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A nanopowder consisting of La2Zr2O7 particles with lithium containing species on their surface was prepared by spray flame synthesis and subsequently added to Li7La3Zr2O12 powder obtained by a conventional solid-state reaction. The spray flame synthesis method utilized in this work yields nanoparticles with a small size of approximately 5 nm, which is unprecedented within the scope of oxide-based ionic conductors for solid-state batteries. Remarkably, the addition of nanoparticles for sintering at a relatively low temperature of 1000 °C significantly improved the ionic conductivity by 50 %. In contrast, there was no influence of incorporating nanoparticles on the conductivity at sintering temperatures at or above 1100 °C, which is the typical temperature range applied for conventional sintering of Li7La3Zr2O12. Compared to prior published work with analogous materials, a more than twofold improvement in conductivity was demonstrated while the sintering temperature was decreased by 100 °C.

A physicochemical mechanism acting between the reactive plasma and the material surface controls the erosion of polycrystalline ceramics in fluorine containing etching plasmas. In this study, a Y2O3/YOF composite was exposed to a fluorine etching plasma. Relocalization enables the direct correlation of crystalline orientation with material response. Our study reveals an orientation dependent surface fluorination of Y2O3, which controls the etching resistance and morphology formation. Orientations near the low index planes (001), (010) and (100) exhibit the lowest stability due to a homogeneous surface reaction. The presented results help to extend the mechanistic understanding of the plasma-material interaction of Y2O3.

The structural reliability of sintered products depends on large defects introduced during powder processing, which cannot be removed by pressureless sintering. Here, we present a model how a large single ellipsoidal void is deformed, and finally disappears by pressure-assisted sintering. Taya-Seidel’s model is applied to predict the shrinkage of a large void in a compressible linear viscous material by using bulk viscosity, shear viscosity, and sintering stress that are determined experimentally for sintering of alumina powder at low stress levels. The application of mechanical stress promotes the densification rate. Its effect is maximum for hot isostatic pressing (HIP) and minimum for sinter forging. The effect is intermediate for hot pressing (HP) and spark plasma sintering (SPS), because the hydrostatic component of stress varies with densification. While a crack-like defect can be removed during densification, a spherical void must be eliminated by shear deformation in the final stage during dwell time.

Garnet-based Li7La3Zr2O12 (LLZO) is considered one of the most promising oxide-ceramic solid electrolyte materials for inorganic all-solid-state batteries. Dopants and substituents like Al, Ta, Nb, Ga, and W were shown to have a high impact on the total ionic conductivity, increasing it from 10−6 S/cm up to 10−3 S/cm. However, natural zirconium sources always contain a small amount of hafnium which could also act as dopant, but the separation of these two elements is complicated and expensive. In this work, we investigate the influence of various Hf-impurity concentrations on the performance of tantalum-doped LLZO. We synthesised Li6.45Al0.05La3Zr1.6−xHfxTa0.4O12 (LLZHO with x = 0 – 1.6) via conventional solid-state synthesis and have demonstrated that up to x = 0.1, hafnium impurities do not have a significant impact on the performance of the material. Above this concentration, the Li-ion conductivity is steadily reduced to around 70% when zirconium is fully substituted by hafnium resulting in Li6.45Al0.05La3Hf1.6Ta0.4O12. As the purity of Zr precursors has a great impact on their price, these findings can help to reduce the price of LLZO in general, as lower grade zirconium can be used in industrial scale applications.

Ce0.8Gd0.2O2-δ-FeCo2O4 membranes, benefiting from their excellent chemical stability, exhibit a broad application potential in oxygen-consuming industrial processes running in harsh environments. For long-term reliable operation, the membrane needs to possess sufficient mechanical strength. This paper characterizes the typical aspects that challenge the mechanical stability of the sintered membrane, including composition and microstructural defects as well as residual stress and residual stress gradients. It is revealed that mechanical strengths of the sintered membranes increase with decreasing iron cobalt spinel content, that the high iron cobalt spinel content induces microcracks, and that high residual tensile stress gradually decreases from the as-sintered surface to the bulk. Although the residual tensile stress can be reduced by applying an extensive elevated temperature dwell time during cooling, it is suggested to limit the iron cobalt spinel content to a nominal value of 15 wt% to eliminate the residual tensile stress while maintaining a high mechanical strength.

