Articoli di riviste sul tema "Multiscale structure/ionic transport properties correlations"

Polymers that simultaneously transport electrons and ions are paramount to drive the technological advances necessary for next-generation electrochemical devices, including energy storage devices and bioelectronics. However, efforts to describe the motion of ions or electrons separately within polymeric systems become inaccurate when both species are present. Herein, we highlight the basic transport equations necessary to rationalize mixed transport and the multiscale material properties that influence their transport coefficients. Potential figures of merit that enable a suitable performance benchmark in mixed conducting systems independent of end application are discussed. Practical design and implementation of mixed conducting polymers require an understanding of the evolving nature of structure and transport with ionic and electronic carrier density to capture the dynamic disorder inherent in polymeric materials.

In the last few years, ionic liquids (ILs) have been the focus of extensive studies concerning the relationship between structure and properties and how this impacts their application. Despite a large number of studies, several topics remain controversial or not fully answered, such as: the existence of ion pairs, the concept of free volume and the effect of water and its implications in the modulation of ILs physicochemical properties. In this paper, we present a critical review of state-of-the-art literature regarding structure–property relationship of ILs, we re-examine analytical theories on the structure–property correlations and present new perspectives based on the existing data. The interrelation between transport properties (viscosity, diffusion, conductivity) of IL structure and free volume are analysed and discussed at a molecular level. In addition, we demonstrate how the analysis of microscopic features (particularly using NMR-derived data) can be used to explain and predict macroscopic properties, reaching new perspectives on the properties and application of ILs.

In this study, molecular dynamics (MD) simulations of hydrated anion-exchange membranes (AEMs), comprised of poly(p-phenylene oxide) (PPO) polymers functionalized with quaternary ammonium cationic groups, were conducted using multiscale coupling between three different models: a high-resolution coarse-grained (CG) model; Atomistic Polarizable Potential for Liquids, Electrolytes and Polymers (APPLE&P); and ReaxFF. The advantages and disadvantages of each model are summarized and compared. The proposed multiscale coupling utilizes the strength of each model and allows sampling of a broad spectrum of properties, which is not possible to sample using any of the single modeling techniques. Within the proposed combined approach, the equilibrium morphology of hydrated AEM was prepared using the CG model. Then, the morphology was mapped to the APPLE&P model from equilibrated CG configuration of the AEM. Simulations using atomistic non-reactive force field allowed sampling of local hydration structure of ionic groups, vehicular transport mechanism of anion and water, and structure equilibration of water channels in the membrane. Subsequently, atomistic AEM configuration was mapped to ReaxFF reactive model to investigate the Grotthuss mechanism in the hydroxide transport, as well as the AEM chemical stability and degradation mechanisms. The proposed multiscale and multiphysics modeling approach provides valuable input for the materials-by-design of novel polymeric structures for AEMs.

Lithium argyrodite superionic conductor has recently gained significant attention as a potential solid electrolyte for all-solid-state batteries because of its high ionic conductivity and ease of processing. One promising aspect of these materials is the ability to introduce halide (Li6-xPS5-xY1+x, Y = Cl and Br ) into the crystal structure, which can greatly impact the lithium distribution over the wide range of accessible sites and structural site-disorder between the S2₋ and Y₋ anion on Wyckoff 4d site, strongly influences the ionic conductivity. However, the relationship between halide substitution, structural site-disorder, and lithium distribution is not fully understood. In this study, we investigate the effect of halide substitution on lithium argyrodite and engineer site-disorder by changing the synthesis protocol. We reveal the lithium substructure and ionic transport correlations using neutron diffraction, solid-state NMR, and electrochemical impedance spectroscopy, We find that higher ionic conductivity is correlated with a negative charge on the 4d site, as replacing the S2− with Br− leads to a lowered average charge on the 4d site and weaker interactions within the Li+ “cage”, promoting a migration pathway for Li+ ions across the Li+ cage. We also identify a new T4 Li+ site, which enables an alternative jump route (T5–T4–T5) with a lower migration energy barrier. The resulting expansion of Li+ cages and increased connections between cages leads to a maximum ionic conductivity of 8.55 mS cm-1 with higher site-disorder, an improvement of 11-fold compared to lower site-disorder. Overall, this work provides a deeper understanding of the structure-transport correlations in lithium argyrodite, specifically how site-disorder and halide substitution impact the lithium substructure and transport properties.

