Perovskenes: two-dimensional perovskite-type monolayer materials predicted by first-principles calculations.

Inspired by the successful transfer of freestanding ultrathin films of SrTiO3 and BiFeO3 onto various substrates without any thickness limitation, in this study, using density functional theory (DFT), we assessed the structural stability of a group of two-dimensional perovskite-type materials which we call perovskenes. Specifically, we analyzed the stability of 2D SrTiO3, SrZrO3, BaTiO3, and BaZrO3 monolayers. Our simulations revealed that the 2D monolayers of SrTiO3, BaTiO3, and BaZrO3 are at least meta-stable, as confirmed by cohesive energy calculations, evaluation of elastic constants, and simulation of phonon dispersion modes. With this information, we proceeded to investigate the electronic, optical, and thermoelectric properties of these perovskenes. To gain insight into their promising applications, we investigated the electronic and optical properties of these 2D materials and found that they are wide bandgap semiconductors with significant absorption and reflection in the ultraviolet (UV) region of the electromagnetic field, suggesting them as promising materials for use in UV shielding applications. In addition, evaluating their thermoelectric factors revealed that these materials become better conductors of electricity and heat as the temperature rises. They can, hence, convert temperature gradients into electrical energy and transport electrical charges, which is beneficial for efficient power generation in thermoelectric devices. This work opens a new window for designing a novel family of 2D perovskite type materials termed perovskenes. The vast variety of different perovskite compounds and their variety of applications suggest deeper studies on the perovskenes materials for use in innovative technologies.

High Cathode Loading and Low-Temperature Operating Garnet-Based All-Solid-State Lithium Batteries - Material/Process/Architecture Optimization and Understanding of Cell Failure.

All-solid-state lithium batteries (ASSLBs) are prepared using garnet-type solid electrolytes by quick liquid phase sintering (Q-LPS) without applying high pressure during the sintering. The cathode layers are quickly sintered with a heating rate of 50-100 K min-1 and a dwell time of 10 min. The battery performance is dramatically improved by simultaneously optimizing materials, processes, and architectures, and the initial discharge capacity of the cell with a LiCoO2 -loading of 8.1 mg reaches 1 mAh cm-2 and 130 mAh g-1 at 25 °C. The all-solid-state cell exhibits capacity at a reduced temperature (10 °C) or a relatively high rate (0.1 C) compared to the previous reports. The Q-LPS would be suitable for large-scale manufacturing of ASSLBs. The multiphysics analyses indicate that the internal stress reaches 1 GPa during charge/discharge, which would induce several mechanical failures of the cells: broken electron networks, broken ion networks, separation of interfaces, and delamination of layers. The experimental results also support these failures.

Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries.

Solid-state batteries with desirable advantages, including high-energy density, wide temperature tolerance, and fewer safety-concerns, have been considered as a promising energy storage technology to replace organic liquid electrolyte-dominated Li-ion batteries. Solid-state electrolytes (SSEs) as the most critical component in solid-state batteries largely lead the future battery development. Among different types of solid-state electrolytes, garnet-type Li7La3Zr2O12 (LLZO) solid-state electrolytes have particularly high ionic conductivity (10-3 to 10-4 S/cm) and good chemical stability against Li metal, offering a great opportunity for solid-state Li-metal batteries. Since the discovery of garnet-type LLZO in 2007, there has been an increasing interest in the development of garnet-type solid-state electrolytes and all solid-state batteries. Garnet-type electrolyte has been considered one of the most promising and important solid-state electrolytes for batteries with potential benefits in energy density, electrochemical stability, high temperature stability, and safety. In this Review, we will survey recent development of garnet-type LLZO electrolytes with discussions of experimental studies and theoretical results in parallel, LLZO electrolyte synthesis strategies and modifications, stability of garnet solid electrolytes/electrodes, emerging nanostructure designs, degradation mechanisms and mitigations, and battery architectures and integrations. We will also provide a target-oriented research overview of garnet-type LLZO electrolyte and its application in various types of solid-state battery concepts (e.g., Li-ion, Li-S, and Li-air), and we will show opportunities and perspectives as guides for future development of solid electrolytes and solid-state batteries.