All-solid-state Li batteries (ASSLBs) are regarded as the systems of choice for future electrochemical energy storage. Particularly, the garnet Li7La3Zr2O12 (LLZO) is one of the most promising solid electrolytes due to its stability against Li metal. However, its integration into ASSLBs is challenging due to high temperature and long dwell time required for sintering. Advanced sintering techniques, such as Ultrafast High-temperature Sintering, have shown to significantly increase the sintering rate. Direct contact to graphite heaters allows sintering of LLZO within 10 s due to extremely high heating rates (up to 104 K min−1) and temperatures up to 1500 °C to a density around 80 %. The LLZO sintered in vacuum and Ar atmosphere has good mechanical stability and high phase purity, but kinetic de-mixing at the grain boundaries was observed. Nevertheless, the Li-ion conductivity of 1 mS cm−1 at 80 °C was comparable to conventional sintering, but lower than for Field-Assisted Sintering Technique/Spark Plasma Sintering.

Dense environmental barrier coatings (EBCs) are an essential prerequisite to exploit the advantages offered by SiC-based fiber reinforced ceramic matrix composites (CMCs) to increase efficiency in gas turbines. Today's state-of-the art materials for application as EBCs are rare-earth (RE) silicates which, however, form amorphous phases upon rapid quenching from the melt. This makes their processing by thermal spray a challenge. Recently, high velocity oxygen fuel (HVOF) spraying was proposed as potential solution since the melting degree of the feedstock can be controlled effectively. This work studies the deposition of ytterbium disilicate (YbDS) at short stand-off distances and variant total feed rates and oxy-fuel ratios of the working gas. It was found that the overall degree of crystallinity could be kept at high level above 90%. The kinetic energy transferred by impinging particles was found to be an effective parameter to control the densification of the coatings. Porosities well below 10% were achieved while fully dense coatings were impeded due to the progressive accumulation of stresses in the coatings.

In this work, nonmonotonic lattice parameter changes and phase transitions in LixNi0.8Co0.1Mn0.1O2 (LixNCM811) during delithiation are studied by combining an extensive set of electrostatic and density functional theory (DFT) calculations. To our knowledge,for the first time we simulated and explained the reason behind the experimentally observed hexagonal to monoclinic (H–M) phase transition at x = 0.50 as well as O3 → O1 phase transition at x = 0.00 in this system. An analysis of atomic and electronic structures of ions at each layer indicated that the H–M phase transition is driven by the Jahn–Teller (J–T) distortion effect. Moreover, it was found that the O3 → O1 phase transition is driven by electrostatic forces. This study also shows that the oxidation of Ni cations as well as their nature of bonds with O are not similar at different Ni/Ni, Ni/Co, and Ni/Mn layers. We also found that the significant decrease in the c lattice parameter for low values of x is due to the disappearance of J–T distortions as well as large covalent O–Ni bonds and oxidation of O and, more importantly, the sliding of O–TM–O layers with respect to each other.

Advanced ceramic materials with tailored properties are at the core of established and emerging energy technologies. Applications encompass high‐temperature power generation, energy harvesting, and electrochemical conversion and storage. New opportunities for material design, the importance of processing and material integration, and the need for long‐term testing under realistic conditions are highlighted in the present perspective.

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 Ti3C2Tx materials and their use in LIB cells, in particular for high-rate applications. The synthesized Ti3C2Tx MXenes are characterized via complementary 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 via galvanostatic and potentiostatic investigations to study the pseudocapacitive behavior of few-layered Ti3C2Tx, exhibiting a stable capacity of 155 mAh g–1 for 1000 cycles at 5 A g–1. The acidic treatment of Ti3C2Tx synthesized via the in situ formation 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 situ XRD 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.

MRS bulletin 46(1), 52-58 (2021). doi:10.1557/s43577-020-00008-w special issue: "Synthesis and Processing Under Electric/Electromagnetic Fields", Published by Springer, Berlin

Journal of materials chemistry / A 9(8), 4831-4840 (2021). doi:10.1039/D0TA11096E, Published by Royal Soceity of Chemistry, London [u.a.]

