Tailoring Solvation Structure via Soft-Hard Segment Synergy in Gel Polymer Electrolytes Enables Dendrite-Free Sodium Batteries with Ultra-Long Cycling.

Abstract

The development of polymer electrolytes with high ionic conductivity, robust mechanical strength, and excellent interfacial stability remains a critical challenge for high-performance sodium metal batteries (SMBs). Herein, a "chemical-structural dual regulation" strategy introduces complementary soft and hard segments into a gel polymer electrolyte (GPE), enabling concurrent optimization of solvation structure and mechanical properties. Soft segments with strong electron-withdrawing -CF₃ groups form solvent-rich domains that weaken Na⁺-solvent interactions, while amide N-H groups create polymer-rich domains that enhance mechanical strength and anchor anions via hydrogen bonding, promoting sodium salt dissociation. Benefiting from this rational molecular design, GPE-9 delivers an outstanding ionic conductivity of 1.11 mS cm^-1 and a high Na⁺ transference number of 0.74 at room temperature, and supports long-term cycling of Na||Na symmetric cell at 0.2 mA cm^-2 for 7000 h. The Na|GPE-9|Na₃V₂(PO₄)₃ (NVP) cell demonstrates excellent rate durability, sustaining 12 000 and 20 000 cycles at 5C and 10C, respectively, with nearly 100% Coulombic efficiency. Furthermore, a 29-layer pouch cell with NVP cathode and hard carbon (HC) anode delivers a high capacity approaching 1.0 Ah. This study demonstrates that designing polymer segments capable of regulating solvation structure and directing interfacial fluorination offers a promising strategy for high-performance GPEs for Na batteries.