Ideal Diffusion Research Articles

Development of portable gas sensing system for measuring gas emission concentration and diffusivity using commercial manometric sensors in gas exposed polymers: Application to pure gases, H2, He, N2, O2 and Ar

Low-cost gas sensing system to measure the emission concentration and diffusion coefficient of the gas emitted from specimens, which were exposed by gas under high pressure, was developed using the commercial manometric sensors. The gas emitted from two polymer specimens [low density polyethylene (LDPE) and nitrile butadiene rubber (NBR)] during desorption produced a measurable increase in pressure; this pressure was recorded by a portable data logger in the specimen container chamber. Thus, the molar concentration and diffusivity of the released gas were calculated via the ideal gas equation and diffusion analysis program. As results, gas sensor immediately responded without any chemical interaction and emitted gas weight per specimen weight up to 1400×10−6 with a controllable sensitivity/resolution. The performance test confirmed that our developed sensing technique had good reliability, adjustable measurable range and independence to fluctuations in temperature and pressure. Consequently, the developed simple sensing system was successfully used for the simultaneous real-time detection and transport characterizations for pure gases (H2, He, N2, O2 and Ar).

Diffusion-induced stress amplification in phase-transition materials for electrodes of lithium-ion batteries

This work sheds the light on the stress amplification in active material particles of electrodes caused by the localized lithium concentration inhomogeneity due to phase transitions. This is a significant issue usually neglected in the literature, as generally the ideal Fickian diffusion model is used to describe the lithium diffusion, which particularly fails when dealing with phase change materials, resulting in the underestimation of the stress. In turn, this results in the underestimation of the fracture behavior of the electrode and the battery degradation, ultimately.To overcome these limitations, this work proposes a mechanical-transport model where the lithium transport is modeled according to the non-ideal solution theory with an equivalent diffusion coefficient depending on the potential of the host material vs Li/Li+. The results show that the proposed model correctly describes the concentration distribution within the particle of phase-change materials (graphite is chosen as a case study), in agreement with the existent experimental measurements. The differences with respect to the traditional Fickian diffusion model is substantial as the stress is up to 85% higher with the proposed model and the concentration distribution can capture the inhomogeneity caused by phase transitions.

Possibility of defective monolayer graphene as potential anode material of metal-ion batteries

The necessitates exploration in the field of rechargeable metal ion batteries demands safe, cost-efficient, and face significant challenges in their development. Defect engineering may be helpful for the ion storage and diffusion in the battery anodes. In this paper, we use density functional theory to investigate the adsorption and diffusion behavior of Li, Mg, and Al atom on single vacancy (SV), Stone-Wales vacancy (SWV), double vacancy (DV) and quadruple vacancy (QV) defective monolayer graphene. It is evident that metal exhibits the strongest adsorption strengthen at the defect center. The DV and QV defective graphene shows the ideal diffusion energy barrier for three metals. Importantly, the QV structure exhibit maximum storage capacities of the 775 mAh/g for Li, 911 mAh/g for Mg, and 1543.4 mAh/g for Al respectively. Additionally, their open-circuit voltages are all in a very safe range. This study can support a strong basis for the experimental research for metal-ion battery anodes.

Influence of physical interactions on spatiotemporal patterns.

Spatiotemporal patterns are often modeled using reaction-diffusion equations, which combine complex reactions between constituents with ideal diffusive motion. Such descriptions neglect physical interactions between constituents, which might affect resulting patterns. To overcome this, we study how physical interactions affect cyclic dominant reactions, like the seminal rock-paper-scissors game, which exhibits spiral waves for ideal diffusion. Generalizing diffusion to incorporate physical interactions, we find that weak interactions change the length- and time scales of spiral waves, consistent with a mapping to the complex Ginzburg-Landau equation. In contrast, strong repulsive interactions typically generate oscillating lattices, and strong attraction leads to an interplay of phase separation and chemical oscillations, like droplets co-locating with cores of spiral waves. Our work suggests that physical interactions are relevant for forming spatiotemporal patterns in nature, and it might shed light on how biodiversity is maintained in ecological settings.

