Search NASA⌕ Search

SEARCH · Search NASA

Results for “Ionic diffusivity”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Kinetic Model for Moisture-Controlled CO 2 Sorption

The understanding of the sorption/desorption kinetics is essential for practical applications of moisture-controlled CO 2 sorption. We introduce an analytic model of the kinetics of moisture-controlled CO 2 sorption and its interpretation in two limiting cases. In one case, chemical reaction kinetics on pore surfaces dominates, in the other case, diffusive transport through the sorbent defines the kinetics. Here, we show that reaction kinetics, which is dominant in the first case, can be expressed as a linear combination of 1st and 2nd order kinetics in agreement with the static isotherm equation derived and validated in a previous paper. The interior transport kinetics can be described by non-linear diffusion equations. By combining all carbon species into a single equation, we can eliminate — in certain limits — the source terms associated with chemical reactions. In this case, the governing equation is ∂θ/∂t = –∇ · (–D eff ∇ θ ). For a sorbent in a form of a flat sheet or a membrane, one can maintain the same functional form of a diffusion equation by introducing a generalized effective diffusivity D M that combines contributions from both surface chemical reaction kinetics and interior diffusive transport kinetics. Experimental data of transient CO 2 flux in a preconditioned commercial anion exchange membrane fit well to the 1st order model as long as very dry states are avoided, validating the theory. The observed DM for a preconditioned commercial anion exchange membrane ranges from 6.6× 10 -14 to 7.1× 10 -14 m 2 s -1 at 35°C. These small values compared to typical ionic diffusivities imply a very slow kinetics, which will be the largest issue that needs to be addressed for practical application. The collected transient CO 2 flux data are used to predict the magnitude of a continuous CO 2 pumping flux in an active membrane that transports CO 2 against a CO 2 concentration gradient. The pumped CO 2 flux is supported by water flux due to a water concentration gradient.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

The nonexistence of a paddlewheel effect in superionic conductors

Since the 1980s, the paddlewheel effect has been suggested as a mechanism to boost lithium-ion diffusion in inorganic materials via the rotation of rotor-like anion groups. However, it remains unclear whether the paddlewheel effect, defined as large-angle anion group rotations assisting Li hopping, indeed exists; furthermore, the physical mechanism by which the anion-group dynamics affect lithium-ion diffusion has not yet been established. In this work, we differentiate various types of rotational motions of anion groups and develop quaternion-based algorithms to detect, quantify, and relate them to lithium-ion motion in ab initio molecular dynamics simulations. Our analysis demonstrates that, in fact, the paddlewheel effect, where an anion group makes a large angle rotation to assist a lithium-ion hop, does not exist and thus is not responsible for the fast lithium-ion diffusion in superionic conductors, as historically claimed. Instead, we find that materials with topologically isolated anion groups can enhance lithium-ion diffusivity via a more classic nondynamic soft-cradle mechanism, where the anion groups tilt to provide optimal coordination to a lithium ion throughout the hopping process to lower the migration barrier. This anion-group disorder is static in nature, rather than dynamic and can explain most of the experimental observations. Our work substantiates the nonexistence of the long-debated paddlewheel effect and clarifies any correlation that may exist between anion-group rotations and fast ionic diffusion in inorganic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A two-dimensional type I superionic conductor

Superionic conductors (SICs) possess liquid-like ionic diffusivity in the solid state, finding wide applicability from electrolytes in energy storage to materials for thermoelectric energy conversion. Type I SICs (e.g., AgI, Ag 2 Se, etc.) are defined by a first-order transition to the superionic state and have so far been found exclusively in three-dimensional crystal structures. Here, we reveal a two-dimensional type I SIC, α-KAg 3 Se 2 by scattering techniques and complementary simulations. Quasi-elastic neutron scattering and ab initio molecular dynamics simulations confirm that the superionic Ag + ions are confined to sub-nanometre sheets, with the simulated local structure validated by experimental X-ray powder pair-distribution-function analysis. Finally, we demonstrate that the phase transition temperature can be controlled by chemical substitution of the alkali metal ions that comprise the immobile charge-balancing layers. Our work thus extends the known classes of SICs and will facilitate the design of new materials with tailored ionic conductivities and phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The ion-ion correlations in organic ionic plastic crystal

