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Lithium Salt Diffusion in Diblock Copolymer Electrolyte Using Fourier Transform Infrared Spectroscopy.
Kyoungmin Kim1,2, Daniel T Hallinan1,2
1Chemical and Biomedical Engineering Department, Florida Agricultural and Mechanical University-Florida State University College of Engineering, 2525 Pottsdamer Street, Tallahassee, Florida 32310, United States.
The Journal of Physical Chemistry. B
|February 20, 2020
Summary
This study measured lithium salt diffusion in a diblock copolymer electrolyte using FTIR-ATR. The diffusion coefficient showed weak, nonmonotonic dependence on salt concentration, potentially due to salt dissociation states.
Area of Science:
- Materials Science
- Electrochemistry
- Polymer Science
Background:
- Solid polymer electrolytes are crucial for advanced battery technologies.
- Understanding ion transport in polymer electrolytes is key to improving device performance.
- Lithium bis-trifluoromethylsulfonimide (LiTFSI) is a common lithium salt used in electrolytes.
Purpose of the Study:
- To investigate the diffusion of lithium bis-trifluoromethylsulfonimide (LiTFSI) in a polystyrene-poly(ethylene oxide) diblock copolymer.
- To determine the mutual diffusion coefficients of LiTFSI as a function of salt concentration.
- To explore the relationship between salt dissociation and diffusion behavior.
Main Methods:
- Utilized time-resolved Fourier Transform infrared spectroscopy attenuated total reflectance (FTIR-ATR) to monitor concentration changes.
- Applied the Beer-Lambert law for quantitative analysis of spectral data.
- Created diffusion gradients by contacting polymer electrolyte membranes with varying LiTFSI concentrations.
Main Results:
- Obtained mutual diffusion coefficients for LiTFSI in the diblock copolymer.
- Found that diffusion coefficients were weakly and nonmonotonically dependent on salt concentration.
- Observed spectral indications of multiple salt dissociation states.
Conclusions:
- The study provides a simple and accurate method for measuring diffusion in polymer electrolytes without electric fields.
- The nonmonotonic concentration dependence of diffusion suggests the presence of different salt populations.
- Further investigation into salt dissociation states is warranted to fully explain diffusion behavior.