Li-based antiperovskites (LiAP, Li3-x OH x X, X = Cl, Br) are an emergent class of Li-ion conductors that are potential candidates for electrolytes in all-solid-state batteries. As a material class, pLiAP shows vast compositional design freedom; however, the resulting properties are susceptible to synthesis and processing methodologies. For example, proton incorporation and halide mixing stabilize the perovskite cubic phase near room temperature, and halides mixtures near the eutectic points drive the solid-state reaction temperature down, allowing for faster synthesis and processing conditions (< 1 h). The mixed halogen compositions, such as Li2OHCl0.37Br0.63, also show a 30-fold improvement in room temperature ionic conductivity of a single halide structure, 1.5 x 10-6 vs. 4.9 x 10-8 S cm-1 (Li2OHCl). Despite the growing interest in these materials, important questions remain about LiAPs on the structure-property correlation upon halide substitution and the correlations between the OH/halide dynamics and the Li-ion transport. We thus attempted to deconvolute how proton dynamics and halide substitution enhance or impede ionic conduction in pLiAP at compositions near the halide salts' eutectic points. We combined infrared spectroscopy and nuclear magnetic resonance (NMR) with first-principles density functional theory (DFT) calculations to deconvolute halide mixing effects from local proton dynamics on Li-ion transport. The NMR results and ab initio molecular dynamics suggest that Li+ transport is more strongly correlated with halide dynamics. While the hydroxide does stabilize the highly conductive cubic structure, it limits correlative ionic transport and thus lowers Li+ conductivity. Experiment design, data analysis, and manuscript preparation (RLS) were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. Synthesis (THB and JN) were supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program. P. J. acknowledges partial support by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-96ER45579. H. F. was supported from U.S. Department of Energy (Award No. DE-EE0008865). This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The NMR characterization part of the work is supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, and Basic Energy Sciences. The NMR work was performed at the W. R. Wiley Environmental Molecular Sciences Laboratory, a DOE User Facility sponsored by the Office of Biological and Environmental Research, located at Pacific Northwest National Laboratory. Figure 1

Two kinds of charge transfer reactions are critical for the performance and life of lithium battery: the desired ion transfer reaction occurring during each charge/discharge cycle, , and the undesired electron transfer reactions leading to the parasitic chemical decomposition of the electrolyte and solid electrolyte interphase (SEI) formation/growth. The heterogeneous multi-component nature of SEI dominates its ionic and electronic transport properties and controls these two charge transfer reactions. Density Functional Theory (DFT)-informed multiscale modeling has been providing valuable insights under the scarcity of quantitative experiments. For example, the LiF/Li2CO3 interface was demonstrated to increase the ionic conductivity of mixed SEI nanocomposite by forming an ionic space charge region near the interface and promoting more Li-ion interstitials in Li2CO3, although LiF itself has low Li-ion conducting carriers and conductivity. To form a LiF-rich SEI layer, the electrolyte compositions need to be designed. Since the SEI formation occurs on the charged surface, the electric double layer (EDL) structure near the charged surfaces needs to be incorporated into the modeling. Here interactive classical molecular dynamics (MD), DFT, and data statistical analysis were combined to illustrate the effect of EDL on SEI formation in two essential electrolytes, the carbonate-based electrolyte for Li-ion batteries and the ether-based electrolyte for batteries with Li-metal anodes. It was found the effectiveness of adding fluoroethylene carbonate (FEC) to form the beneficial F-containing SEI component (e.g., LiF) varies with the electrolyte and temperature, because of the interplay of ion-solvent interactions with the surface charge. These integrated modeling provided quantitative guidance for electrolyte/SEI/Li-metal interface design.