Facet-Engineered Tungsten Disulfide for Promoting Polysulfide Electrocatalysis in Lithium-Sulfur Batteries.

Distinct facets of an electrocatalyst can promote polysulfide (Li2Sn (n = 4, 6, 8) and Li2Sm (m = 1, 2)) redox kinetics in lithium-sulfur (Li-S) battery chemistry. Herein, we report that the (100) facet of tungsten disulfide (e-WS2) generated in situ by electrochemical pulverization exhibits onset potentials of 2.52 and 2.32 V vs Li/Li+, respectively, for the reduction of polysulfides Li2Sn and Li2Sm, which is unprecedented till date. In a comparable study, bulk WS2 was synthesized ex situ. The transmission electron microscopy (TEM) analysis reveals that the (100) facet was dominant in e-WS2, while the (002) facet was pronounced in bulk WS2. The density functional theory (DFT) analysis indicates that the (100) facet displays metallic-like behavior, which is highly desired for enhanced polysulfide redox kinetics. We believe that the e-WS2 produced can potentially be an excellent electrocatalyst for other applications such as hydrogen evolution reaction (HER), photocatalysis, and CO2 reduction.

Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with ap-type low bandgap double perovskite oxide.

Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ(BCNFCo), exhibited an optical absorption edge at ∼800 nm,p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4(CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.

Amphiphilic Cyclodextrin-Based Liquid Crystals for Proton Conduction.

Novel cyclodextrin (CD)-based amphiphilic poly(carboxylic acid)s that self-assemble into highly ordered smectic liquid crystalline mesophases were investigated as a novel class of protonic conductors. These structurally well-defined materials are synthesized from nontoxic and environment-friendly CDs, which possess a unique face-to-face pseudosymmetry. By taking advantage of such geometry, a series of flexible tetraethylene glycol groups terminated with a carboxylic acid functionality were introduced to the CD's secondary face, resulting in the formation of long-range 2D hydrogen-bond networks in the smectic mesophases over a wide temperature window. This new material was found to exhibit impressive proton conductivities in solid states, up to 1.4 × 10-2 S cm-1 at 70 °C and 95% humidity. This constitutes the first report of amphiphilic CD-based liquid crystals applied as proton conductive materials.

Electrical Properties of Hollandite-Type Ba1.33Ga2.67Ti5.33O16, K1.33Ga1.33Ti6.67O16, and K1.54Mg0.77Ti7.23O16.

Electrical conductivity and electrochemical catalytic activity for H2 oxidation of Ti-based hollandite-type Ba1.33Ga2.67Ti5.33O16 (BGT), K1.33Ga1.33Ti6.67O16 (KGT), and K1.54Mg0.77Ti7.23O16 (KMT) were investigated, along with the chemical stability of KMT under H2 at elevated temperature. BGT, KGT, and KMT crystallized in a tetragonal structure with the space-group I4/ m. The electrical conductivity in H2 increases with increasing Ti content, and the highest total electrical conductivity of 2 S/cm at 800 °C in H2 was observed for KMT. KGT:Fe (1:1) + 20% LSGM + 30% porosity composite electrode showed the lowest area specific resistance of ca. 1.6 Ω cm2 at 800 °C for hydrogen oxidation reaction (HOR) under the open circuit condition. Moderate catalytic activity for HOR could be attributed to poor oxide ion conductivity and exclusion of potassium and hydrogen uptake in H2 at elevated temperature. Bond valence sum mismatch map calculation showed that the ionic transport happens along the 1D channel of c-axis in the hollandite oxides.

Negating interfacial impedance in garnet-based solid-state Li metal batteries.

