Ionic Diffusivities Research Articles

Configurational Disorder, Strong Anharmonicity, and Coupled Host Dynamics Lead to Superionic Transport in Li3YCl6 (LYC).

In superionic crystals, liquid-like ionic diffusivities often come hand-in-hand with ultra-low thermal conductivity and soft vibrational dynamics. However, generalized relationships between ion transport and vibrational dynamics remain elusive due to the diversity of superionic materials and complex underlying mechanisms. Here, the links between vibrational dynamics and ion transport in close-packed lithium halide ion conductor Li3YCl6 (LYC) are examined using a suite of atomistic first-principles methods. It is shown that configurational disorder, lattice anharmonicity, and coupled host-mobile ion vibrational dynamics together induce a transition to the superionic state. Statistical correlations between ionic hops and activation of the distribution of vibrational modes are found. However, typical phenomena associated with superionic conductors such as selective breakdown of zone-boundary soft phonons, or long wavelength transverse acoustic modes as in the 'phonon-liquid-electron crystal' concept, are not present. Instead, anharmonic zone-boundary modes aiding Li diffusion are found to broaden and soften selectively but persist across the superionic transition. These anharmonic modes couple Li ion motion with the vibrations of the flexible close-packed anion framework, which remains stable and facilitates ionic hopping. The results provide insights into how configurational disorder and soft-yet-resilient vibrational modes enable ionic hopping, particularly in 3D close-packedcrystals.

Multiscale Modelling of Battery Systems at Low Temperatures: Impact of Microscale on Performance

Lithium-ion batteries (LIB) are currently the most widely spread all-purpose energy storage technology. Although improved energy and power densities continue to widen and foster their adoption in multiple application domains, such as electric mobility, LIBs operating temperatures continue to be typically in a range of 15-35 °C. Particularly, at temperatures around and below 0 °C, the performance of LIBs is dramatically reduced, which prohibits deployment of LIBs in cold climates, high latitudes, mountainous regions, or aerospace applications. Low temperatures impact the cycling performance, safety and, most dramatically, decrease the battery capacity. This degradation in performance is a result of several microscale physical mechanisms affecting both electron and Li-ion transport, as well as reaction rates at electrodes and in electrolyte of batteries. In particular, at low temperatures, the charge transfer at the electrode/electrolyte, lithium diffusion in the solid material and Li-ion transport in electrolyte are diminished when compared to room temperature, yielding a reduction in capacity or even battery inoperability in some applications.To improve the low temperature performance, it becomes important to trace down the microscale mechanisms and identify dominant limiting phenomena to address them individually. Despite the fact that vast literature exists for many cathode and anode materials at low temperatures [1-2], identifying the dominant limiting physical mechanisms is still a topic of debate [3]. Different works attribute the low-temperature performance limitations to different aspects of the battery system, such as sluggish transport in the electrolyte [1], slow solid diffusion processes in the active materials [2], charge transfer disruption in electrode or electrolyte composite media or at the solid-electrolyte interface [4], leaving a multitude of possibilities for a particular battery system. Additionally, the complexity of the microscale phenomena in battery systems makes it difficult to trace the root causes from the macro to the microscale, and thus to tackle this problem effectively.In this context, modelling and simulation of the microscale charge and mass transport phenomena is a useful tool in providing insight into the microscale aspects dictating the macroscale operation. Typically, the Doyle-Fuller-Newman (DFN) multiscale model is applied to predict macroscale performance from microscale properties of the battery system [5]. In this model charge and mass conservation equations are solved for the input physical parameters describing the battery system such as geometry and parameters describing the battery materials comprising electronic conductivities of the electrodes, ionic diffusivities and conductivity of the electrolyte and electrochemical reaction rates at the electrode’s active particles. The balancing between these parameters with respect to each other will influence (and limit) the response of the LIB. Each of these parameters is typically considered to follow an Arrhenius relationship with temperature, where an activation energy controls the coefficients for the transport and reaction processes, such that at lower temperatures an exponential decrease in electronic and ionic transport as well as reaction rates leads to strongly reduced performance. However, the particular effects of low temperatures on these coefficients describing the battery microstructure phenomena and its impact on the macroscale performance remain poorly explored.In this paper, we report low temperature effects on microscale parameters and their influence on the macroscale performance with particular examples targeting low temperature effects in LiFePO4 (LFP) and LiNi1/3Mn1/3Co1/3O2 (NMC) based batteries. By implementing a multiscale DFN model in the finite element modeling software COMSOL Multiphysics®, we perform numerical simulations of these battery systems within a range of temperatures and operating conditions and compare them with experimental data. Our results allow to assess the effect of temperature based on microstructural parameters of the system and corresponding macroscale output. Figure 1 exemplifies typical simulation results of the temperature effect on discharge curves for LFP/Graphite (Figure 1a) and NMC/Graphite cells (Figure 1b). These results hold great potential for understanding battery’s microstructure impact on the overall performance at low temperatures and to inform electrode choice, battery design and manufacturing processes for low temperature battery systems. Acknowledgement This research has received funding from the European Union’s Horizon Europe research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 101062008.

