NASICON-Type Li1+xAlxZryTi2−x−y(PO4)3 Solid Electrolytes: Effect of Al, Zr Co-Doping and Synthesis Method

Replacing liquid electrolytes with solid-state conductors is one of the key challenges to increasing the safety and energy density of next-generation Li secondary batteries. In this work, the NASICON-type Li1+xAlxZryTi2−x−y(PO4)3 with 0 ≤ x, y ≤ 0.2 solid electrolytes were synthesized using solid-state and sol-gel techniques at various sintering temperatures (800, 900, and 1000 °C). Their morphology and conducting properties were studied to determine the optimal dopant content and synthesis method. Li1.2Al0.2Zr0.1Ti1.7(PO4)3 and Li1.1Al0.1Zr0.2Ti1.7(PO4)3 prepared at 900 °C using a solid-state reaction exhibit the highest total conductivity at 25 °C (7.9 × 10−4 and 5.4 × 10−4 S cm−1, respectively), which is due to the optimal size of lithium transport channels, as well as the high density of these samples. The potential profile of Li|Li1.2Al0.2Zr0.1Ti1.7(PO4)3|Li cells was retained during cycling at a current density of 0.05 mA cm−2 for 100 h, indicating a high interfacial Li metal/electrolyte stability.