Garnet-type solid-state electrolytes have attracted extensive attention due to their high ionic conductivity, approaching 1 mS cm-1, excellent environmental stability, and wide electrochemical stability window, from lithium metal to ∼6 V. However, to date, there has been little success in the development of high-performance solid-state batteries using these exceptional materials, the major challenge being the high solid-solid interfacial impedance between the garnet electrolyte and electrode materials. In this work, we effectively address the large interfacial impedance between a lithium metal anode and the garnet electrolyte using ultrathin aluminium oxide (Al2O3) by atomic layer deposition. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) is the garnet composition of choice in this work due to its reduced sintering temperature and increased lithium ion conductivity. A significant decrease of interfacial impedance, from 1,710 Ω cm2 to 1 Ω cm2, was observed at room temperature, effectively negating the lithium metal/garnet interfacial impedance. Experimental and computational results reveal that the oxide coating enables wetting of metallic lithium in contact with the garnet electrolyte surface and the lithiated-alumina interface allows effective lithium ion transport between the lithium metal anode and garnet electrolyte. We also demonstrate a working cell with a lithium metal anode, garnet electrolyte and a high-voltage cathode by applying the newly developed interface chemistry.

Insights into B-Site Ordering in Double Perovskite-Type Ba3Ca1+ xNb2- xO9-δ (0 ≤ x ≤ 0.45): Combined Synchrotron and Neutron Diffraction and Electrical Transport Analyses.

Perovskite-type metal oxides are being used in a wide range of technologies, including fuel cells, batteries, electrolyzers, dielectric capacitors, and sensors. One of their remarkable structural properties is cationic ordering in A or B sites, which affects electrical transport properties under different gaseous atmospheres, and chemical stability under CO2 and humid conditions. For example, a simple-perovskite-type Y-doped BaCeO3 forms BaCO3 and ((Ce,Y)O2-δ) under CO2 at elevated temperature, while B-site-ordered double-perovskite-type Ba3Ca1.18Nb1.82O9-δ remains chemically stable under the same conditions. Early structural studies on Ba3Ca1+ xNb2- xO9-δ (BCN) showed that the B-site ordering (1:1) is sensitive to the Ca content. However, ambiguity rises, as 1:2 B-site ordering was not observed in the parent and doped analogues when x was varied, which motivated us to revisit the complex oxides BCN ( x = 0-0.45) to determine the atomic structure by a mean of combined synchrotron X-ray and neutron diffraction methods. Surprisingly, the B-site ordering increases with increasing Ca/Nb mixing in the B-sites in BCN. In addition, the electrical conductivity of BCN was found to be the highest at x = ∼0.18, and it decreased as the Ca/Nb ratio further increased in BCN. Such a result was very similar to that for the Y-doped BaZrO3, where the mobility of proton carriers was found to decrease as the dopant (Y) increased. A higher Ca/Nb ratio also promotes the growth of grain size, as Ca ions could serve as a sintering aid, improving the structural integrity.

Structure Evolution and Reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.0) System.

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low emissions, high conversion efficiency, no moving parts, and quiet operation, they are considered as a promising energy conversion technology for low carbon future needs. Solid-state oxide and proton conducting electrolytes play a crucial role in improving the performance and market acceptability of SOFCs. Defect fluorite phases are some of the most promising fast oxide ion conductors for use as electrolytes in SOFCs. We report the synthesis, structure, phase diagram, and high-temperature reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.00) oxide defect model system. For all Sc(2- x)V xO3.0 phases with x ≤ 1.08 phase-pure bixbyite-type structures are found, whereas for x ≥ 1.68 phase-pure corundum structures are reported, with a miscibility gap found for 1.08 < x < 1.68. Structural details obtained from the simultaneous Rietveld refinements using powder neutron and X-ray diffraction data are reported for the bixbyite phases, demonstrating a slight V3+ preference toward the 8b site. In situ X-ray diffraction experiments were used to explore the oxidation of the Sc(2- x)V xO3.0 phases. In all cases ScVO4 was found as a final product, accompanied by Sc2O3 for x < 1.0 and V2O5 when x > 1.0; however, the oxidative pathway varied greatly throughout the series. Comments are made on different synthesis strategies, including the effect on crystallinity, reaction times, rate-limiting steps, and reaction pathways. This work provides insight into the mechanisms of solid-state reactions and strategic guidelines for targeted materials synthesis.

