An Analytical Method to Determine Tortuosity in Rechargeable Battery Electrodes

Vijayaraghavan, Bharath Kumar Tirupakuzhi; Ely, David R.; Chiang, Yet‐Ming; Garcı́a-Garcı́a, R.; Garcı́a, R. Edwin

doi:10.1149/2.jes113224

Cited by 121 publications

(111 citation statements)

References 16 publications

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“…Inhomogeneous distribution thereof will adversely affect both electron transfer from the current collector through the electrode and charge transfer at the active particle -electrolyte interfacial area. 8,19,49,50 Electrode processing plays an important role in the electrode microstructure formation. Salient results from the aforementioned experiments are presented below to elucidate the role of evaporation leading to the underlying constituent phase rearrangement and resulting influence on electrode performance.…”

Section: Results and Discussion: Experimentsmentioning

confidence: 99%

Mechanistic Understanding of the Role of Evaporation in Electrode Processing

Stein

Mistry

Mukherjee

2017

J. Electrochem. Soc.

117

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Electrode processing based on the state-of-the-art materials represents a scientific opportunity toward a cost-effective measure for improving the lithium-ion battery performance. In this regard, perhaps the most important is the drying step in a typical non-aqueous based slurry processing which can profoundly impact the electrode microstructure and hence performance. Solvent evaporation during drying plays a critical role in the redistribution of the particulate phases consisting of active particle, conductive additive and binder. In this work, we attempt to provide a mechanistic understanding of the role of solvent evaporation on the electrode characteristics and performance via a combined experimental and theoretical analysis. This study elucidates that a non-uniform distribution of the constituent phases, especially the relatively mobile conductive additive and binder, can develop which depends on the solvent evaporation, particle diffusion and sedimentation attributes. Experimental results and theoretical analysis reveal the impact of evaporation rate on the conductive additive and binder distribution in the electrode microstructure and resulting electrochemical performance. Our analysis has shown that a slower two-stage drying, as opposed to a high-rate single-stage drying, allows for a favorable distribution of binder and conductive additive, thus reducing internal cell resistance and improving electrochemical performance. Increasing concerns about depleting fossil fuel reserves, energy security, and climate change have given rise to interest in the adoption of renewable energy in place of traditional, petroleum-based fuels. The implementation and usage of renewable energies have been limited due to lack of efficient storage and transportation infrastructure. Recent improvements in the energy density and durability of lithiumion batteries (LIBs) have made them an increasingly attractive means of energy storage. [1][2][3][4] Further improvements in lithium-ion technology would increase the viability of widespread adoption of electric vehicles and renewable energy integration into the electric grid. For example, improvements in the capacity of LIBs would not only improve the effective range of electric vehicles, 5,6 but also improve their cycle life by reducing the depth of discharge, which in turn increases the viability of LIBs for use in grid energy storage applications. 7The performance of Li-ion batteries depends on the electrode materials, the choice of electrolyte, and the cell architecture.4,8 A typical LIB positive electrode (cathode) is composed of a combination of Li-containing active material, conductive additive, polymeric binder, and pore space that is filled with an electrolyte. Typically, these are created by casting out and drying a thin film of slurry containing these multi-phase components. 19 but little attention is paid to the physical understanding of the electrode processing. The importance of this electrode preparation step cannot be overemphasized. In addition to determining the cel...

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Section: Results and Discussion: Experimentsmentioning

confidence: 99%

Mechanistic Understanding of the Role of Evaporation in Electrode Processing

Stein

Mistry

Mukherjee

2017

J. Electrochem. Soc.

117

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“…Besides COMSOL Multiphysics, 142,143 researchers have calculated tortuosity by using programs such as Cast3M 144 or custom made models, which focus on a specific electrochemical device, such as Batts3d. 33,55,145 In addition to simulating mass and charge transport, the tortuosity is also computable by exploiting the mathematical similarity between Fourier's law of heat conduction and Fick's law of diffusion shown in Eq. (18) and Eq.…”

Section: Mesh Based Calculation Methodsmentioning

confidence: 99%

“…33,55,103,104 The purpose for this process is to directly evaluate the effect of specific microstructural variations such as porosity, pore size distribution, shape or packing orientation of particles on mass transport.…”

