Synthesis of high purity Li8SiO6 using a citric acid-assisted route

Abstract

Lithium oxosilicate has the highest proportion of lithium among lithium silicates, which is desirable for applications. Although Li8SiO6 is a stable phase, its obtention as a polycrystalline pure phase is not reported yet, probably because of the high sensitivity of the system Li2O–SiO2 to the synthesis conditions. In this work, we adapted a citrate-based route used for the synthesis of Li4SiO4 as a novel approach to the obtention of Li8SiO6. We found that the lowest amount of impurities is achieved by using a Li:C6H8O7 molar ratio of 2.8:1, a pH value of 8.5, and a lithium excess of 20%. In a complementary way, we used the solid-state reaction method as a function of the excess of lithium and optimized the conditions that lead to a minimum amount of impurities. We found that the purest Li8SiO6 phase is obtained with low or no lithium excess. Samples obtained by both methods exhibited a higher purity compared to the reports available in literature. The crystal structure for this phase is confirmed by selected area electron diffraction.