Quantifying Tortuosity of Porous Li-Ion Battery Electrodes: Comparing Polarization-Interrupt and Blocking-Electrolyte Methods

Ionic mass transport including electrolyte diffusivity and conductivity depends on the geometric tortuosity of the electrode. This paper compares two experimental methods that determine tortuosity based on diffusivity or conductivity. The polarization-interrupt method previously developed by our group determines tortuosity in terms of effective diffusivity. The blocking-electrolyte method proposed by Gasteiger and coworkers determines tortuosity in terms of effective ionic conductivity and is analyzed using a generalized transmission-line model to account for multiple sources of impedance. Tortuosity of several commercial-quality electrodes was measured using both methods, producing reasonable agreement between the two methods in most cases. The advantages and disadvantages of each method and variables that can affect the accuracy of the measurement, such as electrode wetting and model fitting, are discussed. For particular electrodes, one method may be advantageous or more conveniently applied than the other.