Synthesis of a Garnet-Type Solid Electrolyte for the All-Solid-State Battery Application

Abstract

The Ga-doped Li₇La₃Zr₂O₁₂ (LLZO) solid state electrolyte (SSE) is synthesized via the solid-state reaction. The structural study of the SSE is conducted with the help of X-ray diffraction and the Rietveld method. The SSE crystallizes in the Li_6.25Ga_0.15La_2.90Zr₂O₁₂ phase with cubic space group number 220 and the unit cell parameter of 13.02081 Å, and the La₂Zr₂O₇ impurity phase with cubic space group number 227 and the unit cell parameter of 10.79475 Å. The obtained lattice planes in the refinement are confirmed by TEM. The core of the Li ion migration channel is defined as the loop formed by Li32, Li1, Li2, and Li22 sites with the minimum Li⋯Li distance and occupational disorganization of Ga-doped LLZO SSE. The electron density plots of the Li_6.25Ga_0.15La_2.90Zr₂O₁₂ phase show the maximum electron distribution inside the unit cell for lanthanum atoms. XPS confirms the presence of all the precursors, i.e., Li, La, Zr, Ga, and O in the synthesized compound. The elemental composition is confirmed by EDX. In the direct current charge-discharge behaviour of the Li symmetric cell, no voltage breakdown is observed even at 6 mA/cm² current density and after 400 charge/discharge cycles for over 200 h.