There are two kinds of bulges during charging and discharging:

1、 Bulging caused by overcharge

Overcharging will cause all the lithium atoms in the positive material to run into the negative material, leading to the deformation and collapse of the original full grid of the positive material, which is also a major reason for the decline of lithium battery power. In this process, more and more lithium ions in the negative electrode are accumulated, and excessive accumulation makes lithium atoms grow into stump crystals, which makes the battery bulge.

2、 Bulging caused by excessive release

During the first charging and discharging process of liquid lithium ion battery, electrode materials and electrolyte react on the solid-liquid interface to form a passivation layer covering the surface of electrode materials. The passivation layer film formed can effectively prevent the passage of electrolyte molecules, but Li+can be freely embedded and removed through the passivation layer, which has the characteristics of solid electrolyte. Therefore, this passivation film is called "solid electrolyte interface", or SEI for short. The SEI film will protect the cathode material, making the material structure not easy to collapse, and can increase the cycle life of the electrode material. SEI membrane is not unchangeable. There will be a little change in the charge discharge process, mainly because some organic substances will change reversibly. After excessive discharge of the battery, the SEI film will be reversible broken, and the SEI of the protective negative electrode material will collapse after it is broken, thus forming a bulge phenomenon.