High lithium ionic conductivity in the garnet-type oxide Li7−X La3(Zr2−X, NbX)O12 (X = 0-2)

Lithium garnet-type oxides Li_7−XLa₃(Zr_2−X, Nb_X)O₁₂ (X = 0-2) were synthesized by a solid-state reaction, and their lithium ion conductivity was measured using an AC impedance method at temperatures ranging from 25 to 150 °C in air. The lithium ion conductivity increased with increasing Nb content, and reached a maximum of ∼0.8 mS cm⁻¹ at 25 °C. By contrast, the activation energy reached a minimum of ∼30 kJ mol⁻¹ at the same point with X = 0.25. The potential window was examined by cyclic voltammetry (CV), which showed lithium deposition and dissolution peaks around 0 V vs. Li⁺/Li, but showed no evidence of other reactions up to 9 V vs. Li⁺/Li.