Melt-casted Li1.5Al0.3Mg0.1Ge1.6(PO4)3 glass ceramic electrolytes: A comparative study on the effect of different oxide doping

The development of Li-ion conducting solid-state electrolytes (SSEs) is crucial to achieve increased energy density, operative reliability, and unprecedented safety to replace the state-of-the-art Li-ion battery (LIB). In this regard, we here present the successful melt-casting synthesis of a MgO-added NASICON-type LAGP glass-ceramic electrolyte with composition Li1.5Al0.3Mg0.1Ge1.6(PO4)3, namely LAMGP. The effects of three different additional oxides are investigated, with the aim to improve grain cohesion and consequently enhance Li-ion conductivity. Specifically, yttrium oxide (Y2O3, 5 mol%), boron oxide (B2O3, 0.7 mol%) and silicon oxide (SiO2, 2.4 %mol) are added, yielding LAMGP-Y, LAMGP-B and LAMGP-Si, respectively. Their effects are exhaustively compared in terms of thermal, crystalline, structural/morphological and ion conducting features. Among the three oxides, B2O3 is able to positively act on grain boundaries without bringing along grains deformation and insulating secondary phases formation, achieving enhanced ionic conductivity of 0.21 mS cm-1 at 20 °C as compared to 0.08 mS cm-1 for a commercial LAGP subjected to the same thermal treatment. A remarkable anodic oxidation stability up to 4.8 V vs Li+/Li is assessed by LAMGP-B system, which accounts for promising prospects for its use in combination with high-energy (high-V) cathodes.