Insights into the structure and Ion transport of pectin-[BMIM][PF6] electrolytes.

We investigate the effect of pectin on the structure and ion transport properties of the room-temperature ionic liquid electrolyte 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) using molecular dynamics simulations. We find that pectin induces intriguing structural changes in the electrolyte that disrupt large ionic aggregates and promote the formation of smaller ionic clusters, which is a promising finding for ionic conductivity. Due to pectin in [BMIM][PF6] electrolytes, the diffusion coefficient of cations and anions is observed to decrease by a factor of four for a loading of 25 wt. % of pectin in [BMIM][PF6] electrolyte. A strong correlation between the ionic diffusivities (D) and ion-pair relaxation timescales (τc) is observed such that D ∼ τc-0.75 for cations and D ∼ τc-0.82 for anions. The relaxation timescale exponents indicate that the ion transport mechanisms in pectin-[BMIM][PF6] electrolytes are slightly distinct from those found in neat [BMIM][PF6] electrolytes (D∼τc-1). Since pectin marginally affects ionic diffusivities at the gain of smaller ionic aggregates and viscosity, our results suggest that pectin-ionic liquid electrolytes offer improved properties for battery applications, including ionic conductivity, mechanical stability, and biodegradability.

Advantages of a Solid Solution over Biphasic Intercalation for Vanadium-Based Polyanion Cathodes in Na-Ion Batteries.

The efficient operation of metal-ion batteries in harsh environments, such as at temperatures below -20 °C or at high charge/discharge rates required for EV applications, calls for a careful selection of electrode materials. In this study, we report advantages associated with the solid solution (de)intercalation over the two-phase (de)intercalation pathway and identify the main sources of performance limitations originating from the two mechanisms. To isolate the (de)intercalation pathway as the main variable, we focused on two cathode materials for Na-ion batteries: a recently developed KTiOPO4-type NaVPO4F and a well-studied Na3V2(PO4)2F3. These materials have the same elemental composition, operate within the same potential range, and demonstrate very close ionic diffusivities, yet follow different (de)intercalation routes. To avoid any interpretation uncertainties, we obtained these materials in the form of particles with merely identical morphology and size. A detailed electrochemical study revealed a much lower capacity and energy density retention for phase-transforming Na3V2(PO4)2F3 compared to NaVPO4F, which exhibits a single-phase behavior over a wide range of Na concentrations. The reasons for the inferior rate capability and temperature tolerance for the phase-separating Na3V2(PO4)2F3 material should be affiliated with slow phase boundary propagation. We hope that the comprehensive information on limiting factors provided for both mechanisms is useful for the further optimization of electrode materials toward a new generation of high-power and low-temperature metal-ion batteries.

