Identification of Impurity-Minimizing Synthesis Pathways for LAGP via Thermodynamic and Chemical Reaction Network-Based Analysis

Solid-state synthesis is a widely used method for synthesizing various inorganic materials. However, impurity formation frequently occurs in multicomponent systems, making it challenging to achieve high phase purity. In this study, the cause of impurity formation in the synthesis of lithium aluminum germanium phosphate (LAGP, Li1.5Al0.5Ge1.5(PO4)3), a NASICON-based solid electrolyte, was analyzed from a thermodynamic perspective. It was confirmed that when traditional precursors are used, impurities are inevitably generated as the reaction proceeds through multiple intermediate steps. To address this problem, a chemical reaction network (CRN)-based screening was performed to systematically identify alternative pathways that minimize impurity formation. Among a total of 95,620 possible reactions, no reaction could form phase-pure LAGP, and only 12 reactions produced GeO2 as a byproduct, which is known to have minimal impact on ionic conductivity. Among these, two reactions were selected as candidate synthesis pathways and demonstrate the utility and scalability of CRN-based analysis in exploring complex reaction networks. This study presents an analytical framework that can be applied to a wide range of multicomponent inorganic systems as a strategy for designing high-purity solid-state synthesis routes.