The effect of Ti to the crystal structure of Li 7-3x M x La 3 Zr 1.8 Ti 0.2 O 12 (M= Ga,In) garnet-type solid electrolytes as a second dopant

Abstract

Garnet-type solid-state electrolytes are promising candidates for solid-state lithium batteries, nevertheless their ionic conductivity is still not enough for commercial applications. On the other hand, doping still is the common way to improve the ionic conductivities of these solid electrolytes. In this study, mono and dual-doped garnet-type solid electrolytes were synthesised by substituting indium (In), gallium (Ga), indium-titanium (In-Ti) and gallium-titanium (Ga-Ti) to the Li₇La₃Zr₂O₁₂ structure by a solid-state reaction method. The contribution of substitutions to the formation of crystal phases was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). On the other hand, morphological analyses were done by scanning electron microscope (SEM) and the ionic conductivities of the solid electrolytes were determined by electrochemical impedance spectroscopy (EIS). The study showed that while Li_7-3xIn_xLa₃Zr₂O₁₂ (for x = 0.05, 0.10, 0.15, 0.20) and Li_7-3xGa_xLa₃Zr₂O₁₂ (for x = 0.05) samples were formed in tetragonal phase with a space group of I41/acd:2, dual substituted Li_7-3xIn_xLa₃Zr_1.8Ti_0.2O₁₂ and Li_7-3xGa_xLa₃Zr_1.8Ti_0.2O₁₂ solid electrolytes for all x values were formed in cubic phase with a space group of I-43d. The highest conductivity is reached for Li_6.85Ga_0.05La₃Zr_1.8Ti_0.2O₁₂. The radial distribution function studies showed that when more In and Ga atoms take place in the sites of Li atoms, more O atoms take place in the vicinity of both substituted In and Ga atoms within the Li₇La₃Zr_1.8Ti_0.2O₁₂ (LLZTO) crystal framework which can eventuate in a change in the conduction mechanism.