Strategies for fitting accurate machine-learned inter-atomic potentials for solid electrolytes

Ion transport in materials is routinely probed through several experimental techniques, which introduce variability in reported ionic diffusivities and conductivities. The computational prediction of ionic diffusivities and conductivities helps in identifying good ionic conductors, and suitable solid electrolytes (SEs), thus establishing firm structure-property relationships. Machine-learned potentials are an attractive strategy to extend the capabilities of accurate ab initio molecular dynamics (AIMD) to longer simulations for larger systems, enabling the study of ion transport at lower temperatures. However, machine-learned potentials being in their infancy, critical assessments of their predicting capabilities are rare. Here, we identified the main factors controlling the quality of a machine-learning potential based on the moment tensor potential formulation, when applied to the properties of ion transport in ionic conductors, such as SEs. Our results underline the importance of high-quality and diverse training sets required to fit moment tensor potentials. We highlight the importance of considering intrinsic defects which may occur in SEs. We demonstrate the limitations posed by short-timescale and high-temperature AIMD simulations to predict the room-temperature properties of materials.

Structural electroneutrality in Onsager–Stefan–Maxwell transport with charged species

We present a method to embed local electroneutrality within Onsager–Stefan–Maxwell electrolytic-transport models, circumventing their formulation as differential systems with an algebraic constraint. Flux-explicit transport laws are developed for general multicomponent electrolytes, in which the ionic conductivity, component diffusivities, and transference numbers relate to Stefan–Maxwell coefficients through invertible matrix calculations. A construction we call a ‘salt–charge basis’ implements Guggenheim’s transformation of species electrochemical potentials into combinations describing a minimal set of neutral components, leaving a unique combination associated with electricity. Defining conjugate component concentrations and fluxes that preserve the structures of the Gibbs function and energy dissipation retains symmetric Onsager reciprocal relations. The framework reproduces Newman’s constitutive laws for binary electrolytes and the Pollard–Newman laws for molten salts; we also propose laws for salt solutions in two-solvent blends, such as lithium-ion-battery electrolytes. Finally, we simulate a potentiostatic Hull cell containing a non-ideal binary electrolyte with concentration-dependent properties.

Transferable Deep Learning Potential Reveals Intermediate-Range Ordering Effects in LiF-NaF-ZrF4 Molten Salt.

LiF-NaF-ZrF4 multicomponent molten salts are promising candidate coolants for advanced clean energy systems owing to their desirable thermophysical and transport properties. However, the complex structures enabling these properties, and their dependence on composition, is scarcely quantified due to limitations in simulating and interpreting experimental spectra of highly disordered, intermediate-ranged structures. Specifically, size-limited ab initio simulations and accuracy-limited classical models used in the past are unable to capture a wide range of fluctuating motifs found in the extended heterogeneous structures of liquid salt. This greatly inhibits our ability to design tailored compositions and materials. Here, accurate, efficient, and transferable machine learning potentials are used to predict structures far beyond the first coordination shell in LiF-NaF-ZrF4. Neural networks trained at only eutectic compositions with 29% and 37% ZrF4 are shown to accurately simulate a wide range of compositions (11-40% ZrF4) with dramatically different coordination chemistries, while showing a remarkable agreement with theoretical and experimental Raman spectra. The theoretical Raman calculations further uncovered the previously unseen shift and flattening of bending band at ∼250 cm-1 which validated the simulated extended-range structures as observed in compositions with higher than 29% ZrF4 content. In such cases, machine learning-based simulations capable of accessing larger time and length scales (beyond 17 Å) were critical for accurately predicting both structure and ionic diffusivities.

Prediction of equilibrium water uptake and ions diffusivities in ion-exchange membranes combining molecular dynamics and analytical models

In recent years, the field of process engineering has witnessed an exponential increase in the usage of ion-exchange membranes (IEM) in light of their pivotal function in green technologies such as electrodialysis (ED), reverse electrodialysis (RED) and fuel cells. One of the key parameters in IEMs performance is the equilibrium water uptake (wu) as this has been shown to have a prominent effect on some of their fundamental properties such as ionic diffusivities. In this work, we have elaborated a molecular dynamics (MD) protocol to reliably predict the water uptake of IEMs by considering a polysulfone (PSU) functionalized with tetramethylammonium (TMA) anion-exchange membrane (AEM) compensated with chloride anions as case study. The procedure led to good agreement with reported experimental data in a wide range of ion-exchange capacities (IEC) and improved the results with respect to the DFT-based approach developed in our previous work. The issue of considering too thin membrane models compared to the actual IEM was found to be relevant and was addressed by proposing an ad-hoc simulation setup; this allowed to reconcile results accuracy with reasonable computational costs. Finally, the computed wu were used to evaluate chloride counter-ion diffusivities within three different theoretical frameworks (the Mackie-Meares, Yasuda-Lamaze-Ikenberry and Manning-Meares models) and it was found that a satisfactory agreement with experiments can be achieved. This confirmed the potential of the current strategy to predict the wu and ion diffusivities in IEM without resorting to experimental data, thus paving the way towards a computationally driven design of new membranes.

