Synthesis and Ionic Conductivity of Lithium Titanium Phosphate-Based Solid Electrolytes

Abstract

The processes occurring during the solid-state synthesis of germanium-doped lithium titanium phosphate have been studied. The formation of LiTi2 – xGex(PO4)3 has been shown to proceed through the titanium pyrophosphate formation followed by its transformation into materials with the NASICON structure. The process is completed at 1073 K. To produce ceramics with an optimal conductivity, annealing at 1173 K is required. Based on the results obtained, a two-stage synthesis procedure was developed. The highest ionic conductivity (3.9 × 10–5 Ohm–1 cm–1 at 433 K) and the lowest activation energy (46 ± 1 kJ/mol) were observed for LiTi2 – xGex(PO4)3 materials with a titanium substitution degree of 20–25% (x = 0.4–0.5). It can be attributed to an optimal size of lithium transport channels.