Ce0.8Gd0.2O2−δ-FeCo2O4 composites are attractive candidate materials for high-purity oxygen generation providing robust chemical stability. Aiming for future industrial applications, a feasible solid-state reaction process with one thermal processing step was used to synthesize 50 wt% Ce0.8Gd0.2O2−δ:50 wt% FeCo2O4 and 85 wt% Ce0.8Gd0.2O2−δ:15 wt% FeCo2O4 composites. Mechanical reliabilities of the sintered membranes were assessed based on the characterized mechanical properties and subcritical crack growth behavior. In general, the fracture strengths of as-sintered membranes were reduced by tensile residual stresses and microcracks. In particular, the enhanced subcritical crack growth behavior, which leads to limited stress tolerance and high failure probability after a 10-year operation, was evaluated in more detail. Further materials and processing improvements are needed to eliminate the tensile stress and microcracks to warrant a long-term reliable operation of the composites.

Dual phase oxygen transport membranes were prepared via solid state reaction at 1200 ℃. The sintered membranes were characterized via X-ray diffraction, back scattered electron microscopy and electron backscatter diffraction, and associated with image analysis and calculations to quantify phase compositions and microstructural features including volume fractions, grain sizes, and contiguity. The characterizations reveal a multi-phase system containing Ce1-xGdxO2-δ’ (x ≈ 0.1) (CGO10), and FeyCo3-yO4 (0.2 < y < 1.2) (FCO), CoO and Gd0.85Ce0.15Fe0.75Co0.25O3 (GCFCO) in the sintered membranes. In addition, a novel model is utilized to assess the evolution of the ambipolar conductivity with respect to microstructural features. Both experimental and calculated results indicate that if the grain sizes of all phases in the composites are similar, the optimal ambipolar conductivity is reached with a volume ratio of ionic conducting phase to electronic conducting phase close to 4:1. Meanwhile, the GCFCO phase dominates the effective electronic conductivity.

Journal of the American Ceramic Society (2020). doi:10.1111/jace.17556, Published by American Ceramic Society, Westerville, Ohio

Aerosol deposition (AD) is a novel deposition process for the fabrication of dense and rather thick oxide films at room temperature. The bonding of the deposited ceramic particles is based on a shock-loading consolidation, resulting from the impact of the ceramic particles on the substrate. However, the deposition mechanism is not fully understood. In addition, many technical challenges have been observed for achieving a successful deposition of the oxides with higher efficiency. In this work, the influence of different processing parameters on the properties of the deposited layer is studied. Proof of concept was done using 8 mol.% yttria-stabilized zirconia (8YSZ) powder as starting material. The window of deposition with respect to carrier gas flows for successful deposition was identified. The influence of this carrier gas flow, the substrate materials and the carrier gas species on the coating thickness, interface quality and coating microstructure was systematically investigated. The derived mechanical characteristics revealed an unexpected behavior related to a gradient microstructure. This study supports understanding of the mechanism of room-temperature impact consolidation and its effect on the mechanical properties of the deposited layer.

Yttria stabilized zirconia (YSZ) has been for several decades the state of the art material for thermal barrier coating (TBC) applications in gas turbines. Although the material has unique properties, further efficiency improvement by increasing the temperature is limited due to its maximum temperature capability of about 1200°C. Above this temperature the deposited metastable tetragonal (t´) phase undergoes a detrimental phase transformation as well as enhanced sintering. Both processes promote the failure of the coatings at elevated temperatures and this early failure has been frequently observed in gradient tests. In this paper we now experimentally shown for the first time that under typical cycling conditions not the time at elevated temperatures leads to the reduced lifetime but the transient cooling rates. If cooling rates were reduced to 10K/s, TBC systems could be operated in a burner rig at a surface temperature well above 1500°C without showing a lifetime reduction. The explanation of these astonishing findings is given by the evaluation of energy release rate peaks during fast transient cooling in combination with the phase evolution during cooling with the used cooling rates.

Rare earth silicate environmental barrier coatings (EBCs) are state of the art for protecting SiC ceramic matrix composites (CMCs) against corrosive media. The interaction of four pure rare earth silicate EBC materials Yb2SiO5, Yb2Si2O7, Y2SiO5, Y2Si2O7 and three ytterbium silicate mixtures with molten calcium‐magnesium‐aluminosilicate (CMAS) were studied at high temperature (1400°C). The samples were characterized by SEM and XRD in order to evaluate the recession of the different materials after a reaction time of 8 hours. Additionally, the coefficient of thermal expansion (CTE) was determined to evaluate the suitability of Yb silicate mixtures as EBC materials for SiC CMCs. Results show that monosilicates exhibit a lower recession in contact with CMAS than their disilicate counterparts. The recession of the ytterbium silicates is far lower than the recession of the yttrium silicates under CMAS attack. Investigation of the ytterbium silicate mixtures exposes their superior resistance to CMAS, which is even higher than the resistance of the pure monosilicate. Also their decreased CTE suggests they will display better performance than the pure monosilicate.