CFD simulation of a vortex-controlled diffuser for a jet engine burner

A computational flow analysis of an ideal vortex-controlled diffuser (VCD) was carried out. The simulation model used is the compressible Reynolds averaged Navier-Stokes equations(RANS), with the application of the RNG based k-ε turbulence model. The effects of important parameters like static pressure recovery, bleed fraction, position of bleed slot, have been studied and comparisons were made with respect to VCD without the bleed configuration and the following features were revealed: radial profiles of velocity at the inlet, mid-planes and exit planes, including diffuser effectiveness (i.e. static pressure recovery), diffuser efficiency, reattachment length and diffuser total pressure loss. Results obtained by applying the RNG turbulence model show an instantaneous improvement in the diffuser efficiency that happens at reasonably minimal suction rates. From the calculations, it has been verified and shown in the analysis that the effect of the bleed positioning offers advantages in relation to where it is located.

Concepts for estimating all types of diffusion coefficients of NiCoFeCr multi-principal element alloys using two dissimilar or a combination of ideal and non-ideal pseudo-ternary diffusion couples

The estimation of diffusion coefficients in multicomponent system is facilitated by strategically designing diffusion couples with constrained diffusion paths. We have demonstrated methods of estimating tracer diffusion coefficients following three different combinations of diffusion profiles: (i) By intersecting a pseudo-ternary diffusion path with a rectilinear pseudo-binary diffusion path, (ii) by considering a combination of two dissimilar pseudo-ternary diffusion paths, and (iii) considering a combination of ideal and non-ideal pseudo-ternary diffusion paths with uphill diffusion characteristics. Equation schemes required for such analyses depending on the type of diffusion profiles are explained in detail. This approach relies on the availability of reliable thermodynamic data for the estimation of the tracer diffusion coefficients. Following, as demonstrated, one can calculate the intrinsic and interdiffusion coefficients of all the elements for a conventional diffusion couple in which all the elements would produce the diffusion profiles.

Structural, raman, optical and electrical studies of pure and compound crystal of magnesium sulphateheptahydrate and threonine

Pure and compound crystal of magnesium sulphate heptahydrate(MSH) and threonine (THR) is grown from aqueous solution by slow evaporation method at room temperature. The reaction between MSH and THR is confirmed by TLC test. Good quality and transparent crystals are harvested. Pure MSH and THR crystallize in orthorhombic crystal system, while compound crystal shows the presence of both the phases of MSH and THR.The crystallite size is found using the various methods are employed to estimate the crystallite sizes and the lattice strain. The Raman spectra show the presence of characteristic normal modes of vibrations of pure MSH and THR in the compound crystal.The optical band gap is estimated by using K-M function. The various optical parameters such as extinction coefficient, refractive index, optical conductivity and skin depth have been calculated and analyzed with incident photon energy. The dielectric constant and loss of all the grown crystals have exhibited normal behavior over the frequency range considered. The total polarizability of the crystals is calculated by two theoretically methods and matches well with experimental results. The complex impedance and modulus spectroscopy studies suggested the presence of grain effect in all the samples and the same is successfully modelled using R-CPE parallel circuit. Non-debye type relaxation is confirmed from β-parameter. From the Jonscher’s plot, the ideal long range pathways and diffusion limited hopping mechanism is confirmed for all the samples. The results of pure crystal of MSH and THR are compared with the compound crystal and discussed accordingly in detail.

