Quantifying Sacrificial Additive Depletion Kinetics in Commercial Lithium Pouch Cells
Sacrificial additive depletion in commercial pouch cells follows pseudo-first-order kinetics, triggering gas evolution and rapid impedance rise when exhausted.
Parasitic Gas Evolution
Meaning
Generation of gaseous species through side reactions that do not contribute to the storage or release of energy. The occurrence of parasitic gas evolution usually signals the decomposition of the electrolyte or the presence of impurities such as moisture. These gases can cause the cell housing to swell and may lead to the activation of safety vents.
Decomposition Chemistry
Breaking of molecular bonds in the solvent molecules releases small molecules like carbon dioxide or hydrogen. High temperatures or extreme voltages often trigger parasitic gas evolution. These reactions are irreversible and consume the liquid electrolyte, leading to dry-out and failure.
Pressure Build
Accumulation of vapor within a sealed cell creates internal stress on the mechanical structure. If parasitic gas evolution is not controlled, the internal pressure can deform the electrodes and disrupt the electrical contact. Pouch cells are particularly sensitive to this swelling, which can alter the stack pressure and the rate of ion transport.
Safety Mechanism
Venting of the gas is a necessary design feature for high-energy batteries. When parasitic gas evolution reaches a critical level, the safety valve opens to prevent a violent rupture of the casing. Managing these side reactions through the use of scavengers and stable coatings is a focus of modern cell design.
The selection of additives that prevent gas formation at high temperatures is a primary consideration for automotive applications.