Which Factors Would Cause The Swelling Of A Lithium Iron Phosphate Batteries ?

The swelling of lithium iron phosphate batteries is mainly caused by four major factors.

1.Swelling of lithium-ion batteries caused by overcharging
Overcharging will cause the positive electrode to release excessive lithium ions. These lithium ions cannot be normally embedded on the surface of the negative electrode, and thus will deposit on the surface of the negative electrode, forming lithium dendrites,resulting in the deformation and collapse of the originally full grid of the positive electrode. This is also an important reason for the decrease in the capacity of the lithium iron phosphate battery pack. In this process, there are more and more lithium ions in the negative electrode. Excessive accumulation causes lithium atoms to form dendritic crystals, making the lithium-ion battery pack swell.

2.Swelling caused by overdischarging
During the first charge and discharge process of a liquid lithium-ion battery, a reaction occurs between the electrode material and the electrolyte at the solid-liquid interface, forming a passivation layer covering the surface of the electrode material. The formed passivation layer film can effectively prevent the passage of electrolyte molecules, but Li+ can freely embed and extract through this passivation layer, which has the characteristics of a solid electrolyte. Therefore, this passivation film is called the SEI.
The SEI film is not static and will change slightly during the charge and discharge process, mainly that some organic substances will undergo reversible changes. After the LFP battery pack is over-discharged, the SEI film undergoes reversible damage. Once the SEI film that protects the negative electrode material is damaged, the negative electrode material collapses, resulting in a swelling phenomenon.

3.Manufacturing level issues
The swelling of the lithium-ion battery may be due to problems in the manufacturing level of the rechargeable Lifepo4 battery, such as uneven electrode coating and relatively rough production processes.

4.Long-term storage without use
Swelling will also occur if the battery is not used for a long time. Because air is conductive to a certain extent, leaving the battery unused for too long is equivalent to directly connecting the positive and negative electrodes of the battery, resulting in a slow short circuit.

Carry Zhang

poeae@liliangbattery.com

www.liliangbattery.com