Sodium Β-alumina Research Articles

High ionic conductive Sodium β-alumina (SBA) and SBA-NaPF6 composite solid electrolytes prepared by cold sintering process

Sodium β-alumina (SBA) electrolytes are among the most excellent candidates for all-solid-state batteries due to their high electrochemical performances and low cost of sodium resources. However, thermally sintering at above 1400 °C is required to fabricate high dense SBA electrolytes, thus giving rise to a huge energy consumption. Here, dense SBA electrolytes and (1-x)SBA-xNaPF6 (x=5, 10, 15, 20 wt%) composites were fabricated using cold sintering process (CSP) below 300 °C with 2 mol/L NaOH solution as transient chemistry. The ionic conductivity of SBA electrolytes is significantly enhanced from 5.53×10-6 S·cm-1 to 5.91 × 10−4 S·cm−1 as 15 wt% NaPF6 was introduced to the composite, which is comparable with the SBA sintered above 1400 °C. CSP may provide a promising approach for the fabrication of solid-state electrolytes by avoiding the detrimental impact of high temperature heat treatment.

Composition and Antithermal Quenching of Noninteger Stoichiometric Eu2+-Doped Na-β-Alumina with Cyan Emission for Near-UV WLEDs.

Phosphors with high quantum efficiency and thermal stability play a key role in improving the performance of phosphor-converted white light-emitting diodes (pc-WLEDs). A near-UV-pumped LED shows a great advantage due to its reduction of the negative effect of blue light on human health. In this work, we propose a series of near-UV excitable cyan-emitting Eu2+-activated phosphors with a nominal composition of Na2-2xAl11O17+a:xEu2+ (x = 0.01-0.40), which crystallize in a sodium β-alumina phase with a composition close to Na1.22Al11O17.11. An excess amount of the sodium carbonate raw material makes up the volatile Na during the high-temperature process. The noninteger stoichiometric composition promotes the rigidity of the crystal structure with a slight excess of Na insertion into layers between spinel blocks of the NaAl11O17 matrix. The nonequivalent substitution of Na+ by Eu2+ generates intrinsic defects acting as carrier traps. As a result, the phosphor with an optimal nominal composition Na1.6Al11O17+a:0.20Eu2+, under the excitation at 365 nm, shows an asymmetric cyan emission band at 468 nm with internal and external quantum efficiencies of 81.3 and 56.9%, respectively. Remarkably, the phosphor exhibits antithermal quenching within 200 °C. A pc-WLED with a high color rendering index (87.2) suggests great potential of the phosphor in pc-WLEDs. Therefore, a combination of a rigid structure and deep trap level is an effective way in exploring new phosphors with high quantum efficiency and thermal stability.

Taming Active Material-Solid Electrolyte Interfaces with Organic Cathode for All-Solid-State Batteries

Summary Attaining stable active material-solid electrolyte interfaces is a great challenge in sulfide-based all-solid-state sodium batteries (ASSSBs). A resistive layer forms at the interface upon charging above the anodic stability potential of sulfide electrolytes. In addition, contact failure at the interface during cycling is long known, but a fundamental solution is not yet available. Herein, we use an organic cathode material, pyrene-4,5,9,10-tetraone (PTO), to enable high-performance ASSSBs. We report, for the first time, a reversible active material-electrolyte interfacial resistance evolution during cycling. We further show for the first time that a low-modulus cathode material such as PTO maintains intimate interfacial contact with solid electrolytes during cycling, thus improving cycle life. The PTO-based cells exhibit a high specific energy (587 Wh kg−1) and a record cycling stability (500 cycles) among ASSSBs. This work reveals an effective cathode material design strategy toward compatibility with solid electrolytes and thus high-performance ASSSBs.

High-performance low voltage operation of indium zinc tin oxide thin film transistors using chemically derived sodium β-alumina dielectric

