Search

Enhancing the reversible Li growth efficiency in "Li-free" solid-state batteries is key for the deployment of this technology. Here, we demonstrate a nanoscale material design path that enables the reversible cycling of a lithium-free solid-state battery, using Li7La3Zr2O12 (LLZO) electrolyte. By means of nanometric Ag–Cu bilayers, directly sputtered onto the LLZO, we can effectively control Li deposition. The robust thin film bilayer, which is compatible with LLZO, enables stable cycling, accommodating the volume changes without the need for extra external pressure. [ABSTRACT FROM AUTHOR]

Solid state batteries are the next generation of safe energy storage devices offering high energy and power. Li7La3Zr2O12 garnets are fast Li-ion conductors and promising electrolytes to be used in solid-state batteries. However, they react with humid air to form LiOH and Li2CO3, reducing the ionic conductivity. In this work, the effect of heat treatment on local Li mobility in LLZO and the chemical evolution and phase transitions during the heating are investigated by a combination of solid state NMR, Raman, and XRD diffraction techniques. The results show that the activation energy for Li jumps obtained by variable temperature solid state NMR decreases after heat treatment at 750 °C and the Li dynamics are comparable to those of sintered pellets. Additionally, we show that the pretreatment of powders is an effective approach for obtaining garnet-rich composite electrolytes with better flexibility and garnet-polymer interphases, improving the prospects of this material towards processing. [ABSTRACT FROM AUTHOR]

In this work, nanoparticles of cerium hydroxycarbonates were synthesized by a facile hydrothermal treatment at 120°C with ammonium carbonate as the precipitating/mineralizer agent in diluted solution. The as-formed amorphous coprecipitate undergoes several morphological and structural modifications as a function of the duration of the hydrothermal treatment, leading after 8 h to the formation of monosized nanoparticles of hexagonal CeCO3OH. A similar behavior has been found when neodymium-based precursors are used as well, whereas the same treatment produces very different results by using different lanthanides-based precursors in terms of formed phases and morphologies, thus leading to the formation of pure tengerite-type structure phases, biphasic systems (tengerite type and hexagonal), or even entirely amorphous systems. Furthermore, the hydrothermal transformation is influenced by the redox behavior of the rare-earth cation (i.e., cerium) too, eventually resulting in the formation of fluorite-like structures. Therefore, a specific pathway of Ce(III) precursor transformations during hydrothermal treatment is proposed in this paper. Definitely, our results show that ammonium carbonate can be used as the precipitating/mineralizer agent to obtain cerium, doped-cerium, and neodymium hydroxycarbonates, which show excellent morphologies (i.e., characterized by spherical, nanosized particles with monomodal size distribution). Therefore, they can be used as optimal precursors for oxide powders. Conversely, when tengerite-type carbonate precursors are formed, their morphology is characterized by large and acicular particles. [ABSTRACT FROM AUTHOR]

Garnet-type electrolyte like Li 7 La 3 Zr 2 O 12 (LLZO) is a promising candidate for solid-state batteries (SSBs) due to its high Li + conductivity. Obtaining a dense microstructure for their practical use typically requires 1200 °C, which often lead to structural issues in addition to concerns on the scale up at industrial level. In this study, we propose a two-step process to fabricate LLZO electrolytes with a high relative density under low temperature. During the first step, a high quasi-isostatic pressure of 5.5 GPa was applied at temperatures below 500 °C (high pressure and low temperature, HPLT), reaching a density of over 97% with absence of grain growth. Then, a brief treatment at moderate temperature below 800 °C was applied to promote grain growth, leading to an ionic conductivity of 3·10−4 S cm−1. A relationship between the microstructure obtained under key parameters: temperature, pressure, and time; and the ionic transport of LLZO electrolytes has been established. Besides the high ionic conductivity obtained via HPLT, stripping and plating of lithium in a symmetric cell demonstrated the practical application. This work provides guidelines on the control of the microstructure of LLZO from processing parameters and contributes to the understanding of the correlations between microstructure and conductivity. • Highly dense ceramics (>97%) are obtained by applying 5.5 GPa and 500 °C. • Extra heat treatment below 800 °C promotes grain growth, increasing conductivity. • Relationships between microstructure, processing parameters and ionic transport. • Electrolytes fabricated at low temperature showed stable cycling with Li metal. [ABSTRACT FROM AUTHOR]

