Improvement of melt quenching technique of Li1+xAlxGe2-x(PO4)3 (LAGP) solid electrolyte for solid-state batteries

Solid-state batteries (SSB) development is the focus area of safe lithium energy storage devices. One of the most promising solid electrolytes for SSBs is Li1+xAlxGe2-x(PO4)3 (LAGP), which stands out for cathode interface stability, air and temperatures stability. However, LAGP ceramic's main challenge remains the low conductivity compared to the bulk phase conductivity. One of the reasons is deviation from stoichiometry due to the loss of volatile components during synthesis and the high synthesis temperature of LAGP-glass. For this reason, the development of methods for obtaining and controlling the composition of LAGPs is required. This study proposes to improve the melt quenching technique by introducing a pre-synthesis stage to obtain LAGP-glass. The effects of pre-synthesis and composition consideration on the structure formation of LAGP were investigated by Fourier-transform infrared spectroscopy. It was shown that NASICON characteristic structural elements had already appeared at the pre-synthesis stage. Through pre-synthesis and component accounting, the synthesis temperature was lowered to 1230 ˚C in 45 minutes. As a result, the polycrystalline Li1,51Al0,51Ge1,75(PO4)2,8 was synthesized with less than 1% side phase content. The conductivity was found to be 5.2·10-4 S·cm-1 (25 ˚C) with cyclic stability exceeding 200 hours at a current density of 200 µA/cm2.