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Nanostructured composite electrode materials play a major role in the fields of catalysis and electrochemistry. The self-assembly of metallic nanoparticles on oxide supports via metal exsolution relies on the transport of reducible dopants towards the perovskite surface to provide accessible catalytic centres at the solid–gas interface. At surfaces and interfaces, however, strong electrostatic gradients and space charges typically control the properties of oxides. Here we reveal that the nature of the surface–dopant interaction is the main determining factor for the exsolution kinetics of nickel in SrTi0.9Nb0.05Ni0.05O3–δ. The electrostatic interaction of dopants with surface space charge regions forming upon thermal oxidation results in strong surface passivation, which manifests in a retarded exsolution response. We furthermore demonstrate the controllability of the exsolution response via engineering of the perovskite surface chemistry. Our findings indicate that tailoring the electrostatic gradients at the perovskite surface is an essential step to improve exsolution-type materials in catalytic converters.

A systematic and comprehensive study of the thermal stability of the cathode active materials LiNi1/3Mn1/3Co1/3O2(NMC111), LiNi0.6Mn0.2Co0.2O2(NMC622), LiNi0.8Mn0.1Co0.1O2(NMC811), and LiNi0.8Co0.15Al0.05O2(NCA) in combination with the garnet solid electrolyte Li6.45La3Zr1.6Ta0.4Al0.05O12was performed, and the respective thermal stability limits in air were assessed. Compared to prior studies on such material mixtures, additional Zr-containing secondary phases were detected, which had not been taken into consideration in a previously published work. Here, these phases were successfully identified for the first time by a combination of X-ray diffraction, Raman spectroscopy, and microstructural analysis.

BaCe0.65Zr0.2Y0.15O3-δ(BCZ20Y15) has raised great interest due to its good protonic conductivity and chemical stability. However, the sintering of the material is considerably challenged by its refractory nature. In the current work, almost fully densified single-phase BCZ20Y15 with grain sizes exceeding 10 μm was successfully fabricated by sintering at 1500 °C by using calcined powders consisting of naturally separated perovskite phases and 0.5 wt% NiO. The role of NiO as sintering aid was elucidated by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atom Probe Tomography (APT) methods, concerning global and local material composition. Furthermore, the mechanism leading to the promoted densification and grain growth is elucidated based on current experimental results and a comprehensive review of the literature.

Vacancy in the transition metal layer of sodium cathode material induces the formation lone-pair electrons in the O 2porbital.Material delivers more capacity from the oxygen redox validated by density functional calculation.Widened dominance of the OP4 phase without releasing O2gas.

MXenes have emerged as one of the most interesting material classes, owing to their outstanding physical and chemical properties enabling the application in vastly different fields such as electrochemical energy storage (EES). MXenes are commonly synthesized by the use of their parent phase, i.e., MAX phases, where “M” corresponds to a transition metal, “A” to a group IV element, and “X” to carbon and/or nitrogen. As MXenes display characteristic pseudocapacitive behaviors in EES technologies, their use as a high-power material can be useful for many battery-like applications. Here, a comprehensive study on the synthesis and characterization of morphologically different titanium-based MXenes, i.e., Ti3C2and Ti2C, and their use for lithium-ion batteries is presented. First, the successful synthesis of large batches (≈1 kg) of the MAX phases Ti3AlC2and Ti2AlC is shown, and the underlying materials are characterized mainly by focusing on their structural properties and phase purity. Second, multi- and few-layered MXenes are successfully synthesized and characterized, especially toward their ever-present surface groups, influencing the electrochemical behavior to a large extent. Especially multi- and few-layered Ti3C2are achieved, exhibiting almost no oxidation and similar content of surface groups. These attributes enable the precise comparison of the electrochemical behavior between morphologically different MXenes. Since the preparation method for few-layered MXenes is adapted to process both active materials in a “classical” electrode paste processing method, a better comparison between both materials is possible by avoiding macroscopic differences. Therefore, in a final step, the aforementioned electrochemical performance is evaluated to decipher the impact of the morphology difference of the titanium-based MXenes. Most importantly, the delamination leads to an increased non-diffusion-limited contribution to the overall pseudocapacity by enhancing the electrolyte access to the redox-active sites.

Exsolution phenomena are highly debated as efficient synthesis routes for nanostructured composite electrode materials for the application in solid oxide cells (SOCs) and the development of next-generation electrochemical devices for energy conversion. Utilizing the instability of perovskite oxides, doped with electrocatalytically active elements, highly dispersed nanoparticles can be prepared at the perovskite surface under the influence of a reducing heat treatment. For the systematic study of the mechanistic processes governing metal exsolution, epitaxial SrTi0.9Nb0.05Ni0.05O3-δthin films of well-defined stoichiometry are synthesized and employed as model systems to investigate the interplay of defect structures and exsolution behavior. Spontaneous phase separation and the formation of dopant-rich features in the as-synthesized thin film material is revealed by high-resolution transmission electron microscopy (HR-TEM) investigations. The resulting nanostructures are enriched by nickel and serve as preformed nuclei for the subsequent exsolution process under reducing conditions, which reflects a so far unconsidered process drastically affecting the understanding of nanoparticle exsolution phenomena. Using an approach of combined morphological, chemical, and structural analysis of the exsolution response, a limitation of the exsolution dynamics for nonstoichiometric thin films is found to be correlated to a distortion of the perovskite host lattice. Consequently, the incorporation of defect structures results in a reduced particle density at the perovskite surface, presumably by trapping of nanoparticles in the oxide bulk.