Organic ionic plastic crystals (OIPCs) are emerging as promising electrolyte materials for solid-state batteries. However, despite the fast ionic diffusion, OIPCs exhibit relatively low DC conductivity in solid phases caused by strong ion-ion correlations that suppress charge transport. To understand the origin of this suppression, we performed a study of ion dynamics in the OIPC 1-Ethyl-1-methylpyrrolidinium bis (trifluoromethyl sulfonyl) imide [P 12 ][TFSI] utilizing dielectric spectroscopy, light scattering, and Nuclear Magnetic Resonance diffusometry. Comparison of the results obtained in this study with the published earlier results on an OIPC with a completely different structure (Diethyl(methyl)(isobutyl)phosphonium Hexafluorophosphate [P 1,2,2,4 ][PF 6 ]) revealed strong similarities in ion dynamics in both systems. Unlike DC conductivity, which may drop more than ten times between melted and solid phases, diffusion of anions and cations remains high and does not show strong changes at phase transition. The conductivity spectra in the broad frequency range demonstrate unusual shapes in solid phases with an additional step separating fast local ion motions from suppressed long-range charge diffusion controlling DC conductivity. We suggested that in solid phases, anions and cations can jump only between the specific ion sites defined by the crystalline structure. These constraints lead to strong cation-cation and anion-anion correlations strongly suppressing long-range charge transport.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Highly Reversible Lithiation of Additive Free T‐Nb 2 O 5 for a Quarter of a Million Cycles

Abstract Fast energy storage via intercalation requires quick ionic diffusion and often results in pseudocapacitive behavior. The cycling stability of such energy storage materials remains understudied despite the relevance to lifetime cost. Orthorhombic niobium oxide (T‐Nb 2 O 5 ) is a rapid ion intercalation material with a theoretical capacity of 201.7 mAh g −1 (Li 2 Nb 2 O 5 ) and good cycling stability due to the minimal unit cell strain during (de)intercalation. Prior reports of T‐Nb 2 O 5 cycling between 1.3–3.1 V versus Li/Li + noted a 50% loss in capacity after 10 000 cycles. Here, cyclic voltammetry is used to identify the role of the voltage window, state of charge, and potentiostatic holds on the cycling stability of mesoporous T‐Nb 2 O 5 thin films. Films cycled between 1.2–3.0 V versus Li/Li + without voltage holds (Li 1.1 Nb 2 O 5 ) exhibited extreme cycling stability with 90.8% capacity retention after 0.25 million cycles without detectable morphological/crystallographic changes. In contrast, the inclusion of 60 s voltage holds (Li 2.18 Nb 2 O 5 ) led to rapid capacity loss with 61.6% retention after 10 000 cycles with corresponding X‐ray diffraction evidence of amorphization. Cycling with other limited voltage windows identifies that most crystallographic degradation occurs at higher extents of lithiation. These results reveal remarkable stability over limited conditions and suggest that T‐Nb 2 O 5 amorphization is associated with high extents of lithiation.

25 ENERGY STORAGE↗
DOE OSTI2021

Fast and Scalable Synthesis of LiNi 0.5 Mn 1.5 O 4 Cathode by Sol–Gel-Assisted Microwave Sintering

High-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising cathode material for high-energy-density and high-power-density lithium-ion batteries (LIBs). The high cost of the currently available LIBs needs to be addressed urgently for wide application in the transport sector (electric vehicles, buses) and large-scale energy storage systems (ESS). Of significance, herein, novel fast and scalable microwave-assisted synthesis of LNMO is reported, which leads to a production cost cut. X-ray diffraction (XRD) analysis confirms the formation of the desired phase with high crystallinity. Field emission scanning (FE-SEM) and transmission electron microscopy (TEM) analyses indicate that the synthesized phase is of nanometric size (50–150 nm) due to an extremely short sintering time (20 min). The material synthesized at 750 °C shows a higher initial discharge capacity (130 mA h g -1 ) than that synthesized at 650 °C (115 mA h g -1 ). The materials heat treated at higher temperatures show better electrochemical performance in terms of initial capacity, rate capability, and improved cycling. The improved electrochemical performance of LNMO at 750 °C is attributed to the formation of a stable crystal structure, low charge transfer resistance at the electrode/electrolyte interface, high electrical conductivity due to the presence of a disorder structure, and improved ionic diffusivity.

