Why do lithium battery packs bulge?

There are three main reasons for lithium battery bulging:

①Manufacturer production process problems

The battery coating is uneven, and dust particles are mixed into the electrolyte. These may cause the lithium battery pack to bulge when the user uses it.

②User daily use habits

If the user uses lithium battery products improperly, such as overcharging and overdischarging, or continuous use in extremely harsh environments, it may also cause lithium batteries to bulge. Among them, the reasons for bulging caused by overcharging and overdischarging are as follows:

Bulging caused by overcharging: Overcharging will cause all the lithium atoms in the positive electrode material to run into the negative electrode material, causing the originally full grid of the positive electrode to deform and collapse, which is also a major reason for the decrease in lithium battery power. In this process, the number of lithium ions in the negative electrode increases, and excessive accumulation causes lithium atoms to grow crystals, causing the lithium battery to bulge.

Bulging caused by overdischarge: During the first charge and discharge process of liquid lithium-ion batteries, the electrode material and the electrolyte react at the solid-liquid interface to form a passivation layer covering the surface of the electrode material. The formed passivation layer 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 a solid electrolyte. Therefore, this passivation film is called "solid electrolyte interface", or SEI for short. The SEI film protects the negative electrode material, making the material structure less likely to collapse, and can increase the cycle life of the electrode material. The SEI film is not static, and there will be a little change during the charge and discharge process, mainly because some organic matter will undergo reversible changes. After the battery is over-discharged, the SEI film is reversibly destroyed, and the SEI that protects the negative electrode material is destroyed, causing the negative electrode material to collapse, thus forming a bulging phenomenon.

These two factors will cause a violent reaction similar to a short circuit to occur inside the battery during use, generating a large amount of heat, which will cause the electrolyte to decompose and gasify, and the battery will bulge.

③ Long-term non-use and improper storage

The battery has not been used for a long time and has not been well preserved. When it is exposed to air for a long time and is not used, and the battery is fully charged. Since air is conductive to a certain extent, if the battery is left for too long, it is equivalent to the positive and negative poles of the battery being in direct contact, causing a chronic short circuit. Once a short circuit occurs, heat will be generated, and some electrolytes will decompose or even vaporize, leading to bulging.

The capacity of bulging lithium batteries is seriously damaged and there are safety hazards. It is recommended not to use them.Waste lithium batteries should be processed through professional recycling channels to prevent environmental pollution.