Analysis of diffusion in a solid polymer electrolyte in the context of a phase-separated system

Area of Science:

• Electrochemistry
• Polymer Electrolytes
• Materials Science

Background:

• High-molecular-weight poly(ethylene oxide) [PEO] is a key polymer electrolyte material.
• Understanding ion transport in PEO-based electrolytes is crucial for battery technology.
• Lithium bis(trifluoromethanesulfonyl)imide [LiTFSI] is a common salt used in polymer electrolytes.

Purpose of the Study:

• To measure salt and ionic diffusion coefficients of LiTFSI in PEO.
• To analyze the interrelationship of diffusion coefficients with electrochemical theory.
• To propose and validate a biphasic model for the conducting amorphous state.

Main Methods:

• Measurement of salt and ionic diffusion coefficients over a broad concentration range.
• Application of the Bruggeman-Landauer theory for data analysis.
• Comparison of experimental data with theoretical models.

Main Results:

• Diffusion coefficients of LiTFSI in PEO were measured.
• A biphasic model, comprising a stoichiometric P(EO)6LiTFSI phase and a disordered phase, was proposed.
• Excellent agreement was found between experimental data and the biphasic model using the Bruggeman-Landauer theory.

Conclusions:

• The proposed biphasic model effectively describes the conducting amorphous state in PEO-LiTFSI electrolytes.
• The study validates the applicability of electrochemical theory and the Bruggeman-Landauer theory to this system.
• Potential limitations of the analysis were identified and discussed.