In the following chart, the instantaneous voltage change is due to cell Cell internal resistance $R_0$, and the exponentially slowing diffusion voltage change is due to diffusion processes:

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Diffusion is also the cause of the Cell overpotential after periods of charge or discharge.

Randles circuit

Randles model follows (imperfectly) the physics of the cell.

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$Z_W$ is a Warburg impedance, it models slow diffusion processes (diffusion voltage).

Warburg impedance is impossible to write down in differential equations, therefore, it's replaced by series of parallel resistor-capacitor circuits.

The RC time constant of these circuits increases with temperature:

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These time constants also depend on the State-of-charge.

See the Quick way to estimate diffusion resistance and capacitance in equivalent-circuit model of a cell.

Related:

References

‣ 2.1.4, 2.3.8