SEI Layer Growth & Battery Capacity Fade

Aging Conditions

Storage / cycling temperature 25°C

Cycling rate 1.0C

Time acceleration 20 days/s

Live Readouts

Elapsed time

0 days

SEI thickness

0.0 nm

Capacity retention

100.0%

Cell impedance

1.00×

How it works

Inside a lithium-ion cell, the graphite (or silicon) anode sits below the electrolyte's stability window. On first charge — and continuously, at a slow trickle, ever after — electrolyte molecules reduce at the anode surface and precipitate into a nanometre-scale passivation film: the solid-electrolyte interphase (SEI). It is electronically insulating but ionically conducting, so it protects the electrolyte from further reduction — at the cost of permanently consuming cyclable lithium and adding resistance.

Because fresh electrolyte must diffuse through the existing film to react, growth is diffusion-limited and follows a parabolic (√t) rate law:

δ(t) = √(2 · k_p · t)          [SEI thickness, diffusion-limited growth]
k_p(T) = k₀ · exp(−E_a / R·T)  [Arrhenius rate constant]
Capacity(t) ≈ Q₀ − c · δ(t)    [lithium trapped in film ∝ new SEI formed]
R_cell(t) = R₀ · (1 + δ(t)/δ_ref)  [added film resistance, Ohm's law]

Temperature — enters through the Arrhenius term; every ~10°C roughly doubles the growth rate, so a hot cell ages far faster than a cool one.
Cycling rate (C-rate) — faster charge/discharge raises local current density and self-heating, accelerating side-reaction kinetics beyond the calendar-aging baseline.
SEI-stabilizing additive — models electrolyte additives (e.g. FEC, VC) that form a denser, less permeable initial film, roughly halving the long-run growth constant k₀.
Time acceleration — the film needs months to years to visibly thicken in a real cell; this control fast-forwards simulated calendar time.

The small spheres are the cyclable lithium-ion inventory diffusing in the electrolyte; as the shell thickens, ions are progressively trapped into the growing film — visualizing exactly the irreversible-capacity-loss mechanism that dominates long-term battery aging.

Graphite anode particle SEI passivation film Cyclable Li⁺ ions

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