Battery Cycle Aging & Capacity Fade

Cycling Conditions

C-rate 1.0C

Cell temperature 25 °C

Depth of discharge 80%

Cell State

Cycle count

State of charge

100%

SEI thickness

5.0 nm

Capacity retention

100.0%

0%80% = end of life

How it works

Each simulated cycle, Li⁺ ions deintercalate from the cathode and intercalate into the graphite anode on charge, then reverse on discharge. A thin fraction of electrolyte is irreversibly reduced at the anode surface every cycle, thickening a solid-electrolyte-interphase (SEI) film that consumes cyclable lithium — the dominant capacity-fade mechanism in Li-ion cells cycled at moderate rates.

The model follows the classic square-root-of-cycles SEI growth law (Broussely et al.), with an Arrhenius temperature term and rate/depth-of-discharge scaling:

k(T,C,DoD) = k0 · exp[-Ea/R · (1/T − 1/Tref)] · √C · (DoD/80)^0.7
Q(n)/Q0    = 1 − k·√n         (capacity retention after n cycles)
SEI(n)     ∝ k·√n              (film thickness, illustrative nm scale)

C-rate — faster charge/discharge accelerates both the visual cycling and, mildly, the fade rate (higher current density stresses the SEI).
Temperature — the Arrhenius term (Ea ≈ 30 kJ/mol) makes heat the strongest lever: cycling hot roughly doubles the fade rate every ~15–20 °C.
Depth of discharge — swinging through a wider state-of-charge window strains the electrode lattice more per cycle, so shallower cycling extends life.
The cell is retired at 80% retention — the industry-standard end-of-life threshold for EV and grid-storage packs.

Charging

Li⁺ ion Cathode (oxide) Anode (graphite) SEI film

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Battery Cycle Aging & Capacity Fade Simulator