Structure, Ionic Conductivity, and Dielectric Properties of Li-Rich Garnet-type Li5+2xLa3Ta2-xSmxO12 (0 ≤ x ≤ 0.55) and Their Chemical Stability.

Lithium garnet oxides are considered as very promising solid electrolyte candidates for all-solid-state lithium ion batteries (SSLiBs). In this work, we present a cubic garnet-type Li5+2xLa3Ta2-xSmxO12 (0 ≤ x ≤ 0.55) system as a potential electrolyte for SSLiBs. Powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) were employed to investigate the structural stability of Li5+2xLa3Ta2-xSmxO12. The results from PXRD and SEM suggested structural and morphological transformation as a function of dopant concentration. In addition to Li-ion transport in Li5+2xLa3Ta2-xSmxO12, the dielectric properties were also investigated in the light of electron energy loss functions, which showed some surface energy loss and negligible volume energy loss for the studied garnets. Surface and volume energy loss functions of a mixed conducting LiCoO2 was studied for comparison. The long-term chemical stability of one of members, Li5.3La3Ta1.85Sm0.15O12, was performed on aged sample using PXRD, SEM, and thermogravimetric analysis.

Profound Understanding of Effect of Transition Metal Dopant, Sintering Temperature, and pO2 on the Electrical and Optical Properties of Proton Conducting BaCe0.9Sm0.1O3-δ.

This study reports the effect of transition metal (TM) substitution on the electrical and optical properties of BaCe0.9Sm0.1O3-δ (BCS). Concentrations of 5-10 mol % of each of Fe and Co have been doped for the B-site of BCS by citric acid autocombustion method. Powder X-ray diffraction has revealed the formation of an orthorhombic perovskite-type structure. FTIR confirmed a distortion in the lattice upon TM-doping in BCS. Scanning electron microscopy (SEM) images of 1400 °C sintered samples have manifested a higher densification in BaCe0.8Sm0.1Co0.1O3-δ (BCSC10) with a grain size ∼11 µm compared to the parent compound BCS (∼2 µm). Thermogravimetric (TG) analysis showed a water uptake in case of BaCe0.85Sm0.1Co0.05O3-δ (BCSC5), while BaCe0.85Sm0.1Fe0.05O3-δ (BCSF5) did not show a noteworthy uptake of water. TG has also proved that the incorporation of Fe and Co in BCS did not improve the chemical stability in CO2 at elevated temperature. The band gap estimated using Kubelka-Munk model based on the diffuse reflectance data was found to be the lowest for BCSC5 (2.47 eV). However, it increases upon lowering oxygen partial pressure (pO2), which was interpreted by a band structure modifications. Among the samples investigated, BCSC10 sintered at 1400 °C showed the highest electrical conductivity of 0.02 S cm(-1) in air at 600 °C, while its proton mobility appears to be negligible under the investigated humidity atmosphere.

Dielectric characteristics of fast Li ion conducting garnet-type Li5+2xLa3Nb2-xYxO12 (x = 0.25, 0.5 and 0.75).