Localized Surface Oxygen Ion Transport in Sto and YSZ Observed Via Quasi in Situ Scanning Probe Microscopy

Ionic transport in solid oxides lays the fundamentals of solid-state electrochemical energy and sensor devices. While ionic transport in polycrystalline oxides has been studied for decades, most studies are reliant upon macro-scale observations where direct revelation of localized transport behavior is not feasible. In this presentation, we report a direct quasi in situ observation of oxygen ion transport in SrTiO3 (STO) and Y2O3-stabilized ZrO2 (YSZ) by leveraging scanning probe microscopy variants.First, a cluster of oxygen vacancies formed by an electrical bias at a tip-sample contact. Then, we exposed the sample to an elevated temperature to allow a facilitated ionic diffusion. The resultant lateral distribution of oxygen vacancies was obtained by Kelvin probe force microscopy (KPFM). Depth-wise distribution of oxygen vacancies were acquired by a combination of in situ etching with a diamond-coated probe and KPFM scans, which enabled an observation of ionic charge transport in a highly localized fashion in both lateral and depth-wise directions.From 3D spatial charge imaging, the activation energies of surface ionic diffusion in the lateral direction (Esurf) and those of bulk diffusion in the depth-wise direction (Ebulk) were quantified; for YSZ, Esurf = 0.34 eV and Ebulk = 1.13 eV, and for STO, Esurf = 0.50 eV and Ebulk = 1.30 eV. It was also found that the surface ion diffusivity of YSZ (1.68 × 10-8 cm2/s) is more than 3 orders of magnitude higher than that of STO (4.86 × 10-12 cm2/s), and that bulk diffusivity of YSZ (1.70 × 10-11 cm2/s) is more than 7 orders of magnitude higher than that of STO (7.61 × 10-19 cm2/s). To the best of our knowledge, this is the first study where the ionic diffusivities along the surface and into the bulk are separately quantified by direct localized observations of 3D distribution of ionic species, as opposed to a bulk measurement from which diffusivities were indirectly deduced.The authors acknowledge the support by National Science Foundation (DMR 1753383).

Impact of asymmetries in valences and diffusivities on the transport of a binary electrolyte in a charged cylindrical pore

Ion transport in porous media is present in a wealth of technologies, e.g., energy storage devices such as batteries and supercapacitors, and environmental technologies such as electrochemical carbon capture and capacitive deionization. Recent studies on flat plate electrodes have demonstrated that asymmetries in ions properties, such as valences and diffusivities, lead to intriguing and counter-intuitive physical phenomena. Yet, the consequences of such asymmetries to ion transport have seldom been explored in porous geometries. To bridge this knowledge gap, we employ direct numerical simulations to solve Poisson-Nernst-Planck equations inside a cylindrical pore for a binary electrolyte with arbitrary valences and diffusivities. Next, we conduct a perturbation expansion in the limit of small potential and derive equations for charge and salt transport under confinement. We obtain good agreement between the perturbation analysis and the direct numerical simulations. Our analysis reveals that the charge and the salt transport are coupled with each other. Further, the coupling between the charge and salt transport processes is enhanced by an increase in valence and diffusivity asymmetries of ions. We observe that the mismatch of the ionic diffusivities induces a non-trivial salt dynamics, producing either transient depletion or enhancement of salt in the pore. In the regime of high static-diffusion-layer conductance, we obtain an analytical solution to our perturbation model. The solution elucidates how electrolyte asymmetry induces two charging timescales that are set by the relative pore size. In the overlapping-double-layer regime, these timescales reduce to the diffusion times of each ion such that the transport of the two ions appears to be decoupled. Overall, our work underscores that the asymmetry in cation and anion diffusivities fundamentally alters the behavior of ionic transport inside a charged cylindrical pore and opens up new avenues of research on electrolyte transport in porous materials.

