What is the reason of lithium battery battery drum shell? Shared by the 18650 lithium ion battery supplier.
The shell features
Lithium, at atomic number 3 and atomic weight of 6.941, is the lightest alkali metal element. To improve safety and voltage, scientists have developed materials such as graphite and lithium cobalt oxide to store lithium atoms. The molecular structure of these materials forms tiny storage lattices at the nanoscale that can be used to store lithium atoms. That way, even if the battery shell breaks and oxygen enters, the molecules are too big to fit into the tiny cells, preventing lithium atoms from coming into contact with oxygen and exploding.
When the lithium battery cell is overcharged to a voltage higher than 4.2v, side effects begin to occur. The higher the overcharge voltage, the higher the risk. When the lithium cell voltage exceeds 4.2v, less than half of the lithium atoms are left in the anode material, and the storage cell often collapses, causing a permanent loss of battery capacity. If the charge continues, the lithium metal will accumulate on the surface of the negative material, since the negative cell is already full of lithium atoms. These lithium atoms grow dendritic crystals from the negative surface toward the lithium ions. These lithium metal crystals will pass through the diaphragm paper, short-circuiting the anode and cathode. Sometimes the battery explodes before a short circuit occurs, because in the overcharge process, materials such as electrolyte will crack and produce gas, causing the battery shell or pressure valve to swell and crack, allowing oxygen to enter and react with lithium atoms accumulated on the negative electrode surface, thereby exploding.
Therefore, when charging lithium batteries, the voltage limit must be set, so that the battery life, capacity and safety can be taken into account at the same time. The optimal upper limit of charging voltage is 4.2v. Lithium cell discharge also have a lower voltage limit. When the cell voltage falls below 2.4v, some of the material begins to be destroyed. And because the battery will self-discharge, the longer it is put, the lower the voltage will be. Therefore, it is better not to stop at 2.4v when discharging. During the period from 3.0v to 2.4v, lithium batteries release only about 3% of the battery capacity. Therefore, 3.0v is an ideal discharge cut-off voltage. Charge and discharge, in addition to the voltage limit, the current limit is also necessary. When the current is too high, the lithium ions don't have time to get into the cell and will accumulate on the surface of the material.
When these lithium ions gain electrons, they create crystals of lithium atoms on the material's surface, which, like overcharging, can be dangerous. In case the battery case breaks, it will explode. Therefore, the protection of lithium ion battery, at least include: charging voltage upper limit, discharge voltage lower limit, and current upper limit three. In general, in addition to the lithium battery core, there will be a protective plate, which mainly provides the three protection. However, the protection plate of the three protection is obviously not enough, the global lithium battery explosion incidents are still frequent. To ensure the safety of the battery system, the cause of battery explosion must be analyzed more carefully.
That's all for the sharing, thanks for your reading, and we also supply 18650 High security rechargeable lithium battery for sale, if you have any demand for our products, just feel free to contact us.