Here, we report the dielectric characteristics of Li-stuffed garnet-type Li5+2xLa3Nb2-xYxO12 (x = 0.25, 0.5 and 0.75) in the temperature range about -53 to 50 °C using AC impedance spectroscopy. All the investigated Li-stuffed garnet compounds were prepared, under the same condition, using conventional solid-state reaction at elevated temperature in air. The Nyquist plots show mainly bulk contribution to the total Li(+) ion conductivity for Li5.5La3Nb1.75Y0.25O12 (Li5.5-Nb) and Li6La3Nb1.5Y0.5O12 (Li6-Nb), while both bulk and grain-boundary effects are visible in the case of Li6.5La3Nb1.25Y0.75O12 (Li6.5-Nb) phase at ∼-22 °C. Non-Debye relaxation process was observed in the modulus AC impedance plots. The dielectric loss tangent of Li5+2xLa3Nb2-xYxO12 are compared with that of the corresponding Ta analogue, Li5+2xLa3Ta2-xYxO12 and showed a decrease in peak intensity for the Nb-based garnet samples which may be attributed to a slight increase in their Li(+) ion conductivity. The relative dielectric constant values were also found to be higher for the Ta member (>60 for Li5+2xLa3Ta2-xYxO12) than that of the corresponding Nb analogue (∼50 for Li5+2xLa3Nb2-xYxO12) at below room temperature. A long-range order Li(+) ion migration pathway with relaxation time (τ0) 10(-18)-10(-15) s and an activation energy of 0.59-0.40 eV was observed for the investigated Li5+2xLa3Nb2-xYxO12 garnets and is comparable to that of the corresponding Ta-based Li5+2xLa3Ta2-xYxO12 garnets.

Dopant Concentration-Porosity-Li-Ion Conductivity Relationship in Garnet-Type Li5+2xLa3Ta2-xYxO12 (0.05 ≤ x ≤ 0.75) and Their Stability in Water and 1 M LiCl.

Highly Li-ion conductive Y-doped garnet-type Li5+2xLa3Ta2-xYxO12 (0.05 ≤ x ≤ 0.75) were studied to understand the effects of yttrium- and lithium-doping on crystal structure, porosity, and Li-ion conductivity using (7)Li MAS NMR, electrochemical ac impedance spectroscopy, and scanning electron microscopy (SEM), as well as ex situ and in situ powder X-ray diffraction (PXRD) to further explore the potential application of garnets in all-solid-state Li-ion batteries. Solid-state (7)Li MAS NMR studies showed an increase in the Li-ion mobility as a function of Y- and Li-doping in Li5+2xLa3Ta2-xYxO12, which is consistent with the results from ac impedance spectroscopy. The SEM studies on sintered pellets indicated a systematic decrease in porosity and an increase in sinterability as the Y- and Li-doping levels increase in Li5+2xLa3Ta2-xYxO12. These results are consistent with the calculated porosity and densities using the Archimedes method. Using the variable-temperature in situ PXRD in the temperature range of 30-700 °C, a thermal expansion coefficient of 7.25 × 10(-6) K(-1) was observed for Li6La3Ta1.5Y0.5O12. To further explore the possibility of a new application for the Li-stuffed garnets, the stability of these materials in aqueous LiCl solution was also studied. A high degree of structural stability was observed in these materials upon 1 M LiCl treatment, making them suitable candidates for further studies as protective layers for lithium electrodes in aqueous lithium batteries.

Highly conductive Li garnets by a multielement doping strategy.

Highly conductive Li7La3Zr2O12 (LLZ) garnet-type solid electrolytes were further optimized to improve Li-ion conduction by La(3+)-sites substitution with Ba(2+) and Zr(4+)-sites substitution with Ta(5+) and Nb(5+). Garnet-structured metal oxides of the nominal chemical compositions Li6.65La2.75Ba0.25Zr1.4Ta0.5Nb0.1O12, Li6.4La3Zr1.4Ta0.6-xNbxO12 (x = 0, 0.1, 0.2, and 0.3), and the parent LLZ, as a reference, were prepared via conventional solid-state reaction to investigate the effect of multielement doping on ionic conductivity. The phase formation, morphology, and Li ion conductivity were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy, and alternating current impedance spectroscopy methods, respectively. In addition, solid-state (27)Al and (7)Li magic-angle spinning (MAS) NMR was used to study the effect of "Al doping" on the investigated multielement doped Li-stuffed garnet metal oxides. All the prepared samples obtained the cubic garnet-type structure (space group: Ia3̅d; No. 230) at 1150 °C, similar to that of cubic LLZ. Except for Li6.4La3Zr1.4Ta0.6O12, all the members show Al content by Al MAS NMR. However, it was not possible to detect Al-based impurity phases using PXRD in any of the investigated garnets. Among the samples investigated in this work, "Al-free" Li6.4La3Zr1.4Ta0.6O12 demonstrated a bulk Li ion conductivity of 0.72 mS cm(-1) at 25 °C, with apparent activation energy of 0.26 eV, significantly higher than the parent LLZ.

