What is "lithium precipitation" in lithium ion batteries?

When a lithium ion battery is charged, lithium ions are intercalated from the positive electrode and inserted into the negative electrode; but when there are some abnormal conditions: such as insufficient space for inserting lithium in the negative electrode, too much resistance to inserting lithium ions into the negative electrode,lithium ions fall off from the positive electrode too quickly, but cannot be embedded into the negative electrode equally.When an abnormalityoccurs, such as a large amount of insertion into the negative electrode, the lithium ions that cannot be inserted into the negative electrode. So that they can only get electrons on the surface of the negative electrode, thereby forming a silver-white metallic lithium element, which is often called "lithium precipitation"

The main manifestations of lithium precipitation are:
Under low temperature conditions, the ionic conductivity of the electrolyte will decrease, the resistance of lithium ions from the positive electrode and the insertion of the negative electrode will be greatly increased, and the increase in the resistance of the negative electrode will be greater, which will cause lithium precipitation.

When the battery is charged at a high rate, a large amount of lithium ions are extracted from the positive electrode and come to the negative electrode. However, because the impedance of lithium ions inserted into the negative electrode is much greater than that of the positive electrode, the rush of lithium ions cannot be 100% guaranteed. If it is too late to insert into the negative electrode, it will get electrons on the surface of the negative electrode and form metallic lithium.

When the positive electrode coating is too heavy or the negative electrode coating is too light, there will be insufficient space for lithium insertion in the negative electrode, so that after lithium ions are extracted from the positive electrode and reach the negative electrode, electrons will be obtained on the surface of the negative electrode and metal lithium will be formed.

After the negative electrode is compacted beyond its limit, it will destroy the body structure of the material and increase the resistance during the insertion of lithium ions, thereby triggering lithium precipitation. If the negative electrode is exposed to the foil, lithium ions will directly gain electrons from the copper foil and carry out lithium precipitation during charging.

A core with a large thickness or an internally tightly wound core is easily deformed after volume separation and will cause poor contact of the pole pieces. The poor contact area will be filled with gas inside the cell, thereby losing the lithium ion migration channel. Eventually, a strip-shaped area with no lithium intercalation is formed, which may be accompanied by lithium precipitation.

The electrolyte acts as a channel for conducting lithium ions. If the amount is small or the pole piece is not sufficiently infiltrated, the knife will cause lithium precipitation.

During the design or manufacturing process of 26650, PLB fully considers the above-mentioned lithium precipitation phenomenon and mechanism, and ensures that the battery does not have lithium precipitation from multiple dimensions such as design, material, and technology, so as to ensure the 26650 cells with the long cycle, high capacity, and high capacity, stable electrochemical performance and other advantages.

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