The increased interest in dual-phase membrane materials for oxygen separation leads to the continuous optimization of their composition. Rare-earth doped ceria is a promising candidate as the ion-conducting phase in the membrane. Spinel-structured FeCo2O4was investigated as an electronic conducting phase forming an additional electronic conducting perovskite-structured phase during sintering when combined with Ce1−xLnxO2−δ. The influence of rare-earth lanthanide elements, i.e., Gd and Sm, as well as their concentration, i.e. x = 0.1 and 0.2, on the final phase composition and microstructure as well as its related functional properties in particular oxygen permeation is analyzed. 20 mol.% doping of either Gd or Sm reveals a multi-phase microstructure after sintering. Moreover, segregation of Gd/Sm, iron, and cobalt is found at the ceria-ceria grain boundaries in Ce0.8Sm0.2O2−δ- and Ce0.9Gd0.1O2−δ-based composites. In contrast, 10 mol.% Gd–doping leads to a dual-phase membrane material without the formation of any other phase. In all cases, the percolation threshold is reached at approx. 20 vol% of the electron-conducting phase in the system leading to similar maximum permeation rates determined by the ionic conductivity of the ceria phase.

Metal exsolution of catalytically active B-site dopants of mixed ion and electron conducting (MIEC) perovskites under reducing conditions can be utilized for the preparation of high-performance electrode materials. To study the underlying mechanisms of the exsolution process with respect to specific material aspects - for example structural properties of the host lattice - advanced model systems with well-defined properties are required. Pulsed laser deposition (PLD), enables the fabrication of such model electrode systems by epitaxial growth of complex oxides with highly defined and tunable structural properties. In this study, we present the development of epitaxial model electrodes of Nb and Ni co-doped strontium titanate (SrTi0.9Nb0.05Ni0.05O3-d, STNNi) by PLD. We discuss epitaxial growth and material properties providing well-defined thin film model electrodes suitable for the investigation of nanoparticle exsolution.

SrTiO3-based materials have been investigated to be a candidate for anode of solid oxide fuel cell (SOFC) due to good chemical stability and high ionic conductivity in reducing atmosphere. However, the electronic conductivity is relatively low, which might be increased by doping. In this work, La, Co-substituted SrTiO3 (LSTC) was fabricated and evaluated as cathode of SOFC. Pechini method was successfully used for material synthesis. By doping of La and Co, the conductivity of materials can be increased to more than 1 S/cm at 800 degC. LSTC|Gadolinium-doped ceria|LSTC symmetric cells were also fabricated for electrode performance testing. The results showed that the interface resistance of LSTC cathode can be optimized to be 0.02 O*cm2 at 800 degC and 0.3 O*cm2 at 600 degC, which indicates possible application of LSTC cathode materials for SOFC. Maximum power density of LSTC cathode on button-sized anode-supported SOFC reached 0.360 W/cm2 at 800 degC.

Beside the standard manufacturing routes for ESCs and ASCs, the co-firing of an all-ceramic inert supported cell concept makes it possible to increase the marketability of SOFCs. Thereby, the co-firing temperature of 1100degC

To prevent spontaneous oxidation during the high-temperature synthesis of non-oxide ceramics, an inert atmosphere is conventionally required1,2. This, however, results in high energy demand and high production costs. Here, we present a process for the synthesis and consolidation of oxidation-prone materials, the ‘molten salt shielded synthesis/sintering’ process (MS3), which uses molten salts as a reaction medium and also to protect the ceramic powders from oxidation during high-temperature processing in air. Synthesis temperatures are also reduced, and the final product is a highly pure, fine and loose powder that does not require additional milling steps. MS3has been used for the synthesis of different ternary transition metal compounds (MAX phases, such as Ti3SiC23, Ti2AlN4, MoAlB5), binary carbides (TiC) and for the sintering of titanium. The availability of high-quality powders, combined with energy and cost savings, may remove one of the bottlenecks for the industrial application of these materials.

The phosphate lithium-ion conductor Li1.5Al0.5Ti1.5(PO4)3(LATP) is an economically attractive solid electrolyte for the fabrication of safe and robust solid-state batteries, but high sintering temperatures pose a material engineering challenge for the fabrication of cell components. In particular, the high surface roughness of composite cathodes resulting from enhanced crystal growth is detrimental to their integration into cells with practical energy density. In this work, we demonstrate that efficient free-standing ceramic cathodes of LATP and LiFePO4(LFP) can be produced by using a scalable tape casting process. This is achieved by adding 5 wt % of Li2WO4(LWO) to the casting slurry and optimizing the fabrication process. LWO lowers the sintering temperature without affecting the phase composition of the materials, resulting in mechanically stable, electronically conductive, and free-standing cathodes with a smooth, homogeneous surface. The optimized cathode microstructure enables the deposition of a thin polymer separator attached to the Li metal anode to produce a cell with good volumetric and gravimetric energy densities of 289 Wh dm–3and 180 Wh kg–1, respectively, on the cell level and Coulombic efficiency above 99% after 30 cycles at 30 °C.