Summary High-resolution X-ray-computed-tomography (CT) images are increasingly used to numerically derive petrophysical properties of interest at the pore scale—in particular, effective permeability. Current micro-X-ray-CT facilities typically offer a resolution of a few microns per voxel, resulting in a field of view of approximately 5 mm3 for a 2,0482 charge-coupled device. At this scale, the resolution is normally sufficient to resolve pore-space connectivity and calculate transport properties directly. For samples exhibiting heterogeneity above the field of view of such a single high-resolution tomogram with resolved pore space, a second low-resolution tomogram can provide a larger-scale porosity map. This low-resolution X-ray-CT image provides the correlation structure of porosity at an intermediate scale, for which high-resolution permeability calculations can be carried out, forming the basis for upscaling methods dealing with correlated heterogeneity. In this study, we characterize spatial heterogeneity by use of overlapping registered X-ray-CT images derived at different resolutions spanning orders of magnitude in length scales. A 38-mm-diameter carbonate core is studied in detail and imaged at low resolution—and at high resolution by taking four 5-mm-diameter subsets, one of which is imaged by use of full-length helical scanning. Fine-scale permeability transforms are derived by use of direct porosity/permeability relationships, random sampling of the porosity/permeability scatter plot as a function of porosity, and structural correlations combined with stochastic simulation. A range of these methods is applied at the coarse scale. We compare various upscaling methods, including renormalization theory, with direct solutions by use of a Laplace solver and report error bounds. Finally, we compare with experimental measurements of permeability at both the small-plug and the full-plug scale. We find that both numerically and experimentally for the carbonate sample considered, which displays nonconnecting vugs and intrafossil pores, permeability increases with scale. Although numerical and experimental results agree at the larger scale, the digital core-analysis results underestimate experimentally measured permeability at the smaller scale. Upscaling techniques that use basic averaging techniques fail to provide truthful vertical permeability at the fine scale because of large permeability contrasts. At this scale, the most accurate upscaling technique uses Darcy's law. At the coarse scale, an accurate permeability estimate with error bounds is feasible if spatial correlations are considered. All upscaling techniques work satisfactorily at this scale. A key part of the study is the establishment of porosity transforms between high-resolution and low-resolution images to arrive at a calibrated porosity map to constrain permeability estimates for the whole core.

The pressing need for highly-performing and environmentally benign energy technologies continues to spur on research on polymer electrolyte fuel cells (PEFC). Among the components that are needed for a well-functioning, durable, and affordable PEFC, the cathode catalyst layer (CCL) continues to stand out. The main function to be provided by the CCL is to facilitate the oxygen reduction reaction (ORR). However, this function entails an intricate interplay of microscopic kinetics with the transport of electrons, protons, oxygen molecules, and water. A hierarchy of structural effects must be considered, as illustrated in Figure 1. Due to the complex composition and multiscale nature of the CCL, physical modeling has gained high importance in efforts to rationalize the dynamic interplay of structure, properties, and performance. The first part of the presentation will briefly review the capabilities of model-based analyses of experimental data to deconvolute and quantify voltage loss contributions,1 extract kinetic and transport parameters from fitting and discover systematic trends and correlations among these parameters,2 provide an activity map of the layer, and evaluate the overall effectiveness factor of Pt utilization.3 Macrohomogeneous modelling can propose or predict the optimal CCL thickness or macroscopic effective composition (for the target range of operating conditions). Recognizing the importance of an optimal water-distribution for a well-functioning CCL, recent efforts in CCL modeling have been focusing on the consistent treatment of aspects like pore size distributions and pore network morphologies as well as wettability properties. The ionomer inclusions in the CCL play a crucial role in this context. At the microscopic scale, the ionomer film that forms an interface with the water-covered catalyst-support surface strongly impacts the local reaction environment that determines the rate of the ORR as well as that of platinum dissolution. Moreover, the structure and distribution of ionomer inclusions determine the wetting behaviour of pores and thus the water sorption properties of the porous composite CCL, which in turn affect the transport properties for oxygen and water. Recent forays in modelling that strive to unravel the intertwined impacts of ionomer and water will be presented. As a final consideration, a CCL cannot be understood and optimized as a stand-alone component. Overarching balances at the PEFC level in terms of reactant, charge, water, and heat fluxes must be considered. Comprehensive modeling approaches must account for the coupling of the corresponding local equilibria and transport phenomena across the whole cell, including polymer electrolyte membrane, diffusion media and flow fields. Efforts focusing on the coupled water fluxes across the cell are underway with promising results to look out for. References. 1 M. Baghalha, J. Stumper and M. Eikerling, ECS Transactions 28, 159–167 (2010). 2 T. Muzaffar, T. Kadyk and M. Eikerling, Sustainable Energy & Fuels 2, 1189–1196 (2018). 3 M. Eikerling and A.A. Kulikovsky, Polymer Electrolyte Fuel Cells – Physical Principles of Materials and Operation, CRC Press Taylor & Francis Group, 2014. Figure 1

