Synergistic Anion‐Cation Regulation in Composite Quasi‐Solid Polymer Electrolytes Enables Stable Sodium Metal Anodes

Abstract Realizing durable, uniform, and dendrite‐free sodium metal deposition is crucial for preventing premature battery failure caused by internal short circuits, which is primarily governed by ion transport and desolvation kinetics during the electrodeposition process. Herein, a composite quasi‐solid polymer electrolyte (LPQSE) is developed through in situ polymerization of poly(ethylene glycol) diacrylate within a porous membrane constructed by in‐house synthesized α‐LiAlO 2 @γ‐Al 2 O 3 (LAO) nanosheets and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVHF). The LAO nanosheets effectively immobilize PF 6 − anions via Lewis acidic sites, while the PEGDA carbonyl groups coordinate Na⁺ cations. This dual‐interaction mechanism simultaneously reduces ion‐pair formation and promotes loose solvation structures, thereby accelerating desolvation kinetics and significantly increasing sodium nucleation density. Consequently, homogeneous sodium deposition with fundamentally suppressed dendrite nucleation is realized. As a result, solid‐state Na||Na symmetric cells demonstrate exceptional cycling stability, and Na 3 V 2 (PO 4 ) 3 (NVP)||Na batteries employing the ∼16‐µm‐thick LPQSE exhibit long‐term cycling stability. Notably, the NVP||Na battery exhibits a high specific discharge capacity of 69.5 mAh g −1 at 10 C and retains 88.7% capacity retention over 1000 cycles at 1C. This work establishes an innovative electrolyte design strategy that strategically coordinates anion immobilization and cation solvation to regulate deposition behavior for achieving dendrite‐free sodium anodes.