Background: Gadolinium-doped ceria is an attractive electrolyte material for potential application in solid oxide fuel cells (SOFCs) operating at intermediate temperatures typically with 10%-20% substitution of Ce+4 by Gd+3. In particular, 10% gadolinium-doped ceria seems to have the highest values of conductivities among the other dopant compositions. Methods: Nanosized powders of gadolinium-doped ceria were prepared by hydrothermal treatment using coprecipitate as a precursor and in the presence of 3 different mineralizer solutions. The powders obtained were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and thermal analysis, while the electrical behavior of the corresponding pellets were ascertained by AC impedance spectroscopy. Results: Nanocrystalline gadolinium-doped ceria powders with fluorite cubic crystal structure were obtained by hydrothermal treatment. Independent of the mineralizer used, these powders were able to produce very dense ceramics, especially when selecting an optimized sintering cycle. In contrast, the electrical behavior of the samples was influenced by the mineralizer solution, and the samples synthesized in the neutral and alkaline solutions showed higher values of electrical conductivity, in the range of temperatures of interest. Conclusions: By the coprecipitation method, it has been possible to synthesize nanosized gadolinium-doped cerium oxide in a fluorite structure, stable in a wide range of temperatures. Hydrothermal treatment directly on the as-synthesized coprecipitates, without any drying step, had a very positive effect on the powders, which can be sintered with a high degree of densification, especially with an optimized sintering cycle. Furthermore, the electrical behavior of these samples was very interesting, especially for the samples synthesized using neutral mineralizer solution and basic mineralizer solution. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to verify the influence of the addition of lithium on the densification and electrical conductivity of a gadolinium-doped ceria electrolyte. The lithium dopant was added directly during the sol-gel synthesis without a grinding step or the use of a dispersant solution. Electrolytes were prepared from powders and sintered at 1250 and 1500 °C. The characterization techniques used were XRD, FTIR spectroscopy, SEM, BET analysis, and electrochemical impedance spectroscopy for ionic conductivity. The densification achieved was >97 and >99 % of the theoretical density at sintering temperatures of 1250 and 1500 °C, respectively, by adding 2 mol % of lithium. The densification of gadolinium-doped ceria is caused by lithium deposition in the grain boundaries, which reduces structural imperfections. The ionic conductivity of lithium-doped pellets sintered at 1250 °C is the same as that of pure ones sintered at 1500 °C with a maximum value of 5.2×10−2 S cm−1 at 800 °C. Lithium addition is an effective strategy to reduce the sintering temperature and retain high conductivity values. [ABSTRACT FROM AUTHOR]

Ceramic electrolytes formed by Bi (4 mol%)-doped 8YSZ, i.e., Y2O3 (8 mol%)-doped ZrO2, were synthesized by a simple co-precipitation route, using ammonia solution as precipitating agent. The amorphous as-synthesized powders convert into zirconia-based single phase with fluorite structure through a mild calcination step at 500 °C. The calcined powders were sintered at very low temperatures (i.e., 900–1100 °C) achieving in both cases very high values of relative densities (i.e., >95%); the corresponding microstructures were highly homogeneous and characterized by micrometric grains or sub-micrometric grains for sintering at 1100 °C and 900 °C, respectively. Very interesting electrochemical properties were determined by Electrochemical Impedance Spectroscopy (EIS) in the best samples. In particular, their total ionic conductivity, recorded at 650 °C, are 6.06 × 10-2S/cm and 4.44 × 10-2S/cm for Bi (4 mol%)-doped 8YSZ sintered at 1100 °C and 900 °C, respectively. Therefore, Bi was proved to be an excellent sintering aid dopant for YSZ, highly improving its densification at lower temperatures while increasing its total ionic conductivity. [ABSTRACT FROM AUTHOR]