Sodium Ion Conductor Research Articles

NaGaPO4F - a KTiOPO4-structured solid sodium-ion conductor.

Advanced ionic conductors are crucial for a large variety of contemporary technologies spanning solid state ion batteries, fuel cells, gas sensors, water desalination, etc. In this work, we report on a new member of KTiOPO4-structured materials, NaGaPO4F, with sodium-ion conductivity. NaGaPO4F has been obtained for the first time via a facile two-step synthesis consisting of a hydrothermal preparation of an ammonia-based precursor, NH4GaPO4F, followed by an ion exchange reaction with NaNO3. Its crystal structure was precisely refined using a combination of synchrotron X-ray powder diffraction and electron diffraction tomography. The material is thermally stable upon 450 °C showing no significant structural transformations or degradation but only a ∼1% cell volume expansion. Na-ion mobility in NaGaPO4F was investigated by a joint experimental and computational approach comprising solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT). DFT and bond-valence site energy (BVSE) calculations reveal 3D diffusion of sodium in the [GaPO4F] framework with migration barriers amounting to 0.22 and 0.44 eV, respectively, while NMR yields 0.3-0.5 eV that, being coupled with a calculated bandgap of ∼4.25 eV, makes NaGaPO4F a promising fast Na-ion conductor.

Double Paddle‐Wheel Enhanced Sodium Ion Conduction in an Antiperovskite Solid Electrolyte

AbstractAntiperovskite structure compounds (X3AB, where X is an alkali cation and A and B are anions) have the potential for highly correlated motion between the cation and a cluster anion on the A or B site. This so‐called “paddle‐wheel” mechanism may be the basis for enhanced cation mobility in solid electrolytes. Through combined experiments and modeling, the first instance of a double paddle‐wheel mechanism, leading to fast sodium ion conduction in the antiperovskite Na3−xO1−x(NH2)x(BH4), is shown. As the concentration of amide (NH2−) cluster anions is increased, large positive deviations in ionic conductivity above that predicted from a vacancy diffusion model are observed. Using electrochemical impedance spectroscopy, powder X‐ray diffraction, synchrotron X‐ray diffraction, neutron diffraction, ab initio molecular dynamics simulations, and NMR, the cluster anion rotational dynamics are characterized and it is found that cation mobility is influenced by the rotation of both NH2− and BH4− species, resulting in sodium ion conductivity a factor of 102 higher at x = 1 than expected for the vacancy mechanism alone. Generalization of this phenomenon to other compounds could accelerate fast ion conductor exploration and design.

Interface Stability between Na3Zr2Si2PO12 Solid Electrolyte and Sodium Metal Anode for Quasi-Solid-State Sodium Battery

Solid electrolytes are renowned for their nonflammable, dendrite-blocking qualities, which also exhibit stability over large potential windows. NASICON-type Na1+xZr2SixP3-xO12 (NZSP) is a well-known solid electrolyte material for sodium metal batteries owing to its elevated room temperature sodium-ion (Na+) conductivity and good electrochemical stability. Nevertheless, the strong electrode–electrolyte interfacial resistance restricts its implementation in sodium metal batteries and remains a significant challenge. In this work, we present an efficacious process to enhance the sodium wettability of Na3Zr2Si2PO12 by sputtering a thin gold (Au) interlayer. Our experimental investigation indicates a substantial reduction in interfacial resistance, from 2708 Ω cm2 to 146 Ω cm2, by employing a fine Au interlayer between the Na metal and the NZSP electrolyte. The symmetrical Na||NZSP||Na with a gold interlayer cell shows a steady Na stripping/plating at a high current density of 320 µA cm−2. A quasi-solid-state battery, with NaFePO4 (NFP) as a cathode, metallic sodium as an anode, and a Au-sputtered NZSP electrolyte with polypropylene (PP) soaked in electrolyte as an intermediate layer on the cathode, exhibited a discharge capacity of 100 mAh g−1 and a ~100% Coulombic efficiency at 50 μA cm−2 after the 50th charge/discharge cycle at room temperature (RT).

