Improvement in Properties of Na-β"-Al₂O₃ Solid Electrolyte with LaNbO₄ Doping

High fracture strength and excellent thermal stability of ion-conducting ceramic materials are important factors for solving the thermal runaway problem currently plaguing the development of alkali-metal batteries, but the high ion-transport resistance they exhibit at room temperature limits the practical performance of all-solid-state batteries. Na-β"-Al₂O₃ (SBA), an ionic conductor ceramics, with a unique layered two-dimensional Na⁺ conduction structure, is explored. LaNbO₄ ceramics with "microelastic" characteristics were synthesized as the second phase to fill and modify the grain gap of SBAs to increase their room temperature ionic conductivity. In the experiment, 0.50 wt.% LaNbO₄ is optimal in terms of enhancement effect, with a room temperature ionic conductivity of 2.061 mS·cm^-1. The activation energy of the doped SBA was also reduced to 0.1545 eV from 0.1714 eV for the pure phase SBA. SEM images of the ceramic cross-section showed that the appropriate content of LaNbO₄ not only enhanced the sintering behavior of the SBAs, but also boosted the crystallization of the SBAs, thus leading to a reduction in the impedance. Symmetric all-solid-state sodium batteries assembled with the doped SBAs could be operated at lower voltages in constant-current charge/discharge at room temperature.