Modeling of desolvation and adsorption of ions at electrochemical interfaces for intercalation and conversion reactions in batteries

Abstract

Most of the commercially available Li ion batteries are based on electrochemical intercalation reactions. While there are many studies for bulk properties of these insertion batteries, there is still quit a gap in our theoretical understanding of the processes at the electrolyte-electrode interface. Desolvation and adsorption on electrode surfaces are still open tasks for developing a consistent theory of batteries. A 2-step-model for electrointercalation was proposed by Bruce et al. [1]. First solvated ions have to partially lose their solvation shell before getting adsorbed on the electrode surface. Then the adions reach a site via surface diffusion, where they become incorporated into the electrode material, while releasing the remaining solvent. This so-called adatom model is confirmed for different insertion materials [2-4]. Also charge transfer reactions in conversion materials are most likely preceded by an adsorption step. To include electrosorption with partial desolvation as an essential step, we determine first the surface charge from thermodynamic and electrostatic considerations. This step is then integrated in standard theories of intercalation and implemented in a thermodynamic consistent reaction-transport model for Li-ion batteries [5]. The model produces a reasonable coverage on the electrode surface and couples desolvation with the transport properties of the cell.

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