How to Measure Solid State Lithium-ion Diffusion using the Atlung Method for Intercalant Diffusion

A systematic investigation of the factors that affect lithium diffusion coefficient measurements in the Atlung Method for Intercalant Diffusion (AMID) is carried out. Single crystal LiNi0.6Mn0.2Co0.2O2 is used for method development. The factors include electrode mass loading, separator thickness, electrolyte solvent choice and salt molarity, voltage interval sizes, open circuit relaxation time, C-rate choice, and charge vs discharge direction. In an ideal diffusivity measurement method, none of these factors listed should impact the true material diffusivity since it should be a purely material property. However, as we demonstrate here, all these experimental parameters should be selected carefully to minimize cell and electrode resistance contributions so that one can measure true lithium diffusivity in a material that is independent of current direction. We propose a low electrode loading cell design that is applicable for all diffusion measurement methods consisting of an ultrathin electrode coating (0.2 mAh cm−2), thin separator and 1.5 M LiPF6 ethylene carbonate: dimethyl carbonate 1:1 electrolyte. Additionally, we show diffusivity is not dependent on charge or discharge direction in NMC622, and we compare AMID results to Galvanostatic Intermittent Titration. Specific to AMID 15 min OCV time with 0.1 V intervals are suitable for this measurement.

Ultrathin waterborne acoustic metasurface for uniform diffuse reflections

Achieving efficient wave manipulations with ultrathin metasurfaces at low frequencies less than 1000 Hz is a challenging research subject, especially for underwater scenes. This work proposes a novel design strategy for ultrathin and highly efficient waterborne reflective pentamode metasurfaces to realize uniform diffuse reflections. To this end, a theoretical model that eases off the demand on the impedance matching is first established for plane waves impinging on an interface layer, and an ideal diffusion field is subsequently constructed. Secondly, the spatially variant equivalent impedances of the metasurface are identified, and their corresponding pentamode material configurations are designed inversely with band structure analyses. Numerical results show that the normalized diffusion coefficient can reach up to 0.81 at the targeted frequency 288 Hz, while the thickness of the designed metasurface is limited to several centimeters, only one hundredth of the working wavelength. Further verifications reveal that the metasurface applies also to a broader frequency range from 200 Hz to 650 Hz. The strategy paves potentially the way towards acoustic wave manipulations of ultrathin waterborne metasurfaces at deep-subwavelength scale.

Analysis of aerodynamic characteristics of car diffuser for dissimilar diffuser angles on Sedan’s using CFD

A vehicle's aerodynamic qualities have a major impact on its performance, handling, safety, and comfort. Variations in aerodynamic characteristics, such as lift and drag forces, have a noticeable impact on vehicle performance at high speeds. Researchers can lessen the frequency of accidents in which a motorist loses control of their car on our roads by lowering the pressure differential between the road and the tires. Manufacturers can save time and money on research and development by using Computational Fluid Dynamics (CFD) instead of wind tunnel testing, appreciations to advancements in computing power. The focus of this study is to learn the different aspects of a vehicle influence on its drag coefficient. Using CFD, the ideal diffuser angle was identified, which maximizes the down force produced by the device. Analysis of the drag and turbulent kinetic energy on the vehicle at varied diffuser angles (10, 11, and 12°) and vehicle speeds was performed using Ansys 16.2 Fluent. As shown by the numerical study, the drag force is reduced to 119.019 N at the 12° diffuser angle, which also provides the highest velocity and the lowest turbulent kinetic energy value. Researchers found that adjusting the diffuser's tilt significantly altered the under-body flow's wake.

3D Porous Collagen Matrices-A Reservoir for In Vitro Simultaneous Release of Tannic Acid and Chlorhexidine.

