Enhanced Al/Ta co-doped Li7La3Zr2O12 ceramic electrolytes with the reduced Ta doping level for solid-state lithium batteries

Garnet Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte (SSE) candidate for advanced solid-state lithium batteries (SSLBs). In this work, Li6.25La3Zr2-yAlxTayO12 (x = 0.25, y = 0; x = 0.2, y = 0.15; x = 0.15, y = 0.3; x = 0.1, y = 0.45; x = 0.05, y = 0.6) and Li6.4La3Zr1.4Ta0.6O12 (LLZT0.6O) ceramic electrolytes, are prepared via a simple sol–gel process. The effect of Al and Ta co-doping levels on the phase, the microstructure and the ionic conductivity of modified LLZO is discussed in detail. Those Al/Ta co-doped LLZO ceramics (LLZATO) with Ta ≥ 0.3 per formula unit, are nearly pure cubic structures with a trace of new phases. The ionic conductivities of Li6.25La3Zr1.55Al0.1Ta0.45O12 (LLZA0.1T0.45O) and Li6.25La3Zr1.4Al0.05Ta0.6O12 (LLZA0.05T0.6O), are greatly improved by co-doping Al and Ta, benefitting from the emergence of self-grown LiAlO2 phase, and the microstructure of large grains contacting small grains. Remarkably, the optimal LLZA0.1T0.45O delivers a high ionic conductivity of 6.70 × 10–4 S cm−1 and a low electronic conductivity ~ 9.83 × 10–8 S cm−1 at 25 °C. This work provides available enhanced Al/Ta co-doped LLZO ceramic electrolytes with the reduced Ta doping level for solid-state lithium batteries.