Abstract
Two calcined products of Li6.4Fe0.2La3Zr2O12 can be synthesized via the solid state method and the sol gel method. Inhomogeneities of the iron distribution in the powder for the solid state method lead to a combination of cubic and tetragonal structure. By using the sol gel method the homogeneity can significantly been increased resulting in the desired pure phase cubic structured powders in I3d. By in situ dilatometer measurements the densification process can be comprehended for the first time for garnet type materials. The density can be significantly increased by the usage of the sol gel synthesis compared to the solid state synthesis with short sintering times of 2 h delivering pure phase pellets for both synthesis methods. Electrical impedance measurements revealed clearly divided semicircles for the bulk and the grain boundary contribution for the solid state synthesis, while the sol gel synthesis showed only one semicircle from the bulk contribution due to a large crystallite size. The total ionic conductivity for the pellet synthesized via the sol gel method is 1.82 mS/cm at 25°C which is the fastest found so far for garnet type or garnet related materials.
Highlights
Experimental PartThe solvent was removed in a rotational evaporator and the starting material mixture was calcined for 12 h in Al2O3 crucibles at a temperature of 950◦C
The research and development of high-performance fast lithiumion conductors, which are thermally and chemically stable, attracts large interest for the use in all solid state batteries.[1,2] Integrating solid electrolytes into lithium-ion batteries, enhanced reliability and safety shall be obtained by replacing the conventionally used organic liquid electrolytes that exhibit safety issues including high toxicity, narrow chemical stability window and flammability.[3]
Properties of the powder after calcination.—Fig. 1 shows the X-Ray diffraction (XRD) pattern of the two calcined products synthesized via the solid state method and the sol gel method
Summary
The solvent was removed in a rotational evaporator and the starting material mixture was calcined for 12 h in Al2O3 crucibles at a temperature of 950◦C. To prevent a reaction with the ambient humidity, the calcined powders and sintered pellets were transferred into a glove box at temperatures above 200◦C at the end of the furnace treatments and stored under Argon.[26,27]. The pellets where sintered on a platinum mesh positioned in an Al2O3 crucible in a furnace at 1225◦C for 2 h with heating and cooling rates of 5 K/min. Powders were measured in Argon atmosphere with a sample holder with polymer dome from PANalytical (Almelo, Netherlands) for the calcined sol gel powders. Between each measurement an EIS between 1 MHz and 0.1 kHz was performed to make sure, that the measurement does not change the cell resistance
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