There are three main reasons why lithium batteries bulge:

The first type: Manufacturer’s production process problems

Due to the large number of manufacturers, many manufacturers, in order to save costs, have poor production environments and use equipment and machines that will be eliminated. This results in uneven battery coatings and dust particles mixed into the electrolyte. All of these may cause lithium battery packs to bulge when used by users, and even pose greater dangers.

The second type: users’ daily usage habits

The second type lies in the user himself. If the user uses the lithium battery product improperly, such as overcharging and overdischarging, or continues to use it in an extremely harsh environment, it may also cause the lithium battery to bulge.

The third type: long-term use and improper storage

If any product is not used for a long time, its original performance will basically decline. If the battery is not used for a long time, it will not be properly stored. When it is exposed to the air for a long time without being used and the battery is fully charged. Since air is conductive to a certain extent, leaving it open for too long means that the positive and negative electrodes of the battery are in direct contact, causing a chronic short circuit. Once short-circuited, it will generate heat, and some electrolytes will decompose or even vaporize, resulting in bulging.

Among them, the causes of bulging caused by overcharge and overdischarge are as follows:：

Bulge caused by overcharging: Overcharging will cause all the lithium atoms in the positive electrode material to flow into the negative electrode material, causing the original full grid of the positive electrode to deform and collapse. This is also a main reason for the decline in lithium battery power. During this process, there are more and more lithium ions in the negative electrode. The excessive accumulation causes the lithium atoms to grow into stump crystals, causing the lithium battery to bulge.

Bulge caused by over-discharge: During the first charge and discharge process of the liquid lithium-ion battery, 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 inserted and detached through the passivation layer, which has the characteristics of a solid electrolyte. Therefore, this passivation film is called the "solid electrolyte interface" "Membrane" (solid electrolyte interface), referred to as SEI. The SEI film protects the negative electrode material, making the material structure less likely to collapse and increasing the cycle life of the electrode material. The SEI film is not static and will undergo slight changes during the charge and discharge process, mainly due to reversible changes in some organic matter. After the battery is over-discharged, the SEI film is reversibly damaged. After the SEI that protects the negative electrode material is damaged, the negative electrode material collapses, resulting in 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 in turn will cause the electrolyte to decompose and vaporize, causing the battery to bulge.

How to safely handle lithium battery bulges?

1、Start replenishing the battery after using up about half of the battery. Only perform a full discharge and full charge maintenance in rare cases (for example, discharge and charge once after using it for several months to half a year. Frequent full charge and discharge may cause crystallization). This can greatly reduce the amount of crystallization and significantly slow down the bulging phenomenon.

2、The bulging lithium battery can be discarded directly, because the power capacity is already very small, and it has no power after a short circuit.

3、Lithium battery packs generally need to be recycled professionally to avoid causing pollution. If there is no way to dispose of them, throw them into classified recycling bins.

The above are the reasons for bulging in lithium batteries and how to correctly handle the lithium battery pack after the bulging.

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