25 ENERGY STORAGE↗
DOE OSTI2024

Topology optimization for the full-cell design of porous electrodes in electrochemical energy storage devices

In this paper, we introduce a density-based topology optimization framework to design porous electrodes for maximum energy storage. We simulate the full cell with a model that incorporates electronic potential, ionic potential, and electrolyte concentration. The system consists of three materials, namely pure liquid electrolyte and the porous solids of the anode and cathode, for which we determine the optimal placement. We use separate electronic potentials to model each electrode, which allows interdigitated designs. As a result, a penalization is required to ensure that the anode and cathode do not touch, i.e., causing a short circuit. We compare multiple 2D designs generated for different fixed conditions, e.g. material properties. A 3D design with complex channel and interlocked structure is also created. All optimized designs are far superior to the traditional monolithic electrode design with respect to energy storage metrics. We observe up to a 750% increase in energy storage for cases with slow effective ionic diffusion within the porous electrode.

25 ENERGY STORAGE↗
DOE OSTI2025

Impact of SO 2 on NiFe Nanoparticle Exsolution and Dissolution from LaFe 0.9 Ni 0.1 O 3 Perovskite Oxides

Ni-doped LaFeO 3 perovskite oxide is a promising cathode material for solid oxide electrolysis cells (SOECs) designed for CO 2 /H 2 O coelectrolysis. Here, the performance of LaFe 0.9 Ni 0.1 O 3 is being investigated under real-world conditions that include exposure to acid gases, such as SO 2 , relevant to SOEC operation. Experiments show that LaFe 0.9 Ni 0.1 O 3 exsolves NiFe nanoparticles, along with the formation of surface SO 4 2– and SO 3 2– after being exposed to 200 ppm of SO 2 . This suggests that the ionic diffusion of Ni 3+ and Fe 3+ between the bulk and the surface remains unaffected throughout the exsolution–dissolution–exsolution cycle. Thermochemical water splitting has been employed as a probe reaction to evaluate the catalytic properties of the exsolved NiFe nanoparticles. These nanoparticles demonstrated improved hydrogen production compared to bare perovskite oxide substrates. However, after exposure to SO 2 , the formation of Fe-rich NiFe nanoparticles led to poor thermocatalytic performance and rapid deactivation of the perovskite at elevated temperatures. Density functional theory (DFT) analysis was utilized to validate the experimental findings, indicating a significantly negative reaction energy for water splitting over exsolved Fe, as well as stronger binding of SO 2 to Fe than to Ni. Computational analysis further suggests that the presence of surface sulfate promotes the formation of Fe-rich NiFe nanoparticles, aligning with the experimental results. Overall, this study clarifies how SO 2 affects the structure of SOEC perovskite oxide candidate materials. Future engineering efforts should focus on enhancing nanoparticle exsolution and sulfur resistance, which is crucial for improving the hydrogen production capacity of La-based perovskite oxides for electro- and thermocatalytic water splitting in real environments containing acid gases.

Najimu, Musa [Univ. of Southern California, Los An↗
DOE OSTI2020

Realistic Ion Dynamics through Charge Renormalization in Nonaqueous Electrolytes

While many practically important electrolytes contain lithium ions, interactions of these ions are particularly difficult to probe experimentally because of their small X-ray and neutron scattering cross sections and large neutron absorption cross sections. Molecular dynamics (MD) is a powerful tool for understanding the properties of nonaqueous electrolyte solutions from the atomic level, but the accuracy of this computational method crucially depends on the physics built into the classical force field. In this study, we demonstrate that several force fields for lithium bistriflimide (LiTFSI) in acetonitrile yield a solution structure that is consistent with the neutron scattering experiments, yet these models produce dramatically different ion dynamics in solution. Such glaring discrepancies indicate that inadequate representation of long-range interactions leads to excessive ionic association and ion-pair clustering. We show that reasonable agreement with the experimental observations can be achieved by renormalization of the ion charges using a “titration” method suggested herewith. This simple modification produces realistic concentration dependencies for ionic diffusion and conductivity in <2 M solutions, without loss in quality for simulation of the structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Beyond Simple Dilution: Superior Conductivities from Cosolvation of Acetonitrile/LiTFSI Concentrated Solution with Acetone

Concentrated solutions of Li salts in acetonitrile are promising alternative electrolytes for the next generation of Li batteries as they may exhibit superior electrochemical properties. However, the reduced mobility of the chemical species is a barrier yet to be overcome, and for this, we explore the utilization of acetone as a cosolvent. Although acetone is a polar compound, we find that its addition to the LiTFSI/acetonitrile solution does not follow the trends expected for a simple dilution process. At a low concentration, acetone subtly shifts acetonitrile from the first to extended solvation sheaths of the ions. Still, most of the original structure of the solution is preserved, and mobile high-concentration clusters are formed in the solution. At higher concentrations, the cosolvation promotes cation–anion interactions but with a different nature from those in the original solution and still allows for a further increase in conductivity. Additionally, the non-coordinating fraction of acetonitrile acquires features resembling the pure solvent, which is a possible additional facilitating factor for ionic diffusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Iron-Doped Sodium Vanadium Oxyflurophosphate Cathodes for Sodium-Ion Batteries—Electrochemical Characterization and In Situ Measurements of Heat Generation

