Role of amphiphilic additives in solvation and diffusion characteristics of zinc ions on anode surfaces in aqueous zinc-ion batteries

초록

A molecular-level understanding of Zn ion behavior near electrode interfaces is critical for optimizing aqueous zinc-ion battery (AZIB) performance. In this study, the influence of oleic acid (OA), a representative amphiphilic additive, on Zn ion solvation structure and mobility is investigated through atomistic simulations. The carboxylic head groups of OA molecules interact directly with Zn ions, perturbing the local solvation shell by altering the orientation of neighboring H2O molecules. While this interaction leads to a partial loss of structural order within the solvation shell, Zn ions near OA head groups exhibit lower diffusivity due to dynamic association with the relatively immobile OA segments. On the other hand, Zn ions that remain outside the direct influence of OA exhibit increased diffusion coefficients. This enhancement is attributed to a reduction in local ion-ion interactions caused by the selective binding of nearby ions to OA, which effectively decreases the density of mobile cations. In addition, OA molecules induce spatial heterogeneity in the electrolyte environment and create structurally distinct zones that facilitate ion transport. These findings highlight the potential of using amphiphilic molecules to selectively engineer interfacial ion behavior. Our results offer molecular-level insights for the rational design of electrolyte additives in AZIBs.

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