Effect of multivalent cation substitution on structure and ionic conductivity of perovskite-type L0.3La0.57T0.99M0.01O3 (M = Ta, Zr, V) solid electrolyte for all-solid-state lithium batteries

The perovskite-type oxide Li 3x La 2/3-x TiO₃ (LLTO) is a promising solid electrolyte but suffers from high grain-boundary resistance. This study compares B-site substitutions (M = Ta⁵⁺, Zr⁴⁺, V 5+ ) in Li 0.3 La 0.57 Ti 0.99 M 0.01 O 3 prepared via the sol–gel method to improve dopant incorporation and assess their impact on grain-boundary resistance. X-ray diffraction confirms a cubic perovskite (Pm-3m) with dopant-dependent lattice changes: Ta 5+ and Zr 4+ expand the unit cell, whereas V 5+ causes slight contraction and conversion to tetragonal perovskite (P4/mmm). Raman spectroscopies reveal systematic shifts of the A 1 g/E g modes, indicative of modified TiO 6 octahedral distortion and bonding. Densification for Ta- and Zr-doped LLTO ceramics is achieved at 1300 °C, while V-doped LLTO tends to form a more porous morphology. Electrochemical impedance spectroscopy demonstrates that Ta⁵⁺ and Zr⁴⁺ incorporation markedly lowers grain-boundary (GB) resistances, enhancing overall ionic transport, while V⁵⁺ deteriorates both bulk and intergranular pathways. The corresponding activation energies confirm facilitated bulk transport for Ta (E a,G = 0.212 eV) and Zr (0.237 eV). Collectively, the structural–spectroscopic–electrochemical evidence establishes a clear structure–transport correlation and identifies Ta 5+ as effective dopants to simultaneously enhance bulk conductivity and intergranular connectivity in LLTO electrolytes. • Multivalent B-site dopants (Ta⁵⁺, Zr⁴⁺, V⁵⁺) were incorporated into LLTO perovskites. • Sol–gel synthesis enabled homogeneous dopant distribution and phase purity. • Ta⁵⁺ and Zr⁴⁺ expanded the lattice and improved grain-boundary connectivity. • V⁵⁺ caused lattice contraction and degraded ionic transport pathways. • Zr⁴⁺ and Ta⁵⁺ doping enhanced total ionic conductivity up to 0.11 mS cm⁻¹.