Eutectic Perturbations Enhance Multivalent-Cation Structural Diffusion in Salt-Concentrated Polymer Electrolytes

Abstract

Cation transport in polymer electrolytes (PEs) is largely limited by insufficient segmental motion. Structural diffusion, often observed in salt-concentrated PEs, is emerging as an appealing transport mode for decoupling the correlation between ionic conductivity and polymer dynamics. However, due to inherently strong ionic association, realizing such a promise for multivalent cations remains challenging. We herein report a eutectic strategy that enhances the structural diffusion dynamics of divalent cations (e.g., Zn²⁺) in salt-concentrated polycationic PEs to approach levels comparable to those of monovalent cations. The strategic introduction of bipolar ligands (solid acetamide), eutectically inserting into the Zn²⁺-anion aggregates without directly plasticizing the polymeric skeleton, gives rise to local coordination distortions that weaken anionic traps on Zn²⁺ mobility. This eutectic perturbation further promotes microphase separation, creating expanded Zn²⁺ long-range percolating pathways independent of polymer backbones, enabling 3 orders of magnitude increase in ionic conductivity (to 2.4 × 10^–5 S cm^–1 at 30 °C) and supporting stable zinc metal cell cycling. Our strategy provides an alternative route toward molecular-scale controls over solid-phase conduction of charge-dense cations in PEs.