Sodium-ion batteries (NaIBs) are increasingly being envisioned for grid-scale energy-storage systems because of cost advantages. However, implementation of this vision has been challenged by the low-energy densities delivered by most NaIB cathodes. Toward addressing this challenge, the authors report the synthesis and characterization of a new iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 cathode using a novel facile hydrothermal route. The synthesized material was characterized using scanning electron microscopy, X-ray diffraction, and Mössbauer spectroscopy techniques. The obtained discharge capacity in the half-cell configuration lies from 119 to 125 to 130 mA h/g at C/10 while tested using three different electrolyte formulations, dimethyl carbonate–ethylene carbonate (EC)–propylene carbonate (PC), diethyl carbonate–EC, and EC–PC, respectively. The synthesized cathodes were also evaluated in full-cell configurations, which delivered an initial discharge capacity of 80 mA h/g with NaTi 2 (PO 4 ) 3 MWCNT as the anode. Ionic diffusivity and interfacial charge transfer kinetics were also evaluated as a function of temperature and sodium concentration, which revealed that electrochemical rate performances in this material were limited by charge-transfer kinetics. To understand the heat generation mechanism of the Na/Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 half-cell during charge and discharge processes, an electrochemical isothermal calorimetry measurement was carried out at different current rates for two different temperatures (25 and 45 °C). The results showed that the amount of heat generated was strongly affected by the operating charge/discharge state, C-rate, and temperature. Altogether, this work provides a new synthesis route for the development of iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 -based high-performance sodium cathode materials aimed at providing a viable pathway for the development and deployment of large-scale energy-storage based on sodium battery systems.

25 ENERGY STORAGE↗
DOE OSTI2026

Mitigating electrochemical degradation in CsPbBr{sub 3} gamma detectors by organic and inorganic encapsulation.

CsPbBr3 perovskite semiconductors have emerged as a leading candidate for nextgeneration radiation detectors because of their exceptional charge transport properties, defect tolerance, and record-breaking sensitivity and energy resolution. Their long-term stability, however, is hindered by electrode-driven electrochemical decomposition, which is accelerated by moisture- and oxygen-assisted ion migration during operation. Here, we investigated organic and inorganic encapsulation strategies as both environmental barriers and means to suppress interfacial degradation pathways. Atomic layer deposition (ALD) of Al2O3 provided a conformal passivation layer that blocked environmental ingress, suppressed ionic diffusion, reduced leakage current, enhanced energy resolution and expanded the operational electric-field window beyond 5 kV∙cm1 . By contrast, organic encapsulants such as paraffin wax and polystyrene slowed moisture diffusion but did not suppress interfacial reactions, with wax extending stability to over 90 days. These results show that ALD-Al2O3 suppresses dominant interfacial degradation pathways, enabling stable, high-field operation and advancing the practical deployment of CsPbBr3 γ-ray detectors.

Unal, Mustafa↗
DOE OSTI2021

Ion Atmosphere of Wormlike Micelles Profiled by Contrast Variation Small-Angle Neutron Scattering

Structural studies of wormlike micelles have so far mostly focused on the conformational properties of surfactant aggregates. The diffuse ionic atmosphere, which has a profound influence on various micellization phenomena such as thermodynamic stability and structural polymorphism, remains largely unexplored experimentally. In this report a strategy of contrast variation small-angle neutron scattering for this crucial structural study is outlined. Underlined by a general criterion established for unbiasedly identifying the length scale relevant to charge association from the spectral evolution, our analytical framework can provide a quantitative description of counterion distribution in a mathematically tractable manner. Overall, our method can be conveniently extended to facilitate structural studies of complex multicomponent systems using contrast variation neutron scattering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Argyrodite-type advanced lithium conductors and transport mechanisms beyond paddle-wheel effect

Abstract Development of next-generation solid-state Li-ion batteries requires not only electrolytes with high room-temperature (RT) ionic conductivities but also a fundamental understanding of the ionic transport in solids. In spite of considerable work, only a few lithium conductors are known with the highest RT ionic conductivities ~ 0.01 S/cm and the lowest activation energies ~0.2 eV. New design strategy and novel ionic conduction mechanism are needed to expand the pool of high-performance lithium conductors as well as achieve even higher RT ionic conductivities. Here, we theoretically show that lithium conductors with RT ionic conductivity over 0.1 S/cm and low activation energies ~ 0.1 eV can be achieved by incorporating cluster-dynamics into an argyrodite structure. The extraordinary superionic metrics are supported by conduction mechanism characterized as a relay between local and long-range ionic diffusions, as well as correlational dynamics beyond the paddle-wheel effect.