We present high performance, low voltage (≤ 3 V) operation of thin film transistors (TFTs) with indium zinc tin oxide (IZTO: In4Sn4ZnO15)-semiconductor. The film of IZTO was fabricated via low-temperature (200 °C) solution combustion processing without incorporating an external fuel. As 2-methoxyethanol is a widely used organic solvent due to its high dissolution capability, serve the purpose of both the solvent and the fuel. On quantification from the balanced redox reaction, 0.3% of 2-methoxyethanol assisted for the action of fuel and helped in the formation of metal oxide, and the rest (99.7%) served the purpose of being dissolution medium. The balanced redox chemistry yielded a significant fraction of (56.5%) metal oxide at 200 °C confirmed via high-resolution oxygen 1s spectrum. Further, the chemically derived thin film of sodium β-alumina with a dielectric constant of ~ 21, while annealing at 350 °C incorporated in the TFT for the realization of low voltage operation. The performance assessment is systematically carried out both silicon dioxide (SiO2) and sodium β-alumina and found that the TFTs with SiO2 and IZTO exhibited a saturation mobility (µsat), Ion/Ioff ratio and the threshold voltage (Vth) of 0.50 ± 0.02 cm2 V−1 s−1, 1.25 × 104 and 6.6 ± 0.79 V respectively. While changing the dielectric to sodium β-alumina presented a µsat, Ion/Ioff ratio and Vth of 4.21 ± 0.18 cm2 V−1 s−1, 1.4 × 102 and 0.47 ± 0.08 V respectively.

Bismuth Islands for Low-Temperature Sodium-Beta Alumina Batteries.

Wetting of the liquid metal on the solid electrolyte of a liquid metal battery controls the operating temperature and performance of the battery. Liquid sodium electrodes are particularly attractive because of their low cost, natural abundance, and geological distribution. However, they wet poorly on a solid electrolyte near its melting temperature, limiting their widespread suitability for low-temperature batteries to be used for large-scale energy storage systems. Herein, we develop an isolated metal-island strategy that can improve sodium wetting in sodium-beta alumina batteries that allows operation at lower temperatures. Our results suggest that in situ heat treatment of a solid electrolyte followed by bismuth deposition effectively eliminates oxygen and moisture from the surface of the solid electrolyte, preventing the formation of an oxide layer on the liquid sodium, leading to enhanced wetting. We also show that employing isolated bismuth islands significantly improves cell performance, with cells retaining 94% of their charge after the initial cycle, an improvement over cells without bismuth islands. These results suggest that coating isolated metal islands is a promising and straightforward strategy for the development of low-temperature sodium-β alumina batteries.

Toward an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage

Veronica Augustyn is an Assistant Professor of Materials Science & Engineering at North Carolina State University. She received her PhD from the University of California, Los Angeles (2013) and was a Postdoctoral Fellow at the University of Texas at Austin (2013–2015). Her research is focused on the synthesis and characterization of materials operating at electrochemical interfaces, and in particular the relationships between material composition, structure, and morphology and the resulting electrochemical mechanisms. Recently, she was the recipient of a 2017 NSF CAREER Award and is a Scialog Fellow in Advanced Energy Storage at the Research Corporation for Science Advancement. Matthew McDowell is an assistant professor in the G.W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering at the Georgia Institute of Technology. He received his PhD from Stanford University (2013) and was a postdoctoral scholar at Caltech from 2013 until 2015. His research is focused on understanding structural and chemical transformations in materials and at interfaces within electrochemical and electrical devices through the use of in situ and operando techniques. He has received the NSF CAREER Award, the AFOSR YIP Award, and the NASA Early Career Faculty Award and is a Scialog Fellow in Advanced Energy Storage. Aleksandra Vojvodic is Skirkanich Assistant Professor of Innovation in Chemical & Biomolecular Engineering at University of Pennsylvania. She received her PhD from Chalmers University of Technology, was Postdoc at Technical University of Denmark and Stanford University, and was Staff Scientist at SLAC National Accelerator Laboratory. Her research focuses on computational-driven materials design including studies of surfaces and interfaces of materials for chemical transformations, energy conversion, and storage. She received the 2017 European Federation of Catalysis Societies Young Researcher Award and the MIT Technology Review 35 Award 2016. She is a CIFAR Bio-Inspired Solar Energy fellow and a Scialog Fellow in Advanced Energy Storage.

Retention of high dielectric constant sodium beta alumina via solution combustion: Role of aluminum ions complexation with fuel

In the present study, solution combustion technique has been explored to synthesize Sodium β-alumina (SBA; NaAl11O17) powder and thin films. Three fuels namely urea, glycine and citric acid have been used to seek the feasibility of synthesizing crystalline SBA powder at low temperature. Also, the effect of nature of fuels used as well as calcination treatment on phase evolution and morphology of the as-combusted powder was investigated. Thermal analysis and X-ray diffraction studies suggest the formation of crystalline SBA powder at temperature as low as 259°C, using urea in the combustion reaction whereas other fuels resulted in amorphous SBA phase and this variation in phase was found due to difference in exothermicity of the fuel used. Thermodynamic and spectroscopic analyses showed that the exothermicity of fuel depends on various factors like (i) standard heat of formation of fuel and (ii) the complexation offered by fuel to metal cations. Furthermore, sodium β-alumina thin film capacitor (metal-insulator-metal) was also fabricated using urea via spray combustion synthesis. The sodium β-alumina thin film showed a high dielectric value (εr) of ~21.

