Meaning
The release of gaseous byproducts during the initial formation or cycling of a soft-packaged lithium-ion battery occurs due to electrochemical reactions. Managing pouch cell outgassing is a necessary task for cell designers because the accumulation of gas causes the flexible pouch to swell and lose pressure on the electrode stack. This swelling can lead to capacity loss and mechanical failure if left unmanaged.
Formation Chemistry
Electrolyte decomposition during the first charge cycles generates carbon dioxide and other gases as the protective solid electrolyte interphase is established. Although some pouch cell outgassing is expected during this formation stage, excessive gas generation indicates that the electrolyte is unstable or that the anode has surface impurities.
Performance Impact
Swelling in the finished cell reduces the physical contact between the electrodes and separators, which increases internal resistance. When pouch cell outgassing occurs during the operational life of the battery, it accelerates the degradation of the active materials and reduces the overall cycle life. This issue is particularly problematic in dense packs where space is limited and swelling can damage neighboring cells.
Designers use rigid plates or external brackets to apply constant compression and mitigate these effects.
Chemical Suppression
Additives in the electrolyte form stable protective layers on the electrodes to limit gas generation. These compounds represent an effective solution for suppressing pouch cell outgassing.
