Intercalation As a Two-Step Process: Modeling of Adsorption at Electrochemical Interfaces in Batteries
Bruce et al.  proposed a 2-step-model for electrointercalation. Figure 1 shows this so called adatom model, where the fully solvated Li-ion in bulk electrolyte partially loses its solvation shell before getting adsorbed on the surface. Then it diffuses to a site, at which it can intercalate into the electrode. After this the adion loses the remaining solvent and gets incorporated in the lattice of the electrode. This proposed mechanism of a two-step-electrointercalation (desolvation/adsorption(=adion formation) and insertion) is confirmed for different insertion materials [2-4].
Considering some conversion materials like for lithium-sulfur-batteries, where Li-ions have to enter carbon spheres before reacting with sulfur, it's equally reasonable to assume first an adsorption step.
To include electrosorption, that is adsorption with partial desolvation, as an important step for intercalation and conversion reactions in batteries at the interface of a concentrated electrolyte and some active material, we derive equations for surface charges from thermodynamic and electrostatic considerations.
These derived equations are used as an intermediate step to couple the transport in the electrolyte and the solid phase with desolvation within a thermodynamic consistent reaction-transport model for Li-ion batteries . Our developed model produces a reasonable coverage on the surface of the electrode while maintaining the transport properties of the cell.
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Schematic diagram of the lithium intercalation reaction at the electrolyte – electrode interface