Polyanion‐Induced Single Na‐Ion Polymer Electrolytes for Ultra‐Stable Sodium Metal Batteries

Abstract Sodium is an abundant resource standing as one of the most promising alternatives to lithium for the next generation of battery anode materials. Solid polymer electrolytes (SPEs) present a prospective choice for realizing sodium‐metal batteries. SPEs exhibit excellent interface compatibility, but the crucial bottleneck is how to achieve high ionic conductivity and Na ⁺ transference number simultaneously. Herein, using a one‐step ion exchange method to synthesize 2‐Acrylamido‐2‐methylpropanesulfonic acid sodium salt (AMPSNa) with low dissociation energy. Subsequently, employing thermally induced free radical polymerization facilitated the bonding of AMPSNa into polymer's backbone to construct a polyanion‐induced single Na‐ion polymer electrolyte, which can effectively improve the cation freedom, realize low potential barrier sodium‐ion migration, thereby constructing a stable electrolyte/Na anode interface. SPE exhibits high ionic conductivity of 4.3 × 10 ⁻⁴ S cm ⁻¹ at room temperature and Na ⁺ transference number of 0.82. The AMPSNa‐rich vesicular surface of the SPE anchors to the sodium surface, providing a 3D Na ⁺ transport channel and inducing the formation of a F, O, and N enriched solid‐electrolyte interphase to inhibit dendrite growth. The highly protective interface also leads to outstanding rate performance in Na||Na ₃ V ₂ (PO ₄ ) ₃ cell, proficiently sustaining over 1300 cycles at 4 C with a high capacity retention of 94.7%.