We report on state-of-the-art JULICH (Forschungszentrum Julich) stack with anode-supported solid oxide fuel cells (AS-SOFCs) that have been tested in bio-syngas derived from wood pellets. The sulfur and chlorine were removed after gasification, but the tars were not reformed in the bio-syngas to study the influence of these tars on the degradation of SOFC stack. The total tar content during test was 3.5 g/Nm3 including benzene, toluene, phenol, m-cresol, naphthalene, and minor traces of undefined tars. The test result shows considerable performance degradation in tar-contaminated syngas. Moreover, the test was stopped after 5 hours of operation due to an increase of the pressure drop in the stack. A post-test analysis was carried out, and heavy carbon deposition was found at the cell anode-support surface and the Ni mesh current collector. Carbon was identified by SEM as numerous carbon fibers. The change of support microstructure was also observed near and under the carbon deposition area, and the dusting of Ni metal was observed in the support and Ni mesh current collector.

The development of high-capacity, high-performance all-solid-state batteries requires the specific design and optimization of its components, especially on the positive electrode side. For the first time, we were able to produce a completely inorganic mixed positive electrode consisting only of LiCoO2and Ta-substituted Li7La3Zr2O12(LLZ:Ta) without the use of additional sintering aids or conducting additives, which has a high theoretical capacity density of 1 mAh/cm2. A true all-solid-state cell composed of a Li metal negative electrode, a LLZ:Ta garnet electrolyte, and a 25 μm thick LLZ:Ta + LiCoO2mixed positive electrode was manufactured and characterized. The cell shows 81% utilization of theoretical capacity upon discharging at elevated temperatures and rather high discharge rates of 0.1 mA (0.1 C). However, even though the room temperature performance is also among the highest reported so far for similar cells, it still falls far short of the theoretical values. Therefore, a 3D reconstruction of the manufactured mixed positive electrode was used for the first time as input for microstructure-resolved continuum simulations. The simulations are able to reproduce the electrochemical behavior at elevated temperature favorably, however fail completely to predict the performance loss at room temperature. Extensive parameter studies were performed to identify the limiting processes, and as a result, interface phenomena occurring at the cathode active material/solid–electrolyte interface were found to be the most probable cause for the low performance at room temperature. Furthermore, the simulations are used for a sound estimation of the optimization potential that can be realized with this type of cell, which provides important guidelines for future oxide based all-solid-state battery research and fabrication.

All-solid-state lithium ion batteries are considered a promising future battery concept due to their high safety and energy density. However, they might suffer from mechanical fatigue upon cycling, caused by mechanical stresses due to the volume changes of the electrode active materials constrained by solid electrolyte. Based on a reconstruction of actual microstructure of a mixed cathode (LiCoO2/Li7La3Zr2O12: LCO/LLZO) in a lab sized cell and using computer aided material design, we calculated the thermal stresses after manufacturing and the electrochemical stresses during cycling. This approach allows us intensively study the impact of microstructural parameters (grain size, solid volume fraction and relative density) on the mechanical stress distribution and conductivities, even for cases not easily manufactural in the lab. We found that the mechanical stresses and conductivities linearly depend on the solid volume fraction of LCO and are correlated to the relative density, whereas the grain sizes influenced neither the mechanical stresses nor the conductivities. We introduced a new factor Knas a ratio of the relative interface area between solid phases and the volume fraction of the solid phase (n = LCO or LLZO) which represents the governing factor for the stresses. On the other hand, the volume fraction of LCO and LLZO are the governing factors of their electronic and ionic conductivities. This allows for a sound forecast and determination of an optimal cathode microstructure for maximum cell performance.

The application of silicon (Si) as potential anode material in Li-ion batteries provides a more than nine-fold increase in gravimetric storage capacity compared to conventional graphite anodes. However, full lithiation of Si induces the volume to increase by approximately 300%. Such enormous volume expansion causes large mechanical stress, resulting in non-elastic deformation and crack formation. This ultimately leads to anode failure and strong decrease in cycle life. This problem can be resolved by making use of structured anodes with small dimensions. Particularly honeycomb-shaped microstructures turned out to be beneficial in this respect. In the present paper, finite element modeling was applied to describe the experimentally observed mechanical deformation of honeycomb-structured Si anodes upon lithiation. A close agreement between simulated and experimentally observed shape changes is observed in all cases. The predictive ability of the model was further exploited by investigating alternative geometries, such as square-based microstructure. Strikingly, dimension and pattern optimization shows that the stress levels can be reduced even below the yield strength, while maintaining the footprint-area-specific storage capacity of the microstructures. The pure elastic deformation is highly beneficial for the fatigue resistance of optimized silicon structures. The obtained results are directly applicable for other (de)lithiating materials, such as mixed ionic–electronic conductors (MIEC) widely applied in Li-ion and future Na-ion batteries.

