Meaning
Mathematical models describe the rate at which a passivation layer thickens when the process is limited by diffusion through the film. Under parabolic growth kinetics, the thickness of the solid electrolyte interface increases as the square root of time. This relationship allows engineers to predict the long-term shelf life of a stored cell.
Layer Thickness
Passivation films on the anode surface grow as the electrolyte reacts with the active material. Following parabolic growth kinetics, the growth rate slows down as the film becomes a more effective barrier. This self-limiting behavior is essential for the stability of lithium ion batteries.
Diffusion Rate
Transport of reactive species through the existing layer determines the speed of further thickening. Parabolic growth kinetics hold true when the movement of ions or solvent molecules is the slowest step in the reaction. High temperatures increase the diffusion coefficient and accelerate this growth.
Measuring the capacity loss over time at different temperatures confirms if the degradation follows this square root law. This analysis helps in distinguishing between simple diffusion and more complex mechanical cracking of the interface.
Passivation Level
Quality of the initial film determines the starting point of the growth curve. Effective parabolic growth kinetics lead to a stable interface that protects the battery from continuous self discharge. A well formed layer ensures that the cell retains its charge during long periods of inactivity.