Interfacial Reactivity Benchmarking of the Sodium Ion Conductors Na3PS4 and Sodium β-Alumina for Protected Sodium Metal Anodes and Sodium All-Solid-State Batteries.

The interfacial stability of solid electrolytes at the electrodes is crucial for an application of all-solid-state batteries and protected electrodes. For instance, undesired reactions between sodium metal electrodes and the solid electrolyte form charge transfer hindering interphases. Due to the resulting large interfacial resistance, the charge transfer kinetics are altered and the overvoltage increases, making the interfacial stability of electrolytes the limiting factor in these systems. Driven by the promising ionic conductivities of Na3PS4, here we explore the stability and viability of Na3PS4 as a solid electrolyte against metallic Na and compare it to that of Na-β″-Al2O3 (sodium β-alumina). As expected, Na-β″-Al2O3 is stable against sodium, whereas Na3PS4 decomposes with an increasing overall resistance, making Na-β″-Al2O3 the electrolyte of choice for protected sodium anodes and all-solid-state batteries.

Short-term and long-term memory operations of synapse thin-film transistors using an In–Ga–Zn–O active channel and a poly(4-vinylphenol)–sodium β-alumina electrolytic gate insulator

In this work, we proposed new type of synapse device with thin-film transistor (TFT) configuration using an In–Ga–Zn–O (IGZO) as active channel and a poly(4-vinylphenol)–sodium β-alumina (PVP–SBA) as gate insulator for emulating brain-like functions.

Synthesis, extrusion processing and ionic conductivity measurements of sodium β-alumina tubes

Pure and Li-doped sodium ?-alumina (NaMg0.67Al10.33O17) ceramics were prepared from the stoichiometric mixture of raw powders. Pellets and tubes were formed from the precursor (NBA-1S) and preformed sodium ?-alumina powder through compaction and extrusion processing, respectively. The obtained specimens were finally sintered to dense ceramics. The ceramics were comparatively evaluated for their density, microstructure, phase formation and electrical properties. Both tubes and pellets processed with the preformed sodium ?-alumina powder (NBA-2S) showed enhanced densification along with relatively better phase purity and crystallinity. The ceramics prepared from the preformed powder exhibited higher density of 94-95% TD (theoretical densities) in comparison to the ceramics processed from the raw mixture (NBA-1S) with a density of 85-87%TD, which are complemented well through fractographs and microstructures. The ceramics processed using the preformed sodium ?-alumina (NBA-2S) also exhibited high room temperature AC conductivity of 1.77?10-4 S/cm (1MHz) with an increasing trend with temperature. The higher ionic conductivity at all temperatures in NBA-2S than in NBA-1S ceramics can be attributed to the relatively high phase purity, crystallinity and higher density values of NBA-2S ceramics.

Structure, Sodium Ion Role, and Practical Issues for β-alumina as a High-k Solution-Processed Gate Layer for Transparent and Low-Voltage Electronics

Sodium β-alumina (SBA)-based gate dielectric films have been developed for all solution-processed, transparent and low voltage field-effect transistors (FETs). Its high dielectric constant has been ascribed to sodium (Na+) ions in the crystal structure; however, there are no published experimental results concerning the contribution of Na+ ions to the dielectric behavior, and the degree of crystallinity of the thin films. In addition, as an ionic conductor, β-alumina could give rise to some issues such as leakage current caused by Na diffusion, threshold voltage shift due to interface charge accumulation and longer response time due to slower polarization of the Na+ ions. This paper will address these issues using zinc tin oxide (ZTO) FETs, and propose possible measures to further improve SBA-based gate materials for electronic devices.

Formation of ultradispersed systems based on sodium polyaluminates from thermal plasma flows

The process of synthesis of sodium β-alumina in a low-temperature nitric plasma is investigated. It is established that the main product of the plasmachemical reaction is sodium polyaluminate Na2O · nAl2O3 of an unknown structure, whose homogeneity range is within the interval of n = 3.5–8.0. The specifics of phase transformations in heating products of plasmachemical synthesis in the temperature interval of 600–1400°C are considered. The formation of the phase with the β-alumina structure (β-and β-Al2O3) proceeds in several stages with the formation of intermediate metastable sodium polyaluminates.