Electrode/Electrolyte Interphases of Sodium-Ion Batteries

The performance of sodium-ion batteries largely depends on the presence and properties of passive films formed on the electrode/electrolyte interfaces. Passive films on negative electrodes inevitably result from the reduction in electrolyte components (solvent and salt anion). They have the properties of a solid electrolyte with sodium ion conductivity and are insulators in terms of electronic conductivity. Usually, they are called SEI—solid electrolyte interphase. The formation of SEI is associated with the consumption of a certain charge, which is an irreversible capacity. Passive films on the surface of positive electrodes (CEI—cathode electrolyte interphase) arise as a result of electrolyte oxidation. The present review summarizes the literature of the recent 15 years concerning the effects of electrode nature (hard carbon, other carbon materials, various metals, oxides, chalcogenides, etc.), electrolyte composition, and other factors on composition and properties of SEIs in sodium-ion batteries. Literary data on CEIs are reviewed as well, although their volume is inferior to that of data on SEIs.

Analcime with High Sodium Ion Conduction as a Solid Electrolyte

Analcime with High Sodium Ion Conduction as a Solid Electrolyte

Electrochemical and Degradation Studies on One-Dimensional Tunneled Sodium Zirconogallate (NZGO) + Yttria-Stabilized Zirconia (YSZ) Composite, Mixed Sodium and Oxygen Ion Conductor

In recent years, multi-phase materials capable of multi-ion transport have emerged as attractive candidates for a variety of electrochemical devices. Here, we provide experimental results for fabricating a composite electrolyte made up of a one-dimensional fast sodium-ion conductor, sodium zirconogallate, and an oxygen-ion conductor, yttria-stabilized zirconia. The composite is synthesized through a vapor phase conversion mechanism, and the kinetics of this process are discussed in detail. The samples are characterized using diffraction, electron microscopy, and electrochemical impedance spectroscopy techniques. Samples with a finer grain structure exhibit higher kinetic rates due to larger three-phase boundaries (TPBs) per unit area. The total conductivity is fitted to an Arrhenius type equation with activation energies ranging from at temperatures below to above The electrochemical performance of multi-phase multi-species, mixed and conductor, is tested under both oxygen chemical potential gradient as well as sodium chemical potential gradient are discussed using the Goldman-Hodgkin-Kats (GHK) and the Nernst equation.

Theoretical design of Na-rich anti-perovskite as solid electrolyte: The effect of cluster anion in stability and ionic conductivity

The next-generation solid-state batteries need safe and efficient solid-state electrolytes. However, the conventional solid-state electrolytes materials often suffer from low ionic conductivity. The emerging anti-perovskites are potential solid electrolytes materials for their rich cations and tunable crystal structure. Here, the first-principles density functional theory (DFT) calculations are employed to investigate the stability, electronic properties, elastic constants and the ions migration of sodium-rich anti-perovskite Na3SA (A ​= ​AlF4¯, ClO4¯, ICl4¯, IO4¯). Calculations show that the clusters substitution at anion position A of Na3SA displays larger band gap and faster Na ion transport than that of halogen anions (e.g., Cl, Br, I). Among them, the band gaps of Na3SAlF4 and Na3SClO4 exceed 3.5 ​eV, which indicates their excellent electrochemical stability. The AlF4¯ cluster exhibits high sodium ion conductivity (6.55 ​× ​10-2 ​S ​cm-1), low activation energy (0.19 ​eV) and small migration barrier (0.46 ​eV) according to the ab initio molecular dynamics (AIMD) simulations and transition states study. Molecular dynamics simulations suggest that the enhanced ionic conductivity is due to the rotation of cluster ions which promotes the migration of sodium ions; moreover, the large volume created by anion clusters leads to larger lattices which is also benefit for fast ion transport. Therefore, this work designs Na-rich anti-perovskite with high ionic conductivity by substitution of anion clusters and also provides the Na ion transport mechanism for reference in solid-state electrolytes.

Electrochemical Desalination Using a Hybrid Redox-Flow Cell with a Ceramic Ion Conductor

Electrochemical desalination is a potentially energy-efficient strategy for distributed, small-scale purification of brackish sources, especially as compared to conventional processes that are reliant on heat or reverse osmosis. One promising subcategory of electrochemical desalination systems features a combination of sodium-intercalating electrodes and polymer-based anion-exchange membranes. Although desalination is technically feasible with this design, polymer-based ion-exchange membranes tend to have imperfect permselectivities and to be susceptible to water crossover between diluate and concentrate streams. These issues result in parasitic losses that increase the energetic cost of desalination.We propose a hybrid flow cell design that features a redox-active electrolyte separated from a solid, anion-converting or anion-intercalating electrode with a solid ceramic ion-exchange membrane. By making use of a dense, ceramic membrane with a far greater selectivity for sodium ion conduction than analogous polymeric ion-exchange membranes, the parasitic issues described above are avoided. We discuss considerations that will impact the relationship among electrode and electrolyte properties, operational parameters (e.g. current density, concentration factor and water recovery percentage) and the energetic cost of desalination.