Redox flow batteries are a promising option for large-scale energy storage but remain too costly for widespread deployment. One approach to increase cost competitiveness is to improve the power density and efficiency of the electrochemical cell. Porous electrodes determine the performance of the cell, and their three-dimensional structure determines the electrolyte transport, fluid pressure drop, and the available surface area for electrochemical reactions [1]. Conventional porous electrodes are fibrous mats assembled in coherent structures [2]; however, they are repurposed from fuel cell gas diffusion electrodes and have not been tailored for redox flow batteries. Hence, an effective means to improve the performance of redox flow batteries is by engineering porous electrode structures to sustain the requirements of liquid-phase electrochemistry. To this purpose, there is a need to develop new manufacturing techniques affording a higher degree of control over the electrode microstructure and resulting properties. Additive manufacturing, or 3D printing, can be employed to manufacture customized, controlled, and deterministic architectures, enabling the fine-tuning of the electrical and hydraulic performance of porous electrodes [3]. In this study, we manufacture model grid structures using stereolithography 3D printing followed by carbonization (Figure 1a) to tune the physiochemical properties of electrodes to be used in redox flow batteries. We employ a suite of microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics to understand the impact of the electrode structure on the mass transport and hydraulic performance of ordered lattice structures in flow cells. Here, the influence of the printing direction, pillar geometry (Figure 1b), and flow field type on mass transport is investigated using an organic electrolyte. We elucidate correlations between the electrode structure and performance metrics, namely surface area, pressure drop, and mass transfer correlations. We find that the printing orientation impacts the electrode performance through a change in electrode morphology caused by resin spreading and surface roughness, affecting the shrinking direction upon carbonization, internal surface area, and thus the charge transfer, mass transfer, and hydraulic resistances. Furthermore, we find that mass transfer rates within the electrode are enhanced by using an interdigitated flow field or by altering the pillar shape to a helical or triangular design, which we hypothesize improves mixing. Compared to commercial carbon-fiber electrodes, the pressure drop is significantly reduced (Figure 1c) as expected due to larger pore sizes (~500 μm for the grids vs. 2-100 μm for the Freudenberg H23 paper electrode and 2-300 μm for the ELAT Cloth electrode). Even though the commercial electrodes feature a superior internal surface area compared to the 3D printed electrodes, their area normalized mass transfer coefficients are lower (Figure 1d). Going forward, the use of printing technologies enabling finer features in combination with carbonization at elevated temperatures can be used to manufacture multiscale electrodes simultaneously providing low hydraulic resistance and excellent electrochemical performance. Additive manufacturing in combination with emerging computational approaches in topology optimization [4] might enable the bottom-up design and manufacturing of advanced electrode materials. References [1] M. van der Heijden, A. Forner-Cuenca, Encyclopedia of Energy Storage, 480-499 (2022) [2] A. Forner-Cuenca et al., J. Electrochem. Soc., 166, 10, A2230-A2241 (2019) [3] V.A. Beck et al., Proc. Natl. Acad. Sci., 118, 32, 1-10 (2021) [4] R. van Gorp & M. van der Heijden et al., Chem. Eng. J., 139947 (2022) Figure 1

