Measurement of Tortuosity and Porosity of Porous Battery Electrodes

DuBeshter, Tyler; Sinha, Puneet K.; Sakars, A.; Fly, Gerald W.; Jorné, Jacob

doi:10.1149/2.073404jes

Cited by 65 publications

(65 citation statements)

References 7 publications

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“…The mismatch between the Bruggeman equation for spherical particles (α = 0.5, dashed blue line in Figure 21) and the MacMullin numbers shown in Figure 21 (compare also Figure 15) is ∼1.5 to ∼3-fold, particularly at low porosities, an observation which has been made before. 18,21,29 For example, higher ionic resistances than suggested by the Bruggemann equation are reported by Thorat et al 18 (brown line in Figure 21), who use Eq. 7 to fit tortuosities obtained from fits of polarization-interrupt experiments.…”

Section: Resultsmentioning

confidence: 89%

Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy

Landesfeind

Hattendorff

Ehrl

et al. 2016

J. Electrochem. Soc.

514

596

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Lithium ion battery performance at high charge/discharge rates is largely determined by the ionic resistivity of an electrode and separator which are filled with electrolyte. Key to understand and to model ohmic losses in porous battery components is porosity as well as tortuosity. In the first part, we use impedance spectroscopy measurements in a new experimental setup to obtain the tortuosities and MacMullin numbers of some commonly used separators, demonstrating experimental errors of <8%. In the second part, we present impedance measurements of electrodes in symmetric cells using a blocking electrode configuration, which is obtained by using a non-intercalating electrolyte. The effective ionic resistivity of the electrode can be fit with a transmission-line model, allowing us to quantify the porosity dependent MacMullin numbers and tortuosities of electrodes with different active materials and different conductive carbon content. Best agreement between the transmission-line model and the impedance data is found when constant-phase elements rather than simple capacitors are used. Motivation.-Advanced battery models are a valuable tool for evaluating the performance, safety, and life-time of lithium ion batteries, since they can provide insight into the kinetics and the transport characteristics of batteries, which are not or only partially accessible by experiments. To obtain quantitative and meaningful numerical results, the choice of appropriate physical models and boundary conditions with the corresponding, accurately determined, kinetic and transport parameters are key issues. For numerical simulations of battery systems, the ion-transport model for concentrated electrolyte solutions introduced by Newman et al.1 is frequently used. Since the microscopic geometry of actually used porous electrodes and separators are largely unknown, a homogenization approach is applied for the macroscopic description of porous media. In this case, the influence of the microstructure on the macroscopic behavior is modeled by additional geometric parameters such as the porosity ε and the tortuosity τ. The porosity ε is a well-defined property of a porous medium, which can be determined easily. In contrast, the effective tortuosity of separators and particularly of electrodes are more difficult to quantify, and, to further complicate the matter, many different definitions for the tortuosity τ are used in the literature. Thus, the different tortuosity definitions will be presented prior to reviewing the literature concerned with determining the tortuosity or the effective ionic conductivity of porous battery separators and electrodes.

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Section: Resultsmentioning

confidence: 89%

Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy

Landesfeind

Hattendorff

Ehrl

et al. 2016

J. Electrochem. Soc.

514

596

View full text Add to dashboard Cite

show abstract

“…The optimum seems to be reached by a certain porosity gradient (Du et al, 2017;Liu et al, 2017). For measuring the porosity numerous methods are available, both bulk methods (DuBeshter et al, 2014;Li et al, 2014) as well as methods with a submicron resolution, such as tomography (Ge et al, 2014;Harks et al, 2015) and FIB-SEM (Hutzenlaub et al, 2014;. The advantage of using NDP is the combination of both length scales, as this measurement represents an average over 1.1 cm 2 electrode, the bulk average porosity is determined with a sub-micron resolution along an axis of interest.…”

Section: Resultsmentioning

confidence: 99%

Operando Neutron Depth Profiling to Determine the Spatial Distribution of Li in Li-ion Batteries

Verhallen

Wagemaker

2018

Front. Energy Res.

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Neutron Depth Profiling (NDP) allows determination of the spatial distribution of specific isotopes, via neutron capture reactions. In a capture reaction charged particles with fixed kinetic energy are formed, where their energy loss through the material of interest can be used to provide the depth of the original isotope. As lithium-6 has a relatively large probability for such a capture reaction, it can be used by battery scientists to study the lithium concentration in the electrodes even during battery operation. The selective measurement of the 6 Li isotope makes it a direct and sensitive technique, whereas the penetrative character of the neutrons allows practical battery pouch cells to be studied. Using NDP lithium diffusion and reaction rates can be studied operando as a function of depth, opening a large range of opportunities including the study of alloying reactions, metal plating, and (de) intercalation in insertion hosts. In the study of high rate cycling of intercalation materials the relatively low Li density challenges counting statistics while the limited change in electrode density due to the Li-ion insertion and extraction allows straightforward determination of the Li density as a function of electrode depth. If an electrode can be (dis)charged reversibly, data can be acquired and accumulated over multiple cycles to increase the time resolution. For Li metal plating and alloying reactions, the large lithium density allows good time resolution, however the large change of the electrode composition and density makes extracting the Li-density as a function of depth more challenging. Here an effective method is presented, using calibration measurements of the individual components, based on which the ratio of the components as a function of depth can be determined as well as the total Li-density. The same principles can be applied to insertion host materials, where the differences in density due to electrolyte infiltration yield the electrode porosity as a function of depth. This is of particular importance for battery electrodes where porosity has a direct influence on the energy density and charge transport.

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“…10 For measuring or calculating tortuosity, there are various methods in the field of electrochemistry. 11 These include: AC impedance-based techniques, [12][13][14][15] a method based on gas diffusion measurement, 16 and 3D visualization techniques, including X-ray tomography and focused-ion beam scanning electron microscope tomography (FIB/SEM), coupled with computational models. [17][18][19][20][21][22] One drawback to the gas diffusion measurement is that the measurement of in-plane diffusivity may not match through-plane diffusivity if the electrodes are not isotropic-in contrast, the present work is focused on throughplane transport measurements, which are more relevant to battery performance.…”

mentioning

confidence: 99%

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

Pouraghajan

Knight

Wray

et al. 2018

J. Electrochem. Soc.

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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.

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Measurement of Tortuosity and Porosity of Porous Battery Electrodes

Cited by 65 publications

References 7 publications

Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy

Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy

Operando Neutron Depth Profiling to Determine the Spatial Distribution of Li in Li-ion Batteries

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

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