A novel sintering approach was developed in order to overcome the issue of insufficient adherence of (La,Sr)(Co,Fe)O3 type cathodes in metal-supported solid oxide fuel cells (MSCs). Investigation of the phase stability of the perovskite structure at high temperature in various atmospheres with low oxygen partial pressures provided the basis for the development of a specific sintering procedure. After detailed investigation of the layer adherence, time dependent mechanical integrity and reversibility of phase transformations, metal-supported cells with cathodes sintered before cell operation (ex-situ sintering) could be produced reliably and were electrochemically characterized in single cell measurements. The novel sintering approach of such cathodes resulted in a significantly enhanced mechanical stability of the cathode layers. The adherence of the cathode to the electrolyte was considerably stronger, which is a substantial improvement in comparison with state-of-the-art MSCs. Furthermore, the electrochemical measurements revealed a beneficial effect regarding the cell performance.

The integration of solid oxide cells (SOCs) into circular economy is crucial to enable efficient preservation of critical and high-cost resources such as rare earth elements, cobalt, and nickel used in conventional SOC applications. Based on the fuel electrode-supported cell (FESC) design, a semi-closed loop recycling approach was applied for cell material from CeramTec/Forschungszentrum Jülich. We show that more than 85 wt% of the ceramic components can be successfully reprocessed to new fuel electrode-based substrate that can be further used in cell production. Reprocessing of sintered bodies requires a multi-stage procedure. Increasing the amount of recyclate in the substrate leads to changes in substrate properties such as higher porosities and reduced shrinkage.

Perovskites show high potential as alternative fuel electrodes in solid oxide electrolysis cells (SOECs) due to their high chemical stability, high conductivity, good catalytic activity and cost-effectiveness. In this work, four perovskites (strontium-iron-niobate double perovskite (SFN), strontium-iron-titanate (STF), lanthanum-strontium-titanate (LST), and lanthanum-strontium-iron-manganese (LSFM)) were examined as fuel electrode materials for SOECs. First, the chemical stability of the perovskites in a reducing atmosphere and the reactivity between the electrode and electrolyte material were analyzed. Besides featuring good chemical stability under reducing conditions, SFN double perovskite and LST exhibit the lowest interaction with the electrolyte (yttria-stabilized zirconia, 8YSZ) after thermal treatment. The results indicate a need for a barrier layer between the tested electrode materials and the YSZ electrolyte to achieve sufficient cell performance throughout its operation in the electrolysis mode. After thoroughly evaluating all preliminary tests, STF was chosen for the first subsequent electrochemical tests. Initial impedance measurements of symmetrical electrolyte-supported cells consisting of pure STF-based electrodes with and without a barrier layer between the electrodes and the electrolyte were conducted to obtain a base for further optimization. For the 5STF fuel electrode, the obtained EIS data confirm the conclusion from the reactivity experiments. Applying a barrier layer at the 5STF fuel electrode/ electrolyte interface is needed to reduce the cell´s ohmic and polarization resistances.

An in-depth post mortem analysis was conducted on cells from a stack with an operation time of 100,000 h. In doing so, the focus of the investigations was mainly on the air electrode side. By utilizing scanning electron microscopy in combination with energy dispersive X-ray spectroscopy the microstructure and the localized chemical composition was investigated. Additionally, the structural changes of the cells were analyzed by X-ray diffraction, by Raman spectroscopy, and by synchrotron-based µ-Laue diffraction measurements. The combination of these advanced analytical tools highlights changes in the structure and chemical composition on the air electrode side caused by various degradation effects after long-term operation.

The bulk diffusion of Na in Na3.4Sc2(SiO4)0.4(PO4)2.6was investigated by 23Na NMR relaxometry in the temperature range from 250 to 670 K. These measurements reveal fast Na diffusion with hopping rates of 3 × 108s–1for the Na+ions at 350 K and activation barriers for single Na+ion jumps of (0.20 ± 0.01) eV. From these values a diffusion coefficient of D= 6.4 × 10–12m2/s and a Na ion conductivity of σNa= 4 mS/cm (both at 350 K) can be estimated. Measurements on two samples, one stored in air and one stored in Ar, do not show significant differences, which reveals that these NMR measurements are probing the bulk diffusion while conductivity measurements usually are also influenced by grain boundaries that can be affected by the moisture level during storage.

The reactivity of mixtures of high voltage spinel cathode materials Li2NiMn3O8, Li2FeMn3O8, and LiCoMnO4cosintered with Li1.5Al0.5Ti1.5(PO4)3and Li6.6La3Zr1.6Ta0.4O12electrolytes is studied by thermal analysis using X-ray-diffraction and differential thermoanalysis and thermogravimetry coupled with mass spectrometry. The results are compared with predicted decomposition reactions from first-principles calculations. Decomposition of the mixtures begins at 600 °C, significantly lower than the decomposition temperature of any component, especially the electrolytes. For the cathode + Li6.6La3Zr1.6Ta0.4O12mixtures, lithium and oxygen from the electrolyte react with the cathodes to form highly stable Li2MnO3and then decompose to form stable and often insulating phases such as La2Zr2O7, La2O3, La3TaO7, TiO2, and LaMnO3which are likely to increase the interfacial impedance of a cathode composite. The decomposition reactions are identified with high fidelity by first-principles calculations. For the cathode + Li1.5Al0.5Ti1.5(PO4)3mixtures, the Mn tends to oxidize to MnO2or Mn2O3, supplying lithium to the electrolyte for the formation of Li3PO4and metal phosphates such as AlPO4and LiMPO4(M = Mn, Ni). The results indicate that high temperature cosintering to form dense cathode composites between spinel cathodes and oxide electrolytes will produce high impedance interfacial products, complicating solid state battery manufacturing.

