Low-cost and facile synthesis of LAGP solid state electrolyte via a co-precipitation method

A solid-state electrolyte with high ionic conductivity and improved safety is a strong competitor in the race for the development of next-generation solid-state lithium batteries, which have stepped into the limelight of materials research. Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with satisfied ionic conductivity (∼10−4 S cm−1) at room temperature, high stability in the ambient atmosphere, and a facile sintering nature shows a promising potential for applications in solid-state lithium batteries. However, the current synthesis methods like solid-state strategy and liquid phase route all require harsh conditions, such as long thermal treatments, expensive raw materials, and complex operation. In this study, we propose a co-precipitation method for synthesizing the LAGP solid electrolyte with low-cost and nontoxic GeO2 as the germanium source. Process optimization in the pH value and water bath temperature was employed as a strategy to eliminate the remnants of GeO2, and the pure LAGP phase is acquired. Moreover, the co-precipitation method can also reduce the sintering temperature of LAGP to 750 °C so that uniform nano-LAGP grains (∼150 nm) can be obtained. During the subsequent processing, denser LAGP pellets are fabricated and exhibit a high ionic conductivity of 5.87 × 10−4 S cm−1 at 30 °C; the Li/Li symmetrical batteries periodically cycle at room temperature for above 310 h with a constant current density of 0.05 mA cm−2.