ABSTRACT
The density, microstructure, and ionic conductivity of solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics prepared by cold sintering using liquid and solid sintering additives are studied. The effects of both liquid (water and water solutions of acetic acid and lithium hydroxide) and solid (lithium acetate) additives on densification are investigated. The properties of cold-sintered LATP are compared to those of conventionally sintered LATP. The materials cold-sintered at temperatures 140-280 °C and pressures 510-600 MPa show relative density in the range of 90-98% of LATP's theoretical value, comparable or higher than the density of conventionally sintered ceramics. With the relative density of 94%, a total ionic conductivity of 1.26 × 10-5 S/cm (room temperature) is achieved by cold sintering at the temperature of 200 °C and uniaxial pressure of 510 MPa using water as additive. The lower ionic conductivities of the cold-sintered ceramics compared to those prepared by conventional sintering are attributed to the formation of amorphous secondary phases in the intergranular regions depending on the type of additives used and on the processing conditions selected.
ABSTRACT
New sodium-based battery concepts require solid electrolytes as ion conducting separators. Besides NaSICON and ß-Al2O3 in the Na2O-R2O3-SiO2 system (R = rare earth), a rarely noticed glass-ceramic solid electrolyte with the composition Na5RSi4O12 (N5-type) exists. The present study addresses the investigation of the ionic conductivity of Na5RSi4O12 solid electrolytes sintered from pre-crystallized glass-ceramic powders. The sintering behavior (optical dilatometry), the microstructure (SEM/EDX), and phase composition (XRD), as well as electrochemical properties (impedance spectroscopy), were investigated. To evaluate the effect of the ionic radii, Y, Sm and Gd rare elements were chosen. All compositions were successfully synthesized to fully densified compacts having the corresponding conducting N5-type phase as the main component. The densification behavior was in agreement with the melting point, which decreased with increasing ionic radii and specific cell volume. Alternatively, the ionic conductivities of N5-phases decreased from Y to Gd and Sm containing samples. The highest ionic conductivity of 1.82 × 10-3 S cm-1 at 20 °C was obtained for Na5YSi4O12 composition. The impact of grain boundaries and bulk conductivity on measured values is discussed. A powder-based synthesis method of this glass-ceramic solid electrolyte using different rare earth elements opens possibilities for optimizing ionic conductivity and scalable technological processing by tape casting.
ABSTRACT
All solid-state batteries offer the possibility of increased safety at potentially higher energy densities compared to conventional lithium-ion batteries. In an all-ceramic oxide battery, the composite cathode consists of at least one ion-conducting solid electrolyte and an active material, which are typically densified by sintering. In this study, the reaction of the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) and the active material LiNi0.6Co0.2Mn0.2O2 (NCM622) is investigated by cosintering at temperatures between 550 and 650 °C. The characterization of the composites and the reaction layer is performed by optical dilatometry, X-ray diffractometry, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, as well as scanning transmission electron microscopy (STEM). Even at low sintering temperatures, elemental diffusion occurs between the two phases, which leads to the formation of secondary phases and decomposition reactions of the active material and the solid electrolyte. As a result, the densification of the composite is prevented and ion-conducting paths between individual particles cannot be formed. Based on the experimental results, a mechanism of the reactions in cosintered LATP and NCM622 oxide composite cathodes is suggested.
ABSTRACT
A zirconia-based potentiometric solid electrolyte gas sensor with internal solid state reference was used to study the response behavior of platinum cermet and indium tin oxide sensing electrodes. Target gases included both oxygen and carbon monoxide in nitrogen-based sample gas mixtures. It was found that with the indium tin oxide sensing electrode, the low-temperature behavior is mainly a result of incomplete equilibration due to contaminations of the electrode surface. On the other hand, some of these contaminant species have been identified as being pivotal for the higher carbon monoxide sensitivity of the indium tin oxide sensing electrode as compared to platinum cermet electrodes.
ABSTRACT
By combining results of adsorption/desorption measurements on powders and electrical conductivity studies on thick and thin films, the interaction of indium tin oxide with various ambient gas species and carbon monoxide as potential target gas was studied between room temperature and 700 °C. The results show that the indium tin oxide surfaces exhibit a significant coverage of water-related and carbonaceous adsorbates even at temperatures as high as 600 °C. Specifically carbonaceous species, which are also produced under carbon monoxide exposure, show a detrimental effect on oxygen adsorption and may impair the film's sensitivity to a variety of target gases if the material is used in gas sensing applications. Consequently, the operating temperature of an ITO based chemoresistive carbon monoxide sensor should be selected within a range where the decomposition and desorption of these species proceeds rapidly, while the surface oxygen coverage is still high enough to provide ample species for target gas interaction.
ABSTRACT
The solid oxide cell is a basis for highly efficient and reversible electrochemical energy conversion. A single cell based on a planar electrolyte substrate as support (ESC) is often utilized for SOFC/SOEC stack manufacturing and fulfills necessary requirements for application in small, medium and large scale fuel cell and electrolysis systems. Thickness of the electrolyte substrate, and its ionic conductivity limits the power density of the ESC. To improve the performance of this cell type in SOFC/SOEC mode, alternative fuel electrodes, on the basis of Ni/CGO as well as electrolytes with reduced thickness, have been applied. Furthermore, different interlayers on the air side have been tested to avoid the electrode delamination and to reduce the cell degradation in electrolysis mode. Finally, the influence of the contacting layer on cell performance, especially for cells with an ultrathin electrolyte and thin electrode layers, has been investigated. It has been found that Ni/CGO outperform traditional Ni/8YSZ electrodes and the introduction of a ScSZ interlayer substantially reduces the degradation rate of ESC in electrolysis mode. Furthermore, it was demonstrated that, for thin electrodes, the application of contacting layers with good conductivity and adhesion to current collectors improves performance significantly.