Deciphering Fast Ion Transport in Glasses: A Case Study of Sodium and Silver Vitreous Sulfides.

High-capacity solid-state batteries are promising future products for large-scale energy storage and conversion. Sodium fast ion conductors including glasses and glass ceramics are unparalleled materials for these applications. Rational design and tuning of advanced sodium sulfide electrolytes need a deep insight into the atomic structure and dynamics in relation with ion-transport properties. Using pulsed neutron diffraction and Raman spectroscopy supported by first-principles simulations, we show that preferential diffusion pathways in vitreous sodium and silver sulfides are related to isolated sulfur Siso, that is, the sulfur species surrounded exclusively by mobile cations with a typical stoichiometry of M/Siso ≈ 2. The Siso/Stot fraction appears to be a reliable descriptor of fast ion transport in glassy sulfide systems over a wide range of ionic conductivities and cation diffusivities. The Siso fraction increases with mobile cation content x, tetrahedral coordination of the network former and, in case of thiogermanate systems, with germanium disulfide metastability and partial disproportionation, GeS2 → GeS + S, leading to the formation of additional sulfur, transforming into Siso. A research strategy enabling to achieve extended and interconnected pathways based on isolated sulfur would lead to glassy electrolytes with superior ionic diffusion.

Effect of succinonitrile on ion transport in PEO-based lithium-ion battery electrolytes

We report the ion transport mechanisms in succinonitrile (SN) loaded solid polymer electrolytes containing polyethylene oxide (PEO) and dissolved lithium bis(trifluoromethane)sulphonamide (LiTFSI) salt using molecular dynamics simulations. We investigated the effect of temperature and loading of SN on ion transport and relaxation phenomenon in PEO-LiTFSI electrolytes. It is observed that SN increases the ionic diffusivities in PEO-based solid polymer electrolytes and makes them suitable for battery applications. Interestingly, the diffusion coefficient of TFSI ions is an order of magnitude higher than the diffusion coefficient of lithium ions across the range of temperatures and loadings investigated. By analyzing different relaxation timescales and examining the underlying transport mechanisms in SN-loaded systems, we find that the diffusivity of TFSI ions correlates excellently with the Li-TFSI ion-pair relaxation timescales. In contrast, our simulations predict distinct transport mechanisms for Li-ions in SN-loaded PEO-LiTFSI electrolytes. Explicitly, the diffusivity of lithium ions cannot be uniquely determined by the ion-pair relaxation timescales but additionally depends on the polymer segmental dynamics. On the other hand, the SN loading induced diffusion coefficient at a given temperature does not correlate with either the ion-pair relaxation timescales or the polymer segmental relaxation timescales.

The electrochemical impedance spectrum of asymmetric electrolytes across low to moderate frequencies

• New mathematical analysis for the electrochemical impedance spectrum of asymmetric electrolytes. • Double plateau behavior in the real part of impedance predicted across low to moderate frequencies. • Low frequency response is caused transient bulk diffusion, or concentration polarization, of salt across an electrochemical cell. We develop new mathematical expressions for the electrochemical impedance spectrum of an asymmetric electrolyte. Specifically, we consider the Poisson-Nernst-Planck (PNP) equations governing ion transport in a binary asymmetric electrolyte with unequal valences and diffusivities, flanked by planar, parallel, blocking electrodes. The electrodes are subject to an oscillating voltage of small amplitude comparable to the thermal voltage scale. We further consider the limit practically applicable to liquid electrolytes of thin Debye layers ∊ = 1 / ( κ L ) ≪ 1 , where κ - 1 is the Debye screening length and L is the length of the half cell. The impedance is then obtained from the current in the external circuit, defined as the rate of change of electric field at either electrode. We identify two distinct asymptotic regimes for the frequency ( ω ) in the limit ∊ → 0 : low frequencies, on the order of the inverse bulk diffusion time ω = O ( D A / L 2 ) ; and moderate frequencies, on the order of the inverse RC charging time scale ω = O ( D A κ / L ) . Here D A = ( z + + z - ) D + D - / ( z + D + + z - D - ) is the ambipolar diffusion coefficient of the salt, z ± are the ionic valences, and D ± are the ionic diffusivities. Our analysis provides new, concise expressions for the impedance at low and moderate frequencies, that account for ionic valence asymmetry. Further, in the moderate frequency analysis, higher order contributions (in ∊ ) to the impedance reveal that the real part (i.e. the resistance) appears to diverge as ω - 1 / 2 in the limit ω L / ( κ D A ) → 0 , akin to a semi-infinite Warburg element. We determine that this occurs due to the existence of oscillating diffusion layers, O ( ∊ 1 / 2 L ) in width, that bridge the ion transport between the O ( ∊ L ) wide Debye layers adjacent to each electrode and the O ( L ) wide bulk electro-neutral electrolyte. In the low frequency regime, however, these diffusion layers relax, and effectively merge across the bulk of the cell; consequently, the resistance spectrum attains a plateau in the limit of zero frequency ω L 2 / D A → 0 . Thus, our asymptotic analysis discerns the electrochemical processes that dictate the impedance of asymmetric electrolytes at the low and moderate frequency regimes.