25 ENERGY STORAGE↗
DOE OSTI2021

The passivity of lithium electrodes in liquid electrolytes for secondary batteries

Rechargeable Li metal batteries are currently limited by electrolyte decomposition and rapid Li consumption. Li plating and stripping greatly depend on the solid electrolyte interphase formed at the Li metal-liquid electrolyte interface. This Review discusses the reactions occurring at this interface from a corrosion science perspective, highlighting the requirements for an ideal passivation layer. Rechargeable Li metal batteries are currently limited by safety concerns, continuous electrolyte decomposition and rapid consumption of Li. These issues are mainly related to reactions occurring at the Li metal-liquid electrolyte interface. Additionally, the formation of a passivation film (that is, a solid electrolyte interphase) determines ionic diffusion and the structural and morphological evolution of the Li metal electrode upon cycling. In this Review, we discuss spontaneous and operation-induced reactions at the Li metal-electrolyte interface from a corrosion science perspective. We highlight that the instantaneous formation of a thin protective film of corrosion products at the Li surface, which acts as a barrier to further chemical reactions with the electrolyte, precedes film reformation, which occurs during subsequent electrochemical stripping and plating of Li during battery operation. Finally, we discuss solutions to overcoming remaining challenges of Li metal batteries related to Li surface science, electrolyte chemistry, cell engineering and the intrinsic instability of the Li metal-electrolyte interface.

25 ENERGY STORAGE↗
DOE OSTI2020

Thermodynamic and kinetic properties of layered-CaCo2O4 for the Ca-ion batteries: a systematic first-principles study

One of the more promising directions in multivalent energy storage is systems based on Ca ion intercalation due to the potential for high voltage and capacity. A major challenge for enabling such a battery is to find cathode materials capable of fast ionic diffusion and reversible insertion of Ca ions. Here, on the basis of first-principles calculations, we have demonstrated that layered CaCo 2 O 4 exhibits favorable thermodynamic and kinetic properties that should enable topotactic Ca ion intercalation reactions. The P3-type layered Ca x Co 2 O 4 (0 < x < 1) with either of space groups of P 1 or P 2 1 / m are stable at multiple Ca concentrations and show a smooth voltage plateau higher than 3 V up to X = 0.5. The energy barriers of the single Ca ion migration are as low as 0.36 eV and 0.27 eV at the dilute and high vacancy concentration limits, respectively. Therefore, although varying the vacancy environments of the diffusing atom influences the migration barriers, they do not exceed 0.6 eV. Stochastic analysis of Ca hopping events performed by ab initio molecular dynamics (AIMD) simulation has shown that the migration barriers are lower than 0.32 eV. Therefore, the Ca diffusivity at room temperature extrapolated from the AIMD results is comparable to Li diffusivity (>10 -10 cm 2 s -1 ) in conventional Li cathode materials, suggesting the feasibility of layered Ca x Co 2 O 4 as multivalent cathode materials. Finally, the structural factors that enable fast diffusion are discussed.

25 ENERGY STORAGE↗
DOE OSTI2022

X-ray nano-imaging of defects in thin film catalysts via cluster analysis

Functional properties of transition-metal oxides strongly depend on crystallographic defects; crystallographic lattice deviations can affect ionic diffusion and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging of local structural distortions across an extended spatial region of thin samples. Yet, localized lattice distortions remain challenging to detect and localize using nanodiffraction, due to their weak diffuse scattering. Here, in this study, we apply an unsupervised machine learning clustering algorithm to isolate the low-intensity diffuse scattering in as-grown and alkaline-treated thin epitaxially strained SrIrO 3 films. We pinpoint the defect locations, find additional strain variation in the morphology of electrochemically cycled SrIrO 3 , and interpret the defect type by analyzing the diffraction profile through clustering. Our findings demonstrate the use of a machine learning clustering algorithm for identifying and characterizing hard-to-find crystallographic defects in thin films of electrocatalysts and highlight the potential to study electrochemical reactions at defect sites in operando experiments.

42 ENGINEERING↗