The treatment of wounds occurring accidentally or as a result of chronic diseases most frequently requires the use of appropriate dressings, mainly to ensure tissue regeneration/healing, at the same time as treating or preventing potential bacterial infections or superinfections. Collagen type I-based scaffolds in tandem with adequate antimicrobials can successfully fulfill these requirements. In this work, starting from the corresponding hydrogels, we prepared a series of freeze-dried atelocollagen type I-based matrices loaded with tannic acid (TA) and chlorhexidine digluconate (CHDG) as active agents with a broad spectrum of antimicrobial activity and also as crosslinkers for the collagen network. The primary aim of this study was to design an original and reliable algorithm to in vitro monitor and kinetically analyze the simultaneous release of TA and CHDG from the porous matrices into an aqueous solution of phosphate-buffered saline (PBS, pH 7.4, 37 °C) containing micellar carriers of a cationic surfactant (hexadecyltrimethylammonium bromide, HTAB) as a release environment that roughly mimics human extracellular fluids in living tissues. Around this central idea, a comprehensive investigation of the lyophilized matrices (morpho-structural characterization through FT-IR spectroscopy, scanning electron microscopy, swelling behavior, resistance against the collagenolytic action of collagenase type I) was carried out. The kinetic treatment of the release data displayed a preponderance of non-Fickian-Case II diffusion behavior, which led to a general anomalous transport mechanism for both TA and CHDG, irrespective of their concentrations. This is equivalent to saying that the release regime is not governed only by the gradient concentration of the releasing components inside and outside the matrix (like in ideal Fickian diffusion), but also, to a large extent, by the relaxation phenomena of the collagen network (determined, in turn, by its crosslinking degree induced by TA and CHDG) and the dynamic capacity of the HTAB micelles to solubilize the two antimicrobials. By controlling the degree of physical crosslinking of collagen with a proper content of TA and CHDG loaded in the matrix, a tunable, sustainable release profile can be obtained.

A Comparison of Global Magnetofrictional Simulations of the 2015 March 20 Solar Eclipse

The solar corona exhibits a wide range of phenomena, from highly non-potential objects such as solar filaments to near-potential structures such as the open magnetic flux. For any global model to be useful in space weather applications, the model must on a single day reproduce all of these phenomena in the same simulation, using the same set of coronal physics and parameters. The purpose of the present paper is to evaluate whether the evolving magnetofrictional model can achieve this goal. Twenty-eight separate simulations are analyzed, where each tries to reproduce both highly non-potential and near-potential phenomena observed in the solar corona on the same day. This day is chosen to be 2015 March 20, the date of the solar eclipse. The study evaluates how the cadence of bipole data, ideal or nonideal coronal physics, and the variety of helicity injection mechanisms affect the accuracy of the simulations. Results show that significantly better agreement arises when using Advective Flux Transport (AFT) synoptic maps to drive the simulations, as compared to 27-day Carrington rotation synoptic maps. Using the nonideal effect of hyperdiffusion leads to the worst agreement with all coronal phenomena. Alternatively, when running either ideal or ohmic diffusion simulations with helicity condensation or bipoles with a self-helicity, a good agreement with both on-disk and limb structures can be found. This suggests that future studies aiming to simulate the corona and reproduce multiple phenomena on a given day should use data products such as AFT and avoid using the nonideal physics of hyperdiffusion.

An intermediate model for fitting triplet–triplet annihilation in phosphorescent organic light emitting diode materials

Triplet–triplet annihilation (TTA) is one of the primary contributors to efficiency roll-off and permanent material degradation in phosphorescent organic light-emitting diodes. The two limiting case models typically used to quantify this quenching mechanism are multi-step Dexter and single-step Förster, which, respectively, assume ideal Fickian diffusion or perfect trapping of triplet excitons. For device-relevant guest doping levels (typically 5–12 vol. %), both significant diffusion of excitons and trapping due to spatial and energetic disorder exist, so neither conventional model fits experimental data well. We develop and validate an intermediate TTA model, which is a weighted average of the limiting cases of pure radiative decay (no TTA) and multi-step Dexter based TTA that returns an effective TTA rate constant and a parameter quantifying the portion of well-isolated excitons. Kinetic Monte-Carlo simulations and time-resolved photoluminescence measurements of an archetype host–guest system demonstrate that our intermediate model provides significantly improved fits with more realistic physical values, is more robust to variations in experimental conditions, and provides an analysis framework for the effects of trapping on TTA.

