Lithium batteries are widely used because of many advantages, especially lithium iron phosphate batteries that can perfectly replace lead-acid batteries. However, as the use time increases, lithium batteries have the problems of swelling, unsatisfactory safety performance and accelerated cycle attenuation.

　　Based on our research and development experience, we divide the causes of lithium battery swelling into two categories, one is the swelling caused by the thickness changes of the battery pole pieces; the other is the swelling caused by the oxidation and decomposition of electrolyte to produce gas.

　　1. Change of electrode thickness

　　During the use of lithium batteries, the thickness of the electrode pole pieces will change to a certain degree, especially the graphite negative electrode. The expansion of graphite anode is mainly caused by irreversible expansion after lithium insertion. This part of the expansion is mainly related to the particle size, the adhesive and the structure of the pole piece.

　　2. Bloating caused by gas production of lithium batteries

　　The gas generated inside the lithium battery is another important reason for the swelling of the lithium battery. Lithium batteries will produce different degrees of swelling and gas generation when they are stored at room temperature, high temperature cycle, and high temperature. According to the current research results, the essence of the cell bloating is caused by the decomposition of the electrolyte.

　　The root cause is the presence of impurities in the electrolyte or excessive moisture inside the lithium battery.