Low-temperature sintering of Li_1.3Al_0.3Ti_1.7(PO₄)₃ electrolytes enabled by cobalt surface modification followed by two-step sintering

Abstract

The surface of NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) particles was modified with Co ions as a sintering aid by a wet chemical method. The effects of the inert and atmospheric sintering conditions on the sinterability of the Co element-modified LATP (Co-LATP) were investigated. With Co addition at x = 0.5 wt %, the densities of Co-LATP sintered at 800 °C in air and argon by the conventional sintering (CS) method were 81 and 66 %, respectively. In the case of the CS method in an air atmosphere, the reaction phases such as LiCoPO₄ (LCP) and lithium phosphate were formed and acted as sintering aids. For the case of the conventional method in Ar, LCP was not formed, but reduction of the Ti of LATP and reduced TiO_2−x were formed. These results suggested that the reaction mechanism of Co-LATP differs under each atmosphere in the conventional method. In conclusion, we succeeded in densifying Co-LATP by a two-step sintering (TSS); the first-step is sintering at 400 °C in air and the second-step is sintering at 800 °C in Ar. Co-LATP (x = 0.0–2.0 wt %) sintered under the optimized TSS condition, Co-LATP at x = 0.5 wt % showed the highest electrical conductivity of 1.3 × 10⁻⁴ S/cm at room temperature.