Electrostatic-field-driven synergistic regulation of molecular conformation and mesostructure enables stable Na plus transport in 12 μm PVDF-HFP-based electrolytes

초록

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 /3-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 mu m ultrathin electrolyte (2Na-PH). EDTA-2Na conquers NaTFSI crystallization, and FT-IR reveals /3-phase fraction increases from 12.1% to 76.9%. Density functional theory (DFT) combined with energy decomposition analysis (EDA) indicates that Na+-F electrostatic coupling serves as the dominant driving force for the PVDF-HFP conformational transition from TGTG' to TTTT, while EDTA-2Na contributes synergistically to this structural evolution. 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 demonstrate sound cycling stability. This work demonstrates molecular-level electrostatic regulation for high-performance PVDF-HFP-based electrolytes for advanced SSMBs.

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