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Improving the total ionic conductivity (σ) of solid polymer electrolytes (SPEs) is critical to the development of solid–state sodium (Na) batteries. In this work, we investigate the effect of two–dimensional (2D), dual–Lewis hexagonal boron nitride (h–BN) filler on polymer structure and ion transport properties of P(EO)24:Na+ and P(EO)4:Na+ mixtures of poly (ethylene oxide) (PEO)–bis (fluorosulfonylimide) (NaFSI). Below the critical percolation concentration threshold for the h–BN flakes, x–ray diffraction (XRD) and differential scanning calorimetry (DSC) studies show that an increase in h–BN concentration initially induces an increase in PEO crystallinity followed by a decrease due to competing effects between heterogeneous nucleation of PEO lamellae and its spherulitic confinement, respectively. Raman spectroscopy reveals that h–BN improves NaFSI dissociation in the semi–dilute SPEs which is supported by density functional theory (DFT) calculations. Our calculations suggest that PEO can almost fully dissociate an NaFSI molecule with a coordination number of 6. We propose an h–BN–‘assisted’ mechanism to explain this observation, wherein h–BN aids PEO in better matching the dissociation energy of the NaFSI salt by virtue of its dual–Lewis surface chemistry. A corresponding 4x increase in σ is observed for the P(EO)24:Na+ SPEs using electrochemical impedance spectroscopy (EIS). The P(EO)4:Na+ SPEs do not show this increase likely due to a significantly different local solvation environment wherein contact ion pairs (CIPs) and aggregates (AGGs) dominate. Our findings highlight the role of filler chemistry in the design and development of composite solid polymer electrolytes for Na batteries.
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This content will become publicly available on November 4, 2025
Effect of Confinement on the Structure–Conductivity Relationship in PEO/LiTFSI Electrolytes in 3D Microporous Scaffolds
Because 3D batteries comprise solid polymer electrolytes (SPE) confined to high surface area porous scaffolds, the interplay between polymer confinement and interfacial interactions on total ionic conductivity must be understood. This paper investigates contributions to the structure-conductivity relationship in poly(ethylene oxide) (PEO)–lithium bis(trifluorosulfonylimide) (LiTFSI) complexes confined to microporous nickel scaffolds. For bulk and confined conditions, PEO crystallinity decreases as the salt concentration (Li+:EO (r) = 0.0.125, 0.0167, 0.025, 0.05) increases. For pure PEO and all r values except 0.05, PEO crystallinity under confinement is lower than in the bulk, whereas glass transition temperature remains statistically invariant. At 298 K (semicrystalline), total ionic conductivity under confinement is higher than in the bulk at r = 0.0167, but remains invariant at r = 0.05; however, at 350 K (amorphous), total ionic conductivity is higher than in the bulk for both salt concentrations. Time–of–flight secondary ion mass spectrometry indicates selective migration of ions towards the polymer–scaffold interface. In summary, for the 3D structure studied, polymer crystallinity, interfacial segregation, and tortuosity play an important role in determining total ionic conductivity and, ultimately, the emergence of 3D SPEs as energy storage materials.
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- PAR ID:
- 10554965
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- ACS Macro Letters
- Issue:
- 13
- ISSN:
- 2161-1653
- Page Range / eLocation ID:
- 1577 to 1583
- Subject(s) / Keyword(s):
- microporous, polymer composite, structure-conductivity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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