The development of the new electrolytes is essential to increase the energy density of the Li-ion batteries (LIBs)1. Solid electrolytes have attracted the interest of researchers as a next-generation electrolyte for LIBs due to their superior physical and chemical stability, large working potential windows, high transference number, and intrinsic safety2 3. In this study, we have designed and synthesized novel organic electrolytes for LIBs with a naphthalene mesogenic moiety bearing a lithium sulfonate group connected to two flexible long-alkyl chains. Starting from the lithium 4-aminonaphthalene-1-sulphonate building block, alkyl-tails were successfully doubly grafted on the amine function with N, N-di-isopropylethylamine in N, N-di-methylformamide. Once the reaction was completed, a washing, purification and neutralization step was carried out to obtain the desired product. Those electrolytes have been synthesized with 95 % purity as suggested from the NMR and mass spectrum. The chains length were differ by the number of alkyl groups in the chains from 8, 12, and 16, namely lithium 4 - (dioctylamino) naphthalene – 1 – sulfonate (BS-Li-8), lithium 4 - (didodecylamino) naphthalene – 1 - sulfonate (BS-Li-12), and lithium 4 - (dihexadecylamino) naphthalene – 1 – sulfonate (BS-Li-16). We have employed molecular dynamics simulations and various experimental techniques for a comprehensive understanding of the bulk structure and transport mechanism of those electrolytes. Simulated static structural factor, radial distribution functions, and experimental small angle x-ray scattering spectrum suggest that degree of aggregation, ionic correlations, and structural properties of materials at the nanoscale of the electrolyte molecules varies with the length of the alkyl chains. The Li+ ion mobility calculated from experimental Electrochemical Impedance Spectra, using a symmetrical cell with blocking electrodes and molecular dynamics simulations reveal that BS-Li-12 is the most conductive (approximately 10-3 S / cm at 1400 C) owing to the weaker cation-anion correlation than others. It was observed that the conductivity of the Li+ ions is directly related to the coordination number between Li+ and anionic centers, since, in BS-Li-12, Li+ coordinates with two anionic centers while for others, it is three. During the conduction, Li+ move from one anionic site to another by changing their coordination number with anion. We successfully synthesized next-generation organic electrolytes with well-organized Li+ conduction channels. The comprehensive study of the influence of the nonpolar alkyl chain on the bulk structural arrangement and conductivity of such electrolytes will contribute significantly to the development of future LIBs electrolytes. References: (1) Armand, M.; Tarascon, J.-M. Building Better Batteries. Nature 2008, 451 (7179), 652–657. https://doi.org/10.1038/451652a. (2) Manthiram, A.; Yu, X.; Wang, S. Lithium Battery Chemistries Enabled by Solid-State Electrolytes. Nature Reviews Materials 2017, 2 (4), 16103. https://doi.org/10.1038/natrevmats.2016.103. (3) Quartarone, E.; Mustarelli, P. Electrolytes for Solid-State Lithium Rechargeable Batteries: Recent Advances and Perspectives. Chem. Soc. Rev. 2011, 40 (5), 2525–2540. https://doi.org/10.1039/C0CS00081G. Figure 1

Today, post-lithium energy storage technologies are now rapidly progressing due to the high price of a net Li-ion battery, which also depends on the desired capacity and power. Among sodium, potassium, calcium, magnesium, and even aluminum-based alternatives, young potassium-ion batteries demonstrate high capacity and energy density, notable ionic transport in electrolytes, the possibility to employ graphite anodes, and a wide variety of possible electrode materials: layered oxides, polyanionic, organic compounds, Prussian Blue analogs. However, the latter ones are generally considered as the most promising and practically viable. Prussian Blue analogs form a big family of electrode materials with the general formula KxM1[M2(CN)6]∙nH2O, where x=0...2, and Mi are any possible 3d transition metals. The most well-known and commercially available is based on a hexacyanoferrate anion [Fe(CN)6]n-, while other transition metals can also form hexacyanometallate complexes, but are poorly studied or not known at all. The most part of published works shed light on the morphology and low content of water defects inside crystallites counting the lack of hexacyanoferrate, and their influence on realized capacity and capacity fades, while the fundamental principles and real water position presence which guide the electrochemical activity of high- and low-spin cations in these materials are totally missed. In our work, we also started with the intrinsic water defects and their impact on crystal and physicochemical properties in K2Mn[Fe(CN)6]∙nH2O but with sensitive to light atoms neutron diffraction technique. We observed that water content does not effect the whole crystal symmetry but slightly amend unit cell parameters. Besides the fact of decreasing a decomposition temperature in “watered” Prussian Blue analog, electrochemical properties were found close. Therefore, we concluded that intrinsic water does not notably influence material properties. Continuing with potassium manganese hexacyanoferrate and electronic structure impact to the compound properties, to reveal the best synergetic stabilizing agent during cycling, we synthesized and studied the system K2-γMn1-xCox[Fe(CN)6]∙nH2O with x=0, 0.05,...1. In addition to symmetry and composition transformations, magnetic and electrochemical properties also significantly differ, while higher cobalt content increases the redox potential of iron, but drastically decreases total capacity due to the inability of reaching iron oxidation. The fact of notable changing of redox potentials in K2-γMn1-xCox[Fe(CN)6]∙nH2O is inspiring, and we have been extending with other hexacyanometallates. Hexacyanomanganate-ion [Mn(CN)6]n- is one of the promising pathways to investigate such systems with a more fundamental point of view, and the obtained experimental results confirm the hypothesis. We discovered that cation position exchange totally alters the electrochemistry of the Prussian Blue cathode materials, and the interpretation still raises a lot of questions and assumptions, and together with computational chemistry, we will try to answer the fundamental questions about electronic, crystal structures and electrochemical properties. In this report we will present the new correlations of redox potential in Prussian Blue analogs depending on transition metal position and electronic structure, evaluate diffusion of potassium in these materials, and try to answer the possibility to use these compounds in potassium-ion batteries.

