materials will begin to be damaged. Because the battery will self-discharge, the longer it is discharged, the lower the voltage will be. Therefore, it is best not to stop discharging at 2.4V. During the period when the lithium battery is discharged from 3.0V to 2.4V, the energy released only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage. When charging and discharging, in addition to voltage restrictions, current restrictions are also necessary. When the current is too large, lithium ions will not have time to enter the storage cell and will gather on the surface of the material.
After these lithium ions obtain electrons, lithium atoms will be crystallized on the surface of the material, which is dangerous just like overcharging. If the battery shell is broken, it will explode. Therefore, the protection of lithium-ion batteries must at least include: upper limit of charging voltage, lower limit of discharging voltage, and upper limit of current. In general, in addition to the lithium battery cell, there will be a protection board in the lithium battery pack, which mainly provides these three protections. However, these three protections of the protection board are obviously not enough, and lithium battery explosions are still frequent around the world. To ensure the safety of the battery system, it is necessary to conduct a more careful analysis of the causes of battery explosions.