Electrostatic-Field-Driven Synergistic Regulation of Molecular Conformation and Mesostructure Enables Stable Na+ Transport in 12 μm PVDF-HFP-Based Electrolytes

Solid-state sodium metal batteries (SSMBs) are promising for next-generation energy storage due to abundance sodium resources and inherent safety. However, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based solid polymer electrolytes suffer from high crystallinity, low β-phase content, and limited tunability, hindered ionic transport and mechanical performance in ultrathin membranes. Herein, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) is introduced into PVDF-HFP/sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) matrix to fabricate a 12 μm ultrathin electrolyte (2Na-PH). EDTA-2Na conquers NaTFSI crystallization, and FT-IR reveals β-phase fraction increases from 12.1% to 76.9%. Density functional theory (DFT) and energy decomposition analysis (EDA) demonstrate dominant Na+-F electrostatic coupling drives PVDF-HFP conformational transition from TGTG’ to TTTT. A sponge-like porous architecture forms, constructing continuous Na+ transport pathways and enlarging free volume. 2Na-PH revelations a 5.34 V wide electrochemical stability window, 0.15 eV activation energy, and 22.67 MPa tensile strength. Na||Na symmetric cells tolerate a current density of 0.53 mA cm-2 with low nucleation overpotential and enable stable cycling over 1800 h, enabled by the formation a thin and dense NaF-based solid electrolyte interphase that effectively defeats dendrite growth. Na3V2(PO4)3-based full cells deliver 111.07 mA h g-1 initial capacity and 80.91%; NaNi1/3Fe1/3Mn1/3O2-based full cells also also demonstrate sound cycling stability. This work demonstrates molecular-level electrostatic regulation for high-performance PVDF-HFP-based electrolytes for advanced SSMBs.