Section: μMmentioning

confidence: 99%

Tortuosity in electrochemical devices: a review of calculation approaches

Tjaden

Brett

Shearing

2016

International Materials Reviews

192

188

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The tortuosity of a structure plays a vital role in the transport of mass and charge in electrochemical devices. Concentration polarisation losses at high current densities are caused by mass transport limitations and are thus a function of microstructural characteristics. As tortuosity is notoriously difficult to ascertain, a wide and diverse range of methods has been developed to extract the tortuosity of a structure. These methods differ significantly in terms of calculation approach and data preparation techniques. Here, we review tortuosity calculation procedures applied in the field of electrochemical devices to better understand the resulting values presented in the literature. Visible differences between calculation methods are observed, especially when using porosity-tortuosity relationships and when comparing geometric and flux based tortuosity calculation approaches.

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“…Furthermore, we assume that the tortuosity of the electrolyte in the LCO-gel ORP composite has the same dependence on electrolyte volume fraction as has been found in other composite electrodes. 13 These assumptions need experimental confirmation. Ohm-m 2 0.01 * Density assumed for dry polymer.…”

Section: Mathematical Modelmentioning

confidence: 99%

Design of Composite Electrodes with Anion-Absorbing Active Materials

Thomas‐Alyea

Aryanpour

2016

J. Electrochem. Soc.

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Organic radical polymers (ORP) and conjugated polymers provide exceptional rate capability as cathode materials for lithium-ion batteries, albeit low volumetric energy density. To optimize overall power and energy density, we consider a composite of ORP with oxide cathode. Upon charge (oxidation), ORP absorb anions from the electrolyte, which causes the salt content in the cell to decrease during charge. Even if the ORP is only 10 volume% of the cathode, the cell's salt content will decrease by >0.6 M in practical cell designs. Furthermore, the conductivity of typical electrolytes varies strongly with concentration. We use electrochemical modeling of a composite positive electrode containing both lithium-releasing and anion-absorbing active materials to explore the tradeoffs and design implications among salt concentration, porosity, and volume fraction of ORP. Organic-radical polymers (ORP) have demonstrated exceptionally high rate capability for lithium batteries, accepting over 80% of capacity at charge rates exceeding 1000 C.1,2 The high rate capability is achieved because the polymers form a gel with liquid electrolytes, which means they have high interfacial area with the electrolyte and polymer-phase transport lengths on the order of tens of nanometers. Diffusion therefore occurs predominantly in the liquid electrolyte, whose diffusivity is several orders of magnitude higher than the solidphase diffusivity which limits the capability of conventional oxide cathode materials.Many important applications, such as electric vehicles and portable power, highly value volumetric energy density and fast charge capability. While ORPs have been discovered with good gravimetric capacity (up to 150 mAh/g), they suffer from low density (∼1 g/cm 3 ). In contrast, oxide cathodes have high density (4.6 to 5.0 g/cm 3 ), but charging and discharging rates are limited by diffusion resistance. Therefore we consider a composite electrode comprised of ORP with an oxide cathode, e.g. LiCoO 2 (LCO). The goal of the composite is to combine the high energy density of LCO with the high rate capability of ORP to maximize the overall volumetric and gravimetric power and energy density. 4,5The reaction mechanism of a prototypical ORP, 2,2,6,6-tetramethylpiperidin-1-oxyl (PTMA), is shown in Figure 1. During charge, the nitroxide radical is oxidized and the charge is balanced by absorption of an anion, e.g. PF 6− , from the electrolyte. In contrast, traditional inorganic cathode materials release lithium cations into the electrolyte during charge. All known negative electrode materials for lithium-ion batteries absorb lithium cations during charge. If a lithium-absorbing cathode is paired with a lithium-releasing anode, then there is no net change in the salt content of the cell (although there will be gradients in salt composition as lithium ions are transported from the anode to the cathode). However, the salt content will decrease during charge of a cell with cation-absorbing negative electrode and anion-absorbing positive electrode. T...

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An Analytical Method to Determine Tortuosity in Rechargeable Battery Electrodes

Cited by 121 publications

References 16 publications

Mechanistic Understanding of the Role of Evaporation in Electrode Processing

Mechanistic Understanding of the Role of Evaporation in Electrode Processing

Tortuosity in electrochemical devices: a review of calculation approaches

Design of Composite Electrodes with Anion-Absorbing Active Materials

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