Design of a Boron-Containing PTHF-Based Solid Polymer Electrolyte for Sodium-Ion Conduction with High Na+ Mobility and Salt Dissociation

Solid polymer electrolytes based on semi-interpenetrating polymer networks (semi-IPNs) were developed for sodium-ion conduction using a boron-centered moiety with polytetrahydrofuran (PTHF) chains. The resulting solid polymer electrolytes (SPEs) combined the anion-trapping properties of the boron with the weakly coordinating PTHF to achieve enhanced salt dissociation and transference number. The structure of the polymer was confirmed by 1H NMR, 13C NMR, and 11B NMR, and the cross-linking reaction with hexamethylene diisocyanate (HMDI) was confirmed by Fourier transform infrared (FTIR) spectroscopy. The mechanical and thermal stabilities of the samples were evaluated, and FTIR spectroscopic analysis showed the efficiency of the boron centers in complexing with ClO4–. Dielectric studies also indicated the predominance of free Na+ in samples. The highest room-temperature ionic conductivity was delivered by boron-containing electrolytes with O/Na: 5, 7.54 × 10–5 S cm–1, and O/Na: 10, 1.13 × 10–5 S cm–1. Linear sweep voltammetry (LSV) revealed suitable electrochemical stability against Na metal, and the measured transference number was 0.88, confirming that electrolytes benefit from the looser coordination of Na+ ions with PTHF chains combined with the anion-trapping performance of boron moieties, indicating a potential direction in polymer electrolyte design.

Design Principles for Rotational Cluster Anion [BH4]− Promote Superionic Conductivity in Sodium-Rich Antiperovskite Na3OBH4

The ionic conductivity is determined by the activation energies and the jump attempt frequencies of carrier migrations between adjacent sites. However, few works in the past have considered the influence of the attempt frequency. In this work, the attempt frequencies of carrier migrations in Na3OBH4 and Na3OBr are calculated using density functional theory and written as the contribution of each element using frequency analysis, which can be used to calculate the conductivity of a carrier in combination with the defect concentration, migration barrier of carrier migration in equilibrium. The results show that the conductivity of sodium cations can be greatly improved by substituting Br− with the [BH4]− tetrahedral anion in an antiperovskite structure due to two reasons: (1) the paddle-wheel mechanism (PWM) of the [BH4]− anionic groups can effectively reduce the activation energy and (2) the [BH4]− anionic groups with a high vibration frequency undoubtedly improve the carrier jump attempt frequency by the buffering effect. The quasi-harmonic approximation (QHA) is used to describe the isobaric behavior of Na3OBH4 and Na3OBr, and the results show that carriers have a higher jump attempt frequency in the zero-pressure compared with the constant volume. The ionic conductivity (σ) in Na3OBr and Na3OBH4 are obtained from the Arrhenius equation. The results show that the calculated sodium ionic conductivity of Na3OBH4 is 3–4 orders of magnitude higher than that of Na3OBr at room temperature. The calculated sodium ionic conductivity is lower than the experimental measurement, and the discrepancy is attributed to the overestimation of the calculated migration barrier and the underestimation of the defect concentration.

Montmorillonite as a sodium–ion–conductor interface for stable sodium metal anodes

The sodium anode is an ideal anode material in next-generation high-energy batteries due to its high theoretical capacity (1165 mA h g−1), low potential (−2.71 V) and natural abundance of Na resources. However, its practical application is restricted by irregular growth of sodium dendrites, which arises from unstable solid electrolyte interface (SEI) and high activity of sodium. To prevent dendrite growth, herein, a highly sodiophilic Na+-intercalated montmorillonite (Na-MMT) is directly embedded into sodium metal through a simple mechanical-rolling method. In the Na@Na-MMT composite anode, Na-MMT is highly dispersed into the whole sodium electrode, which affords a stable sodium–ion–conductor interface to provide faster diffusion channels and effectively lower the nucleation potential of Na, thus guiding the uniform deposition of sodium. By optimizing the mass ratio between sodium and montmorillonite, the as-prepared Na@Na-MMT anode exhibits superior plating/stripping reversibility (over 600 h at 1 mAh cm−2) and fast electrochemical kinetics (200 h at 4 mA cm−2 with a capacity of 4 mAh cm−2) in a carbonate-based electrolyte, which outperforms the performance of Na@Ca-MMT and bare Na anodes. Moreover, the Na full cell (Na@Na-MMT||Na3V2(PO4)3) exhibits a long cycling stability over 1000 cycles and good rate capability (30 C).

