There are four main factors that cause lithium iron phosphate batteries to bulge.
1. Overcharging causing lithium-ion battery swelling
Overcharging causes all the lithium atoms in the positive electrode material to migrate into the negative electrode material, leading to the deformation and collapse of the originally full grid in the positive electrode. This is a major reason for the decrease in the capacity of lithium iron phosphate battery packs. During this process, the number of lithium ions in the negative electrode increases, and excessive accumulation causes lithium atoms to grow into stump crystals, resulting in the swelling of the lithium-ion battery pack.
2. Bulging caused by over-discharge
During the initial charge and discharge of a liquid lithium-ion battery, the electrode material and the electrolyte react at the solid-liquid interface, forming a passivation layer covering the surface of the electrode material. This passivation layer effectively prevents the passage of electrolyte molecules, but Li+ ions can freely intercalate and deintercalate through it, exhibiting characteristics of a solid electrolyte. Therefore, this passivation film is called the SEI (Sediment Electrode Intake).
The SEI film is not static; it undergoes slight changes during charging and discharging. Importantly, some organic components undergo reversible changes. Over-discharging of lithium iron phosphate battery packs causes reversible damage to the SEI film. The destruction of the SEI protecting the negative electrode material leads to the collapse of the negative electrode material, resulting in bulging.
3. Manufacturing level issues
Swelling of lithium-ion batteries may be due to manufacturing issues with lithium iron phosphate battery packs, such as uneven electrode coatings and a relatively rough production process.
4. Not used for a long time
Batteries can also bulge if left unused for a long time. This is because air is conductive to some extent, so leaving the battery unused for too long is equivalent to the positive and negative terminals coming into direct contact, resulting in a slow short circuit.