In current-rate flash-sintering experiments the current is injected into the specimen from the very start and then increased at a constant rate, while the furnace is held at a constant temperature. The power supply remains under current control. The flash is induced at low current densities which reduces local heating at the electrodes. It leads to a uniform grain size across the entire gage length of the dog-bone specimen. This work pertains to 10 mol.% gadolinium-doped ceria flash sintered at current-rates ranging from 50 mA min−1 to 1000 mA min−1 at a furnace temperature of 680 °C. Full densities are obtained at a current density limit of 200 mA mm–2. Densification is shown to depend only on the instantaneous value of the current density, and not on the current-rate. The grain size, however, is shown to become finer at higher current-rates. A preliminary analysis of the “energy deficit”, that is, the estimated power input corresponding to the temperature as measured with a pyrometer, and the actual power consumption, estimates that huge concentrations of Frenkel defects may be introduced in the flash process.

The production of traditional and advanced ceramics is an energy-intensive activity, which requires high temperatures and long dwelling times to activate diffusional processes necessary for densification. Electric field assisted processing has received considerable attention recently, due to its potential to significantly reduce the costs of required heat treatments. However, the effect of electric fields on the densification and coarsening of oxide ceramics is still not completely understood, and the mechanisms behind, in particular for fields, are still under debate. The potential influence of electric field on the sintering parameters (uniaxial viscosity and uniaxial sintering stress) and microstructure of polycrystalline yttria doped ceria were studied. Sintering parameters were measured without and with AC electric fields (14 V/cm and 28 V/cm, 50 Hz) which were below the “flash regime”. During all sintering measurements, the sample temperature was adjusted by lowering the furnace temperature according to the temperature measurements using densified samples. Major findings are: (i) The densification behavior is clearly modified by these moderate electric fields, although temperature increase due to macroscopic Joule heating is excluded. (ii) The densification rate remains proportional to the applied stress under electrical fields. (iii) Sintering parameters are significantly affected by the applied electric fields.

To make ceramic based all-solid-state batteries competitive for the battery market, a shift from the separator supported cell-design for lab cells to a scalable, cathode-supported one is necessary to improve the energy density. Using tape casting, we were able to demonstrate for the first time all-ceramic free-standing LiCoO2 (LCO)/Li6.45Al0.05La3Zr1.6Ta0.4O12 (LLZO) mixed cathodes with high capacities and active material utilization. Further morphology engineering by introduction of a sequential layer casting enabled us to tailor the microstructure of the mixed cathodes resulting in opposite concentration gradients for the active material and the electrolyte over the thickness of the cathode. With this optimized microstructure, we were able to increase the discharge capacity of the free-standing mixed cathodes to 2.8 mA h cm(-2) utilizing 99% of the theoretical capacity. For the oxide garnet-based system, both the scalable fabrication method and the achieved electrochemical performance demonstrates industrial relevance for the first time. Additionally, the obtained free-standing cathodes have sufficient mechanical stability to allow the application of hybrid and ultra-thin separators to further increase the energy density on the full cell level.

Phosphate lithium ion conductors are outstanding electrolyte materials for solid-state lithium batteries. As polycrystalline ceramics, they have to be sintered at high temperatures. Lithium tungstate Li 2 WO 4 (LWO) is reported for the first time as an effective sintering aid to reduce the sintering temperature for one of the most common solid-state lithium ion conductors, Li 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 (LATP). While densification of LATP without sintering aids requires temperatures of at least 950°C to obtain a relative density of 90%, here relative densities of 90-95% are achieved even at 775°C when 5 wt.% of LWO is added. At 800°C the LATP containing 5 - 7 wt.% LWO densifies to a relative density of 97.2%. The ionic conductivity of LWO containing LATP is generally higher than that of pure LATP sintered at the same temperature. LATP containing 7 wt.% LWO shows high ionic conductivity of 4.4 × 10 -4 S/cm after sintering at 825°C. A significant reduction in sintering temperature, an increase in density and in the ionic conductivity of LATP as well as its non toxicity render LWO a very promising sintering aid for the development of LATP-based solid state batteries.

Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on ion transport properties is still debated. Here, we focus on Na1+xZr2SixP3-xO12 (0 ≤ x ≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on Na-transport properties. Although there is a large body of data available on this NASICON system, transport properties extracted from experiments or theory vary by orders of magnitude, signifying the need to bridge the gap between different studies. Here, more than 2,000 distinct ab initio-based kinetic Monte Carlo simulations have been used to map the statistically vast compositional space of NASICON over an unprecedented time range and spatial resolution and across a range of temperatures. We performed impedance spectroscopy of samples with varying Na compositions revealing that the highest ionic conductivity (~ 0.1 S cm–1) is achieved in Na3.4Zr2Si2.4P0.6O12, in line with our predictions (~0.2 S cm–1). Our predictions indicate that suitably doped NASICON compositions, especially with high silicon content, can achieve high Na+ mobilities. Our findings are relevant for the optimization of mixed polyanion solid electrolytes and electrodes, including sulfide-based polyanion frameworks, which are known for their superior ionic conductivities.

The materials typically used for oxygen transport membranes, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) tend to decompose due to their low thermochemical stability under reducing atmosphere. Fe- and Co-doped SrTiO3 (SrTi1-x-yCoxFeyO3-δ, x + y ≤ 0.35) (STCF) materials showing an oxygen transport comparable to LSCF have great potential for application in ion-transport-devices. In this study, the thermochemical stability of pure perovskite-structured STCF was investigated after annealing in a syngas atmosphere at 600–900 °C. The phase composition of the materials after annealing was characterized by means of X-ray diffraction (XRD). The thermodynamic activities of SrO, FeO, and CoO in the STCF materials were evaluated using Knudsen effusion mass spectrometry (KEMS). Co-doped SrTiO3 (STC) materials were not stable after annealing in the syngas atmosphere above 5 mol% Co-substitution. Ruddlesden-Popper-like phases and SrCO3 were detected after annealing at 600 °C. In contrast, Fe substitution (STF) showed good stability after annealing in syngas upto 35 mol% substitution.

Suspension plasma spraying (SPS) as a relatively new spraying technology has great potential on depositing high performance thermal barrier coatings (TBCs). In some cases, however, columnar SPS TBCs show premature failure in thermal cycling test. To explain the reasons of such failure, a failure mechanism for columnar SPS TBCs was proposed in this work. The premature failure of TBCs might be related to the radial stresses in the vicinity of top coat/bond coat interface. These radial stresses were introduced by the thermal misfit and the roughness of bond coat. According to this mechanism, two architecture designs of SPS TBCs were applied to improve the thermal cycling lifetime. One was a double layered top coat design with a lamellar atmospheric plasma sprayed (APS) sub-layer and a columnar SPS top-layer. The other one was a low roughness bond coat design with a columnar SPS top coat deposited on a low roughness bond coat which was grinded before the spraying. With both designs, lifetimes of SPS TBCs were significantly extended. Especially, a lifetime even better than conventional APS TBCs was achieved with the double layered design.

Titanium silicon carbide (Ti3SiC2) powder was synthesized by molten salt shielded synthesis route of elemental reactants. Potassium bromide (KBr) was used for gas-tight encapsulation of the consolidated reaction mixture for further high temperature processing. The synthesis of Ti3SiC2 powder was carried out in air, the salt cladding and molten salt pool provided for the protection of the material against oxidation both at low and high temperature. The process yielded free flowing Ti3SiC2 powders without the need of a milling step. Al addition to the reaction mixture resulted in a high purity (96 wt. %) of Ti3SiC2 at a synthesis temperature of 1250 °C. The synthesized micro-metric Ti3SiC2 can be milled to nano-metric powders.

Higher electric fields lower the temperature for the onset of flash. We explore the question “what can be the lowest temperature for initiating flash?”. Constant heating rate experiments at increasing electric fields reveal a surprising characteristic: the Debye temperature emerges as a the lower bound for the onset of flash. Data for flash temperature for three oxides are shown to exhibit this behavior in a universal plot.