Low Na-β′′-alumina electrolyte/cathode interfacial resistance enabled by a hydroborate electrolyte opening up new cell architecture designs for all-solid-state sodium batteries

Development of low-resistance electrode/electrolyte interfaces is key for enabling all-solid-state batteries with fast-charging capabilities. Low interfacial resistance and high current density were demonstrated for Na-β′′-alumina/sodium metal interfaces, making Na-β′′-alumina a promising solid electrolyte for high-energy all-solid-state batteries. However, integration of Na-β′′-alumina with a high-energy sodium-ion intercalation cathode remains challenging. Here, we report a proof-of-concept study that targets the implementation of a Na-β′′-alumina ceramic electrolyte with a slurry-casted porous NaCrO2 cathode with infiltrated sodium hydroborates as secondary electrolyte. The hydroborate Na4(B12H12)(B10H10) possesses similar sodium-ion conductivity of 1 mS cm−1 at room temperature as Na-β′′-alumina and can be fully densified by cold pressing. Using the Na4(B12H12)(B10H10) secondary electrolyte as interlayer between Na-β′′-alumina and NaCrO2, we obtain a cathode-electrolyte interfacial resistance of only 25 Ω cm2 after cold pressing at 70 MPa. Proof-of-concept cells with a sodium metal anode and a NaCrO2 cathode feature an initial discharge capacity of 103 mAh g−1 at C/10 and 42 mAh g−1 at 1 C with an excellent capacity retention of 88% after 100 cycles at 1 C at room temperature. Ion-milled cross-sections of the cathode/electrolyte interface demonstrate that intimate contact is maintained during cycling, proving that the use of hydroborates as secondary electrolyte and as an interlayer is a promising approach for the development of all-solid-state batteries with ceramic electrolytes.

Synthesis and sodium ionic conductivity for perovskite-structured Na0.25La0.25NbO3 ceramic

In this work, a perovskite-structured sodium ion conductor, Na0.25La0.25NbO3 (NLNO) was developed from analogous Li0.25La0.25NbO3 ceramic. NLNO ceramic was successfully synthesized by solid state reaction. The sodium ionic conduction in Na0.25La0.25NbO3 ceramic was studied and the effect of sintering temperature on the microstructure, phase structure, density and sodium ionic conductivity for Na0.25La0.25NbO3 was also discussed. Single phase of perovskite was successfully obtained from NLNO sintered at 1200 °C and 1250 °C, and the result shows high sintering temperature leads to a large grain size, large lattice parameters and high density. With an increase of sintering temperature from 1150 °C to 1250 °C, the conductivity of samples increases gradually. NLNO sintered at 1250 °C presents a high sodium ionic conductivity of 1.06 × 10−5 S cm−1 at 30 °C, which is much higher than that of electronic conductivity in NLNO sintered at 1250 °C.

Fast Ion Transport Mechanism and Electrochemical Stability of Trivalent Metal Iodide-based Na Superionic Conductors Na3XI6 (X = Sc, Y, La, and In).

The exploration of solid-state sodium superionic conductors with high sodium-ion conductivity, structural and electrochemical stability, and grand interface compatibility has become the key to the next-generation energy storage applications with high energy density and long cycling life. Among them, halide-based compounds exhibit great potential with the higher electronegativity of halogens than that of the sulfur element. In this work, combined with first-principles calculation and ab initio molecular dynamic simulation, the investigation of trivalent metal iodide-based Na superionic conductors C2/m-Na3XI6 (X = Sc, Y, La, and In) was conducted, including the fast ion transport mechanism, structural stability, and interface electrochemical compatibility with electrode materials. Along with the tetrahedral-center saddle site-predominant three-dimensional octahedral-tetrahedral-octahedral diffusion network, C2/m-Na3XI6 possesses the merits of high Na ionic conductivities of 0.36, 0.35, and 0.20 mS cm-1 for Na3ScI6, Na3YI6, and Na3LaI6, respectively. Benefiting from its structural stabilities, C2/m-Na3XI6 exhibits lower interface reaction energy and better electrochemical compatibility in contact with both Na metal and high-voltage poly-anion (fluoro)phosphate cathode materials than those of sulfide-based ones. Our theoretical work provides rational design principles for screening and guiding iodide-based C2/m-Na3XI6 (X = Sc, Y, La, and In) as promising Na superionic conductor candidates used in all-solid-state energy storage applications.