Ion transport in nanocrystalline materials: a computer simulation study

The results of molecular dynamics simulations of ionic transport in nanostructured materials are presented. Two types of materials are considered, the single component nanostructured oxide, sodium β-alumina and the mixed phase composite LiI/Al 2O 3. In nanostructured β-alumina, the conductivity is observed to be considerably lower than in crystalline β-alumina. Blocking grain boundaries between the nanosized grains cause the reduction. In the case of the composite, a crystallite of LiI with (0 0 1) surface planes was sandwiched between α and γ-Al 2O 3, respectively. In both cases Li +-ions were observed to transfer from LiI to tetrahedral sites in the Al 2O 3 surface, α-alumina having the higher surface charge density. As a result, a defective region develops near the interface in the LiI and lithium transport along the surface can occur. The ions migrate through vacancy hopping in the defective regions in LiI. The defective region is only two Li +-layers thick. When the thickness of the LiI slab becomes comparable with the thickness of the defective region, the LiI becomes more disordered. The activation energy for Li +-diffusion decreases, but this is more than compensated for by a reduction in charge carriers.

Toward Commercialization of the Beta-Alumina Family of Ionic Conductors

The beta-alumina family of materials has played a central role in the field of solid-state ionics. β- and β-alumina have been a principal theme in the field ever since Yao and Kummer reported the extraordinarily high conductivity for sodium β-alumina. The material “came of age” at a time when there was great interest in the science and technology of highconductivity solid electrolytes. A previous MRS Bulletin review introduced this broad family of materials, examining the range of compositions and the two major structures. The beta-alumina family emerged as almost an ideal system in which to explore structure-property relations, as its unusual structure is responsible for its remarkable ion-transport properties. Although the initial interest in this material, and the one which endures to this day, is its rapid sodium-ion transport, the rich ion-exchange chemistry added a dimension to this material that few inorganic systems can match, let alone exceed. β-alumina, in particular, is an almost universal solid electrolyte for cations. It constitutes a broad family of solid electrolytes whose properties are dependent upon the nature of the ion inserted into the conduction plane. As a result, the β-aluminas have served as model systems for a wide range of studies: proton transport and mixed-ion diffusion, order-disorder reactions, and superlattice phenomena. Moreover, these β-alumina compositions demonstrated that fast-ion transport was not limited to a few monovalentions, but could be extended to divalent and even trivalent cations. With the latter materials, the interest was not necessarily ion transport, but optical properties instead. The presence of trivalent cations in this unusual structure, coupled with the ability to control the chemistry of the local environment, enabled the β-aluminas to exhibit a number of novel optical properties.

Sensing mechanism of high temperature hydrogen sulphide sensor based on sodium β-alumina

A hydrogen sulphide galvanic probe for reducing gas mixtures (e.g., coal gasification) has been developed. Sodium β-alumina was selected as the electrolyte. The reference consists of a sodium ferrite and ferric oxide powder mixture open to the air. The equilibrium thus generated fixes a constant sodium reference activity. Both measuring and reference electrodes consist of Pt layers. Conditioning of the as-fabricated probes was performed by exposure to a H 2S/H 2 gas mixture at the operating temperature. The performance of the probes was evaluated in synthetic gas mixtures containing well defined H 2S/H 2 partial pressures as well as in an actual coal gasifier. In this paper a possible sensor reaction mechanism is discussed in detail using (electro)chemical as well as thermodynamic considerations. The results are in agreement with the hypothesis that oxygen ions on Na 2O sites in the conduction planes at the surface of the electrolyte were in situ catalytically exchanged by sulphur ions. The activity of Na corresponds to Na x S within β-alumina rather than to pure Na x S. At the measuring electrode, sulphur partial pressures are then automatically converted to sodium activities without the need for a macroscopic auxiliary layer. At higher temperatures (e.g., 860 K), it is postulated that Na 2S is incorporated within the β-alumina structure, while at lower temperatures (e.g., 593 K), NaS appears to be the preferred product in the ion-exchange reaction.

