Titanium Dioxide Doping toward High-Lithium-Ion-Conducting Li1.5Al0.5Ge1.5(PO4)3 Glass-Ceramics for All-Solid-State Lithium Batteries

Developing solid electrolytes with high lithium-ion conductivity is crucial to realize high-performance all-solid-state lithium batteries. The substitution of ions with larger ionic radius can enlarge the Li+ migration tunnels and therefore enhance the lithium-ion conductivity. In this work, Ti4+ is employed to partially replace Ge4+ in Li2O–Al2O3–GeO2–P2O5 glass-ceramics electrolyte in order to improve its conductivity. The highest total lithium-ion conductivity of 1.07 × 10–3 S cm–1 at room temperature is obtained from Li1.5Al0.5Ge1.5(PO4)3-7.5 wt % TiO2 sample sintered at 900 °C for 6 h. The bulk and grain boundary conductivities are 1.67 × 10–3 S cm–1 and 2.99 × 10–3 S cm–1, respectively, which are superior than that of the pristine Li1.5Al0.5Ge1.5(PO4)3 counterpart. Both bulk and grain boundary conductivities of the sample have been significantly improved, which could be attributed to the increase of bottleneck sizes of the Li+ migration tunnels and the decrease of grain boundary area. All-solid-state lithium batteries employing LiFePO4 as cathode and solid electrolyte as separator and ionic conductor are assembled. A reversible capacity of 132.3 mAh g–1 is delivered after 200 cycles under a current density of 0.1C with a capacity retention ratio of 91.1%, showing the solid electrolyte is ideal for all-solid-state lithium-battery applications.