Determination of the τ/ε-Ratio for Gas Diffusion Substrates and Microporous Layers in an Operating Fuel Cell

Proton-exchange-membrane fuel cells (PEMFCs) are expected to play a major role in the electrification of the transportation sector,[1] with recent focus shifting to the heavy-duty market. One essential aspect for increasing the power density of a PEMFC is optimizing the mass transport in the gas diffusion layer (GDL) on the cathode side of the cell. A careful choice of the commonly used carbon fiber based GDL is therefore necessary to optimize the performance at different relative humidity conditions. Among other important GDL properties such as the pore size distribution and the thermal conductivity, the porosity (ε) and the tortuosity (τ) are important descriptors. The τ/ε-ratio has been characterized for diffusion media using in-situ or ex-situ techniques.[2-3] This study is based on the theory developed by Baker et al.[2] In addition to their work, which solely considers molecular diffusion, we will present a method to include Knudsen diffusion occurring in smaller pores for the in-situ evaluation of the τ/ε-ratio. This adaptation makes it possible to evaluate GDL substrates to which carbon black (creating small pores) has been added to increase the electrical conductivity,[4] and also to extend the theory to the microporous layer (MPL).In this study, we characterize the τ/ε-ratio for two GDL substrates (without the addition of an MPL), one from Toray and one from Freudenberg, using limiting current measurements in an operating fuel cell. The τ/ε-ratio describes the deviation of the effective diffusivity compared to ideal molecular diffusion. However, depending of the range of pore diameters in the gas diffusion medium, a mixture of molecular diffusion and Knudsen diffusion has to be taken into account. Fig. 1 shows the theoretical contribution ratio of Knudsen diffusion and molecular diffusion (left y-axis) versus the relevant range of pore diameters for different pressures. The graphic illustrates that Knudsen diffusion dominates at lower pore sizes, while molecular diffusion is mostly present at larger pore sizes. An increase in pressure shifts the regime of molecular diffusion to smaller pores. In addition to the theoretical contribution ratio, Fig. 1 depicts the pore size distribution of a Toray and a Freudenberg GDL substrate determined by mercury intrusion porosimetry (MIP). While the Toray paper has a narrow pore size distribution at pores of 30-50 µm, where only molecular diffusion occurs, the Freudenberg GDL contains a broader range of larger pores at 10-40 µm (molecular diffusion) together with the presence of small pores at ca. 70-80 nm that derive from the addition of carbon black and that present a medium where Knudsen and molecular diffusion occur.After the validation of the principle, the method is transferred to determine the τ/ε-number of a microporous layer based on vapor-grown carbon-fibers (VGCF), whose transport properties in a PEMFC have been described previously.[5] References [1] O. Gröger, H. A. Gasteiger, J.-P. Suchsland, J. Electrochem. Soc. 2015, 162, A2605-A2622.[2] D. R. Baker, D. A. Caulk, K. C. Neyerlin, M. W. Murphy, J. Electrochem. Soc. 2009, 156, B991.[3] D. Kramer, S. A. Freunberger, R. Flückiger, I. A. Schneider, A. Wokaun, F. N. Büchi, G. G. Scherer, Journal of Electroanalytical Chemistry 2008, 612, 63-77.[4] K.-D. Wagner, A. Bock, K. Salama, A. Weller, Vol. US 2010/0219069 A1, Carl Freudenberg KG 2010.[5] C. Simon, J. Endres, B. Nefzger-Loders, F. Wilhelm, H. A. Gasteiger, J. Electrochem. Soc. 2019, 166, F1022-F1035. Acknowledgements We gratefully acknowledge funding from the Swiss National Foundation under the funding scheme Sinergia (project grant number 180335). We also thank Michael Striednig and Christoph Simon for initial work on the topic. Figure 1: Left y-axis: theoretical contribution ratio of Knudsen (green) and molecular diffusion (orange) versus pore diameter for different absolute pressures of 115 kPaabs (solid lines), 150 kPaabs (dashed lines), 200 kPaabs (dotted lines), and 300 kPaabs (dash-dotted lines). With smaller pores and lower pressures, more contributions from Knudsen diffusion can be expected. Right y-axis: log. differential intrusion measured by MIP analysis for the Toray (blue) and the Freudenberg (grey) GDL substrates, whereby the Freudenberg GDL shows pores at ~70-80 nm that are caused by the addition of carbon black. Figure 1

Graphdiyne/Graphene/Graphdiyne Sandwiched Carbonaceous Anode for Potassium-Ion Batteries.

