Molecular Tailoring of Succinonitrile Reshapes Na⁺ Solvation and Interfacial Chemistry in High-Voltage Solid-State Polymer Electrolytes for Sodium Metal Batteries

Here, molecular tailoring of succinonitrile yields a novel plasticizer (SGa) featuring retained amide groups and a stable gauche conformation. This design suppresses the plasticizer self-aggregation within the poly(ethylene oxide) matrix, enhances polymer chain interactions, and optimizes Na⁺ solvation structures.

Consequently, the resultant SPE achieves a high ionic conductivity of 0.352 mS cm^–1 and a Na⁺ transference number of 0.71. Molecular dynamics simulations reveal that SGa weakens strong Na⁺ coordination while anchoring TFSI^– anions, establishing a Na⁺-dominated fast conduction network. Crucially, the modified SPE induces a uniform, robust solid electrolyte interphase enriched in inorganic Na₃N, significantly stabilizing the Na anode.