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

Abstract

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.

The electrode tortuosity factor: why the conventional tortuosity factor is not well suited for quantifying transport in porous Li-ion battery electrodes and what to use instead

“…5, R ion can also be determined approximately since the length of the 45°sloped region spans across approximately R ion /3 along the real axis. 19 Likewise, Pouraghajan et al 20 showed different methods to quickly estimate R ion that all provide a reasonable estimate with minor discrepancy as compared to using the fit of Eq. 4.…”

“…Malifarge et al 18 developed a more general analytical expression of the symmetric cell impedance that takes into account an arbitrary electronic resistance of the conductive matrix. More recently, Pouraghajan et al 20 developed a generalized TLM that takes into account additional possible sources of impedance, such as a contact resistance with the current collector, the charge-transfer resistance, and the electronic resistance of the electrode solid phase.…”

“…whereZ Ã ElÀsim is the normalized-simulated impedance given by eSCM from TauFactor;Z Ã El is the normalized-fitting impedance given by Eq. 4, p is a weighing factor 20 . However, it should be noted that the value of τ e can be extracted from just the values ofZ Ã El at ω !…”

“…work of Pouraghajan et al 20 , since for commercial electrodes of typical porosity, the pore network might contain mostly throughpores with only small fraction of dead-end pores.…”

“…A recent comparison of these two methods for commercial battery electrodes was made by Pouraghajan et al 20 , which showed a reasonable agreement between these two approaches in cases where both of them can be implemented. Nevertheless, in many cases 20 , the eSCM seems to be faster and more convenient to implement than the eRDM, which requires a current-collector-free Schematics of experimental setup and the physics underlying the two methods for determining tortuosity factors of porous electrodes: a eRDM 16 , and b eSCM 17,18 . The arrows show different conducting pathways traveled by charged particles(ions/electrons).…”