Enhancing Salt Diffusivity of Battery Electrolytes: Insights from Dynamic Ion Correlation Analysis

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Ion transport in electrolytes is critical for Li-ion battery performance.
• Concentration polarization negatively impacts battery rate capability.
• Understanding ion correlations is key to optimizing electrolyte properties.

Purpose of the Study:

• To investigate the effect of glyme co-solvents on electrolyte properties and Li-ion battery performance.
• To elucidate the relationship between ion correlations and salt diffusivity.
• To identify strategies for mitigating concentration polarization and enhancing rate capability.

Main Methods:

• Dynamic ion correlation analysis was employed to study ion behavior in electrolytes.
• Salt diffusivity (D_salt) was measured in carbonate-based electrolytes with varying glyme co-solvents.
• Performance of LiCoO₂ symmetric cells was evaluated at high charge/discharge rates (4C).

Main Results:

• Monoglyme co-solvent increased D_salt by 30% and improved cell rate capability by 70% at 4C.
• Enhanced D_salt in monoglyme was attributed to increased cation-anion self-correlations, reduced viscosity, and smaller solvation shells.
• Diglyme co-solvent decreased D_salt and worsened rate capability due to increased cation-cation anti-correlations, despite reduced viscosity.

Conclusions:

• Microscopic ion correlations significantly influence macroscopic transport properties in battery electrolytes.
• Monoglyme is a promising co-solvent for enhancing Li-ion battery performance by optimizing ion dynamics.
• Careful selection of co-solvents is crucial for balancing ion correlations and achieving high battery performance.