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Nanoconfinement effects on the dynamics of an ionic liquid-based electrolyte probed by multinuclear NMR
Andrei Filippov1, Maiia Rudakova1, Victor P Archipov2
1Chemistry of Interfaces, Luleå Tekniska Universitet, Luleå SE-97187, Sweden. andrei.filippov@ltu.se.
Soft Matter
|October 14, 2024
Summary
Measuring ion diffusion in nanoporous materials using Pulsed-Field Gradient (PFG) NMR is challenging. This study used multinuclear NMR to analyze ion dynamics in a battery electrolyte confined within silica glasses, revealing complex diffusion behaviors influenced by pore structure and ion solvation.
Area of Science:
- Materials Science
- Electrochemistry
- Physical Chemistry
Background:
- Pulsed-Field Gradient (PFG) NMR is a key technique for measuring ion diffusivity.
- Enhanced NMR relaxation in nanoporous materials complicates diffusivity measurements.
- Understanding ion dynamics in confined electrolytes is crucial for battery development.
Purpose of the Study:
- To investigate ion dynamics of a fluorine-free battery electrolyte confined in nanoporous silica glasses using multinuclear NMR.
- To elucidate the effects of pore structure and confinement on ion diffusion.
- To explore the temperature-dependent behavior of ion transport and ion solvation.
Main Methods:
- Employed multinuclear (1H, 31P, and 7Li) NMR spectrometry and diffusometry.
- Studied a fluorine-free battery electrolyte ([P4,4,4,4][MEEA] ionic liquid with LiMEEA salt) confined in SiO2 glasses (3.7, 7, and 98 nm pores).
- Analyzed complex diffusion decays considering pore structure, including pore "necks" and "partially isolated volumes".
Main Results:
- Confinement induced NMR resonance line broadening and chemical shift variations.
- Diffusion decays were explained by ion exchange between narrow and large pores in a slow exchange regime.
- Temperature-dependent ion diffusivities deviated from Arrhenius law, and Li+ diffusivity was slower than larger organic ions, indicating Li+ solvation.
Conclusions:
- The study successfully measured ion diffusion coefficients in nanoporous materials using PFG NMR.
- Complex pore structures significantly influence ion dynamics and temperature dependence of diffusion.
- Observed Li+ solvation within the pores provides insights into ion transport mechanisms in confined electrolytes.