Recent developments have proven the economic potential of electrochemical reduction of CO2 to value added chemicals, where single cells are now capable of achieving high energetic efficiencies at industrially relevant current densities. 1 These advances are in no small part due to the increased ionic conductivity, hydroxide stability and commercial availability of anion exchange membranes (AEMs). However, there currently exists little understanding as to how these materials affect the efficiency of CO2 conversion devices because the research community is only now beginning to understand the variety and complexity of the transport processes involved. 2 In collaboration with Ionomr Innovations Inc. and the National Research Council of Canada, and as part of the Energy for Clean Materials Challenge Program, we have made advances in the understanding of how AEM properties affect device performance and how we can develop materials tailor-made for CO2 electrolyser technology. Here, we demonstrate the development of a zero-gap single cell design, utilizing first generation Aemion® materials for the conversion of CO2 to CO with an energetic efficiency of 40% at 200 mA cm-2. 3 Despite the initially high energetic efficiency, we demonstrate how the crossover of carbonate dianions results in the reduction of anolyte pH and deconvolute how this results in a diminished cell efficiency over extended operation. From this, we show how functionalization of the polymer electrolyte structure can reduce this degradation mechanism while retaining high energetic efficiencies. In addition, we demonstrate how under milder electrolysis conditions, the total cell efficiency has a significant dependency on the flux of alkali metal cationic species from the supporting anolyte to the cathode. We show that due to the large promotion effect of cations for the electrochemical CO2 reduction, AEM design not only influences ohmic resistances in the cell, but also greatly affects the charge transfer resistance (RCT) of the cathode to a much greater extent than other electrochemical conversion devices. We thus make correlations between water permeability and perm-selectivity of AEMs to the overall CO2 conversion efficiency. We then discuss the incorporation of anion exchange ionomers in the cathode catalyst layer of CO2 electrolysis cells and how the ionomer parameters define the efficiency and selectivity of Ag catalysts towards electrochemical CO2 reduction. Through this work, we demonstrate the influencing factors of AEM and ionomer materials on the efficiency of electrochemical CO2 conversion and conclude that further advances are paramount for the adoption of this promising technology, which is integral in closing the carbon loop of the petrochemical industry and meeting our wider climate change targets. References: P. De Luna et al., Science, 364, eaav3506 (2019). D. Salvatore, C. Gabardo, A. Reyes, and S. Holdcroft, Nat. Energy, 6, 339–348 (2021). P. Mardle, S. Cassegrain, F. Habibzadeh, Z. Shi, and S. Holdcroft, J. Phys. Chem. C, 125, 25446–25454 (2021). Figure 1

