Quantifying Sodium Oxalate Decomposition Kinetics on Automated Formation Lines
Sodium oxalate oxidation kinetics dictate pouch formation degassing timing, where 3.85 V step holds prevent cell swelling and minimize solvent evaporation.
Pouch Ballooning
Meaning
Mechanical distension events occur when gas pressure builds up inside a flexible battery enclosure. Pouch ballooning is a visible sign of electrolyte decomposition or moisture contamination within the cell. Because the aluminum laminate used for pouch cells has little structural rigidity, it expands outward as internal gases like carbon dioxide or hydrogen are released during a failure or overcharge.
Gassing Source
Chemical breakdowns of the liquid electrolyte are the most common cause of the increased internal pressure. While some gas is expected during the initial formation cycle, pouch ballooning during regular use indicates a serious problem with the cell chemistry. Moisture ingress through a faulty seal reacts with the lithium salts to produce gas.
This reaction not only swells the pack but also creates acidic products that further damage the electrodes.
Seal Failure
Excessive expansion places a high level of stress on the heat-sealed edges of the container. If pouch ballooning continues unchecked, the integrity of the seal is eventually compromised and the flammable electrolyte can leak out. This exposure to oxygen can lead to a fire or the release of toxic fumes.
Maintaining a tight control over the operating voltage and temperature prevents the internal reactions that lead to this mechanical stress.
Operational Life
Performance of the battery drops as the layers of the cell are pushed apart by the gas. Pouch ballooning increases the distance between the anode and cathode, which slows down the ion transfer and raises the internal resistance. Once a cell has swollen, it can no longer be used safely in a tight-fitting device or vehicle pack.
Monitoring the thickness of the cell is a standard way to detect the end of its useful life.