A study on the improvement of ion conductivity of lithium aluminum titanium phosphate-based solid-state electrolyte by the addition of divalent cations

Na like super ionic conductors (NASICON)-structure Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolyte have attracted attention as high ion conductivity and chemical stability. The M1–M2 voids between the TiO₆ octahedra and PO₄ tetrahedra in a Li_1.3Al_0.3Ti_1.7(PO₄)₃-based solid electrolyte is a major path for lithium-ion conduction, and it can be widened to increase lithium-ion conductivity by doping. In this study, divalent ions are doped into the Li_1.3Al_0.3Ti_1.7(PO₄)₃-based electrolyte and widened ion-conduction path and improved ion conductivity. Making doped Li_1.3Al_0.3Ti_1.7(PO₄)₃ samples starts with melting, then transformed into glass, pulverized, and then subjected to uniaxial compression molding and sintering, after which they are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their impedance resistances were measured. The LiTi₂(PO₄)₃ is generated by thermal treatment and crystallized to form an electrolyte whose lattice parameter values depend on the dopant ion and its content, with each divalent ion distorting the lattice and the M1–M2 bottleneck structure differently. Only Mg²⁺ doping led to a structural change that increases Li-ion conductivity to 1.55 × 10⁻³ S/cm at 5 mol% of magnesium ion, with the observed threefold increase in conductivity compared to the 4.73 × 10⁻⁴ S/cm ion conductivity of LATP ascribable to a widening of the ion-conduction path. Overall, doping an LATP-based solid electrolyte with an appropriate divalent cation is a promising way of improving performance in a manner that has various applications.