Solid State Synthesis of Aluminum Doped Li7La3Zr2O12 Garnet with Enhanced Thermal Processing Stability

Abstract

Lithium lanthanum zirconium oxide garnet (LLZO) is a solid-state lithium ion conducting electrolyte being studied extensively for all-solid-state batteries (ASSB) owing to its high lithium conductivity and chemical stability against lithium metal anodes. This material, though useful, is highly sensitive to lithium stoichiometry in terms of crystalline stability and functional properties including conductivity. Stabilizing agents such as aluminum oxide and excess lithium are needed to preserve the cubic phase and compensate for lithium volatility during high temperature processing. Material engineering that allows LLZO to be fabricated with lower sensitivity to processing conditions is an important enabler in ultimate implementation of this material.Given the range of ceramic materials processing constraints such as ball milling, calcination, and sintering at temperatures above 1000oC, lithium volatility can drive deleterious phase formation. This study was designed to consider mechanisms that reduce the processing sensitivities of aluminum doped LLZO along its path to being utilized in a ceramic-manufacturing optimal ASSB. Processing sensitivities ameliorated via direct incorporation of excess lithium within LLZO lattice provides a key advantage towards the densification over topical additions of excess lithium precursors. By utilizing thermogravimetric analysis in conjunction with in-situ XRD analysis of solid state LLZO precursor synthesis the sensitivity of the LLZO cubic phase to lithium volatility can be reduced via early incorporation of excess lithium carbonate during initial formation. Details of in-situ phase evolution of LLZO from precursors were further clarified via temperature resolved mapping of diffraction patterns. The improved suppression of lithium volatilization has helpful implications for the scalable production of LLZO powders and assembly of ASSBs.