Exceptionally high sodium ion conductivity and enhanced air stability in Na3SbS4 via germanium doping

In addition to the widely used lithium-ion secondary batteries, more and more concerns have been paid to solid-state batteries (SSBs) in the research on future-generation energy storage systems. The availability of sodium solid electrolytes, especially those with excellent ambient temperature conductivity and prominent chemical stability, is crucial for sodium-based SSBs. In this study, Na3.1Ge0.1Sb0.9S4, a novel sodium-ion solid-state electrolyte, was obtained via a solid-state chemical reaction utilizing the economical Na2S·9H2O as one of the raw ingredients. The properties of this new electrolyte were examined by using X-ray diffractometry, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy, and electrochemical techniques. The Na3.1Ge0.1Sb0.9S4 electrolyte, which released low amounts of H2S under ambient conditions, demonstrated the ionic conductivity of 5.1 × 10−3 S/cm at normal atmospheric temperature and the conducting activation energy of 0.156 eV. The enhanced ionic conductivity was attributed to the improvement of crystallinity and the unit cell enlargement caused by interstitial sodium defects.

An asymmetric bilayer polymer-ceramic solid electrolyte for high-performance sodium metal batteries

Manufacturing an excellent solid electrolyte compatible with a high-voltage cathode is viewed as a critical tactic for improving the energy density of solid-state sodium-ion batteries (SSIBs). A novel asymmetric bilayer solid electrolyte of the PEO-SN-NaClO4|NZSP-NSO with an anti-reduction PEO-SN-NaClO4 layer close to the Na side is constructed by solution casting. The ionic conductivity is enhanced by using succinonitrile (SN) in polyethylene oxide (PEO) polymer electrolyte. The anti-oxidation layer of Na3Zr2Si2PO12 with Na2SiO3 (NZSP-NSO) is served as the support of the membrane on the cathode, which could improve the interface compatibility and electrochemical performance of SSIBs. The asymmetric bilayer solid electrolyte simultaneously features a wide electrochemical stability window (4.65 V vs. Na+/Na) and a high conductivity (2.68 × 10–4 S cm−1). Furthermore, the solid electrolyte demonstrates stable Na plating/stripping over 700 h and remarkably improves cycling stability in Na/Na3V2(PO4)3 batteries with an ultra-high capacity retention of 99.6% after 100 cycles at 50 °C and 0.5 C. This study provides an effective strategy for designing asymmetric high sodium ion conductivity solid-state electrolytes for high-performance SSIBs.

Medium-Temperature Sodium-Iodine Battery System

A medium-temperature sodium-iodine battery system is presented. The rechargeable molten-sodium system works at approx. 100 °C with high efficiency, and potentially lower cost than existing high-temperature sodium-batteries (which are usually operating at a temperature of around 300 °C). Our battery system uses an aqueous iodine/iodide solution as catholyte and sodium-ion conductive Zr-based NaSICON ceramic material as solid electrolyte. The free halogen, which is formed upon charge, is complexed as highly soluble triiodide. Long-term stability of sodium-ion conductive material in contact with aqueous electrolytes, generally, is a concern. NaSICON-based ceramic material has shown not only an enhanced stability [1] against these electrolytes but also an increased sodium-ion conductivity [2], compared to sodium β″-alumina used in sodium-sulfur batteries. The sodium-iodine system has shown to operate in a stable manner with a catholyte allowing for a high total iodine concentration (>3.0 mol/L) [1]. Substitution in the NaSICON composition allows for increased ionic conductivity and enhanced stability against the aqueous cathode. In the case of fissuring of the NaSICON ceramic separator, only solid products are formed. This stops the direct reaction of active materials.[1] M. Holzapfel, D. Wilde, C. Hupbauer, K. Ahlbrecht, T. Berger, Electrochim. Acta 237 (2017), 12-21.[2] S. Naqash, Q. Ma, F. Tietz, O. Guillon, Solid State Ionics 302 (2017), 83-91.This work is funded by the German Federal Ministry of Education and Research in the project „MiTemp – Mitteltemperatur-Natriumbatterien mit flüssiger Natriumanode und wässriger Iodkathode“ (03XP0183A). Figure 1