Graphdiyne (GDY) has been considered as an appealing anode candidate for K-ion storage since its triangular pore channel, alkyne-rich structure, and large interlayer spacing would endow it with abundant active sites and ideal diffusion paths for K-ions. Nevertheless, the low surface area and disordered structure of bulk GDY typically lead to unsatisfied K storage performance. Herein, we have designed a GDY/graphene/GDY (GDY/Gr/GDY) sandwiched architecture affording a high surface area and fine quality throughout a van der Waals epitaxy strategy. As tested in a half-cell configuration, the GDY/Gr/GDY electrode exhibits better capacity output, rate capability, and cyclic stability as compared to the bare GDY counterpart. In situ electrochemical impedance spectroscopy/Raman spectroscopy/transmission electron microscopy are further applied to probe the K-ion storage feature and disclose the favorable reversibility of GDY/Gr/GDY electrode during repeated potassiation/depotassiation. A full-cell device comprising a GDY/Gr/GDY anode and a potassium Prussian blue cathode enables a high cycling stability, demonstrative of the promising potential of the GDY/Gr/GDY anode for K-ion batteries.

MDS block hankel-like rhotrices using conjugate elements and self-dual bases of finite fields

Maximum Distance Separable (MDS) matrices offer ideal diffusion properties and are of great importance in design of block ciphers and hash functions. A rhotrix as defined by Sani, is a coupled matrix which when used in a cryptosystem provides double security. Many authors constructed MDS Rhotrices over finite fields using matrices which are cryptographically significant. Hankel matrices have wide range of applications in engineering, coding theory and cryptography. In the present paper, we define block rhotrix and block Hankel- like rhotrix. Further, we construct MDS block Hankel-like rhotrices using self-dual basis and conjugate elements of Fpn.

Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet-C Dosimeters.

Effective ultraviolet-C (UV-C) decontamination protocols of N95 respirators require validation that the entire N95 surface receives sufficient dose. Photochromic indicators (PCIs) can accurately measure UV-C dose on nonplanar surfaces, but often saturate below doses required to decontaminate porous, multilayered textiles like N95s. Here, we investigate the use of optical attenuators to extend PCI dynamic range while maintaining a near-ideal angular response-critical for accurate measurements of uncollimated UV-C. We show analytically that tuning attenuator refractive index, attenuation coefficient, and thickness can extend dynamic range, but compromises angular response unless the attenuator is an ideal diffuser. To investigate this tradeoff empirically, we stack PCIs behind model specular (floated borosilicate) and diffuse (polytetrafluoroethylene) attenuators, characterize the angular response, and evaluate on-N95 UV-C measurement accuracy within a decontamination system. Both attenuators increase PCI dynamic range >4×, but simultaneously introduce angle-dependent transmittance, which causes location-dependent underestimation of UV-C dose. PCI-borosilicate and PCI-polytetrafluoroethylene stacks underreport true on-N95 dose by (1) 14.7% and 3.6%, respectively, when near-normal to the source lamp array, and (2) 40.8% and 19.8%, respectively, in a steeply sloped location. Overall, we demonstrate that while planar attenuators can increase PCI dynamic range, verifying near-ideal angular response is critical for accurate UV-C measurements.

Electrochemical Modeling of GITT Measurements for Improved Solid-State Diffusion Coefficient Evaluation

Galvanostatic Intermittent Titration Technique (GITT) is widely used to evaluate solid-state diffusion coefficients in electrochemical systems. However, the existing analysis methods for GITT data require numerous assumptions, and the derived diffusion coefficients typically are not independently validated. To investigate the validity of the assumptions and derived diffusion coefficients, we employ a direct pulse fitting method for interpreting GITT data that involves numerically fitting an electrochemical pulse and subsequent relaxation to a one-dimensional, single-particle, electrochemical model coupled with non-ideal transport to directly evaluate diffusion coefficients that are independently verified through cycling predictions. Extracted from GITT measurements of the intercalation regime of FeS2 and used to predict the discharge behavior, our non-ideal diffusion coefficients prove to be two orders of magnitude more accurate than ideal diffusion coefficients extracted using conventional methods. We further extend our model to a polydisperse set of particles to show the validity of a single-particle approach when the modeled radius is proportional to the total volume-to-surface-area ratio of the system.

