SEI Growth: Reaction-Diffusion Moving Boundary (2D) |…

What is SEI Growth

Solid electrolyte interphase (SEI) forms at the interface between the lithium metal or lithium-ion battery electrode and the electrolyte. This layer plays a crucial role in protecting the electrode from degradation, but it also hinders ion transport, affecting battery performance.

The growth of SEI is governed by coupled reaction-diffusion processes where ions diffuse through the electrolyte to react with the electrode surface, forming a protective layer.

Reaction-Diffusion Dynamics

Fick's law describes how ions move from regions of high concentration to low concentration in response to a concentration gradient. In SEI growth, this diffusion is coupled with an interfacial reaction where the reacting species are consumed at the electrode-electrolyte interface.

The Damköhler number (Da) quantifies the relative importance of these two processes: Da = τ_react / τ_diff, where τ_react and τ_diff represent characteristic timescales for the reaction and diffusion respectively.

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Temperature and C-Rate Effects

Changes in temperature and charging rate (C-rate) significantly affect SEI growth. Higher temperatures generally increase both the reaction rate and diffusion coefficient, leading to a transition from a reaction-limited regime where the growth is primarily determined by the interfacial reaction kinetics to a diffusion-limited regime where ion transport becomes the bottleneck.

The growth exponent computed from the simulated trajectory provides insights into whether SEI growth is more influenced by reactions or diffusion at different conditions.

SEI Stabilizing Additives

Adding electrolyte additives can stabilize the SEI, reducing its thickness and improving battery performance. These additives can alter the reaction-diffusion dynamics, potentially shifting the growth regime from parabolic to linear.

By toggling an SEI-stabilizing additive in the simulation, one can observe how such modifications impact the SEI morphology and growth kinetics.

Frequently asked questions

What is the Damköhler number (Da) and why does it matter?

The Damköhler number (Da) compares the timescales of reaction to diffusion. A Da value greater than 1 indicates a reaction-limited regime, while a Da less than 1 suggests a diffusion-limited regime, which is crucial for understanding SEI growth dynamics.

How do temperature and C-rate affect SEI growth?

Temperature increases both the reaction rate and ion mobility, potentially shifting the growth from being dominated by reactions to being limited by diffusion. Higher C-rates can lead to faster SEI formation but may also result in a thicker, less stable SEI layer.

What is the significance of the growth exponent?

The growth exponent provides a quantitative measure of how the SEI thickness changes with time. A parabolic growth (exponent = 0.5) indicates diffusion-limited growth, while linear growth (exponent = 1) suggests reaction-limited conditions.

How do electrolyte additives affect SEI stability?

Electrolyte additives can stabilize the SEI by promoting a more uniform and thinner layer. This stabilization improves battery performance by reducing internal resistance and enhancing cycle life, but it also depends on the specific additive and operating conditions.

Try it live

Everything above runs in your browser — open SEI Growth: Reaction-Diffusion Moving Boundary (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open SEI Growth: Reaction-Diffusion Moving Boundary (2D) simulation