A study on the enhancement of structural behavior and ionic conductivity of divalent-doped Li1.3Al0.3Ti1.7 (PO4)3 solid electrolytes for lithium-ion batteries

Solid-state electrolytes (SSEs) represent a promising future power solution for electric vehicles (EVs) and electronic devices, owing to their improved safety characteristics, high energy density, and non-flammable properties. The NASICON-based Li_1.3Al_0.3Ti_1.7 (PO₄)₃—LATP structure is leading the way among oxide-based electrolytes, showcasing excellent Li-ion conductivity and stability in air. However, the development of high-performing oxide-based electrolytes poses challenges owing to their naturally rigid and fragile characteristics, which hinder the formation of an ideal interface between the cathode and anode. The M1–M2 voids situated between the TiO₆ octahedra and PO₄ tetrahedra in a LATP-based solid electrolyte serve as a primary pathway for lithium-ion transport, which can be enhanced for increased conductivity through doping. This study investigates the introduction of divalent ions into the Li_1.3Al_0.3Ti_1.7 (PO₄)₃-based electrolyte, widening the ion-conduction pathway thereby boosting ion conductivity. Creating doped Li_1.3Al_0.3Ti_1.7 (PO₄)₃ samples is performed via quenching method with melting before transforming into glass, followed by grinding, uniaxial compression molding, and sintering, after which they undergo analysis through scanning electron microscopy (SEM), X-ray diffraction (XRD), as well as impedance resistance measurements. The electrochemical evaluation indicated that the divalent incorporated LATP electrolytes displayed better structural behavior and consistent high ionic conductivity performance at low operating temperatures ranging 373–773 K when compared to LATP. This groundbreaking research underscores the potential of hybrid solid electrolytes that integrate Mg-doped LATP as a promising candidate for practical solid-state lithium batteries. The thermal treatment leads to the formation of LiTi₂(PO₄)₃, crystallizing to produce an electrolyte whose lattice parameter values are influenced by the type and amount of dopant ion, with each divalent ion inducing different distortions in the lattice and M1–M2 bottleneck structure. Notably, doping resulted in a structural change that boosted Li-ion conductivity to 3.41 × 10⁻³ S/cm at a 3 mol% magnesium ion concentration, with the threefold increase in conductivity compared to LATP (1.83 × 10⁻⁵ S/cm) attributable to the widening of the ion-conduction path. In summary, doping an LATP-based solid electrolyte with an appropriate divalent cation presents a promising method for enhancing performance, with numerous potential applications.