Preparation and chemical compatibility of lithium aluminum germanium phosphate solid electrolyte

The NASICON-type Li1.5Al0.5Ge1.5(PO4)3 electrolytes were synthesized by a facile aqueous-based sol-gel process with alcohols free. Compared with the samples prepared by solid-state reaction, the modified sol-gel derived Li1.5Al0.5Ge1.5(PO4)3 electrolyte exhibited a rhombohedral crystal symmetry without impurity phase and higher ionic conduction behavior. After sintered at 850 °C for 5 h, the sol-gel specimen showed a total ionic conductivity of 3.1 × 10− 4 S/cm at 30 °C and 1.0 × 10− 3 S/cm at 60 °C. In addition, the chemical and phase stability of the as-prepared Li1.5Al0.5Ge1.5(PO4)3 with three types of cathode materials (i.e. LiNi0.8Co0.15Al0.05O2, LiNi0.5Mn1.5O4 and Li3V2(PO4)3) was investigated in the temperature range of 500 to 700 °C. This work proposes a synthesis choice for Li1.5Al0.5Ge1.5(PO4)3, and also favors to the electrode identification for all-solid-state lithium secondary battery using NASICON-type electrolyte.