In order to industrialize NaSICON materials, modern fabrication techniques have to be used and one of those techniques for producing large-scale electrolyte sheets with 10–300 μm thickness is tape casting. Such technique however requires a sintering step at high temperatures leading to sodium depletion due to evaporation. The sodium loss becomes more significant for large-area and thin components. In order to investigate and compensate the sodium loss, NaSICON compositions with sodium excess were prepared, i.e. Na3Zr2Si2PO12 + x Na2O (0 ≤ x ≤ 0.2). The sodium loss can be reduced by applying a two-step sintering process (1250 °C for only 0.5 h and then at 1230 °C for 5 h). Several characterization techniques were used to analyze the resulting ceramics, the sodium depletion and its consequence on electrical conductivity. Chemical analyses indicated that all compositions were sodium deficient. Furthermore, the weight loss was investigated by thermogravimetric analysis confirming the reduction of weight loss by a factor 2 by applying a two-step sintering procedure with lower second sintering temperature. Initial thermodynamic calculations of the phase equilibria at high temperatures confirm the predominant evaporation of sodium. The highest electrical conductivity (1.6 ⋅ 10−3 S cm−1 at 25 °C) was measured for the composition showing the least sodium deficiency (x = 0.2). Furthermore, the activation energy of bulk and grain boundary conductivity decreased with increasing x in system.

By Plasma Spray-Physical Vapor Deposition (PS-PVD), major fractions of the powder feedstock can be evaporated so that the coating builds up mainly from vapor phase. In this work, the deposition mechanisms at different PS-PVD conditions were investigated. Depending on the plasma flow conditions and the substrate temperature, the columns in the coatings possess successively pyramidal, cauliflower, and lamellar shaped tops. In addition, the different microstructures show characteristic crystallographic textures, in which different in-plane and out-of-plane orientations were observed by pole figures. Based on investigations by electron back-scatter diffraction (EBSD), the overall coating growth process can be roughly divided into three subsequent stages: equiaxed growth, competitive growth, and preferential growth. Influences of diffusion and shadowing on final coating microstructure and orientation were discussed. The formation of equiaxed grains was proposed to be caused by high nucleation rates, which are probably induced by large undercooling and super-saturation at the beginning of deposition. The preferential growth orientation was preliminarily explained based on an evolutionary selection mechanism.

High-pressure field assisted sintering (FAST/SPS) of half-cell for all-solid-state Li batteries was proposed and tested. The half-cell included the layer of lithium lanthanum zirconate (LLZO) electrolyte and the layer of mixed cathode. The mixed cathode consisted of lithium cobalt oxide (LCO) used as energy storage material and LLZO used as ionic conductor. A tool made of TZM molybdenum alloy was used to apply a high pressure of 440 MPa during FAST/SPS at a temperature of 675 °C ensuring stability of materials. An average relative density of sintered half-cell was around of 95%. The half-cell was assembled with a lithium anode and electrochemically tested. The results were compared with the performance of a half-cell sintered in an established graphite tool at the same temperature but under a lower pressure of 50 MPa and with a lower density (around of 78%). The battery with half-cell sintered at high pressure showed two-fold larger surface storage capacity. Further optimization of materials and processing is in progress.

Scandium-substituted NASICON (Na3.4Sc0.4Zr1.6Si2PO12) is a promising electrolyte material for sodium-ion solid state batteries, with the highest ionic conductivity reported to date for a NASICON material. Low-temperature densification and control of microstructure are important factors to enable the low-cost manufacturing of such new battery type. Non-conventional sintering techniques such as Field Assisted Sintering Technology / Spark Plasma Sintering (FAST/SPS) and Cold Sintering are therefore investigated and compared to conventional free sintering. FAST/SPS enables to get rapidly dense samples (99% TD) at lower temperatures than the ones required by conventional sintering routes and with similar electrical properties. Cold sintering experiments, involving the addition of aqueous solutions as sintering aids and high mechanical pressure, enable a moderate densification, but at temperatures as low as 250 °C. Further heat treatments still below the conventional sintering temperature increased the achieved density and ionic conductivity.

Dense protective layers are needed to reduce chromium-related degradation in SOFC stacks. In particular, atmospheric plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) coatings demonstrated low degradation rates in stack tests. We show that short-term annealing in air induces crack healing within these coatings. Parallel to this effect, a phase transformation is observed originating from oxidation that proceeds by solid state-diffusion. The present contribution reveals the basic mechanisms of the microstructural and phase changes of coatings in long-term annealing tests of up to 10,000 h at 700 °C. The layer develops differently at the air-facing surface and in the bulk. Due to cation deficiency, oxidation is dominated by cation outward diffusion, leading to a Co-enriched surface layer. The bulk displays a fine distribution of the initial (rock salt) and the final (spinel) phases. Understanding the mechanisms leading to these irreversible changes enables predictions to be made concerning durable protectivecoatings in SOFCs.

