Batteries are swelling up when Li ions are moving back and forth between cathode and anode. The swelling is dependent on the electrode chemistries used. Some electrode materials such as silicon expand by more than 300% during the intake of Li. Additionally, battery swelling can occur when gas accumulates inside a lithium-ion battery, causing it to expand. This is especially obvious for pouch cells. The gas generation can result from various factors, including overcharging, high temperatures, and manufacturing defects. Swollen batteries pose a safety risk and should be replaced promptly.