Al-contaminated Ta-substituted Li7La3Zr2O12(LLZ:Ta), synthesized via solid-state reaction, and Al-free Ta-substituted Li7La3Zr2O12, fabricated by hot-press sintering (HP-LLZ:Ta), have relative densities of 92.7% and 99.0%, respectively. Impedance spectra show the total conductivity of LLZ:Ta to be 0.71 mS cm–1at 30 °C and that of HP-LLZ:Ta to be 1.18 mS cm–1. The lower total conductivity for LLZ:Ta than HP-LLZ:Ta was attributed to the higher grain boundary resistance and lower relative density of LLZ:Ta, as confirmed by their microstructures. Constant direct current measurements of HP-LLZ:Ta with a current density of 0.5 mA cm–2suggest that the short circuit formation was neither due to the low relative density of the samples nor the reduction of Li–Al glassy phase at grain boundaries. TEM, EELS, and MAS NMR were used to prove that the short circuit was from Li dendrite formation inside HP-LLZ:Ta, which took place along the grain boundaries. The Li dendrite formation was found to be mostly due to the inhomogeneous contact between LLZ solid electrolyte and Li electrodes. By flatting the surface of the LLZ:Ta pellets and using thin layers of Au buffer to improve the contact between LLZ:Ta and Li electrodes, the interface resistance could be dramatically reduced, which results in short-circuit-free cells when running a current density of 0.5 mA cm–2through the pellets. Temperature-dependent stepped current density galvanostatic cyclings were also carried out to determine the critical current densities for the short circuit formation. The short circuit that still occurred at higher current density is due to the inhomogeneous dissolution and deposition of metallic Li at the interfaces of Li electrodes and LLZ solid electrolyte when cycling the cell at large current densities.

All-solid-state lithium batteries are promising candidates for next-generation energy storage systems. Their performance critically depends on the capacity and cycling stability of the cathodic layer. Cells with a garnet Li7La3Zr2O12(LLZO) electrolyte can show high areal storage capacity. However, they commonly suffer from performance degradation during cycling. For fully inorganic cells based on LiCoO2(LCO) as cathode active material and LLZO, the electrochemically induced interface amorphization has been identified as an origin of the performance degradation. This study shows that the amorphized interface can be recrystallized by thermal recovery (annealing) with nearly full restoration of the cell performance. The structural and chemical changes at the LCO/LLZO heterointerface associated with degradation and recovery were analyzed in detail and justified by thermodynamic modeling. Based on this comprehensive understanding, this work demonstrates a facile way to recover more than 80% of the initial storage capacity through a thermal recoverry (annealing) step. The thermal recovery can be potentially used for cost-efficient recycling of ceramic all-solid-state batteries.

Developing cost-effective and reliable solid-state sodium batteries with superior performance is crucial for stationary energy storage. A key component in facilitating their application is a solid-state electrolyte with high conductivity and stability. Herein, we employed aliovalent cation substitution to enhance ionic conductivity while preserving the crystal structure. Optimized substitution of Y3+with Zr4+in Na5YSi4O12introduced Na+ion vacancies, resulting in high bulk and total conductivities of up to 6.5 and 3.3 mS cm–1, respectively, at room temperature with the composition Na4.92Y0.92Zr0.08Si4O12(NYZS). NYZS shows exceptional electrochemical stability (up to 10 V vs. Na+/Na), favorable interfacial compatibility with Na, and an excellent critical current density of 2.4 mA cm–2. The enhanced conductivity of Na+ions in NYZS was elucidated using solid-state nuclear magnetic resonance techniques and theoretical simulations, revealing two migration routes facilitated by the synergistic effect of increased Na+ion vacancies and improved chemical environment due to Zr4+substitution. NYZS extends the list of suitable solid-state electrolytes and enables the facile synthesis of stable, low-cost Na+ion silicate electrolytes.

The increasing demand for safe energy storage has led to intensive investigations of solid-state Li+-ion conductors in the Li2O-M2O3–ZrO2–SiO2–P2O5system. As a continuation of the cation substitution in this system, which we reported on very recently, a study of the impact of polyanionic substitutions on ionic conductivity was carried out here in two series, Li3+xSc2SixP3-xO12(0 ≤ x ≤ 0.6) and Li1.2+xSc0.2Zr1.8SixP3-xO12(0.3 ≤ x ≤ 2.8), with the aim of increasing ionic conductivity, determing the phase stability, and optimizing the processing conditions – especially decreasing the sintering temperatures – depending on the level of substitution.