Multiple evidences of dynamic heterogeneity in hydrophobic deep eutectic solvents.

Hydrophobic deep eutectic solvents (HDESs) have gained immense popularity because of their promising applications in extraction processes. Herein, we employ atomistic molecular dynamics simulations to unveil the dynamics of DL-menthol (DLM) based HDESs with hexanoic (C6), octanoic (C8), and decanoic (C10) acids as hydrogen bond donors. The particular focus is on understanding the nature of dynamics with changing acid tail length. For all three HDESs, two modes of hydrogen bond relaxations are observed. We observe longer hydrogen bond lifetimes of the inter-molecular hydrogen bonding interactions between the carbonyl oxygen of the acid and hydroxyl oxygen of menthol with hydroxyl hydrogen of both acids and menthol. We infer strong hydrogen bonding between them compared to that between hydroxyl oxygen of acids and hydroxyl hydrogens of menthol and acids, marked by a faster decay rate and shorter hydrogen bond lifetime. The translational dynamics of the species in the HDES becomes slower with increasing tail length of the organic acid. Slightly enhanced caging is also observed for the HDES with a longer tail length of the acids. The evidence of dynamic heterogeneity in the displacements of the component molecules is observed in all the HDESs. From the values of the α-relaxation time scale, we observe that the molecular displacements become random in a shorter time scale for DLM-C6. The analysis of the self-van Hove function reveals that the overall distance covered by DLM and acid molecules in the respective HDES is more than what is expected from ideal diffusion. As marked by the shorter time scale associated with hole filling, the diffusion of the oxygen atom of menthol and the carbonyl oxygen of acid from one site to the other is fastest for hexanoic acid containing HDES.

Determination of Lithium Diffusion Coefficient in FeS2 through Improved Galvanostatic Intermittent Titration Technique (GITT) Modeling

Significant, recent efforts have been directed towards modeling lithium-ion batteries to optimize their performance and design. These models depend highly on physical parameters that must be evaluated experimentally for the system of interest. One of the most critical of these parameters is the chemical diffusion coefficient for lithium inside the active cathode material. Galvanostatic Intermittent Titration Technique (GITT) is a commonly used technique that can evaluate the diffusion coefficient, as well as other important information about the cell such as the reaction rate constant and open circuit potential. Despite its popularity, there remain several issues with the existing method of analyzing GITT data. Notably, the conventional method for extracting diffusion coefficients from GITT data relies on numerous assumptions, applies only at short discharge times, and lacks evidence validating the obtained coefficients.In this work, we describe a new method of extracting diffusion coefficients from GITT data. This method involves directly fitting a GITT pulse to a one-dimensional, single particle electrochemical model and can be applied for both ideal and non-ideal solution theory. We apply this approach to experimental measurements at two temperatures for the intercalation regime of FeS2, a conversion cathode material. Results are compared to the conventional method of evaluating diffusion coefficients from GITT data as well as diffusion coefficients obtained from electrochemical impedance spectroscopy. Diffusion coefficients are found to be higher for direct fitting, and more than an order of magnitude difference is observed between ideal and non-ideal diffusion coefficients. The modeling is also extended to a distribution of particles, and we show that the distribution behaves as a single particle with an effective particle radius proportional to the total volume to surface area ratio. Finally, the new diffusion coefficients are validated against discharge data for the cell, and it is shown that a reasonable prediction to the experimental data can be achieved using a single particle model. However, this is only possible with a non-ideal diffusion model, and high variation is observed across predictions obtained using other diffusion coefficient evaluation methods. This work demonstrates the susceptibility of electrochemical modeling to transport parameters and offers a simple, yet improved, method for evaluating diffusion coefficients from experimental GITT measurements.Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.