Synthesis of Li_3+xP_1-xGe_xS_4-2xO_2x electrolyte materials with high ionic conductivity and air stability by doping of GeO₂ for all-solid-state lithium batteries

Sulfide-based materials were widely investigated as electrolytes for all-solid-state lithium batteries owing to their good ionic conductivity and safety. However, their applications are hindered by the air sensitivity and Limited ionic conductivity. Here, a series of GeO₂-doped Li_3+xP_1-xGe_xS_4-2xO_2x (x = 0,0.02,0.04,0.06,0.08) solid electrolytes were synthesized through a modified solid-state method and characterized comprehensively. The lithium ionic conductivity of Li_3.04P_0.96Ge_0.04S_3.92O_0.08 solid electrolytes reached 3.54 mS cm^–1 at room temperature and the H₂S emission was only 0.31 cm⁻³ g when the electrolytes were exposed to air for 300 min. Importantly, the critical current density of Li_3.04P_0.96Ge_0.04S_3.92O_0.08 electrolytes was 1.2 mA cm^–2, which was twice of Li₃PS₄. In addition, the ASSLB of LiCoO₂@SSEs/Li_3.04P_0.96Ge_0.04S_3.92O_0.08/Li delivered an initial discharge capacity of 126.9 mAh g⁻¹ at 0.1 C at room temperature, and it showed excellent rate performance, e.g., 126, 103, 55, 39, mAh g⁻¹ at 0.1, 0.2, 0.5, and 1 C at RT. The cell achieved a reversible capacity of 84 mAh g⁻¹ when the current reverted to 0.3 C. The electrochemical performance and chemical stability of Li₃PS₄ were improved by co-doping of Ge and O, and provided a promising approach to achieve excellent chemical and electrochemical stability for the large-scale application of sulfide-based solid state electrolytes.