Ion diffusion is important in a variety of applications, yet fundamental understanding of the interaction of lattice vibrations (phonons and vibrational motifs) and the mobile species in solids is still missing. Particularly, for Li super ionic conductors (LISICONs), several studies have reported on the important role of the poly-anion octahedral rotations (rocking modes) in facilitating solid-state Li+ ion migration.[1], [2] However, direct calculation of the contribution of these rocking modes to the Li+ hop is missing, and the provided arguments in these reports are mostly based on establishing correlations between different properties of the rocking modes and the migration properties of the hopping Li+ ion without directly quantifying the contribution of the rocking modes to the Li+ hop. For instance, rocking modes have been argued to be able to (i) provide a softer lattice environment for Li+ ion vibration,[3] (ii) increase the bottleneck area of diffusion (4-O square area),[2] (iii) induce additional force on the carrier sublattice,[1] and (iv) maintain a relatively constant coordination number for Li+ ion during its hop[1] – all conducive to Li+ hop in the lattice. Although insightful, we still lack understanding of the exact vibrational frequencies (density of states) of the rocking modes, and, more importantly, the degree of their contribution to Li+ hop with respect to other phonon modes in the structure. In this work, using a combination of ab initio nudged elastic band (NEB) and lattice dynamics calculations based on the recently proposed formalism,[4] we identify the direct contributions of all phonons, including the rocking ones, to Li+ hop in the perovskite solid-state Li+ conductor Li0.5La0.5TiO3 (LLTO). We set up our NEB Li+ hop calculations considering (i) different orderings of the LLTO lattice,[5] and (ii) different Li+ hopping mechanisms (single and concerted (cooperative)) that can occur in the LLTO lattice.2 To sample such a high degree of complexity, we performed 22 independent NEB calculations of Li+ hop in three different LLTO structures with distinct Li|La orderings and based on two different ion hop mechanisms (single and concerted). Our calculations determined that the following two groups of vibrational modes dominate the contributions to the Li+ hop in the LLTO lattice: (i) rocking modes, and (ii) modes that induce large vibrational energies on the hopping Li+ along its hopping direction. Specifically, our results confirmed that the top 5% (10%) contributing modes to the Li+ hop in the LLTO lattice were responsible for 48% (61%) of the total contributions to the Li+ hop, and the two rocking and highly energetic modes comprised >95% (>85%) of these top 5% (10%) contributing modes. Notable from our calculations was that the rocking modes were only present in the < 5.5 THz frequency region, and in this < 5.5 THz frequency region, they comprised 33% of the vibrational modes and contributed 50% to all the possible contributions to the Li+ hop in this low frequency THz region. Moreover, through static modal excitement calculations, we determined that highly contributing rocking modes of vibration were important in solid-state Li+ ion migration because of their ability to (i) increase the O-4 square bottleneck area of conduction[6] and (ii) amplify the force on the hopping Li+ ion. In summary, our observations demonstrated the strong importance of the THz vibrational region to Li+ hop in the lattice, which can be accessible for further explorations using THz spectroscopy techniques to deepen our understanding of the relation between solid-state transport of Li+ and different vibrational motifs in the lattice. References [1] J. G. Smith and D. J. Siegel, ‘Low-temperature paddlewheel effect in glassy solid electrolytes’, Nat Commun, vol. 11, no. 1, pp. 1–11, 2020. [2] S. Stramare, V. Thangadurai, and W. Weppner, ‘Lithium lanthanum titanates: a review’, Chemistry of materials, vol. 15, no. 21, pp. 3974–3990, 2003. [3] X. Li and N. A. Benedek, ‘Enhancement of ionic transport in complex oxides through soft lattice modes and epitaxial strain’, Chemistry of Materials, vol. 27, no. 7, pp. 2647–2652, 2015, doi: 10.1021/acs.chemmater.5b00445. [4] K. Gordiz, S. Muy, W. G. Zeier, Y. Shao-Horn, and A. Henry, ‘Enhancement of ion diffusion by targeted phonon excitation’, Cell Rep Phys Sci, vol. 2, no. 5, p. 100431, 2021. [5] M. Catti, ‘Ion mobility pathways of the Li+ conductor Li0. 125La0. 625TiO3 by ab initio simulations’, The Journal of Physical Chemistry C, vol. 112, no. 29, pp. 11068–11074, 2008. [6] C. Chen and J. Du, ‘Lithium ion diffusion mechanism in lithium lanthanum titanate solid‐state electrolytes from atomistic simulations’, Journal of the American Ceramic Society, vol. 98, no. 2, pp. 534–542, 2015.

