Correlating Li+ jump pathways and vibrational properties in lithium aluminum germanium phosphate glasses

Abstract

Lithium aluminum germanium phosphate (LAGP) glass ceramics have attracted considerable attention as promising solid electrolytes for next-generation lithium batteries owing to their improved safety and thermal stability. Despite significant progress, fundamental questions regarding Li⁺ hopping processes, effective charge carrier concentration, and carrier mobility in glassy systems remain unresolved. In this work, we investigate the fundamental relationship between fast lithium-ion transport and the network structure in xLi₂O–0.25Al₂O₃–1.5GeO₂–1.5P₂O₅ (xLi₂O-AGPO; 0.75 ≤ x ≤ 2.5) glasses. The dc conductivity increases by nearly three orders of magnitude, from 1.73 × 10⁻⁹ S cm⁻¹ (x = 0.75) to 1.67 × 10⁻⁶ S cm⁻¹ (x = 2.5) at 50 °C, while the dc activation energy decreases with increasing Li₂O content. The effective charge carrier concentration is evaluated from the conductivity data, and the corresponding carrier mobility is estimated. The charge carrier concentration increases nearly proportionally with Li₂O content, whereas the carrier mobility exhibits an exponential increase, similar to the trend observed for the dc conductivity. These results indicate that the exponential enhancement of dc conductivity with increasing x is primarily governed by the increase in carrier mobility. The facile migration of Li⁺ is attributed to fractal conduction pathways formed by non-bridging oxygen sites, which are generated through the depolymerization of the phosphate network.