There are two main reasons why lithium-ion batteries bulge. One is manufacturing issues, such as poor production environments or outdated equipment, which can lead to uneven battery coatings and the introduction of dust particles into the electrolyte. These factors can cause lithium-ion battery packs to bulge during user use, and may even pose a greater danger.
Another reason lies with the user. If the user uses lithium-ion battery products improperly, such as overcharging or over-discharging, or using them continuously in extremely harsh environments, lithium-ion batteries may bulge.
Besides the two main reasons mentioned above, there is another, less common cause: the battery has not been used for a long time and has not been properly stored. When a battery is fully charged and left unused for an extended period without being used, the positive and negative terminals of the battery come into direct contact due to the conductivity of air, resulting in a slow short circuit.
The key principle behind lithium-ion battery swelling is that a violent reaction, similar to a short circuit, occurs inside the battery, generating a large amount of heat. This leads to the decomposition and vaporization of the electrolyte, causing the lithium-ion battery to swell.
When a lithium-ion battery pack bulges, it's best to stop using the problematic battery. The expanded cells, if pushed beyond a certain limit, could potentially explode, posing a significant danger.
