NMR self diffusion and relaxation time measurements for poly (vinylidene fluoride) (PVDF) based polymer gel electrolytes containing LiBF4 and propylene carbonate

- Temperature and salt concentration study of PVDF/PC/LiBF4 polymer gel electrolytes.
- Lithium ions were found to be located in two distinct phases in the gel structure.
- NMR PFG diffusion and T2 relaxation measurements both confirm lithium ion location in two mobile liquid-like phases.
- The liquid-like phases are attributed to a liquid electrolyte and solvated amorphous PVDF phase with distinct viscosities.
- Fluorinated BF4 anion gave less of an indication of presence in both phases.

Polymer gel electrolytes (PGEs) have been prepared using lithium tetrafluoroborate (LiBF4), propylene carbonate (PC) and poly (vinylidene fluoride) (PVDF). Self diffusion coefficients have been measured using pulse field gradient nuclear magnetic resonance (PFG-NMR) for the lithium cation, BF4 anion and solvent molecules using 7Li, 19F and 1H nuclei, respectively. It was found that lithium ion diffusion was slow compared to the much larger fluorinated BF4 anion, which is attributed to a large solvation shell around the lithium ions. The 7Li and 1H diffusion measurements also exhibited two unique environments for the diffusive species. The measurement of NMR transverse relaxation times has confirmed the presence of lithium ions in multiple phases as shown by the diffusion measurements.

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