At the nanoscale material properties can be tuned by altering the size and shape of the specimen. Such effects are quite well investigated for metallic materials. On the other hand inorganic compounds have received relatively little interest due to the more demanding experimental procedures. While the size effects are similar for any kind of inorganic material, the degree of size-dependent changes depends on the bond strength and bond nature of the material at the surface: the higher the surface energy, the stronger the size dependence. These thoughts are demonstrated in this contribution by investigating the size-dependent thermodynamic properties of monodisperse, size-selected bismuth oxide (Bi2O3) nanoparticles in the range between 6 and 50 nm. This first part is mainly concerned with evaporation, while the second part (J. Phys. Chem. C2014, 10.1021/jp509841s) covers size-dependent melting. Heating experiments up to the evaporation of the particles were performed with a new, custom method based on loss of matter caused by evaporation. The results in this part show the validity of the Kelvin equation and a size-dependent evaporation behavior of this oxide.

Melting of nanocrystalline bismuth oxide particles between 6 and 50 nm was investigated in situ in the transmission electron microscope (TEM). It revealed a size-dependent melting behavior with a strong melting point reduction (−55% at 6 nm). One reason is a −230 K offset in the bulk melting temperature which is apparently caused by the β-phase in which the nanomaterial resides. As a second reason, a strong size dependency was observed from which an approximate solid-surface energy of 0.3 J/m2was determined. Yet, the conditions in the TEM could cause a lowering of the transition temperatures compared to chemically neutral conditions, although theoretical considerations predict reduction in the solid state to be negligible. Everything indicates that no stable, liquid surface layer forms prior to melting. In spite of the covalent-ionic bonds in this oxide material the qualitatively same size dependence shows like in metals. Combined with size-dependent evaporation examined in a companion study [Guenther et al. J. Phys. Chem. C2014, 10.1021/jp412531t], a size-dependent phase diagram is proposed for this oxide material.

Abstract

Sodium (Na) metal is considered as the promising anode for next‐generation high‐energy‐density Na‐metal batteries owing to its highest specific capacity and lowest electrochemical potential among all Na‐based anode candidates. However, the Na metal anode suffers from considerable volume change, nonuniform Na deposition, and an unstable electrode–electrolyte interface, which result in rapid capacity fade and poor cycling stability, hampering its practical application. To tackle aforementioned issues, many strategies have been developed to accommodate and guide Na nucleation/growth as well as stabilize the interface, including structure stabilization by applying 3D host materials, electrolyte modification and interface engineering to form stable interfaces and guide the Na deposition, etc. The present review is intended as a guideline through the fundamental challenges affecting the performance of Na metal anodes along with corresponding mitigation strategies. Moreover, the specific mechanisms for stabilizing Na metal anodes are discussed in detail. Apart from the stabilization of the Na metal anode in contact with liquid electrolytes, attention has also been paid to the review of stabilization of the Na metal anode in contact with solid‐state electrolytes. Furthermore, unresolved challenges and promising perspectives for stable Na metal anodes in practical applications are presented. This review provides the fundamental challenges of Na metal anodes in contact with organic liquid and solid‐state electrolytes along with progressive solution strategies. The mechanisms of strategies for stabilizing Na metal anodes are discussed in detail. Furthermore, unresolved challenges and promising perspectives for stable Na metal anodes are presented.

A soft lithography technique was used to introduce surface patterns on the surface of sintered bioactive glass substrates. Osteoblast‐like MG‐63 cells and rat mesenchymal stem cells (rMSC) seeded on micropatterned bioactive glass surfaces showed different behavior with rMSC exhibiting a better initial attachment than MG‐63 cells. Both cytoskeleton formation and cell spreading of rMSC were supported by the bioactive surfaces. In addition, the structured surfaces seemed to guide MG‐63 cells to a larger extent than rMSC. The in vitro results are important considering the continuous development of bone tissue scaffolds based on silicate bioactive glasses.

Patterned ceramic films with constant thickness can be processed by a soft lithographic method. By using micromolding in capillaries, the slurry is forced to flow through channels created in an elastomer stamp. After drying, layers deposited on an amorphous carbon substrate were sintered under inert atmosphere. Free‐standing ceramic structures with high aspect ratio were obtained with lateral resolution better than 1 µm. Dimensional changes were monitored in comparison to films deposited on stiff sapphire substrate. This technique enables to process a large variety of structures, from optical or electronic components to sieve and MEMS applications.

In our work we demonstrate a facile, water-free synthesis of amorphous lithium niobate (LiNbO3) layers. Our developed method also enables the coating of substrates in inert atmosphere with simple, industrial scalable methods. As verification, a 120 nm thin LiNbO3layer was deposited on the garnet type lithium ion conductor Li6.45Al0.05La3Zr1.6Ta0.4O12(LLZTO) to improve its interface to lithium metal and reduce dendrite formation. The application of the thin film reduced the interface resistance between LLZTO and lithium metal to 1.02(13) Ω∙cm2and increased the critical current density for dendrite formation to at least 0.5 mA cm−2. The chemical stability of the LiNbO3thin film in contact with Li-metal was verified by SEM, XPS and ToF-SIMS.