Intrinsic weaknesses of Co-free Ni–Mn layered cathodes for electric vehicles

Co-free Li[NixMn1−x]O2 (NM) cathodes have received considerable attention owing to their cost competitiveness and cycling stability. However, Ni-rich, Co-free NM cathodes have not been extensively studied and the reasons for their poor performance at low temperatures remain unclear. Herein, the fundamental properties and electrochemical performances of Co-free Li[NixMn1−x]O2 and conventional Li[NixCoyMn1−x−y]O2 (NCM) cathodes (x = 0.8 and 0.9) at various temperatures are compared. Although the cycling stability and rate capabilities of Co-free NM cathodes are comparable with those of NCM cathodes at elevated operating temperatures, their performances are significantly inferior to those of NCM cathodes at low temperatures. The absence of Co in layered oxide cathodes not only increases diffusion-hindering cation disorder in their Li layers but also reduces the tolerance of their ionic diffusivities to low temperatures, leading to poor rate capabilities at high C-rates and low temperatures. To improve the practical viability of Co-free layered oxide cathodes, it is necessary to resolve their serious weakness of poor low-temperature performance.

Confinement effect on thermopower of electrolytes

Ionic Seebeck effect of electrolytes has shown promising applications in harvesting energy from low-grade heat sources with small temperature differences from the environment, which can power sensors and Internet-of-Things devices. Recent experiments have demonstrated giant thermopower (∼10 mV/K) of electrolytes under confinement due to the overlapping of electric double layer (EDL). Nonetheless, there has been no consensus on the theory of the ionic Seebeck effect, especially whether the thermopower depends on ionic diffusivities, imposing confusion on the theoretical interpretation of experimental discoveries of the giant thermopower of confined electrolytes. This article presents a linear perturbative solution of Poisson-Nernst-Planck (PNP) equations to describe the ionic Seebeck effect of confined liquid electrolytes. We provide analytical and numerical solutions to the PNP equations for both closed systems and open systems connected to reservoirs of electrolytes. The analytical solution captured the confinement effect both along and perpendicular to the temperature gradient, and showed excellent agreement with numerically solved PNP equations for a wide range of EDL potentials, channel widths, and lengths. Finally, we show that for polyelectrolytes with largely mismatched diffusivities, thermopower can only be enhanced for the closed system through confinement perpendicular to the temperature gradient.

Chemo-mechanical Model of Lithium Dendrite Growth Impacted By External Pressure and Plastic Deformation