Ion-containing polymers are soft materials composed of polymeric chains and mobile ions. Over the past several decades they have been the focus of considerable research and development for their use as the electrolyte in energy conversion and storage devices. Recent and significant results obtained from multiscale simulations and modeling for proton exchange membranes (PEMs), anion exchange membranes (AEMs), and polymerized ionic liquids (polyILs) are reviewed. The interplay of morphology and ion transport is emphasized. We discuss the influences of polymer architecture, tethered ionic groups, rigidity of the backbone, solvents, and additives on both morphology and ion transport in terms of specific interactions. Novel design strategies are highlighted including precisely controlling molecular conformations to design highly ordered morphologies; tuning the solvation structure of hydronium or hydroxide ions in hydrated ion exchange membranes; turning negative ion-ion correlations to positive correlations to improve ionic conductivity in polyILs; and balancing the strength of noncovalent interactions. The design of single-ion conductors, well-defined supramolecular architectures with enhanced one-dimensional ion transport, and the understanding of the hierarchy of the specific interactions continue as challenges but promising goals for future research.

ABSTRACTAn analysis of RMC structure models of ion conducting glasses in terms of our bond softness sensitive bond-valence method enables us to identify the conduction pathways for a mobile ion as regions of sufficiently low valence mismatch. The strong correlation between the volume fraction F of the “infinite pathway cluster” and the transport properties yields a prediction of both the absolute value and activation energy of the dc ionic conductivities directly from the structural models. Separate correlations for various types of mobile cations can be unified by employing the square root of the cation mass as a scaling factor. From the application of this procedure to RMC models of mixed alkali glasses, the mixed alkali effect, i.e. the extreme drop of the ionic conductivity when a fraction of the mobile ions is substituted by another type of mobile ions may be attributed mainly to the blocking of conduction pathways by unlike cations. The high efficiency of the blocking can be explained by the reduced fractal dimension of the pathways on the length scale of individual ion transport steps.

AbstractStructural properties, single-particle dynamics, and the charge transport are studied in superionic conductor Ag2Se using the molecular dynamics (MD) technique. The calculations are based on a model of interionic potentials in which ions interact through Coulomb interaction, steric repulsion and charge-dipole interaction due to the large electronic polarizability of the selenium ions. Structural and dynamics correlations are studied at five temperatures in the superionic phase. Among the structural correlations the results are presented for partial pair correlation function, coordination numbers, bond angle distributions and wave-vector dependence of the Bragg intensities. Detailed comparison with neutron and x-ray single crystal diffraction experiments. The calculated temperature dependence of the self-diffusion constant of silver is in good agreement with the tracer diffusion measurements. The spectra of velocity autocorrelation functions and the frequency dependent ionic conductivity are calculated. The Haven's ratio is also in good agreement with experiments.Effective interatomic potentials consisting of two-body (steric effect, charge transfer and charge-dipole interactions) and three-body covalent forces are proposed for GeSe2. Using these interaction potentials in MD simulations, the nature of short-range and medium-range order is investigated in glassy and molten GeSe2. All the features in the static structure factor, S(q), including the first sharp diffraction peak (FSDP), are in good agreement with experiments. The FSDP arises from Ge-Ge and Ge-Se correlations between 4-8Å, and the anomalous decrease in its height on cooling is due to frustration enhanced by the increased density.

Abstract Thanks to recent advances in integral field spectroscopy (IFS), modern surveys of nearby galaxies are capable of resolving metallicity maps of H ii regions down to scales of ∼50pc. However, statistical analysis of these metallicity maps has seldom gone beyond fitting basic linear regressions and comparing parameters to global galaxy properties. In this paper (the first of a series), we introduce techniques from spatial statistics that are well suited for detailed analysis of both small- and large-scale metallicity variations within the interstellar media (ISMs) of local galaxies. As a first application, we compare the observed structure of small-scale metallicity fluctuations within 7 local galaxies observed by the PHANGS collaboration to predictions from a stochastic, physically motivated, analytical model developed by Krumholz & Ting. We show that while the theoretical model underestimates the amount of correlated scatter in the galactic metallicity distributions by 3 − 4 orders of magnitude, it provides good estimates of the physical scale of metallicity correlations. We conclude that the ISM of local spiral galaxies is far from homogeneous, with regions of size ∼1 kpc showing significant departures from the mean metallicity at each galactocentric radius.