Electrochemical Desalination Using a Hybrid Redox Flow Cell

Electrochemical desalination is an attractive, energy-efficient strategy for small-scale, distributed water purification systems, as compared to conventional thermal desalination or reverse osmosis. Many incumbent electrochemical desalination cells feature a combination of sodium-intercalating electrodes and polymer-based anion-exchange membranes with non-ideal permselectivities. We propose a hybrid flow cell design that features a redox-active electrolyte separated by a cation exchange membrane from a solid, anion-converting or anion-intercalating electrode. This design makes use of a dense, ceramic membrane with a greater selectivity for sodium ion conduction than polymeric ion-exchange membranes, which are also susceptible to energy losses from water crossover between dilute and concentrated salt streams. We discuss considerations that will impact the relationship among electrode and electrolyte properties, operational parameters (e.g. current density, concentration factor and water recovery percentage) and the energetic cost of desalination.

Anharmonic Lattice Dynamics in Sodium Ion Conductors.

We employ terahertz-range temperature-dependent Raman spectroscopy and first-principles lattice dynamical calculations to show that the undoped sodium ion conductors Na3PS4 and isostructural Na3PSe4 both exhibit anharmonic lattice dynamics. The anharmonic effects in the compounds involve coupled host lattice–Na+ ion dynamics that drive the tetragonal-to-cubic phase transition in both cases, but with a qualitative difference in the anharmonic character of the transition. Na3PSe4 shows an almost purely displacive character with the soft modes disappearing in the cubic phase as the change in symmetry shifts these modes to the Raman-inactive Brillouin zone boundary. Na3PS4 instead shows an order–disorder character in the cubic phase, with the soft modes persisting through the phase transition and remaining Raman active in the cubic phase, violating Raman selection rules for that phase. Our findings highlight the important role of coupled host lattice–mobile ion dynamics in vibrational instabilities that are coincident with the exceptional conductivity of these Na+ ion conductors.

Conversion Kinetics and Ionic Conductivity in Na-β"-Alumina + YSZ (Naβ"AY) Sodium Solid Electrolyte via Vapor Phase Conversion Process.

Sodium ion batteries have been receiving increasing attention and may see potential revival in the near future, particularly in large-scale grid energy storage coupling with wind and solar power generation, due to the abundant sodium resources, low cost, and sufficiently high energy density. Among the known sodium ion conductors, the Na-β”-alumina electrolyte remains highly attractive because of its high ionic conductivity. This study focuses on the vapor phase synthesis of a Na-β”-Alumina + YSZ (Naβ”AY) composite sodium electrolyte, which has higher mechanical strength and stability than conventional single phase β”-Alumina. The objectives are the measurement of conversion kinetics through a newly developed weight-gain based model and the determination of sodium ionic conductivity in the composite electrolyte. Starting samples contained ~70 vol% α-Alumina and ~30 vol% YSZ (3 mol% Y2O3 stabilized Zirconia) with and without a thin alumina surface layer made by sintering in air at 1600 °C. The sintered samples were placed in a powder of Na-β”-alumina and heat-treated at 1250 °C for various periods. Sample dimensions and weight were measured as a function of heat treatment time. The conversion of α-Alumina in the α-Alumina + YSZ composite into Naβ”AY occurred by coupled diffusion of sodium ions through Na-β”-alumina and of oxygen ions through YSZ, effectively diffusing Na2O. From the analysis of the time dependence of sample mass and dimensions, the effective diffusion coefficient of Na2O through the sample, , was estimated to be 1.74 × 10−7 cm2 s−1, and the effective interface transfer parameter, , was estimated as 2.33 × 10−6 cm s−1. By depositing a thin alumina coating layer on top of the bulk composite, the chemical diffusion coefficient of oxygen through single phase Na-β”-alumina was estimated as 4.35 × 10−10 cm2 s−1. An AC impedance measurement was performed on a fully converted Naβ”AY composite, and the conductivity of the composite electrolyte was 1.3 × 10−1 S cm−1 at 300 °C and 1.6 × 10−3 S cm−1 at 25 °C, indicating promising applications in solid state or molten salt batteries at low to intermediate temperatures.