Effect of Li3AlF6 as sintering-aids on the structure and conductivity of Li0.25La0.25NbO3 ceramic solid electrolytes

With the growing demand for high-safety and high-energy-density energy storage systems, all-solid-state lithium batteries (ASSLBs) have attracted extensive attention due to their excellent safety and potential high performance. Among them, the solid electrolyte is a key component. This study systematically investigates the effects of Li 3 AlF 6 as a sintering aid on the sintering behavior, crystal structure, microstructure, and electrochemical performance of LLNO (Li 0.25 La 0.25 NbO 3 ) ceramics. LLNO ceramic samples with different Li 3 AlF 6 doping levels (0-8 wt.%) were prepared via a solid-state reaction method and sintered at 1050 °C and 1100 °C. The samples were characterized by XRD, SEM, AC impedance spectroscopy, and DC polarization testing. The results indicate that Li 3 AlF 6 significantly reduces the sintering temperature of LLNO and promotes the densification process. However, excessive doping (8 wt.%) leads to the formation of impurity phases such as AlF 3 , increases grain boundary resistance, and reduces ionic conductivity. The sample with 5 wt.% Li 3 AlF 6 sintered at 1050 °C exhibits the best overall performance: an ionic conductivity of 2.08 × 10 -6 S·cm -1 and an activation energy of 0.340 eV. Although its conductivity is slightly lower than that of pure LLNO (4.12 × 10 -6 S·cm -1 ) sintered at 1100 °C, the introduction of Li 3 AlF 6 provides a feasible route for low-temperature sintering, which is beneficial for future co-sintering integration with electrode materials.