Asymmetric oxygen transport membranes have been extensively studied revealing the importance of the support porosity. In this study, asymmetric membranes with vertically channelled pores were prepared from Ba0.5Sr0.5(Co0.8Fe0.2)0.97Zr0.03O3-δ(BSCF-Z) by phase inversion tape casting. The rate-limiting effects of the membrane layer thickness, the support structure, and the activation layers were thoroughly analysed. This entails comparing the permeation rate of the samples with the membrane layer on different sides of the channelled supports. Pore tortuosity and computed permeability were evaluated from 3D-X-ray computed tomography and compared to previously reported asymmetric membranes prepared by tape-casting and freeze-drying. Due to a lower pore tortuosity, the channelled supports have an advantage in gas transport over the tape cast and freeze cast supports. However, this is compensated by a thicker membrane layer (∼54 μm) resulting in similar performance compared to the thinner membrane layers (∼20 μm) with freeze cast and tape cast supports.

This study provides for the first time a detailed investigation of the cold sintering of LiMn2O4(LMO). Aqueous based cold sintering aid facilitated densification of LMO at lower temperature range of 400 °C to 600 °C within a dwell time of merely 1 min to the relative density of 70%–80%, without any non—stoichiometry or the need of post annealing in air atmosphere. Connected porosity was observed in the cold sintered structure as confirmed by Mercury porosimetry and scanning electron microscopy analysis. Cold sintered and dry milled LMO delivered a specific discharge capacity of 121 mAh g−1for the first discharge cycle at 0.1 C with an appreciably low capacity drop to 107 mAh g−1at 15 C. In contrast, LMO powder, without any cold sintering treatment, provided merely 84 mAh g−1at 0.1 C as initial discharge capacity and only 6 mAh g−1at 2 C. This difference was interpreted as the removal/thinning of insulating Li2CO3layer from the LMO particles after being cold sintered as confirmed by X-ray diffraction, thermal analysis and Raman spectroscopy.

Li-ion conducting oxides (Li7La3Zr2O12, LLZO) with a cubic garnet-type structure are among the most promising candidates to be used as solid electrolytes in all-solid-state Li batteries. However, the environmental instability of the electrolyte, induced by interaction between the material and gas molecules commonly found in air, namely, water and carbon dioxide, poses challenges for its manufacture and application. Herein, a combined experimental kinetic and thermodynamic study was performed as a function of temperature to clarify the mechanism of hydration of a garnet-type LLZO electrolyte in moist air. It was found that the kinetics of LLZO hydration is diffusion-limited and the hydration mechanism at room temperature and at higher temperatures differs. The hydration of LLZO increases up to 200 °C. Above this temperature, stagnation of water uptake is observed due to the onset of a competing dehydration process. The dehydration of LLZO takes place up to 400 °C. The partial pressure of water significantly affects the extent of hydration. Expanding this combined kinetic and thermodynamic approach to LLZO materials with a variety of chemical compositions and morphologies would allow prediction of their reactivity in a humid atmosphere and adjustment of the processing conditions accordingly to meet the requirements of technological applications.

The garnet-type Li7La3Zr2O12(LLZO) ceramic solid electrolyte combines high Li-ion conductivity at room temperature with high chemical stability. Several all-solid-state Li batteries featuring the LLZO electrolyte and the LiCoO2(LCO) or LiCoO2–LLZO composite cathode were demonstrated. However, all batteries exhibit rapid capacity fading during cycling, which is often attributed to the formation of cracks due to volume expansion and the contraction of LCO. Excluding the possibility of mechanical failure due to crack formation between the LiCoO2/LLZO interface, a detailed investigation of the LiCoO2/LLZO interface before and after cycling clearly demonstrated cation diffusion between LiCoO2and the LLZO. This electrochemically driven cation diffusion during cycling causes the formation of an amorphous secondary phase interlayer with high impedance, leading to the observed capacity fading. Furthermore, thermodynamic analysis using density functional theory confirms the possibility of low- or non-conducting secondary phases forming during cycling and offers an additional explanation for the observed capacity fading. Understanding the presented degradation paves the way to increase the cycling stability of garnet-based all-solid-state Li batteries.

Solid oxide cell (SOC) technology currently attracts great attention due to its unique potential for substantially contributing to a carbon‐neutral power supply. The variety in possible designs and applications—covering oxygen ion and proton conductors and the ability to convert surplus electricity to easily storable synthetic fuels, as well as to produce electricity from these fuels according to demand and availability—provides the excellent position of SOCs with regard to decentralized power generation and distribution. Herein, a reference work on cell performance is provided by highlighting specific advantages of the different cell types, designs, and materials with regard to certain operating conditions, including challenges concerning operational modes, processing, and degradation. In conjunction with a critical examination in terms of relevance and technical feasibility, the data provided enable an assessment of the general potential of the cell types for technology development and connect scientific research to industrial considerations. Material development, processing, and design of solid oxide cells are reviewed with a focus on cell performance comparison. A large number of performance values from fuel cells and electrolysis operation provide basis for an application‐oriented assessment of cell setups. Optimization of traditional materials and development of new strategies enable equally large advancements in the field, encouraging collaboration between researchers and industry.