During the last decade, Suspension Plasma Spraying (SPS) attracted a lot of interest as an alternative process to produce columnar Thermal Barrier Coatings (TBCs). In this study, columnar TBCs were deposited with SPS. After spraying, samples were isothermally annealed at 1373 K for 1 h, 3 h, 10 h and 50 h, respectively. Microstructures and mechanical properties of the ceramic coatings were investigated as a function of annealing time. Annealing resulted in healing of micro-cracks, coarsening of pores, growth of domain size, companied with a decrease of porosity within columns. The change of coating microstructure led to change of mechanical properties. In addition, residual stress in SPS coatings was also investigated. Furthermore, as-sprayed coatings and pre-annealed coatings were subjected to burner rig tests. Short time pre-annealing allowed to enhance thermal cycling lifetime of such SPS coatings. The thermal cycling results were related to microstructure modifications of coatings.

Sintering stress and bulk viscosity for viscous sintering of glass were determined by two methods; sinter-forging and X-ray microtomography methods. Calcium aluminosilicate (CAS) glass with the diameter of 2.7 µm was chosen in sinter-forging experiment, while soda-lime glass with the diameter of 160 μm was observed by X-ray microtomography. Sintering stress of CAS glass and soda-lime glass was normalized by surface energy and the initial particle size. The normalized sintering stress of CAS glass determined by sinter-forging method was in fair agreement with values estimated from the X-ray microtomography data of soda-lime glass, despite the differences in particle shape and chemical composition. Bulk viscosity were also normalized by glass viscosity, and the normalized bulk viscosity obtained by sinter-forging method agreed fairly well with that estimated by X-ray microtomography method.

Cathode processing is one of the main challenges in the manufacturing of metal-supported solid oxide fuel cells (MSCs). Cathodesintering in ambient air is not applicable to MSCs, as oxidation of the metal substrate and the metallic Ni of the anode damagesthe cell. A recently developed ex situ sintering procedure for the LSCF cathode in an argon atmosphere was shown to significantlyimprove cathode adherence. However, the stability of the sintered cathode layer posed a challenge during storage in ambient air. In thepresent work, adapting the ex situ sintering approach to LSC/GDC dual-phase cathodes not only enabled the ex situ sintering processto be applied to LSC-based cathodes, but also resulted in the superior stability of the cathode after sintering. Despite the hygroscopicproperties of the partially decomposed perovskite, LSC/GDC dual-phase cathodes were shown to withstand more than 1 year ofstorage in ambient air without failure. Electrochemical single-cell measurements and post-test analysis confirmed the reversibilityof phase transformations and the electrochemical activity of such dual-phase cathodes. Current densities of 1.30 A cm−2 at 750°C,0.85 A cm−2 at 700°C, and 0.54 A cm−2 at 650°C were obtained at a cell voltage of 0.7 V.

The development of high-performance Li7La3Zr2O12 (LLZO)-based all-solid-state lithium batteries (SSLB) is usually hampered by highly resistive interfaces due to the need for sintering at elevated temperatures to form ionic diffusion paths through the grains. Many strategies have been proposed to solve the problem but the achievements have been limited. Herein, a new design principle is introduced, based on co-sintering crystalline LCO and Ta-substituted LLZO instead of using the more reactive Li–Co–O precursors and Al-substituted LLZO, which allows the fabrication of high specific areal density and low cell area resistance without the interface modification of LLZO-based SSLB. Detailed studies using micro-Raman and EDS mapping revealed that the well-sintered interfaces are free from detrimental secondary phases. To demonstrate that a true bulk-type SSLB can be constructed by this straightforward strategy, the material loading for a composite positive electrode was increased to about 10 times that in previous reports, which resulted in a high areal capacity of 1.63 mA h cm−2 (i.e. 110 mA h g−1) when discharged with a current density of 50 μA cm−2. It also allows one to discharge the fabricated SSLB at a very high current density of 500 μA cm−2 at 50 °C due to the minimized cell areal resistance. The new fabrication strategy for the LLZO-based SSLB paves the way for achieving SSLB with high safety and energy density.

