Phase Evolution and Crystallization Mechanism of Glass Ceramic Solid-State Electrolyte from In Situ Synchrotron X-ray Diffraction

Lithium aluminum germanium phosphate (LAGP) is a promisingsolidstate electrolyte system for all solid state lithium ion batteries.A common route for the synthesis of LAGP is through the crystallizationof the glass precursors hence detailed understanding of crystallizationbehavior is critical for the synthesis of pure phase and highly conductiveLAGP based solid state electrolyte. In this work, in situ synchrotronX-ray diffraction was used to investigate the nucleation and crystallizationprocesses of LAGP Li1.5Al0.5Ge1.5(PO4)(3) based solid-state electrolytes togetherwith scanning electron microscopy, atomic force microscopy, and atomisticcomputer simulations. Structural models from molecular dynamics simulationswere used to interpret the diffraction patterns acquired from synchrotrondiffraction. The strain and average size of crystal grains were calculatedby using the Williamson-Hall equation, and the results suggesta compressive stress on the grains in the early stage of nucleation.This stress increases the solubility of Al in the nuclei that wasexplained by the Gibbs-Thomson effect. It was also found thataliovalent ion-substituted pure phase LAGP can be obtained by heattreatment at a temperature significantly lower than previously reportedthrough the two-step heat treatment process.