Three different ceramic matrix composites (CMCs) were produced using Cr2AlC as a matrix, and carbon, SiC and Al2O3short fibers as a secondary phase. Cr2AlC powders were synthesized by solid-state reaction, followed by mixing with the fibers, and full densification using a field-assisted sintering technique. Of the three different fiber types, Carbon fibers reacted strongly with Cr2AlC, while the reaction with SiC fibers was more limited and alumina fibers didn’t show any reaction. Oxidation tests of the monolithic Cr2AlC and the composites were performed by thermogravimetric analysis. An alumina layer formed at 1000 °C on every sample, well attached and worked as a good oxidation barrier. Under realistic conditions using a burner rig for cyclic oxidation at 1200 °C for 500 cycles, the oxidation resistance of the alumina fiber CMC is good, as no defects or degradation are visible and the alumina layer is well attached.

MXenes, as an emerging class of 2D materials, display distinctive physical and chemical properties, which are highly suitable for high-power battery applications, such as lithium ion batteries (LIBs). Ti3C2Tx(Tx= O, OH, F, Cl) is one of the most investigated MXenes to this day; however, most scientific research studies only focus on the design of multilayered or monolayer MXenes. Here, we present a comprehensive study on the synthesis of few-layered Ti3C2Txmaterials and their use in LIB cells, in particular for high-rate applications. The synthesized Ti3C2TxMXenes are characterized viacomplementary XRD, Raman spectroscopy, XPS, EDX, SEM, TGA, and nitrogen adsorption techniques to clarify the structural and chemical changes, especially regarding the surface groups and intercalated cations/water molecules. The structural changes are correlated with respect to the acidic and basic post-treatment of Ti3C2Tx. Furthermore, the detected alterations are put into an electrochemical perspective viagalvanostatic and potentiostatic investigations to study the pseudocapacitive behavior of few-layered Ti3C2Tx, exhibiting a stable capacity of 155 mAh g–1for 1000 cycles at 5 A g–1. The acidic treatment of Ti3C2Txsynthesized viathe in situformation of HF through LiF/HCl is able to increase the initial capacity in comparison to the pristine or basic treatment. To gain further insights into the structural changes occurring during (de)lithiation, in situXRD is applied for LIB cells in a voltage range from 0.01 to 3 V to give fundamental mechanistic insights into the structural changes occurring during the first cycles. Thereby, the increased initial capacity observed for acidic-treated MXenes can be explained by the reduced co-intercalation of solvent molecules.

Based on previous studies of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3, La0.97Ni0.5Co0.5O3(LNC) is chosen as the most promising air-electrode material in the series for solid oxide cells (SOCs). The properties of the material itself have been investigated in detail. However, the evaluation of LNC97 air electrodes in practical SOCs is still at a very early stage. In the present study, SOCs were prepared based on LNC97 air electrodes. The I-U performance of the SOCs in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes, i.e. reversible SOCs (r-SOCs), was investigated systematically for different air-electrode designs, temperatures and fuel gases. In general, the performance of the r-SOCs tested in the present study is higher than the published results of other LaFeO3–LaCoO3–LaNiO3-based SOCs and is comparable to or even better than state-of-the-art La1−xSrxFe1−yCoyO3(LSCF)-based SOCs. Mid-term operation of about 1000 h for SOCs in both SOFC and SOEC modes primarily proved the stability of LNC97-based air electrodes. Impedance spectra were systematically applied to understand the polarization processes of the SOCs.

All-solid-state sodium batteries (Na-ASSBs) are regarded as an ecologic and economical alternative to their Li congeners for stationary applications. Ceramic-based Na-ASSBs benefit from the high conductivity of the oxide Na-ion conductors used as electrolyte, as well as from their good mechanical, chemical and thermodynamic stability. However, so far Na-ASSBs suffer from severe contact problems in the positive electrodes and subsequently unsatisfactory cell performance. In this report, the inter-ceramic contact problems are solved by combining the infiltration of a porous electrolyte scaffold by precursor solution with in situsynthesis of electrode active material (chemical infiltration) to fabricate model cells using Na3V2P3O12(NVP), Na3.4Zr2Si2.4P0.6O12(NZSP) and Na as the positive electrode, electrolyte and negative electrode materials, respectively. Optimized interface between NVP nano layer and NZSP backbone was formed, providing effective ion transfer and minimizing the stress caused by volume change of electrode active material during charging and discharging processes. The interface resulted in a highly stable battery performance at 25 °C. The performances, achieved without using any liquid or polymer phase as an accommodation medium, suggest a promising future for chemical infiltration as fabrication process for ceramic-based ASSBs.

Metal exsolution of catalytically active B-site dopants of mixed ion and electron conducting (MIEC) perovskites under reducing conditions can be utilized for the preparation of high-performance electrode materials. To study the underlying mechanisms of the exsolution process with respect to specific material aspects - for example structural properties of the host lattice - advanced model systems with well-defined properties are required. Pulsed laser deposition (PLD), enables the fabrication of such model electrode systems by epitaxial growth of complex oxides with highly defined and tunable structural properties. In this study, we present the development of epitaxial model electrodes of Nb and Ni co-doped strontium titanate (SrTi0.9Nb0.05Ni0.05O3-δ, STNNi) by PLD. We discuss epitaxial growth and material properties providing well-defined thin film model electrodes suitable for the investigation of nanoparticle exsolution.