Garnet-type solid-state fast Li ion conductors for Li batteries: critical review.

Batteries are electrochemical devices that store electrical energy in the form of chemical energy. Among known batteries, Li ion batteries (LiBs) provide the highest gravimetric and volumetric energy densities, making them ideal candidates for use in portable electronics and plug-in hybrid and electric vehicles. Conventional LiBs use an organic polymer electrolyte, which exhibits several safety issues including leakage, poor chemical stability and flammability. The use of a solid-state (ceramic) electrolyte to produce all-solid-state LiBs can overcome all of the above issues. Also, solid-state Li batteries can operate at high voltage, thus, producing high power density. Various types of solid Li-ion electrolytes have been reported; this review is focused on the most promising solid Li-ion electrolytes based on garnet-type metal oxides. The first studied Li-stuffed garnet-type compounds are Li5La3M2O12 (M = Nb, Ta), which show a Li-ion conductivity of ∼10(-6) at 25 °C. La and M sites can be substituted by various metal ions leading to Li-rich garnet-type electrolytes, such as Li6ALa2M2O12, (A = Mg, Ca, Sr, Ba, Sr0.5Ba0.5) and Li7La3C2O12 (C = Zr, Sn). Among the known Li-stuffed garnets, Li6.4La3Zr1.4Ta0.6O12 exhibits the highest bulk Li-ion conductivity of 10(-3) S cm(-1) at 25 °C with an activation energy of 0.35 eV, which is an order of magnitude lower than that of the currently used polymer, but is chemically stable at higher temperatures and voltages compared to polymer electrolytes. Here, we discuss the chemical composition-structure-ionic conductivity relationship of the Li-stuffed garnet-type oxides, as well as the Li ion conduction mechanism.

Studies on polymorphic sequence during the formation of the 1:1 ordered perovskite-type BaCa(0.335)M(0.165)Nb(0.5)O(3-δ) (M = Mn, Fe, Co) using in situ and ex situ powder X-ray diffraction.

Here, we report a synthetic strategy to control the B-site ordering of the transition metal-doped perovskite-type oxides with the nominal formula of BaCa(0.335)M(0.165)Nb(0.5)O(3-δ) (M = Mn, Fe, Co). Variable temperature (in situ) and ex situ powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), scanning/transmission electron microscopy (SEM/TEM), and thermogravimetic analysis (TGA) were used to understand the B-site ordering as a function of temperature. The present study shows that BaCa(0.335)M(0.165)Nb(0.5)O(3-δ) crystallizes in the B-site disordered primitive perovskite (space group s.g. Pm3̅m) at 900 °C in air, which can be converted into the B-site 1:2 ordered perovskite (s.g. P3̅m1) at 1200 °C and the B-site 1:1 ordered perovskite phase (s.g. Fm3̅m) at 1300 °C. However, the reverse reaction is not feasible when the temperature is reduced. FTIR revealed that no carbonate species were present in all three polymorphs. The chemical stability of the investigated perovskites in CO2 and H2 highly depends on the B-site cation ordering. For example, TGA confirmed that the B-site disordered primitive perovskite phase is more readily reduced in dry and wet 10% H2/90% N2 and is less stable in pure CO2 at elevated temperature, compared to the B-site 1:1 ordered perovskite-type phase of the same nominal composition.