Lithium diffusion in LiMn2O4 pellets is studied by means of isotope exchange and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). A 6Li-enriched film deposited by Pulsed Laser Deposition (PLD) on a dense LiMn2O4 pellet with natural abundance of lithium isotopes is used to study the tracer diffusion of lithium. The measured profiles are analyzed by numerical models describing the 6Li tracer diffusion from the film into the pellet. Experiments in the Harrison type B regime of diffusion kinetics allow for the distinction and simultaneous determination of bulk and grain boundary diffusion coefficients. Changing the experimental conditions to reach Harrison type A behavior yields effective diffusion coefficients for lithium tracer diffusion in LiMn2O4. Activation energies for bulk and grain boundary diffusion were obtained from experiments at different temperatures. Our values are critically compared to previous studies.

Low-temperature NOx storage materials for lean NOx traps based on nanocomposites containing perovskite-type oxides of La0.5Sr0.5Fe1-xMxO3-δ (M = Ti, Nb or Zr; x = 0.25 or 0.5) are prepared in a highly porous alumina with different loadings of 15−25 wt. %. The resulting storage materials are characterised by X-ray diffraction, BET and transmission electron microscopy with coupled ASTAR system for crystallite phase mapping. For all nanocomposites high surface areas around 100 m²/g are found. With perovskite loadings of 20 wt. % the platinised composites reveal NOx storage capacities between 120–164 μmol/g below 300 °C with a performance ranking of Zr > Ti > Nb. After hydrothermal ageing at 750 °C only for the Nb and Zr containing composites a decrease of the NSC up to 20 % can be observed. The NSC of the LSFT system can be improved by decreasing the perovskite loading to 15 wt. %.

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., Ti3C2 and Ti2C, and their use for lithium-ion batteries is presented. First, the successful synthesis of large batches (≈1 kg) of the MAX phases Ti3AlC2 and 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 Ti3C2 are 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.

Polymer–ceramic all-solid-state Li batteries (ASSLBs) combine the advantages of fully inorganic and polymer-based ASSLBs. In particular, the application of proposed polymer–ceramic composite cathodes could be essential for the enhancement of the energy storage capacity of ASSLBs. The use of a modified field-assisted sintering technique with adjustable pressure and with alternative mica foil enables the fabrication of porous cathodes at a reduced sintering temperature and without side phase formation. This allows sintering of a porous LiCoO2/Li7La3Zr2O12:Ta composite network suitable for polymer infiltration and assembly in an ASSLB from the cathode side. The ceramic LiCoO2/Li7La3Zr2O12:Ta composite cathodes infiltrated with an ion-conducting polymer have shown an enhanced areal storage capacity.

Herein, stable cationic and anionic redox in an O3-type layered Na[Ni2/3Ru1/3]O2 cathode for sodium-ion batteries (SIBs) is revealed. Density functional theory (DFT) calculation shows that the electron density features change in density of state with mixing of delocalized valence states as well as localized deeper energy states of O(p), Ni(d), and Ru(d) for the highly desodiated Na1−x[Ni2/3Ru1/3]O2 electrode, revealing the covalent characteristic of the transition metal (TM)O and TMTM bonds in the charged system. These properties lead to cycling stability for 200 cycles, with ≈79% of the capacity retained at a rate of 1C (210 mA g−1). Operando X-ray diffraction, X-ray absorption spectroscopy, and DFT calculations reveal the reversible electrochemical activity of the Ni2+/Ni3+ and O2−/O1− redox reactions, which are sustainable throughout the cycles. In addition, no loss of oxygen from the crystal structure of Na[Ni2/3Ru1/3]O2 occurs according to differential electrochemical mass spectrometry. The findings provide additional insight into the complex mechanism of the oxygen redox activity of high-capacity O3-type cathode materials for SIBs, encouraging further studies on their development.

Na3V2(PO4)3 (NVP) is a promising electrode material for sodium‐ion batteries. However, many of its electrochemical properties like ionic conductivities have never been systematically studied. In the present paper, a battery cell with controlled morphology of NVP was prepared and the electrochemical impedance spectra were measured at various voltages. The ionic conductivity of NVP was calculated in dependence on applied potentials. NVP has a total conductivity of 1×10−6 S cm−1 at 2.9 V, which decreases to 8×10−8 S cm−1 at 3.5 V. This low conductivity, especially at higher voltages, influences the performance of batteries with an NVP electrode, especially by limiting the high‐rate cycling of solid‐state batteries.

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-δ thin 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.

Journal of the American Ceramic Society (2021). doi:10.1111/jace.17907, Published by Wiley-Blackwel, Oxford [u.a.]