Thermoelectric Power Studies on α-Alumina–Sodium β-Alumina Composite Electrolyte

In the context of electrical characterization of fast ionic conductors, there is an urgent need for thermoelectric power (TEP) measurements on new solid electrolyte materials. A composite electrolyte made of α-alumina and sodium β-alumina which was used for monitoring very low oxygen potentials in the range of up to Al(l)/Al2O3, neither the electrical conductivity nor the TEP has hitherto been reliably reported. Hence, TEP measurements were carried out on the composite which yielded an average value of 430 μV/K over the temperature range 620 to 1250 K. From these data, an activation energy of 17.5 kJ mol—1 was derived for this exclusive sodium ionic conductor in its present form as a composite.

Growth of crystalline doped β-alumina thin films by laser ablation

Crystalline thin films of sodium β-alumina and β-aluminogallate for optical applications have been deposited onto various single-crystal substrates by the pulsed laser deposition technique. Films with a smooth surface morphology were obtained by using Cr-doped targets. Despite Na loss in the films with respect to the target composition, the β-alumina crystalline phase was grown at elevated temperature (700–800 °C), and highly textured (00l) films were obtained, whatever the substrates: MgO, ZrO 2 , Al 2 O 3 or Si. The optical properties were studied by measuring the refractive index of the films and performing the emission spectrum of the Cr 3+ ions, providing results very similar to those of the bulk single-crystalline material.

The use of sodium β-alumina for controlling the rate of sodium addition to aluminium alloys

Sodium, when added at concentrations of 30–200 ppm, can be used to modify the microstructure and properties of a number of aluminium alloys. This has traditionally been achieved by physically adding a sodium rich alloy or flux to the melt. However, this method suffers from considerable inefficiency since much of the sodium burns or evaporates on the surface of the metal generating fumes and dross. A much cleaner and more efficient process is under development using a sodium ion conducting solid electrolyte to separate a source of sodium from the molten aluminium alloy. Under the influence of an applied potential, sodium is transported through the solid electrolyte with the rate of sodium addition to the melt controlled by the current flow. An additional advantage of using an electrochemical sodium addition method is that it lends itself to control via a solid state sodium sensor. This can be used to continuously measure changes in sodium activity in the alloy leading to improved process control. In practice, this system gives a much greater level of control over the rate of sodium addition and because the additions are made continuously within the molten metal, dross and fumes are virtually eliminated from the process. Experiments have been performed in laboratory, intermediate and industrial environments and this has been shown to be a viable method of controlling the sodium content of aluminium alloys at industrial scales. Small portions of solid electrolyte have been shown capable of withstanding a current density in excess of 1.3 A cm −2. A standard 200 × 30 mm electrolyte tube has been operated at a current density of approximately 0.6 A cm −2, supplying sodium at a rate of 1.8 g min −1 to a launder of aluminium. This rate of addition from a single tube is able to continuously supply the desired quantity of sodium to two tonnes per hour of aluminium alloy. Alternatively, smaller static pots of aluminium may be rapidly brought up to the desired sodium concentration and maintained at that level by adding more sodium to compensate for any evaporation.

Optical properties of sodium β-alumina single crystals doped with neodymium and chromium–neodymium

Single crystals of sodium β-alumina have been grown by two methods: flux evaporation and a new process, solid–vapour reaction. These compounds were doped with neodymium through a homogeneous ion-exchange reaction. Their X-ray diffuse scattering patterns show a two-dimensional (2D) superstructure (a√3; a√3) for Nd β-alumina. The optical behaviour of NaNd β-alumina single crystals is reported here. A strong absorption occurs at 580nm. Nd3+ emission shows a broad band (FWHM about 30 nm) centred at 1.06 µm and the Nd3+ lifetime measured at room temperature is about 530 µs. Finally, chromium-neodymium co-doped samples of β-alumina single crystals are investigated. Timeresolved spectroscopy and lifetime analysis indicate that Cr→Nd energy transfer takes place in this host matrix.

Site-selective spectroscopy of Pr3+ ions in sodium [MATH]-alumina crystals

We report of the results of a low-temperature optical spectroscopy study of Pr 3+ -exchanged sodium β-alumina single crystals (Na + /Pr 3+ β-Al 2 O 3 ), containing different amounts of luminescent ions, in which excitation and fluorescence spectra have been carried out in σ and π polarization. The 3 P 0 → 3 H 4 emission spectra, obtained under broad band excitation, show an intriguing structure consisting of several components even with crystals containing low Pr 3+ concentrations. The excitation spectra indicate the presence of at least two sets of different sites, available to Pr 3+ in the conduction plane of β-alumina. Independently of the crystal composition, a quite satisfactory site-selective emission from each sets of centres has been achieved under cw excitation of the 465.8 nm and 476,5 nm lines of an Ar + ion laser