SPS sintering and characterization of Li_7La_3Zr_2O_12 solid electrolytes

Abstract

In recent years, solid-state electrolyte material such as lithium lanthanum zirconium oxide (LLZO) has become a promising candidate for application in electrical energy storage to replace the liquid electrolyte used in lithium-ion battery technology. Obtaining dense cubic LLZO requires heating of the sample in a furnace at higher temperature for a longer period. This could lead to unwanted evaporation of lithium and excessive cost. Spark plasma sintering (SPS) is used in this study to obtain a dense ceramic cubic LLZO solid electrolyte at temperature as low as 850 °C through solid-state synthesis. This is far lower than the sintering temperature for obtaining cubic LLZO reported in the literature. X-ray diffraction (XRD) patterns exhibit a predominantly cubic phase with minor impurities of pyrochlore and unreacted La_2O_3. The phase composition of the impurities and their effect on ionic conductivity were investigated. The microstructural changes and the density of the pellets obtained were analysed. The trend of the calculated lattice parameter was consistent with the refined lattice parameter. Pellets with relative density as high as 99.9% were produced. The highest ionic conductivity of 4.9 × 10^–4 S/cm with activation energy of 0.18 eV was recorded for the sample sintered at 950 °C for 30 min. Compared to the pressureless method of sintering, SPS appears promising for obtaining LLZO cubic phase with higher ionic conductivity at relatively low temperature over a short period. Graphical abstract The solid-state processing route of LLZO sintered by SPS technique