High energy density and low coulombic efficiency of lithium metal anodes has made Li-ion batteries a standout area of research for improving commercial battery performance; however, there are operation and safety concerns that must be addressed before expanding their applications. During cell operation lithium dendrites form on surface inhomogeneities of the rough anode, which push through the separator, decrease cell efficiency, and eventually short-circuit the cell. Mechanical stress caused by an external pressure applied to the cell has been shown to mitigate lithium plating, though its addition leads to inhomogeneous ion transport between the separator and anode. As choice of electrolyte is also crucial for mitigating dendrite growth, the combined effects of stress and electrochemical transport properties on the propensity of plating are of interest. In this work we present a 3-D mesoscale model of a typical porous separator brought into contact with a lithium protrusion during cycling. The protrusion is characteristic of an inhomogeneity on a rough Li anode surface. The effects of lithium plastic deformation under high stress are modeled as the materials are brought into contact; previous work neglected this complexity. Partial contact between the materials creates an electrolyte-filled gap which drastically impacts the electrochemical response across the Li-separator interface. Propensity of plating is related to the combined effects of internal stress and various material properties; protrusion shape, separator porosity and modulus, separator/electrolyte ionic diffusivities, and applied current density are of specific interest in this study. The conditions for which dendrite formation is encouraged or suppressed are reported and may be used to inform choice of materials and cell manufacturing methods.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.

Electrochemical deposition method for load-induced crack repair of reinforced concrete structures: A numerical study

Cracking has been a severe threat to the durability of reinforced concrete structures. Electrochemical deposition is a promising rehabilitating method for crack repair with the additional advantages of chloride removal and realkalization of embedded rebars. This work presents a comprehensive numerical study of three coupled subprocesses involved in the electrochemical deposition treatment: concrete cracking, multi-ionic transport and crack repair, which can reveal the underlying mechanisms from a fundamental point of view. A multi-phase cracking model was developed considering local mechanical property variances in concrete composites. Interconnections and chemical reactions among various ions in concrete composites were elaborated thoroughly. Unlike most existing studies, the overall improvement of impermeability and compactness of structural components was well reflected by considering porosity changes and corresponding time-dependent ionic diffusivities. A detailed parametric analysis on influencing factors revealed that the current density of 0.5 A/m2 possesses the best repair effect with a complete closure in 15 days, but the chloride removal efficiency is not ideal. Increasing the ambient temperature can promote the crack repair rate, and the most obvious improvement is between 0 ℃ and 10 ℃. The findings could provide the basis for optimal selection during electrochemical deposition treatment.

Interior Electroneutrality in Nernst–Planck–Navier–Stokes Systems

We consider the limit of vanishing Debye length for ionic diffusion in fluids, described by the Nernst-Planck-Navier-Stokes system. In the asymptotically stable cases of blocking (vanishing normal flux) and uniform selective (special Dirichlet) boundary conditions for the ionic concentrations, we prove that the ionic charge density $\rho$ converges in time to zero in the interior of the domain, in the limit of vanishing Debye length ($\epsilon\to 0$). For the unstable regime of Dirichlet boundary conditions for the ionic concentrations, we prove bounds that are uniform in time and $\epsilon$. We also consider electroneutral boundary conditions, for which we prove that electroneutrality $\rho\to 0$ is achieved at any fixed $\epsilon> 0$, exponentially fast in time in $L^p$, for all $1\le p<\infty$. The results hold for two oppositely charged ionic species with arbitrary ionic diffusivities, in bounded domains with smooth boundaries.

Effect of Sodium Chloride on Internal Quasi-Liquid Layers in Ice Ih

We consider the effect of sodium chloride on the properties of internal interfaces in ice Ih. For this purpose, we employ molecular dynamics simulations to investigate the role of sodium and chloride ions in the properties of grain boundaries (GB), which are the interfacial regions separating adjacent crystal grains with different orientations. The results show that the presence of the ions significantly affects both the structural and dynamical characteristics of the disordered layers at the GB regions. Compared to pristine ice samples, in addition to reducing the degree of water structure, the ions enhance the mobility of the water molecules in the GB region. Even so, the briny GB regions display quasi-liquid behavior in that both the molecular and the ionic diffusivities are substantially lower than in the corresponding bulk liquid solutions at the same conditions of temperature, pressure, and salinity. Finally, the presence of sodium chloride in the GB regions is found to facilitate the GB sliding process, which is consistent with experimental insight.

Assigning ionic properties in perovskite solar cells; a unifying transient simulation/experimental study

A voltage decay based method to probe ionic concentrations and diffusivities in perovskite solar cells is herein presented and verified with a newly developed drift-diffusion simulation tool.