Evaluation of fundamental transport properties of Li-excess garnet-type Li(5+2x)La(3)Ta(2-x)Y(x)O(12) (x = 0.25, 0.5 and 0.75) electrolytes using AC impedance and dielectric spectroscopy.

The fundamental electrical transport properties including ionic conductivity, dielectric constants, loss tangent, and relaxation time constants of Li-excess garnet-type cubic (space group Ia3̄d) Li5+2xLa3Ta2-xYxO12 (x = 0.25, 0.5 and 0.75) have been studied in the temperature range of -50 to 50 °C using electrochemical AC impedance spectroscopy. A correlation has been established between the excess Li content and the Li(+) ion migration pathways. The loss tangent (tan δ) for all samples exhibits a relaxation peak corresponding to the dielectric loss because of dipolar rotations due to Li(+) migration. Comparing the modulus analysis of Li-excess garnets with fluorite-type oxygen ion conductors, we propose the local migration of Li(+) ions between octahedral sites around the "immobile" Li(+) ions in tetrahedral (24d) sites. In the samples with x = 0.25 and 0.5, Li(+) ions seem to jump from one octahedral (96h) site to another bypassing the tetrahedral (24d) site between them (path A), both in local and long-range order migration processes, with activation energies of ∼0.69 and 0.54 eV, respectively. For the x = 0.75 member, Li(+) ions exhibit mainly long-range order migration, with an activation energy of 0.34 eV, where the Li hopping between two octahedral sites occurs through the edge which is shared between the two LiO6 octahedra and a LiO4 tetrahedron (path B). The present AC impedance analysis is consistent with the ab initio theoretical analysis of Li-excess garnets that showed two conduction paths (A and B) for Li ion conduction with different activation energies.

Amphoteric oxide semiconductors for energy conversion devices: a tutorial review.

In this tutorial review, we discuss the defect chemistry of selected amphoteric oxide semiconductors in conjunction with their significant impact on the development of renewable and sustainable solid state energy conversion devices. The effect of electronic defect disorders in semiconductors appears to control the overall performance of several solid-state ionic devices that include oxide ion conducting solid oxide fuel cells (O-SOFCs), proton conducting solid oxide fuel cells (H-SOFCs), batteries, solar cells, and chemical (gas) sensors. Thus, the present study aims to assess the advances made in typical n- and p-type metal oxide semiconductors with respect to their use in ionic devices. The present paper briefly outlines the key challenges in the development of n- and p-type materials for various applications and also tries to present the state-of-the-art of defect disorders in technologically related semiconductors such as TiO(2), and perovskite-like and fluorite-type structure metal oxides.

Diamino-Substituted Quinones as Cathodes for Lithium-Ion Batteries.

This study introduces a sustainable approach to designing organic cathode materials (OCMs) for lithium-ion batteries as a potential replacement for traditional metal-based electrodes. Utilizing green synthetic methodologies, we synthesized and characterized five distinct quinone derivatives and investigated their electrochemical attributes within Li-ion battery architectures. Notably, the observed specific capacities were lower than the theoretical predictions, suggesting limitations in achieving efficient redox reactions in a coin-cell configuration. Among the quinone derivatives studied, one variant derived from natural vanillin showed superior cycle stability, maintaining 58% capacity retention over 95 charge-discharge cycles, and achieving a Coulombic efficiency of 90%. Importantly, we discovered that the commonly used Super-P conductive carbon did not yield any measurable battery performance; instead, these quinones necessitated the incorporation of graphene nanoplatelets as the conductive matrix. Through a facile one-step synthesis in ethanol or water, we have demonstrated a viable synthetic route for producing OCMs, albeit with moderate performances, which have attempted to address common concerns of high solubility and poor redox reactivity of previous OCMs, thereby offering a sustainable pathway for the development of organic-based energy storage devices.