Accurate Characterization of Ion Transport Properties in Binary Symmetric Electrolytes Using In Situ NMR Imaging and...

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Accurate ionic transport parameters are vital for predicting Li-ion battery performance.
• Existing methods for determining diffusion coefficients and transference numbers have limitations, especially in concentrated electrolytes.

Purpose of the Study:

• To develop and validate a novel method combining NMR imaging (MRI) and inverse modeling (IM) for precise determination of ionic diffusion coefficients and transference numbers.
• To assess the critical impact of these parameters on the reliability of porous electrode models.
• To investigate the concentration dependence of these transport properties in electrolyte solutions.

Main Methods:

• Utilized in situ (19)F MRI to obtain concentration profiles of ionic species.
• Employed inverse modeling based on an extended Planck-Nernst model to derive material properties.
• Applied variational optimization and Monte Carlo analysis for reconstruction and uncertainty quantification.

Main Results:

• The MRI+IM method successfully determined concentration-dependent diffusion coefficients and transference numbers.
• Diffusion coefficients obtained via MRI+IM were consistent with pulsed field gradient NMR (PFG-NMR) results within 95% confidence bounds.
• The Li(+) transference number's concentration dependence derived from MRI+IM aligned with electrochemical methods and theoretical models for concentrated solutions, unlike PFG-NMR data.

Conclusions:

• The combined MRI+IM approach offers a robust and accurate method for characterizing ionic transport in Li-ion battery electrolytes.
• This technique provides crucial, concentration-dependent transport data essential for advancing the predictive accuracy of battery models.
• The findings highlight the limitations of PFG-NMR in capturing transport number dependencies in concentrated electrolyte systems.